NTID300.13
        TRANSPORTATION NOISE
AND NOISE FROM EQUIPMENT POWERED BY
    INTERNAL COMBUSTION ENGINES
           DECEMBER 31, 1971
    J.S. Environmental Protection Agenc'
          Washington, D.C. 20460

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                                                                          NTID300.13
                    TRANSPORTATION NOISE
         AND NOISE FROM EQUIPMENT POWERED BY
               INTERNAL COMBUSTION ENGINES
                        DECEMBER 31, 1971
                           Prepared by

                     WYLE  LABORATORIES
                               under
                     CONTRACT 68-04-0046
                              for the
               U.S. Environmental Protection Agency
              Office of Noise Abatement and Control
                      Washington, D.C. 20460
       This report has been approved for general availability. The contents of this
       report reflect the views of the contractor, who is responsible for the facts
       and the accuracy of the  data presented herein, and do not necessarily
       reflect the official views or policy of EPA. This report does not constitute
       a standard, specification, or regulation.
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.
                Price $4.30 domestic postpaid or $3.75 OPO Bookstore

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                            TABLE  OF  CONTENTS

                                                                         PAGE
1 .0      INTRODUCTION                                                     1
2.0      TRANSPORTATION  SYSTEMS                                         5
         2.1      Commercial Aircraft                                          8
                 2.1.1     Introduction                                        8
                 2.1.2     Source Noise Characteristics                        9
                 2.1.3     Environmental Noise Characteristics                19
                 2.1 .4     Industry Efforts in Noise Reduction                  27
                 2.1.5     Noise Reduction Potential                          45
         2.2      V/STOL Aviation                                           53
                 2.2.1     Introduction                                       53
                 2.2.2     Source Noise Characteristics                       54
                 2.2.3     Environmental Noise Characteristics                60
                 2.2.4     Industry Efforts in Noise Reduction                  64
                 2.2.5     Noise Reduction Potential                          72
         2.3      General Aviation Aircraft                                   74
                 2.3.1     Introduction                                       74
                 2.3.2     Source Noise Characteristics                       75
                 2.3.3     Environmental Noise Characteristics                79
                 2.3.4     Industry Efforts in Noise Reduction                  83
                 2.3.5     Noise Reduction Potential                          87
         2.4      Highway Vehicles                                           92
                 2.4.1     Introduction                                       92
                 2.4.2     Source Noise Characteristics                       94
                                      in

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                                                                          PAGE
                 2.4.3     Environmental Noise Characteristics               112
                 2.4.4     Industry Efforts Toward Noise Reduction            117
                 2.4.5     Noise Reduction Potential                         119
         2.5     Rail Systems                                               133
                 2.5.1     Introduction                                     133
                 2.5.2     Source Noise Characteristics                      133
                 2.5.3     Environmental Noise Characteristics               145
                 2.5.4     Industry Efforts in Noise Reduction                 147
                 2.5.5     Noise Reduction Potential                         157
         2.6     Ships                                                      161
                 2.6.1     Introduction                                     161
                 2.6.2     Source Noise Characteristics                      161
                 2.6.3     Environmental Noise Characteristics               165
         2.7     Recreation Vehicles                                        166
                 2.7.1     Introduction                                     166
                 2.7.2     Source Noise Characteristics                      167
                 2.7.3     Environmental Noise Characteristics               176
                 2.7.4     Noise Reduction-Industry Efforts and  Potential     179
3.0      DEVICES POWERED BY SMALL INTERNAL COMBUSTION
         ENGINES                                                         190
         3.1     Introduction                                               190
         3.2     Source Noise Characteristics                                190
         3.3     Environmental Noise Characteristics                         198
         3.4     Industry Efforts Towards Noise Reduction                      201
         3.5     Noise Reduction Potential                                  205
4.0      ENVIRONMENTAL IMPACT FOR TRANSPORTATION VEHICLES
         AND SMALL INTERNAL COMBUSTION ENGINES                    206
         4.1     Total  Noise  Energy Output per Day for
                 Transportation Systems                                      208
                                      IV

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         4.2     Contribution of Transportation System Components
                 to the Residual Background Noise Level in an
                 Average Community
         4.3     Relative Annoyance Potential of Intruding
                 Single Event Noise
         4.4     Overall  Assessment of Noise Impact by the
                 Transportation System on Non-Participants
         4.5     Impact on Participant or Passengers in
                 Transportation Systems
         4.6     Environmental Impact for Internal Combustion
                 Engine Devices
5.0      CONCLUSIONS  AND RECOMMENDATIONS
         5.1      Noise Impact on People
         5.2     Interaction Between Public and Industry
         5.3     Federal Action to Reduce Source Noise
         5.4     Recommendations for Noise Reduction
REFERENCES
APPENDIX A
APPENDIX B
MEASUREMENT STANDARDS
      FAR36 - Summary
      ISO Recommendation R362 - Summary
      SAE Standards - Summary
      California Administration Codes - Summary
      Part 36 - Noise Standards Aircraft Type Certification
METHODOLOGY FOR IMPACT ANALYSIS
B.I  Total Noise Energy
B.2  Residual Noise Levels
B.3  Single  Event Noise Levels for Major Transportation
      Noise  Sources as a Function of Distance
PAGE

213

215

221

226

230
233
234
240
242
243
252
A-l
A-4
A-5
A-6
A-10
A-13
B-l
B-l
B-6

B-25

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                                                                       PAGE
          B.4    Noise Impacted Land Areas Around Freeways
                 and Airports                                            B-28
          B.5    Noise Impact on Operators or Passengers of
                 Transportation Vehicles and Internal Combustion
                 Engines                                                 B-40
          B.6    Glossary of Terminology                                  B-41
          References                                                     B-45
APPENDIX C     NOISE GENERATOR CHARACTERISTICS                   C-l
          C.I    Jet  Engine Noise                                        C-l
          C.2    Propeller and Rotor Noise                                 C-22
          C.3    Internal  Combustion Engine Noise                         C-31
          C.4    Tire Noise                                              C-47
          References                                                     C-59
                                      VI

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                                LIST OF TABLES
 Table
Number                                                                    Page
 2-1       Growth in the Transportation System,  1950 - 1970                    7
 2.1-1     Passenger Environment                                            22
 2.1-2     Maximum Perceived Noise Levels of the DC-10-10
           Relative to Those of Current 4-Engine Jet  Transport                 39
 2.1-3     NASA Acoustically Treated Nacelle Program                       40
 2.1-4     NASA Quiet Engine Program                                      42
 2.1-5     Federal Noise Abatement  Programs                                 46
 2.1-6     Estimated Aircraft Noise Reduction  Potential for Takeoff             46
 2.2-1     Estimated Noise Reduction Potential for Helicopters                 73
 2.3-1     Interior Noise Level  Objectives                                   87
 2.3-2     Potential General Aviation Aircraft Noise Reduction                90
 2.4-1     Diesel Truck Noise Component Contributions to
           Maximum Noise Levels at 50 Feet from Vehicle                    102
 2.5-1     Summary of  the Noise Reduction Potential by Applying
           Current Technology to Existing Transit Vehicles                    158
 2.7-1     Example of Further Noise  Reduction Using
           Existing Technology                                              188
 3-1       Estimated Noise Reduction Potential for Devices
           Powered by  Internal Combustion Engines                           205
 4-1       Example of Potential Noise Reduction for  Externally
           Radiated Noise for Transportation System Categories                209
 4-2       Estimated Noise Reduction Potential for Devices
           Powered by  Internal Combustion Engines                           210
 4-3       Estimated Noise Energy for Transportation  System
           Categories in 1970                                              211
 4-4       Example of Estimated  Future Change in Noise Energy
           for Major Surface Transportation System Categories
           with Three Options for Noise Reduction                           212
 4-5       Predicted Contributions to Daytime  Residual  Noise
           Levels by Highway Vehicles for a Typical  Urban
           Community in 1970                                              214
                                       VII

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 Table
Number                                                                    Page

 4-6       Comparison of Major Surface Transportation System
           Categories According to Typical Maximum Noise
           Levels, Single  Event Noise Exposure Levels (SENEL),
           and the Distance Within Which the SENEL is
           Greater than 72 dB                                              219

 4-7       Summary of Estimated Noise Impacted Land (Within
           CNEL 65 Contour) Near Airports and Freeways from
           1955 to the Year 2000 with Future Estimates Based on
           Option 2 and Option 3 Examples                                  225

 4-8       Typical Passenger Separation Distances and Speech
           Interference Criteria Compared to Average  Internal
           Noise Levels for Major Transportation Categories                   229

 4-9       Summary of Noise  Impact Characteristics of Internal
           Combustion Engines                                              231
 5-1       Approximate  Number of People (Operators and
           Passengers) in Non-Occupational Situations Exposed
           to Potentially Hazardous Noise with Respect to
           Hearing Damage from Various Significant Sources                   239
                                      VIII

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                                LIST  OF  FIGURES

 Figure
Number                                                                    Page

 2-1       General Characteristics of the Transportation
           Industry in  1970                                                   6
 2.1-1     Characteristics  of Commercial Aircraft                              10

 2.1-2     Noise Limits and Spectra of 4-Engine Low Bypass
           Ratio Turbofan Aircraft                                            11

 2.1-3     Noise Levels and  Spectra of 2-3 Engine Low Bypass
           Ratio Turbofan Aircraft                                            13

 2.1-4     Noise Levels and  Spectra of 4-Engine High Bypass
           Ratio Turbofan Aircraft                                            14
 2.1-5     Mean Noise Level Spectra  for Various Types of Aircraft
           at Approximately 1000 Ft Altitude, During
           Takeoff                                                          15
 2.1-6     Mean Noise Level Spectra for Various Types of Aircraft
           at Approximately  1000 Ft Altitude,  During Landing                  16

 2.1-7     Nature of the Sonic Boom Phenomenon                              18

 2.1-8     Time Histories of Typical Cabin Noise Levels                       20
 2.1-9     Interior Cabin Noise Levels and Spectra for
           Commercial Jet Aircraft                                           21

 2.1-10    Noise Exposure  Forecast vs Slant Range (Takeoff)
           for an Equivalent  Large Airport                                     24

 2.1-11    Noise Exposure  Forecast vs Slant Range (Approach)
           for an Equivalent  Large Airport                                     25

 2.1-12    NEF 30 Contours for Representative (Single Runway) Airport          26

 2.1-13    Projected Change in Commercial Aircraft Fleet Composition
           (Based on Projected Passenger Capacity Demand Increasing
           at 5  Percent/Year)                                                29

 2.1-14    Projected Growth of Commercial Aircraft Traffic                    30
 2.1-15    FAR-36 Noise Certification Measurement Positions                   33
 2.1-16    Effective Perceived Noise Level for Landing
           for Today's Aircraft Compared to FAR-36 Limits                     35
                                       IX

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 Figure
Number                                                                    ftjge
2.1-17    Effective Perceived Noise Level for Takeoff for Today's
           Aircraft Compared to FAR-36 Limits                               36
2. 1-18    Effective Perceived Noise Level at Sideline for Today's
           Aircraft Compared to FAR-36 Limits                               37
2.1-19    Trends in Jet Engine Noise Generation                             38
2. 1-20    Flyover Noise Levels - DC-10-10 Compared to Current
           Jet Transports Powered by (4) JT3D-3B Engines                      41
2.1-21     Effects of Flight Procedure Changes on Noise Reduction
           for the  Case of a 4-Engine Turbofan Aircraft                        44
2. 1-22    Estimated Noise-Impacted Areas (30 NEF or Higher) as
           Function of Jet Engine Noise Reduction Goals                      49
2. 1-23    Noise- Impacted Areas (30 NEF or  Higher) vs Traffic
           Growth (Projection for Year 3000)                                 51
2.2-1      Characteristics of V/STOL Aircraft                                55
2.2-2      Potential 1985 U.S. V/STOL Fleet                                56
2.2-3      Typical Noise Spectra of  Light Piston-Engined Helicopters           57
2.2-4      Typical Noise Spectra of  Heavy Helicopters                        58
2.2-5      Typical Frequency Characteristics of Propulsion Systems
           for 40 to 80 Passenger STOL Aircraft (excluding power
           plant) at 500 Feet                                                61
2.2-6      Comparison of Typical V/STOL Aircraft Noise Levels with
           Community Ambient Noise Levels (Lp/J                             63
2.2-7    Current Design Approaches to Helicopter Noise Reduction           66
2.2-8    Effect of Design Changes on a Light Helicopter Noise
          Signature (Demonstrated)                                          66
2.2-9    Demonstrated Noise Reduction of a Heavy- Helicopter
          Twin-Rotor System                                                67
2.2-10   Exhaust Noise Suppression of Light Piston-Engined  Helicopters       67
2.2-11    Trend of Helicopter  Noise Levels with Gross Weight
          and Seating Capacity                                             71

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 Figure
Number                                                                    Page
 2.3-1     Characteristics of General Aviation Aircraft                         76
 2.3-2     Noise Levels and Spectra of General Aviation
           Propeller Aircraft                                                 77
 2.3-3     Noise Levels and Spectra of Executive Jet Aircraft                  78
 2.3-4     Interior Cabin Noise Levels and Spectra for
           General Aviation Propeller Aircraft                                 80
 2.3-5     Noise Exposure  Forecast Values for an  Example of a
           Representative General Aviation Airport with
           Daytime Use Only  (Takeoff)                                       81
 2.3-6     Noise Exposure  Forecast Values for an  Example of a
           Representative General Aviation Airport with
           Daytime Use Only  (Approach)                                      82
 2.3-7     Number of General Aviation Aircraft with
           Projections for 1975, 1980, and 1985                               85
 2.3-8     Comparison of Noise Levels at  Various Angles from
           Engine at Approximately 3000  Ibs Thrust                             88
 2.3-9     Noise Levels Generated by General  Aviation Aircraft               91
 2.4-1     Characteristics of Highway Vehicles                                93
 2.4-2     Single Vehicle Noise Output as a Function of Vehicle Speed         95
 2.4-3     Diesel Truck and Automobile Noise at Highway Speeds,
           Cruise and Coasting (at 50 Feet)                                   96
 2.4-4     Typical Octave Band Spectra for Diesel Truck and Automobile
           (Full Throttle Acceleration at 35 mph at 50 Feet)                    98
 2.4-5     Octave Band Spectra of Diesel  Engine  Inlet and Exhaust
           Noise Illustrating the Effects of Silencing for the
           Exhaust and the Intake                                             99
 2.4-6     Typical Example of Diesel Truck Noise                            101
 2.4-7     Effect of Various Tires Mounted on the Drive Axle,
           Loaded Single Chassis Vehicle  Operating  on Concrete
           Road Surface (Levels at 50 Feet)                                  106
 2.4-8     Typical Examples of Automobile Noise                             109
 2.4-9     Typical Octave Band Spectra for Highway Bus                      111
                                      XI

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 Figure
Number                                                                   Page
 2.4-10    Typical Octave Band Spectra for Garbage Compactor
           During Compacting Operations (Levels at 50 Feet)                  113
 2.4-11    Typical Average Noise Levels Near Freeway
           (Diesel Trucks <3 Percent of Total)                               114
 2.4-12    Range of Typical Interior Noise Levels for Domestic
           and Imported  Passenger Cars at Highway Speeds                    116
 2.4-13    Typical Industry  Production/Timing Schedule                       120
 2.4-14    Effect of Potential Noise Reduction for Highway Vehicles           121
 2.4-15    Effect of Potential Noise Reduction for Diesel  Trucks               124
 2.5-1     Characteristics of Rail Systems                                    134
 2.5-2     Wayside Noise Levels and Spectra of Railroad  Equipment            136
 2.5-3     Train Vehicle Interior Noise  Levels and  Spectra                    139
 2.5-4     Wayside Noise Levels and Spectra for Rapid Transit Vehicles        143
 2.5-5     Subway Noise Levels and Spectra                                 144
 2.5-6     Noise Level as a Function of Distance from Train
           for Railroad and Rapid Transit                                    146
 2.5-7     Comparison of Interior Noise Levels in Subway Transit Vehicles      150
 2.5-8     Noise Levels at 50 Feet from Steel Wheel Transit Vehicles
           on Tie and Ballast Trackbed for Maximum Vehicle Speed            155
 2.6-1     Noise Levels and Spectra on  Ships                                164
 2.7-1     Characteristics of Recreation Vehicles                             168
 2.7-2     Typical Ranges of Noise Levels Produced by Various
           Pleasure Boat Types (db(A) at 50 Feet)                             170
 2.7-3     Motorcycle Noise Levels for Various Operating Modes              171
 2.7-4     Motorcycle Noise                                               172
 2.7-5     Snowmobile Noise                                               175
 2.7-6     Typical Octave Band Spectra for V.W. Powered Dune Buggy
           Equipped with "Megaphone"  Exhausts  (Levels at 50 Feet)            177
 2.7-7     Potential Noise Reduction for Recreational Vehicles     .           180
                                      XII

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 Figure
Number                                                                   Page

 2.7-8     Examples of Demonstrated Further Noise Reduction                 185

 3-1        Characteristics of Devices Powered by Internal
           Combustion Engines                                              191

 3-2        Typical Noise Characteristics of Generators                       193
 3-3        Typical Noise Characteristics of Rotary Lawnmowers                194

 3-4        Typical Noise Characteristics of Chain Saws                       196

 3-5        Measured Noise Characteristics of Muffled and
           Unmuffled  Model Airplane Engines                                197
 4-1        Estimated Long-Term Trend in Outdoor Residual Noise
           Levels in a Typical Residential Urban Community                   216

 4-2        Decay of Noise Level with Distance  from Single Source
           Defines Relative Bounds of Annoyance Zone                       217
 4-3        Approximate Growth of a Few Types  of Noisy Recreational
           Vehicles and Outdoor Home Equipment                            220

 4-4        Potential Hearing Damage Contributions from Transportation
           System Categories in Terms of Equivalent 8-Hour Exposure
           Levels, for Passengers or Operators                               227
                                     XIII

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1.0         INTRODUCTION
            The outdoor noise environment for man today is the summation of noise
energy generated by all of the machines used to transport people and goods, machines
used to make and build things or save human labor, machines used by the consumer for
leisure activity, machines to make the other machines run, and people in their various
activities.  Development of  this machinery has been fostered by growth in technology
itself, as well as  by pressures induced by changes in our life style and by population
growth.  This report presents a detailed evaluation of noise of transportation vehicles
including those used commercially, as well as many of the private and non-industrial
devices powered by internal  combustion  engines.
            The report has been prepared by Wyle Laboratories for the Environmental
Protection Agency in response to the directives contained in the Clean Air Amend-
ments Act of 1970, specifically, Section 401 "Noise Pollution and Abatement Act
of 1970."  It forms part of the major study accomplished by the Office of Noise Abate-
ment and Control, of the Environmental  Protection Agency, which is summarized in its
                  •*
report to Congress.
            The noise sources considered in this report are encountered throughout
man's residential, recreational and working community.  Sound is important to most
of the animal kingdom, including man.  Some sounds provide warnings of danger,
which are essential for survival. These sounds may evoke basic reactions of startle,
fear or anger, which in turn  assist in causing an appropriate response. Acoustic
warning devices such as sirens and horns utilize this principle, and the noise of an
approaching automobile is often the first clue of danger to the pedestrian or the child
playing  ball in the street.
            Other sounds evoke pleasure or are generated by an animal to reinforce or
communicate pleasure.  The  purring of a kitten and the ecstatic shouts of a child at play
  Throughout this report, references are identified by superscripts.

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are familiar examples to all.  Some pleasant sounds are relaxing,  lulling an animal to
sleep, and others are stimulating.  Music, developed by man,  covers this broad spec-
trum, appealing to a wide variety of desires and needs at both  the basic and intel-
lectual levels.
            For man, sound has even more importance.  His ability to communicate by
speech is the keystone of civilization and its spiritual, social,  political, economic
and technical progress.  Without speech communication, man would never have emerged
from a primitive state and developed the body of knowledge which could be passed from
generation to generation.  Nor would he be able to interact with  his fellow man in any-
thing beyond the most rudimentary  levels such as are displayed by the higher primates.
            The undesirability or desirability of noise in the environment must be judged
with reference to its effects on man's basic  and  intellectual perceptions and actions.
Noise is undesirable when it causes impairment  of hearing acuity, interferes with speech
communication, causes unnecessary distraction, or warns of danger when none is present.
However, noise is desirable when it provides a relatively steady background which masks
unwanted distractive sounds, or provides speech privacy so that others do not overhear a
private conversation.  Consequently, the goals  for noise control must be designed such
that the desirable qualities are retained and the undesirable qualities are minimized.  This
is a most difficult task, particularly with transportation noise which provides  the all-
pervasive almost steady outdoor residual noise level essential for speech privacy, and
also is responsible for  many of the most intrusive and undesirable noises.
            To provide a clear understanding of the significance of noise from these
sources on our environment, several aspects are considered in this report:
            •   Nature and economic significance of the  industry associated
                with the source.
            •   Basic noise characteristics  of each type of source.
            •   Environmental noise attributes of each type of source.
            •   Past and present efforts toward  reducing noise.
            •   Estimated potential noise reduction for the future with
                today's technology.

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            Chapter 2 presents these findings for all types of vehicles in our trans-
portation system, including those used for recreation.  Chapter 3 considers these same
aspects for many of the devices powered by internal combustion engines.  This over-
view of the existing and potential noise characteristics of these sources provides the
basis for an assessment of the impact of their contribution to our total noise environ-
ment which is presented in Chapter 4.  The impact is discussed from several  viewpoints
for each basic source type in our transportation system,  as well as for internal com-
bustion engine devices, and a projection is made of possible future impact to the
year 2000.  Finally, the implications of the overall results of this study are sum-
marized in Chapter 5 and recommendations made for further action to reduce the over-
all noise impact of the noise sources considered.
            Appendix A summarizes several of the more significant national standards
for noise measurement or control which are applicable to this report.  It includes a copy
of pertinent sections of Federal Aviation Regulation (FAR)  Part 36— Noise Standards:
Aircraft Type Certification.  This regulation represents the most complete and compre-
hensive noise measurement and noise regulation standard ever developed by the Federal
Government and is playing a major role in fostering development of quieter non-military
jet aircraft.
            Appendix B presents in more detail the basis for the various impact evalu-
ation models utilized in Chapter 4.  Appendix C gives a detailed  discussion of the
principal sources which dominate the noise generation by all of the systems or devices
considered in this  report.  These are the propulsion systems of aircraft and motor vehicles,
including  turbojets,-turbofans, propellers, rbtors,  reciprocating engines and tires.
            Throughout this report, single-number noise  levels are commonly specified
in terms of A-weighted noise levels in decibels, abbreviated dB(A),  defined in
Appendix  B. The A-weighted sound (or noise) level is the most commonly-used single-
number scale for quantifying approximately the subjective noisiness of sounds, par-
ticularly those from vehicles other than aircraft.  It is also readily measured with the
use of  a standard sound level meter employing the A-weighting network.  Other

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single-number scales for evaluating  aircraft noise are introduced as necessary.  Wnere

appropriate, frequency content of the noise generated by the various sources are

specified in terms of octave or one-third octave band sound pressure levels in decibels
                                                                    2
relative to 20 newtons per square meter (equivalent to 0.0002 dynes/cm ).

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2.0         TRANSPORTATION SYSTEMS

            One of the most significant forces acting on the life style in the United
States is the ever-in creasing demand for improved modes of transportation.  This force
is, in itself, a natural  product of the pressure of increasing population and  economic
growth. As the size of urban areas has increased, so has the demand for methods of
transporting people to and from their residences and places of employment.  As the
interdependency between and within urban areas has increased, so has the demand for
transporting goods and services between and within our urban centers.   These demands
have been met by an ever-increasing development of more efficient, larger and faster
modes of transportation.  First, the steam locomotive, then the automobile, next the
propeller airplane, and most recently,  the jet transport —all have acted to transform
the structure and style  of our lives by providing a wide range of transportation methods.
            The transportation industry represents,  in total, approximately  14.5 per-
cent of  the gross national product in  1970 and employed approximately 13.3 percent
of the total labor force.  This major section of the nation's economy is defined,  for
this report, as the  sum  total of the:
            •    Commercial aircraft and airline industry
            •    General aviation industry
            •    Highway vehicle industry
            •    Recreational vehicle industry
            •    Railroad and urban mass transit industry
            •    Commercial shipping industry
            The economic structure of this  industry and the general division and magni-
tude of  the transportation services provided are illustrated in Figure 2-1. ~   The rapid
growth of several segments  of the transportation system since 1950 is summarized in
Table 2-1.     While  there are  many important sources of noise which intrude on our
everyday lives, noise from  all types of transportation vehicles  tends to dominate most

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    Transportotion Service and Equipment Product
              ($145 Billion in 1970)
               Transportation Service and Equipment
                       Capital Investment
                      ($114 Billion in 1970)
   Transportation Service and Equipment Employment
              (11.3 Million in 1970)
                                  Freight Traffic
0.81 Air Freight
            Waterborne ~ Short Tons
      1.4
            (Passenger and Freight)
                  Rail Freight
                   Trucking
                  i   i  i  i  i
                                     I	I   I  I  I I  M
                              10
                               Ton-Mi les~ Bill ions
100
          408
               765
                       1000
                                                                                                   Buses
                                              Air Carriers
                                                                             Passenger Traffic
                                              Passenger Trains        11
                                                                                                                                 27
                                                                                           130
                                                                                                   Passenger Vehicle Miles  (Estimate)
                                                                                                         i    i   i   I i  i i  i I
                                                                                                                                     i   i  I  i  i 111
10                     100
  Passenger Miles~ Billions
                                                                                                               1000
1000
                                         Figure  2-1.    General Characteristics of the Transportatiori"Industry in  1970

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                                     Table 2-1
                   Growth in the Transportation System, 1950-1970
Source
Population (in millions)
Passenger Cars (in millions)
Trucks and Buses (in millions)
Motorcycles (in millions)
(Highway)
Motorcycles (in millions)
(Off-road)
Snowmobiles (in millions)
2-3 Engine Turbofan Aircraft
4- Engine Turbofan Aircraft
General Aviation Aircraft
Helicopters
1950
151
40.4
8.8
0.45
-
0
0
0
45,000
85
1960 N .
181
61.7
12.2
0.51
-•
0.002
0
202
76,200
634
1970
204
87.0
19.3
1.2
1.8
1.6
1174
815
136,000
2800
residential areas.  In fact,  the cumulative effect of the increase in noise intrusion by
transportation vehicles is, to a large extent, responsible for the current concern with
noise pollution.  This  section briefly describes the general nature of transportation
system noise sources and considers their overall impact in the  United States today.
Aircraft,  one of the more dominant sources of noise in the transportation industry,
will be considered, first.

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2.1         Commercial Aircraft


2.1.1       Introduction


            There has been a significant increase in air travel during the last decade


which is closely related to the  introduction and growth of the commercial jet aircraft


fleet.  Since 1958, when the first commercial jet aircraft started operating, passenger


air travel has grown at an average annual rate of 13.2 percent,  to a total of 132


billion passenger miles  in 1970.  In 1970, 170 million passengers were flown by the


airlines, producing an operating revenue of $7.6 billion. In addition, 5 billion ton-


miles of air freight were transported for a revenue of $715 million.  The scheduled air-


lines employed 300,000 people.  The aerospace and related manufacturing  industries


employed 765,000 people and had a total of $8.6 billion in commercial aircraft

  ,  1,2
sales.
          i                        ,

            The advantages of jet-powered passenger airplanes — greater speed and


reduced operating cost  per passenger-mile —have led to a gradual  phasing out of the


older propeller-driven commercial aircraft.   Only a small percentage of piston-


powered aircraft  now remains in the fleet, and the turboprop aircraft in use are
            '                                        i
primarily short range  twin-engine types used  on light traffic routes.


            The original commercial jet aircraft were powered by turbojet engines.


These engines have been largely replaced by quieter and more powerful turbofan
        i          *

engines.  There are two basic types of jet aircraft in the  current commercial fleet.


The first type  is the 4-engine turbofan aircraft such as the Boeing 707 and 720 and


the McDonnell-Douglas DC-8.  These aircraft are used primarily on medium and long


range flights and  are  almost exclusively powered  by first-generation turbofan engines.


The second basic aircraft type is exemplified by the Boeing 727 and 737 and the


McDonnell-Douglas DC-9. These aircraft are powered by two or three more advanced
                         f
and quieter turbofan engines and are used on short and  medium range flights.


            Two  new types of commercial jet aircraft have recently been introduced
          i                                                     ,

in the fleet.  These are powered by advanced technology turbofan  engines that are


much more powerful and quieter than  engines used in the previously mentioned aircraft
                                          8

-------
types.  The 4-engine 747 widebody jet,  introduced in 1969, is intended for long

range transcontinental and intercontinental flights.  The 3-engine widebody aircraft,

DC-10 and L-1011,  will be used on  high density, medium length flight routes.

            Figure 2.1-1 summarizes the category of commercial aircraft in terms of

                                              2-13
type, application, passenger capacity and noise.

                                                      \           i
2.1.2      Source Noise Characteristics
                  '                                                *
            The noise associated with jet aircraft is primarily generated by the jet

engines.  Noise is an operational by-product of these power plants.  The primary pur-

pose of a jet engine  is to produce the thrust necessary to push the aircraft through the

air.  A jet engine produces thrust by taking in air through the inlet, raising the air

temperature and pressure inside the engine, and then expelling it to the rear with a

high velocity from the jet nozzle. Noise is produced by several  of the processes that
    •
take place both within and outside the engine.  By far the dominant source of noise .

from the early turbojet engines was the broadband jet noise  generated in the exhaust

wake.  Jet noise is caused by the turbulent mixing that occurs along the boundary

between the  high velocity exhaust jet and the ambient air.  The  sound power generated

increases very rapidly with increasing jet velocity, hence the high noise levels are

associated with the high velocity exhausts of turbojet engines.

            The turbofan engines that have replaced  the turbojets offer substantial jet

exhaust noise benefits because they  take in larger quentities of air and  expel this air

at lower jet velocities.  This change has been accomplished by the use  of a fan section
                         •                                               \
in the engine that takes  in air, raises its pressure, and expels it through a separate

nozzle, thus bypassing the burner and turbine sections of the engine with part of the

total airflow.  However, with reduced levels of jet noise and with a noise radiation

path rearward out the fan duct and forward out the inlet, fan whine was elevated from

a secondary noise source to one of dominant importance, particularly at approach powers.

            Figure 2.1-2 shows typical noise levels and spectra measured during takeoff

and approach operations for 4-engined aircraft with low bypass engines.^  The engine
                                                         t
thrust, and thus the jet exhaust velocity, is higher during takeoff than during approach

-------

1
2-3 Engine
Turbofan

Commercial Aircraft

1.
4 Engine
Turbofan



4 Engine
Widebody
Turbofan


1 1
3 Engine
Widebody
Turbofan

Propeller
Aircraft
» Short to
Medium Range
» B727, B737
» DC -9, BAC-11
• Medium to
Long; Range
e B707, B720
1 • DC -8
• Long Range
• B747


• Medium Range
• DC-10,
L- 1.0 11

• Short Range
• F-27
• CV340/440
• DC-3
Average Passenger Capacity
100
150
365 1
250
40
                                Typical Range - Miles
250-1500
                    1000-4000
1000-2500
                            Growth of Aircraft Fleet
1960 65 70        I960 65 70         1960 65  70




                               Typical  Noise Levels
                                                       I960 65  70
IOUU
1
|l200
<
14-
O
_g 600
E
0
1
209
r
1
174

202
712

815
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1 — 1
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1163

380

                 196065  70
1 10


1 f\f\
IUU
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£§ 90
I
1 80
« 70
in / v
5
Z 60
50
_ Approach and Takeoff Noise Levels Measured at 1000 feet
105 im
100 100

-
—


-
90
85
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                Figure 2.1-1.  Characteristics of Commercial Aircraft

-------
                                                           Jet/Turbine
Z
 3-
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CN
 £
CO
T3
 
^5
•-







Total


               Contributing Subsources for Typical Aircraft

                     Figure 2.1-2. Noise Limits and Spectra of 4-Engine
                           Low Bypass Ratio Turbofan Aircraft
                                          11

-------
and consequently the low frequency jet noise is significantly higher at takeoff than at

approach.  However, the high frequency fan noise is relatively insensitive to engine

power setting and thus becomes clearly dominant at approach engine conditions.

            Typical noise  levels and spectra for the 2- to 3-engine turbofan aircraft,

powered by later model turbofan engines, are shown in Figure 2.1-3.   The noise pro-

duced by these aircraft is lower than that shown in Figure 2.1--2.  The jet noise is

lower because of slightly reduced  jet velocities, and the high frequency fan noise is
            '                         i
considerably reduced due to fundamental improvements in fan design.
                                                 '
            The 4-engine  turbofan widebody aircraft, which are powered by new

technology engines, incorporate several advancements both with respect to propulsion
                    (                               t
efficiency  and reduced noise generation.  These engines pass a high percentage of the

total  airflow through the fan section, and are therefore considered  high bypass  ratio
             t                        .                   -i         '
turbofan'engines in comparison with the earlier low bypass ratio engines. The low jet

exhaust velocity made possible with these new engines has resulted in a significant

reduction in  jet noise.  This reduction is clearly shown by comparing the noise  levels
        I                                                      /- o'
and spectra presented in Figure 2.1^-4 with those of Figure 2.1-3.     The fan noise

dominates both during takeoff and approach operations.  Despite the considerable

technological advances that were  incorporated in the  fan design, the discrete frequency

fan whine  forms the major  obstacle to achieving significant noise reduction.

            The new 3-engine turbofan wTdebody aircraft uses  similar engines, but
                                           o     I
with additional improvements in fan noise reduction.  These improvements will  be dis-

cussed in Section 2.1.4 and furfher information on the mechanisms  of jet engine noise

generation may be  found in Appendix  C . i  ,

            The noise generated by commercial propeller aircraft is dominated  by pro-

peller noise.  Typical  noise spectra and levels for various types of commercial propeller

aircraft are compared with  the noise of the original turbojet aircraft in Figures 2.1-5

and 2.1-6.   The  increase in aircraft noise which occurred with the introduction of

the jets is  evident.  Because propeller aircraft constitute such a small  percentage of

commercial aviation aircraft, especially so with respect to  their relative noise impact,
                                        ,12

-------
                                                           Jet/turbine
                                       Fan
                                    Compressor
   no
z
a
o
CN

fi'
OQ
-
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-------
               Fan/Compressor
                                                   Jet/Turbine
CN



 z
  D-

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-------

-------
CN
    100
     90
I
 o
 CN
 CO
 -o
  
-------
the detailed discussion of propeller noise will be deferred to the General Aviation
Category for which it forms the dominant characteristic noise.
            The noise level in the interior of jet aircraft is dominated by a different
noise source.  Because these aircraft travel at high speeds,  the  pressure fluctuations
generated by the turbulent mixing that occurs in the boundary layer between the air-
craft fuselage and the surrounding air become  significant.   These fluctuations cause
the fuselage walls to vibrate and radiate noise  into the aircraft  interior.  The "boundary
layer" noise dominates at most interior locations except at the aft end of the aircraft,
at which low frequency jet noise impinging on  the fuselage and transmitted through to
the interior may becomes the dominant noise source.'0-13
Sonic Boom
           'Supersonic aircraft introduce a new element into the aircraft noise problem.
Whereas the noise from subsonic aircraft is primarily a phenomenon associated with the
airport environment, the sonic boom generated by aircraft  flying at  supersonic speeds
creates a ground impact underneath  its entire flight path.  Although supersonic flights
by military aircraft over populated and areas within the United  States have been pro-
hibited,  supersonic military aircraft continue to produce an estimated 6000 sonic booms
annually over sparsely populated areas.'^
            When an airplane flies at supersonic speed, it compresses the surrounding
air,  pushing a shock wave,  much like a boat creates a spreading bow wave. This bow
wave, or cone of increased air pressure, spreads out behind the airplane.  Correspond-
ing waves are generated  at locations of airflow discontinuities along the length of the
airplane.  At  great distances, the separate waves or shocks interact with each other
and  coalesce into two waves, a  bow shock and a tail shock. In this form the pressure
signature is called an  N wave.  Figure 2.1-7 shows that as the distance from the
airplane is increased, the distance between the bow and tail wave is also increased.'"
The  intensity of the sonic boom depends on such factors as speed, altitude,  weighted
shape of the airplane, atmospheric conditions, and type of terrain over which the air-
craft is passing.
                                        17

-------
/ —
                                   Atmospheric Pressure
Figure 2.1-7.   Nature of the Sonic Boom Phenomenon
                         18

-------
            Community impact studies conducted in anticipation of the United States
supersonic transport aircraft have suggested that the sonic booms generated by a fleet
of this aircraft would produce a clearly unacceptable noise impact on populated areas.
For example, sonic booms generated by the military B-58 aircraft, at a strength of 1.7
pounds per square foot nominal peak overpressure, were judged  by residents of a sub-
urban community to be equal in acceptability to the noise from  a subsonic jet at about
107 dB(A), which is clearly an unacceptable value.   This result, together with the
vigorous complaints, political and legal actions encountered in  other sonic boom over-
flights,  has  led to an administrative decision at the Federal level to  prohibit supersonic
military and commercial flights over populated areas.  This prohibition in the United
States, and  similar prohibitions in other countries,  are expected to continue until new
technology developments result in supersonic aircraft concepts that produce acceptably
low sonic boom levels.
2.1.3      Environmental Noise Characteristics
            The noise generated by commercial aircraft results  in two types of noise
environments that differ in terms of the noise levels and duration of exposure,  as well
as in  the aircraft operations that generate the noise impact.  The participant,  or pas-
senger,  is exposed to moderately high noise levels  throughout the entire history of air-
craft  operations from the time of boarding the aircraft,  takeoff,  cruise to the flight
destination, and landing.  Figure  2.1-8 gives time histories of  typical cabin noise
levels for  the flight duration.   If the aircraft makes intermediate stops, the passenger
may be subject to this set of operations several times during a single  flight.
            Commercial jet aircraft are designed to maintain  interior noise levels during
cruise operations which enable passengers to converse at normal voice with good speech
intelligibility.   As  is shown in Figure 2.1-9,  the cruise interior noise levels range
typically from 79 to 88 dB(A), depending on the interior  location, with a characteristic
                 O  i o
value of 82  dB(A).       During takeoff and landing operations,  the noise levels in
aircraft with wing  mounted engines are up to 12 dB higher, but  only  for periods of up
to 1 minute  during each operation.  The statistical  characteristics of the passenger
                                                             i o
environment, summarized in Table 2.1-1,  refer to  1970 figures.'/z
                                        19

-------
   100
    90
CO
TJ
g  80

.3
0>
*/>
'5
Z
    70
    60
                 Liftoff
                                      	Boeing 720B - Seat 22F

                                     	  McDonnell-Douglas DC-8 - Seat 64A
                                         —  Boeing 727 - Seat 19A
                        Landing
                       Preparation
                              Thrust Reversers
                         Engine
                Power
Cutback

Climbout

Cruise

Descent

Cutback

J'j
                   0       5      10     15      20

                   Time From Brake Release - Minutes
                                                                                                         fi
                               II

20      15     10      5        0

  Time To Touchdown - Minutes
                                   Figure 2.1-8.. Time Histories of Typical Cabin Noise Levels

-------
                                                    Jet/Turbine
                                           Fan
                                        Compressor
    110
    100
     90
                 —Jet Noise-
CM
 o
 CN
 |  80
  a>
  o
 eo
  o
  t>
  O
     70
     60
     50
                              Boundary Layer Noise
                     	Typical Spectrum
                        100
           1000


Frequency in Hertz
10000
100

S" 80
TJ
I 60
5
» 40
•- 20
o
-^
z o
—


—

— •



85
>9








Aerodynamic
Noise "
(Fuselage)

<
» .
ft

65








Jet




89
79









Tot




                              Contributing Subsources

                     Figure 2.1-9.  Interior Cabin Noise Levels and spectra
                                 for Commercial Jet Aircraft

                                       21

-------
                                  Table 2.1-1
                              Passenger Environment-
        Number of Passengers/Day                            —  465,000
        Characteristic Cruise Noise  Level                     —  82 dB(A)
        Average Duration of Exposure                         —  1.4 hours
        Characteristic Takeoff and Landing Noise Level        — <95 dB(A)
        Approximate Duration of Exposure per Operation       — ^ 1 minute
            With respect to the nonparticipant environment, the noise impact from
commercial  air operations is experienced in the vicinity of the airports, and to a
lesser extent further from the airport under the climbout and approach paths.  For-
tunately, during cruise operations, current commercial  aircraft fly at too high an
altitude to generate a significant noise impact on the ground.  However,  takeoff and
landing operations generate very high noise levels on the ground that"extend over
large areas, and where the airport is  close to a city, large numbers of people may
live within the noise impacted areas.
            The growth of the noise impact due to commercial aircraft operations is
very closely related to the introduction of the commercial jet aircraft in 1958 and the
manner of growth of air travel during  the following decade.  First, as illustrated in
Figures 2.1-5 and 2.1-6, the jet aircraft were approximately 12 to 20 dB noisier on
approach and  takeoff than  piston-engined aircraft which they replaced.'^ Secondly,
although the number of major airports has increased only slightly since the late 1950's,
the number of commercial aircraft in  the fleet has grown many times' over.  Finally,
vast new residential communities have been established in the vicinity of nearly all
busy airports.  This combination of expanding air travel and'residential growth has
resulted in a serious airport-community noise problem.
            In order to assess  the impact of aircraft noise on the community, the
Noise  Exposure Forecast (NEF) method has been widely used. This method gives a
single  number rating of the cumulative noise produced in the vicinity of an airport by
                                        22

-------
aircraft operations, taking into account the total mix of aircraft utilizing the airport,
subje'ctive noise levels generated by each aircraft class, flight paths,  number of opera-
tions in day and night periods,  et cetera. Figures 2.1-10 and 2.1-11 show an example
of NEF values versus slant range, for takeoff and landing operations, respectively, for
the various types and numbers of commercial aircraft that are expected to utilize a
typical large airport.'/2  It  is readily apparent in this example that the 4-engine  turbo-
fan aircraft  powered by the first-generation low bypass ratio turbofan engines (B707,
B720,  DC-8) give  the maximum NEF values, primarily because they have the highest
noise  levels together with having about 30 percent of the total operations.  On the
other  hand,  the low NEF values of the Boeing  747,  shown in  this example,  primarily
reflect its relatively small percentage of total  operations.  The NEF 30 contours result-
                                               7 8
ing from this example are  shown in Figure 2.1-12. '  For simplicity, the aircraft are
assumed to operate in the  same  direction on a single runway, and the contour combines
the effects of both takeoffs and landings.  Operations by the  4-engine  low bypass ratio
turbofan aircraft (Boeing 707 and 720, McDonnell-Douglas DC-8) contribute 69 percent
of the total  impact area, despite comprising only 30 percent of the total number of
operations.
            Current Federal guidelines for planning recommend that new residential
construction should not be undertaken  in areas around airports exposed  to values of the
NEF rating of 30 and higher.'"  In addition, they state that individuals in existing
private residences  may complain about noise, perhaps vigorously, when the NEF is
between 30  and 40. When the  NEF exceeds 40, residential use is considered incom-
  «                  •''.-'                  "
patible with the noise.  The community reaction scale ° essentially agrees with this
expected complaint level .when the outdoor residual noise level in the community  may
be classified as urban residential, a condition  which is generally met in the vicinity
of our major airports.   However,  if  the outdoor residual  noise level in the community
has a  lower  value,  such as would be expected  for quiet or normal suburban residential,
                                                                                   l ft
it is suggested that the NEF values for equivalent reaction must be lowered accordingly.
However, for simplicity in this report, a constant value  of NEF 30 will be used for the
                                      23

-------
   80
70  -
                          B707, B720, DC-8
                          DC-8 (Stretched)
                          B727-100, B737, DC-9
                          B727-200
                          B747 (Jumbo)
                          Propeller Aircraft
                          Total Impact
   60
                                                   Equivalent Large Airport (1970)
   50
CO
TJ
 ID
                                                Commercial
                                                Aircraft Type
                                             6727^100, B737, DC-9
                                             B727-200
                                             B707,B720,DC-8
                                             DC-8 (Stretched)
                                             B747 (Jumbo)
                                             Propeller Aircraft
                                                                       No. of
                                                                      Ope r./Day
   40
   30
   20
   10
              TAKEOFF
          * Total operations, 86.3 percent of which
            occur during daytime (0700-2200 hours) and
            13.7 percent of which occur during night time
            (2200-0700 hours).
      200
               400
4,000     7,000 10,000
              700    1,000       2,000
              Slant Distance to Aircraft - Feet

Figure 2.1-10.  Noise Exposure Forecast vs Slant Range (Takeoff)
              for an Equivalent Large Airport

                       24

-------
                       B707,  B720, DC-8
70
   	DC-8 (Stretched)
   	 B727-100,  B737, DC-9
   	 B727-200
   	B747 (Jumbo)
   —- —	 Propeller Aircraft
   	— Total  Impact
                                Equivalent Large Airport (1970)
                                       Commercial
                                       Aircraft Type
                                                     No. of
                                                 Operations/Day
50
                          B727-100, B737, DC-9
                          B727-200
                          B707, B720, DC-8
                          DC-8 (Stretched)
                          B747 (Jumbo)
                          Propeller Aircraft
                          X
                            X
                             X
30
20
10
 0
            APPROACH
Total operations, 86.3 percent of
which occur during daytime (0700-
2200 hours) and 13.7 percent of which
occur during night time (2200-0700 hours).
                          700    1,000    ,    2,000
                          Slant Distance to Aircraft — Feet
                                                  4,000      7,000 10,000
            Figure 2.1-11. Noise Exposure Forecast vs Slant Range (Approach)
                           for an  Equivalent Large Airport
                                  25

-------
     20 _
o
     10
0)
1§
Ǥ-
o
c
Q
l/>
Q
     10
     20
                    Representative Large Airport (1970)
                     Commercial
                    Aircraft Type
               B727-100, B737, DC-9
               B727-200
               B707, B720,  DC-8
               DC-8 (Stretched)
               B747 (Jumbo)
               Propeller Aircraft
                         Landing
  Number of
Operations/Day

      140
      40
      108
      18
       6
      54
      366*
                                                              Total operations, 86.3$of which occur during
                                                              daytime (0700-2200 hours) and 13.7$ of which
                                                              occur during nighttime (2200-0700 hours).
           Total No. of Aircraft
                4 Engine Low Bypass Turbofan
                     All Other Aircraft
                                               NEF 30 Contours
                                                                             Takeoff
       50       40        30       20
                     Distance to Threshold
                            1000 ft
                                             10
               0
1-0       20        30       40
   Distance from Brake Release
            1000ft
50
                   Figure 2.1-12.   NEF 30 Contours for Representative (Single Runway) Airport

-------
purpose of discussing the noise impact- from aircraft operations.  The use of this value
to define  the boundary of the noise impact zone is conservative, but it should not
impair any qualitative conclusions, since the majority of the currently impacted area
is in the residential urban ambient noise level category.
            Within the United States, the total area within which NEF 30 is exceeded
has grown from approximately 100 square miles in 1958 to approximately 1450
                    •JO on
square miles in 1970.  '    These areas are estimated to contain respective populations
of approximately 500 thousand and 7.5  million people.  A considerably larger number
of people  are undoubtedly annoyed by aircraft noise, because of the conservatism
indicated  above, and because over 30 percent of the population exposed to NEF 30
are expected to be very much annoyed with the  noise, and approximately 20 percent
are very much annoyed when exposed to NEF 20.
2.1.4      Industry Efforts  In Noise Reduction
            The commercial jet airplane and jet engine manufacturers have generally
been  involved with the military as well  as the civilian aircraft marker.  In fact,  the
jet engines that were responsible  for ushering in the new era  in commercial air trans-
portation were  originally developed for military purposes, and the first commercial jet
aircraft were based on technology fall-out from  the development of large  military jet
aircraft.
            Noise impact has never been a  major design constraint in the majority of
military applications of jet-powered aircraft.  It is not surprising, then, that military
jet engines have been, and  still are, extremely noisy.  The civilian derivatives of
these engines have thus had their basic  characteristics designed without any noise
criteria.  Both  the airframe  and engine  manufacturers have been aware of the potential
community noise problems due to  the excessive noisiness of jet aircraft, and have
carried on research and development work on jet engine noise reduction since well
before the introduction of the first commercial jet airplanes.  Unfortunately, the rapid
development of the commercial jet fleet market demanded technological advances in
jet engine performance and  noise acceptability  faster than the embryonic  jet engine
                                       27

-------
noise technology was able to accommodate. The first turbojet engines were made
modera'rely quieter by means of jet noise suppressors mounted on the engine tailpipes,
but still  generated unacceptably high noise levels.  The introduction of the low bypass
ratio turbofan engines was anticipated to reduce the jet noise problem.  However, the
appearance of fan noise as a dominant noise source negated some of the expected
benefits.
            The high bypass ratio turbofan engine represented the first commercial jet
engine for which engine noise technology was sufficiently well developed to measurably
influence the basic design.  Although these engines did not rely on noise considerations
as the primary basic design input, they did  include the most advanced practical con-
cepts of  low noise generation.  As will be discussed below, later models of these
turbofan engines have incorporated still more noise-reduction features.
            Figure 2.1-13 shows the present and a projected composition of the United
                ~ ' •                71
States commercial jet aircraft fleet/   The low bypass ratio turbofan aircraft form the
great majority of the fleet and will continue to  be dominant until  1985.   Hence, the
introduction of the quieter high bypass ratio turbofan aircraft will not automatically
.result in a reduction of the community noise problem except on a long-term basis.  This
becomes even more apparent on examining the projected growth in commercial  aircraft
airport operations, presented in Figure 2.1-14.  This figure has been prepared on the
assumption of a 5 percent annual increase in the number of passenger emplanements
and a corresponding annual increase of 3 percent in the number of aircraft operations.
The increased number of operations is sufficient to offset the potential benefits  of the
quieter aircraft unless steps are taken to reduce the noise generation  by the older
turbofan aircraft.
            The commercial jet aircraft industry has been strongly committed to the
reduction of jet engine noise,  especially so during the last 7 years, and  has carried
out extensive research and development programs both at industry expense and with
the assistance of Federal funding.  These  efforts have  been aimed both at the develop-
ment of advanced noise technology for use in the design of future jet engines, and the
                                       28

-------
   2500
   2000
E
u
   1500
                       2-3 Engine Low Bypass Turbofan




                       4-Engine Low Bypass Turbofan
—	  4-Engine Wide Body (747) High Bypass Turbofan




—	3-Engine Wide Body High Bypass Turbofan




	  New Technology CTOL or STOL (125- 150 Passenger)
 E

 E
 o

U
   1000
 (D

_Q

 E



Z
    500
      0
               1970
                       1975
1980
1985
                                            Year
            Figure 2.1-13.   Projected Change in Commercial Aircraft Fleet Composition


                         (Based on Projected Passenger Capacity Demand

                                  Increasing at 5 Percent/Year)
                                       29

-------

700
^
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 Annual Increase in Number
Operations of Aircraft Operations

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   1970
1975
1980
1985
2000
Figure 2.1-14.   Projected Growth of Commercial Aircraft Traffic
                              30

-------
development of practical concepts and hardware to permit retrofitting of present jet
engines.  Although these programs have yet not been singularly successful in reducing
the noise  impact, encouraging progress is being made.  The adoption of Federal regu-
lations governing the permissible noise impact by new airplanes and their anticipated
extension to coverall commercial aircraft will hopefully spur the implementation of
the technology developments in  the aircraft fleet.  These  regulations will be discussed
in a separate section below.
            The anticipated development of large (125  to 150 passenger) STOL com-
mercial aircraft during the next  decade will create new demands on the industry's
noise abatement technology. These aircraft will  operate out of short field length gen-
eral aviation and new urban airports as well as the large commercial airports, and
must be able to meet stringent noise  level standards in order not to  impose pollution-
level noise impacts at their operation centers.  The concept and technology develop-
ments planned for these future air transports will be discussed in a  later section.
Federal Government Regulations of Aircraft Noise
            After receiving authority from Congress, the FAA initiated a lengthy and
far-reaching rule-making process which culminated in Federal Aviation Regulation,
Part 36 — Noise Standards: Aircraft  Type Certification, published in the Federal
Register of 21  November 1969.   The noise limits of this regulation apply only to
subsonic jet aircraft in the following categories:
            •   Airplanes that have turbofan  engines with bypass  ratios of 2 or more
                (i.e., new technology high bypass engines used by the new wide-
                bodied transport aircraft) and  for which application for certification
                was or is made  on or after January  1, 1967.
*
 The technical requirements of FAR-36 are reproduced in Appendix A.
                                          31

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            •    For new airplanes that have turbofan engines with bypass ratios of 2
                 or more, which do not meet FAR-36 noise levels and where applica-
                 tion for certification was made prior to January  1, 1967, the FAA
                 will place a time period in the type certificate.  At the expiration
                 of this time period, the type certification will be subject to suspension
                 unless the type design of aircraft produced under that type certificate
                 after the end of this time period is modified to comply with the noise
                  I*  • «.
                  imits.
            • .    Airplanes that do not  have turbofan engines with bypass ratios of 2 or
                 more (i.e.,  pure jets  or low bypass turbofans as  found on most current
                 aircraft) and  for which application for certification was made after
                 December 1, 1969.
            FAR-36 defines noise limits such aircraft must meet at certain locations
with respect to the airport runway, shown in  Figure 2.1-15.
            Three measurement locations are required in certification.  They are:
            •    Landing — 1  nautical mile  from threshold, directly under the aircraft
                 path,
            •    Takeoff— 3.5 nautical miles from brake, release, directly under the
                 aircraft path, and
            •    Sideline —at the location  of maximum noise along a line parallel  to
                •and at a distance of 0.35  nautical miles  from the runway centerline,
                 for aircraft which have four or more engines; and 0.25 nautical  miles
                 from the runway centerline, for aircraft which have three or fewer
                 engines.
            Additional restrictions are imposed to insure that aircraft become pro-
gressively quieter at flight positions further from the airport.
            The noise limits at the three measurement positions are given in terms of
the aircraft's maximum certificated gross weight. The permissible variation with  gross
                                         32

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CO
CO
           Measurement
           Point
                                                                    Assumed position of brake
                                                                    release for takeoff and
                                                                    threshold for landing
                                             . Sideline Measurement
                                                                                               Takeoff
                                                                                               Measurement
                                                                                               Point
                                 Figure 2.1-15.    FAR-36 Noise Certification Measurement Positions

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weight gives implicit recognition to the fact that for a given technology in engine
design, the absolute noise from an airplane must increase with required thrust — which
in turn must increase with gross weight.  For many airline  flights, the aircraft operate
at less than maximum gross weight, and hence, less noise.
The Effect of FAR-36 on the Noise of Future Aircraft
            Most of the turbofan aircraft which .constitute the bulk of the  present jet
aircraft fleet exceed the  FAR-36 noise  limits.  Figures 2.1-16 to 2.1-18 make these
comparisons for the landing, takeoff and sideline  noise measurement points, respectively.
It is obvious that the noise levels of most current aircraft are significantly  higher than
the noise  limits of FAR-36, particularly for takeoff and landing.
            The comparisons show the  amount  of noise reduction that will  be  accom-
plished by designing and  producing future aircraft which meet the certification
requirements.  Effective perceived noise levels of future aircraft will be reduced by
as much as 14 EPNdB for  takeoff and landing,  and 5 EPNdB along the  sideline.
Noise Reduction  Progress
            In the previous section, it  was noted  that the research efforts  by the
industry have been directed towards both the development of advanced technology
quiet engines and the development of retrofit concepts for current engines. At this
time, both efforts have yielded results that are in evidence in new aircraft in the
current aircraft fleet.   Figure 2.1-19 shows the noise  levels generated by  the older
turbojet and low  bypass ratio turbofan engines  compared with  the new  advanced tech-
nology high bypass ratio turbofans. ' '   It is  noted that the second generation turbofan
engines of the older type are up to 8 EPNdB quieter than the first types on the basis of
equal thrust.  The JT9D high bypass ratio engine  is also quieter, despite producing
250 percent more thrust.  The newest engine shown/ the CF6, generates noise levels
up to 16 EPNdB less per unit thrust than the first turbofan engines. This engine
represents a significant advancement in the application of noise reduction  technology,
and will be discussed in more detail.
                                        34

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       125
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 0)
       	1	


        The "%" symbols indicate

        levels produced by

        existing aircraft
       120
115
       105
                                 ^ftf-
       100
        95
                                           JL
J_
                            75,000              150,000             300,000             600,000



                                               Takeoff Gross Weight in Pounds



                      Figure 2.1-16.  Effective Perceived Noise Level for Landing for Today's Aircraft

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               The "0" symbols indicate
               levels produced by
               existing aircraft
        115
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 >
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 105
 tj
 £
 LLJ
        100
         95
         90
                                                  150,000
                                                              300,000
600,000
                                                  Takeoff Gross Weight in Pounds

                         Figure 2.1-17,  Effective Perceived Noise Level for Takeoff for Today's Aircraft
                                                 Compared to FAR-36 Limits

-------
                   120
                         The "%" symbols indicate
                         levels produced by
                         existing aircraft
                   115
              CO
              -o

              Q_
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                    95
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                         I
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                                         75,000
                                          150,000              300,000

                                          Takeoff Gross Weight in Pounds
                                      600,000
                                    Figure 2.1-18.  Effective  Perceived Noise Level at Sideline for Today's Aircraft-
                                                             Compared to FAR-36 Limits

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   70
Q_
   60
_c
I—
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_0
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 I

Z 50
Q_
   40
           Turbojet
         'JT3C
        (13,500 Ib)
                                Low Bypass
                                 Turbo fan
 High Bypass
  Turbofan
                           JT3D
                         (18,000 Ib)
                                     JT8D
                                   (13,500 Ib)
    *9D
(45,000 I
                                                                        %
                                                                 \
                                                                       CF6
                                                                    (40,000 Ib)
             •  Takeoff Condition

             o  Approach Condition

             1000 ft from Aircraft
                                                                       \  -
                  1960
                                           1965
         1970
                                       Year
                Figure 2.1-19.  Trends in Jet Engine Noise Generation  .
                                    38

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            Three basic features of the CF6 engine are dominantly responsible for its
low noise characteristics.  The first is the selection of high bypass ratio in order to
reduce the  jet exhaust velocity and hence greatly reduce the jet exhaust noise.   The
second is the advanced technology design of the fan section to minimize the genera-
tion of discrete frequency turbomachinery noise.  The third, and perhaps the most
significant noise reduction feature, is the use of long inlet and fan discharge ducts
that are  lined with sound-absorptive treatment in order to reduce the transmission of
turbomachinery noise out from the interior of the  engine. This combination of features
has resulted in noise levels that make the DG-10-10 aircraft,  powered by the CF6
engine,  much quieter than current aircraft as shown  in Table 2.1-2 below:

                                  Table 2.1-2
           Maximum Perceived Noise Levels of the DC-10-10 Relative to
                     Those of Current 4-Engine Jet Transport^
• Current
s Relative

Takeoff
Full Thrust
75 Percent Thrust

Approach
Typical Thrust
Jet Transports Powered by Four JT3D-3B
Levels in PNo'B
1000 Feet
Outdoors
-11.5
-13.5
400 Feet
Outdoors
-10
Engines

3500 Feet
Indoors
-15
-13
1500 Feet
Indoors
-11
                                       39

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            Figure 2.1-20 shows the noise spectrum of the DC-10-10 compared with
that of a current 4-engine  turbofan aircraft.  It is apparent that both  the jet exhaust
noise and the high frequency turbomachinery noise have been significantly reduced.
            NASA has funded several research and development programs aimed at
developing technology for  the retrofit of current turbofan  engines.  The NASA
Acoustically Treated Nacelle Program attempted to reduce the fan noise radiation
from the inlet and discharge ducts of 4-engine low bypass ratio turbofan aircraft by
          i    "                               OO
treating the nacelle with sound absorbing lining.   Independent studies were carried
out by both  Boeing and McDonnell-Douglas on B707-320B and DC-8-55 aircraft.
These programs achieved a  significant reduction  in approach  noise, but only a slight
reduction in takeoff and sideline noise. However, the weight and cost penalties
involved are too severe to  be readily accepted by the aircraft operators.  The main
results of the programs a re summarized below in Table 2.1-3.

                                  Table 2.1-3
                                              i
                 NASA Acoustically Treated Nacelle  Program^!
              Variable
    Boeing
McDonnell-Douglas
   Reduction' of Approach Path
   Noise (3° approach at 1 n.mi.)
   Range Effect
   Weight Penalty
   Cost of Retrofit per Aircraft
   (300 to 400 aircraft)
   Increase in Direct Operating
   Costs
15.5 EPNdB

200 n.mi. loss
3140 pounds
$1,000,000 ,

9.6 percent
   10.5 EPNdB

   150 n.mi. gain
   332 pounds
   $655,000

   4.2 percent
                                      40

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                       Frequency in Hertz
Figure 2.1-20.   Flyover Noise Levels - DC-10-10 Compared to
   Current Jet Transports Powered by (4) JT3D-3B Engines'    '
                        41

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            Another NASA-funded program is aimed at demonstrating the capability
of advanced fan design technology and nacelle acoustic treatment to guide the design
of a new high bypass ratio turbofan engine with takeoff and approach noise  levels
significantly lower than have been achieved to date.  Carried out by General Electric
and Boeing, this Quiet Engine Program is due to be completed during 1973.23 Integra-
tion studies conducted by McDonnell-Douglas show that substitution of an engine with
the design parameters of the Quiet Engine for the old turbofan engines on DC-8 and
B707 aircraft would result in improved performance as well as dramatically reduced
            f\ A
noise  levels.   However, the high cost of engine replacement, and the  fact that only
experimental component hardware will  come out of the program, throws doubt on the
prospects of its  immediate implementation.  Rather, the Quiet Engine Program should .
be viewed as a  development of new technology which can be applied in  design of new
engines for future aircraft. The expected results of the Quiet Engine Program are
summarized below in Table 2.1-4, with the CF6 engine included  for comparison:

                                 Table 2.1-4
                          NASA Quiet Engine Program
Noise Level Goals Compared with B707/DC-822
Flight Condition
Takeoff
Approach
Noise Reduction - EPNdB at
FAA Measurement Positions
Bare
Quiet Engine
13
17.5
Acoustically Treated
Quiet Engine
23
25.5
CF6 Engine
(DC- 10)
18
11.5
                                     42

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            An alternative approach to noise reduction for the current fleet of aircraft
 is that of altering flight procedures.  At some airports, the concept of reduced thrust
 takeoff has been adopted. This procedure consists of a full thrust takeoff and initial
 climb, after which the aircraft climbs over heavily populated areas at a reduced
 thrust for some distance before resuming a normal climb.  By this method, maximum
 noise reductions at the FAA takeoff measurement position of 6 to 10 EPNdB may be
 expected for 2- to 3-engine  low bypass ratio turbofan aircraft and 3 to 6 EPNdB for
                                         oc
 4-engine low bypass ratio turbofan aircraft.    For new aircraft incorporating the CF6
•engine technology, thrust reduction does not appreciably change the noise levels/*
 Additional  fan noise suppression will be necessary to realize the potential of this
 operational procedure for these advanced technology engines.
             In order to reduce the noise impact during approach, a  "two-segment"
 landing procedure has been proposed. This consists of an initial approach glide slope
 of 6 degrees down to a yet unspecified distance from the end  of the runway,  at which
 the standard 3 degree  approach is resumed.  In analytical studies carried out by
 NASA, reduction of 10 PNdB or more was achieved at 1.5 nautical miles from the
                                                                ")f\ 97
 runway threshold for profiles with an intercept altitude of 400 feet. °'    Figure 2.1-21
 illustrates this procedure fora  current 4-engine turbofan aircraft and shows the effect of
                                                           OQ
 retrofit with the NASA Acoustically Treated Nacelle concept/0 However,  it must be
 realized that feasibility of the steep approach  in terms of airplane operational  safety
 has not been verified.  This factor must be thoroughly evaluated and assessed before a
 decision on the adoption of this landing procedure  can be made.
 Plans for Future Suppression of Noise
             The commercial  jet transport industry, together with several  Federal
 agencies, is expected to continue and in some areas intensify its research and develop-
 ment programs aimed at achieving quieter air transportation systems.  These programs
 include the development of practical and economical retrofit hardware, research into
 quiet engine  technology beyond  the scope of the Quiet Engine  Program, and the
 development of STOL  transportation  concepts.
                                      43

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                                   Approach  FJight Paths
    o
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                                                 3000 ft
                                                           V
                            -Select Landing Flaps     >~ Vecfor Altitudes

                            T                    1500ft
                          Normal Glide Slope
                            4       6        8       10



                              Distance from Threshold, n. mi.
                                                 12'    '   14
                                                                         16

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            On the basis of the technology developments resulting from the NASA
Acoustically Lined Nacelle Program,  FAA is funding a development program to design
and manufacture noise reduction packages suitable for retrofitting the current low
                           29
bypass ratio turbofan engines.    The  possible future implementation  of these retrofit
packages in the aircraft fleet will insure compliance with the FAA noise regulations.
            NASA is funding several preliminary studies to determine the feasibility of
a future advanced technology transport aircraft.  Three separate noise objectives are
being considered:  the current  FAA noise regulations (FAR-36), FAR-36 minus  10 PNdB,
and FAR-36 minus 20 PNdB.  NASA anticipates a 6 to 10 year development program
                                           o/\
for this aircraft, starting in the middle 1970's.    The future development of short-
range V/STOL transportation systems is discussed fully in the V/STOL section of this
report.  However,  the potential  large  jet-powered STOL aircraft falls logically within
the scope of commercial jet transportation. NASA  is currently funding preliminary
development of STOL jet propulsion systems, and has proposed the development of a
                                                                      i   • •
150 passenger STOL airplane, with the concurrent  development of a quiet STOL jet
engine. These developments include a primary!emphasis on noise reduction, with the
planned requirement of a maximum noise level of 95  PNdB at'a  distance of 500 feet
from the aircraft.  The Sryear prototype STOL program is currently scheduled for
completion at the end of 1975.30'31
            Table 2.1-5 summarizes some of the  major Federally-funded technology
development programs that are exclusively oriented toward jet engine noise reduction
or include noise  reductions as a primary requirement  (anticipated future programs
included).
2.1.5       Noise  Reduction Potential
  !      '    -^———————r-—————
            The  potential noise reduction achievable by means  of current and poten-
tially available technology, starting with the technology demonstrated in the CF6
engines and those of the  Federally-funded research programs, is summarized in Table
2.1-6.4/23  The noise levels are specified in terms of the FAR-36 takeoff measure-
ment posi'tion.
                                     45
                                   3. - 7 9

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                     Table 2.1-5
    Federal Noise Abatement Programs^, 29,30,32
Program
NASA Acoustically Lined
Nacelle Program
NASA Quiet Engine Program
DOT Retrofit Program
STOL Noise Reduction
Demonstrator Program
Augmentor Wing STOL
Program
STOL Prototype Program
STOL Quiet Engine Program
Advanced Technology
Program
Approximate Program Cost
Millions of Dollars
15
22
7-15
8
1.5
100
58
250
Scheduled
Completion Date
1968
1973
1973
1972
1972
1975
1975
1983
                    Table 2.1-6
Estimated Aircraft Noise Reduction Potential for Takeoff
EPNdB at FAA Measurement Position

DC- 10- 10 Technology
Quiet Engine
Quiet Engine with
Optimum Jet Noise
Technology
Further Fan and Core
Noise Reduction:
Optimum Quiet Engine
Jet Noise
EPNdB
95
94
88
88
Fan and Core
Noise Reduction
dB re DC- 10- 10
o
-10
-10
-16
Total
EPNdB
100
95
91
89
                          46

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            This analysis suggests that-a noise reduction of 11 EPNdB below the
 noise levels generated by the DC-10-10 aircraft is possible.  It must be realized,
 however, that a high level  of investment by Federal Agencies and the aircraft
 industry in research and development will be necessary to achieve this  goal, partic-
 ularly in the area of core noise reduction.
            The requirement of 95 PNdB  at 500 feet for the 150-passenger STOL
 transport must be examined  in order to assess whether this noise  level is attainable
 with current potential jet engine technology. Application  of the optimum Quiet
 Engine concept discussed above results  in a noise  level 5 to 10  PNdB higher than the
                                                         !
 objective.  It must be realized,however, that the STOL aircraft will have a some-
 what lower critical  requirement for cruise efficiency than do conventional jet aircraft.
 Hence,  the STOL power plant may incorporate a sonic inlet to  further  reduce forward
 radiated fan  noise and a geared fan concept that permits still higher bypass ratios with
 resulting lower jet velocity.  The combined effect of these  features  may be sufficient
 to gain the extra noise reduction, but there may be unavoidable performance
 penalties associated with the requirement.
            The potential noise reduction discussed above will  be examined in light
 of the future requirements.  In attempting to establish specific noise reduction objec-
 tives for the  commercial jet aircraft fleet,  it is  instructive to consider  the growth of
.the noise impact during the last decade due to commercial aircraft operations, and
 attempt to predict future trends on the basis of current and potential jet engine noise
 reduction technology.  Obviously, the projected  rate of growth of commercial air
 traffic will influence these  estimates.  Extrapolating from the traffic growth during
 the 1960's and predicting the impact of the anticipated social and economic changes
 during the next decades, FAA and others have arrived at projected annual rates  of
 growth of up to 12 percent. 3/34 Recent estimates by the commercial aircraft industry
 on the future commercial aircraft market, however, are consistent with an annual
 growth rate of 5 percent. '  The latter  figure, although realistic from the point of
 view of the growth in population and gross  national product,  is  sufficiently low that
 it may be considered a conservative estimate, or a lower bound.
                                       47

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            Figure 2.1-22 shows the growth in noise-impacted areas since the intror
duction of commercial jet aircraft, and projects the future trend in noise impact on
the assumption of a 3 percent annual growth in the total number of aircraft operations,
corresponding to the 5 percent annual growth in the  number of passenger emplanements
discussed above.    The use of this constant ratio assumes  that the current trend toward
increased aircraft  capacity will continue, and  may well cause an underestimate of the
growth of operations beyond  1985 if the trend does not continue.
            The following factors were considered in the calculation of the noise-
impacted areas:
            •   Airport land,  surrounding industrial  land, and other compatible land
                are included in the total noise-impacted areas.  The airport land
                above is estimated to cover 250 square miles in 1970, and this figure
                may increase in the future.
            •   The growth  of air freight is not sufficient to become a controlling
                factor.
            • '  A 5 dB reduction in the NEF value  was assOmed to give a 55 percent
                reduction in area.
            •   The constant mix of daytime-nighttime operation remains unaltered.
            •   No change  in aircraft aerodynamic .performance or flight procedures.
            •   The trends in the growth or decrease of the,impacted areas are con-
                sidered to be reasonably accurate.   The expected accuracy of the
                actual values,, however, are probably only with ±50 perce.nt.
            •   NEF 30 was used to define the impact boundary.  This is a relatively
                high noise exposure criterion, particularly for suburban communities.
                Therefore the areas represent minimum estimates of impact.
            Figure 2.1-22 shows a great range in  the projected impact area depending
on the application of noise reduction  technology to the future commercial aircraft fleet.
As an extreme example,  maintaining the current aircraft noise levels would result in
an increase in impacted areas to 185 percent of the  1970 figure, by the year 2000.
                                       48

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    3000
-SJ  25,00
ii
 o-
to
    2000
 o
u
LU
Z
 c
• •^
• •^

 *
to
    1500
                                    5$ Projected Annual Growth
                                    in Passenger Enplanements
                                    and Air Freight Tonnages
                                                             New Aircraft Similar to
                                                            Current Types of Aircraft
                                                             w/o FAR-36 Restriction
    1000
z
o
     500
                                             Retrofit to FAR-36
                                               (1973 to 1977)
                                            and all New Aircraft
                                               Meet FAR-36
                          All New Aircraft After
                               1985 Meet
                            FAR-36  -lOEPNdB
                                                             All New Aircraft After
                                                                   1980 Meet
                                                               FAR-36  -4 EPNdB
        1960
                       1970
1980
1990
2000
2010
                                              Year
                 Figure 2.1-22.  Estimated Noise-Impacted Areas (30 NEF or Higher)
                         as Function of Jet Engine Noise Reduction Goals
                                           49

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 The application of retrofit to the existing aircraft fleet to ensure that all  commercial
 aircraft comply with FAR-36 criteria would result in a significant initial decrease
 in impact area in the 1976-1987 time period.  This significant decrease demonstrates
 the effectiveness  of aircraft certification for noise accomplished by the FAA, coupled
 with the significant 10+dB reduction  in noise between 1958 and 1968 accomplished by
 government and industry research and development.  However, by year 2000  the land
: area will again have increased measurably due to the projected increased number of
 aircraft operations.  The two additional curves show the  effects of further reduction in
 aircraft noise levels.  The attainment of aircraft noise levels corresponding to FAR-36
 minus 10 EPNdB would result in a 83 percent reduction in impact area below  the 1970
 value by year 2000.
             In order to further illustrate the implications of these noise reduction values,
 Figure 2.1-23 shows the dependence of the respective noise impact areas on the choice
 of the annual rate of growth in aircraft operations, assuming a constant rate of growth
 in the period from 1970 to 2000. The noise reduction effect of changes in operational
 procedures has also been included.  The lower bound in impact area for which this
 effect may be considered reflects the assumption that these  procedures may  be applied
 only above certain critical aircraft altitudes during the takeoff and approach  operations,
 corresponding to a ground distance of 8000 feet from threshold on approach,  and
 12,000 feet from  aircraft rotation on takeoff.25"*28
             The philosophy  may be adopted that the tremendous growth in noise impact
 since 1960 has been due to the fact that commercial jet aircraft have been  excessively
 noisy, and hence, the noise reduction objectives should be aimed at reducing the noise
 impact areas to the pre-1960 values.  This criterion may seem  somewhat arbitrary in
 view of the  considerable expansion in airport areas since 1960.  However,  it includes
 consideration of the fact that whereas the NEF 30 contour lies outside the most vigorous
 complaint area  for urban residents,  it still has a considerable annoyance associated with
 its noise levels (more than 30 percent of the populace registers annoyance), and it  is
                                                     18
 in the vigorous complaint area  for quiet suburban areas.
                                        50

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            Referring to Figure 2.1-23, the NEF 30 impact- area may be reduced to,
within its 1960 value of 200 square miles by year 2000, i.e., the airport and sur-
rounding industrial area, for annual aircraft operation growth rates of up to 8 percent
if new aircraft after 1985 comply with a noise criterion of FAR-36 minus  15 EPNdB.
Using the DC-10-10 aircraft as a baseline, this noise reduction objective corresponds
to 89 EPNdB on  takeoff and 93 EPNdB on approach at the FAR-36 measurement
positions.   This takeoff requirement is equivalent to the  potential noise reduction
for an  optimum quiet engine, previously discussed together with Table 2.1-6.
                                        52

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2.2         V/STOL  Aviation
2.2.1       Introduction
            Although current Vertical/Short Takeoff and Landing (V/STOL) aircraft
are inherently part of both the commercial and general aviation fleet,  their unique
capability of operating from very small airfields or from urban centers tends to distin-
guish them in terms of noise impact from the remainder of the aviation transportation
industry.
            The present V/STOL fleet is predominantly comprised of helicopters (VTOL).
The STOL fleet is not yet a significant reality, but is currently undergoing considerable
Federal and industry study.  The principal objective  of STOL aircraft is to move much
of the inter-city air transportation (short-haul) away from the  congested major-hub
airports and toward the urban community where the public will be better served.
Tentative noise goals have been proposed for aircraft operating from the projected
peripheral STOL ports, but as yet a community-compatible noise goal has not been
defined for the intra-city heliports now in operation, or  for those which will serve as
                                       1-4
city-feeder terminals for the  STOL ports.
            Figure 2.2-1  shows the typical subcategories of the present V/STOL fleet
and their major applications.  Of the current total of 3260 vehicles, approximately
1900 are based in counties with population densities  in excess of 1000 people per
square mile.  The most significant increase of usage in recent  years has been by civil
government agencies, with 120 operator agencies in  1971 compared with 80 in  1969.
In particular,  the number of city police helicopters is rapidly  increasing,  with a total
of about 150 vehicles in present use.  '
            Commercial helicopter service grew until 1967, when a total  of 29.7 million
revenue-passenger miles were flown.  Since 1967 this service  has declined to 11.3 mil-
lion passenger miles for a  revenue of $7.6 million in 1970.  Cargo traffic  has followed
the same trends with 34 thousand  ton-miles transported in 1970 for a revenue of
$350 thousand.  Manufacturers shipped approximately 500 completed rotor aircraft
in 1970/'&
                                       53

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V/STOL Aviation
1
1 1
Light Utility
Helicopters
(2-7 Seats)

Medium Weight
Helicopters
(10-15 Seats)


1
Heavy Transport
Helicopters
(20-50 Seats)
1 SI
1 A!
' (40-1
                                                                                      I
Air-Taxi
Law Enforcement
Executive Travel
Rescue/Ambulance
Agriculture
Traffic Monitor
Scenic/Survey
• Commercial Charter
• Company Transport
• Executive Travel
• Fire Control
• Coast Guard
Scheduled Transport
Industrial Cargo
Construction Lift
Coast Guard
       STOL
      Aircraft
      )-150_Sea

• Commercial Transport
                                   Number in Service


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Typical Noise Levels
96
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92 94
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                    Figure 2.2-1. Characteristics of V/STOL Aircraft

                                         54

-------
            Commercial usages are predominantly charter air-service operations, with
only about 15 vehicles on scheduled intra-city air carrier routes.  The  average route
stage length of the latter services is 20 miles, in 10 minutes flight time, compared
with' a possible 40 minutes (or more) by city road transport.  This market potential can
be expected to be more fully exploited with  the introduction of urban STOL ports.
Figure 2.2-2 shows one projection (DOT/NASA,  1971) of the  expected 1985 V/STOL
fleet.9
2.2.2      Source Noise Characteristics
VTOL Aircraft
            The helicopter is unique in that its noise signature is characteristically
different from all other common noise generators.  This difference is attributable to
the main (lifting) rotors which rotate at relatively  low revolutions per s.econd, but
generate very high amplitude pulsating sound pressures at their blade tip regions.
The resulting noise, observed both at ground level  and within the aircraft cabin,  is a
distinctive low frequency throbbing  sound which often suddenly increases in level
and exhibits more  of a slapping  nature during descent, maneuver, and high-speed
cruise operations.   Due to the predominance of the low frequency content of the
noise, it is extremely difficult to control its intrusion  into the passenger cabin or
into ground buildings by sound-insulation methods,  which are notably inefficient in
the low frequency range.  This problem is further complicated by the fact that low
frequency sound propagates through  the atmosphere more efficiently than higher
frequencies.   Thus, helicopter noise can be distinguished at greater distances than
can most other sources of equal  noise level.  Typical noise spectra  for two classes of
current commercial helicopters, shown  in Figures 2.2-3 and 2.2-4, demonstrate these
frequency characteristics.
            The noisiness value of rotor noise is often under-predicted by current
subjectively weighted noise scales such as dB(A) and EPNdB. These scales do not
account for the attention-gathering  potential of a  helicopter, which results from
                                        55

-------
Intraurban
0-50 mi
Short Haul Interurban
50-500 mi
(4-10 Passengers)
STOL/VTOL Taxi
(80-100)
STOl/VTOL |
1 f I 1
(40-80)
1 1 STOL/VTOL Bus
.1. i i I
       200   400     600   800    1000   1200
                         Number of Aircraft
1400   1600
Figure 2.2-2.   Potential 1985 U.S. V/STOL Fleet
                    56

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^  100
o
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 £  80


 I
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O
     70
    60  -
    50
                      \I\lS\

                     Interior Cabin
                        \
                      Ground Level at- 500 feet
                        100
                                                  1000
10000
                                      Frequency in Hertz
       Figure 2.2*-3. Typical Noise Spectra of Light Rston-Engined Helicopters
                                        57

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                               Main Rotor
                     Power Plant
                 anooannoDD
CM
 3
 o
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  I
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               Ground Levels at 1000 feet
60
                                Frequency in Hertz
            Figure 2.2-^4.   Typical Noise Spectra of Heavy Helicopters
                                  58

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throbbing or slapping noise of the rotor, analogous to a flashing light compared with
a steady one.   Most other sources of noise,  including propellers, are more analogous
to a steady light due to absence of  low frequency modulation, and consequently are
better assessed by the current scales.   Other noise sources on the helicopter, notably
the tail (stabilizing) rotor and piston or gas  turbine engine,  can be particularly
annoying in certain conditions.  Additional  information relating to the noise generating
mechanisms of helicopter rotors is presented in Appendix C.
            In areas close to the takeoff/landing terminal,  prolonged periods of
engine-idle operation during the (dis)embarking of passengers are  accompanied by
the piercing whine of the gas turbine or the equally disturbing bark of a piston engine
exhaust.  As the tail rotor is usually direct-geared to the powerplant, it is also rotating
at a sufficient speed, during these idle operations, to generate an additional noise
nuisance.  In some cases, the tail rotor and engine noises exceed  the main rotor in
subjective (nuisance) impact during flyover. This problem is more common on  light
utility helicopters which have lower main rotor loading and piston engine powerplant,
as shown in Figure 2.2-3.
            Other subsources, such as  the transmission system between engine and
rotors, can be distinguished in the passenger cabin and at very close external regions.
Their significance is generally low compared to the rotors and powerplant, but in the
few cases where they are notably present, the noise is of an annoying nature if prolonged.
STOL Aircraft
            Current design concepts of commercial STOL aircraft are based on a
                                                                          1 2
projected requirement for operation from 2000-foot length STOL port runways.  '
The economic  viability of the proposed STOL fleet relies on both its payload capa-
bility and its ability to operate from terminals close to the potential customer — the
urban community.  Each of these requirements has a distinct bearing on the propulsion
systems to be incorporated in the fleet  aircraft, arid on the noise characteristics to be
expected and allowed of STOL aircraft.  A  tentative limit of 95 PNdB (approximately
80 dB(A)) has been proposed by the  FAA to be applied at a 500-foot distance from
                                        59

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each aircraft.'^  The alrframe and propulsion system industries are vigorously pursuing
this noise goal.  Consequently, the final flight-ware systems may radically differ from
the basic breadboard systems now under test and development.  Of these systems, those
now in development for application to the 40-80 seat category aircraft are:
            •   Compound (single and twin rotor) helicopters, V/STOL
            •   Quiet-Propeller, STOL
            •   Tilt-Rotor, V/STOL
            •   Prop-Fan, STOL
            •   Lift-Fan, V/STOL
            •   Jet-Flap, STOL
            Full-scale or model acoustic testing of these concepts has indicated that
the 95 PNdB limit can be met by the 40-80 seat passenger V/STOL systems.     The
typical frequency spectra noise characteristics of the propeller,  rotor and prop-fan
systems are shown in Figure 2.2-5.       Note that these spectra do not include the
engine-noise contribution.  The main difference in the spectra are attributable to the
rotational speeds (revolutions per second) and number of blades typical of each system.
The prop-rotor is a  3-blade low speed  system.  The propeller is also a 3-blade system,
but operates at about three times typical rotor speeds.  The ducted prop-fan has about
12 blades operating at speeds slightly higher than the propeller.
            Present estimates of the  larger (80-150 passenger) STOL system projections
indicate  that the proposed 95 PNdB limit at 500 feet will not be met by designs based
on current technology.  The sideline distance corresponding to the 95 PNdB level is
projected to be between 3000 and 4000 feet for current designs, and will expectedly
                                                          3
converge toward the 500-foot goal as technology is improved.
2.2.3       Environmental Noise Characteristics
            The significance of helicopter noise in the community environment is not
immediately apparent from the statistics of total number of helicopters in operation.
As discussed earlier in the report, the  present aircraft noise  problem primarily involves
                                       60

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Prop-rotor
JS. «. r "\ «


    Propeller
© © £|D © ©

   Prop-fan
                     100
                 1000

      Frequency in Hertz
         10000
         Figure 2/2-5.    Typical Frequency Characteristics of Propulsion Systems
          for 40 to 80 Passenger STOL Aircraft  (excluding powerplant) at 500 feet
                                     61

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a large number of people living near airports affected by landing and takeoff operations.
For conventional aircraft, the cruise condition flight is usually at high altitude and
therefore does not contribute much to the ground noise exposure.  However, helicopters
are most commonly operated at low altitudes due to short stage distances, ground
observation requirements of the service, or simply to provide the added attraction of
a panoramic view to the intra-city passenger.  This extended low altitude operation,
most often directly over urban and suburban regions, significantly increases the noise
impact potential of the helicopter.  The increasing  incidence of police patrol operations
over populated areas further aggravates this situation due to the prolonged noise intrusion
of a hovering or surveying helicopter, operating at  low altitude.
            Because  the helicopter flight route patterns  are essentially random at
present, it is practically impossible to define their current  impact on the environment
in terms of exposure duration, land area or population.  A  sustained public reaction
has not materialized, despite the intrusive  nature of the sound/probably because of
the irregularity  of this usage pattern.   However, widespread complaints have arisen
                                                                               9
due to air taxi services in New York, police operations  in  Los Angeles, and others.
This is not surprising  since the noise levels  at 500 feet from a commercial helicopter
are in the 80 - 90 dB(A) range, as are the levels from a  police helicopter at 250-foot
  u-i.  A   10~12
altitudes.
            The  introduction of the STOL fleet as a convenient commuter mode of
transportation will bring many benefits to the urban resident.   However, it will also
bring a new source of noise into  his environment,  and the total community acceptance
will be dependent on the effectiveness of STOL port planning, aircraft routing, and
noise abatement procedures currently being designed.
            Figure 2.2-6 shows a comparison of various  V/STOL noise  levels with
                                                3
those of the community ambient noise levels (Lg-.).   A difference of 25 - 30 dB(A)
or greater between a single-event intruding noise and the ambient  (LOf)) will annoy
many people in  the community.  If the single event at such a level is repeated suffi-
ciently often, an appropriate community reaction may be anticipated.  For example,
                                        62

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s.
CO
I   80-
             Rural
             Quiet
            Suburban
   Urban
 Suburban
Residential
                                           Urban
                                        Commercial
                           Downtown
                          Commercial
   Urban
Commercial
   Urban
 Suburban
Residential
  Rural
  Quiet
Suburban
                                                                      I
Light Piston Heli-
 copter at 500 ft.
                                                                Heavy
                                                              Helicopter
                                                             at 1000 ft.
                                                         I STOL at 500 ft.  T/O I
                                         Light Turbine Heli
                                          copter at 500 ft.
                                                         rSTOLat2000ft. T/Oj
            Figure 2.2-6.   Comparison of Typical V/STOL Aircraft Noise Levels with Community Ambient Noise Levels (I-9Q)

-------
10 overflights per hour during day and evening of a helicopter meeting the 80 dB(A)
noise goal would cause a community noise equivalent level of 60 dB(A).   No commu-
nity reaction would be expected in a noisy urban residential community, whereas
"widespread complaints" to "threats of legal action" would be expected in a quiet  .
suburban community. To reduce the expected reaction of the quiet suburban commu-
nity to "no reaction", the minimum altitude  over the community should be approximately
4000 feet for this assumed frequency of operation and vehicle noise characteristic.
            Figure 2.2-6 also illustrates the problems faced by .the city heliport and
urban STOL port planner.  The desire for  central-city operations  must be tempered by
the constraints imposed by the local outdoor  noise levels.  Solutions being considered
are the use of industrial areas suitable for port  locations, and the optimal use of high-
rise, non-residential  buildings to shield the noise from residential areas.
            From the viewpoint  of the potential V/STOL passengers, who are predicted
                                                                       9
to comprise more than half the total revenue passenger complement, in 1985 ., the
internal noise of rotor and propeller powered vehicles will  require significant reduction
from their present levels if the service is to be  considered attractive. The noise level
                                                             10-14
inside many current helicopters ranges between 90 and 100 dB(A)     , representing
a definite risk of hearing damage to the constant traveler, particularly if his exposure
exceeds 1/2 hour per day. .Also, the occasional passenger may accept poor speech
communication during short flights, but the regular-commuter passenger will consider
such features a distinct inconvenience.  In such cases, it maybe expected that manu-
facturers will attempt to alleviate the problem  from a solely commercial standpoint.
2.2.4       Industry  Efforts'in Noise Reduction              '  '  •
VTOL Aircraft                 ,
            The helicopter manufacturing industry .is primarily engaged  in
military helicopter requirements, which account for approximately 80 percent of the
more than 20 thousand production vehicles produced prior to January 1970.   The
                                                        j
vulnerability of military helicopters during reconnaisance or evacuati.ve missions
                                        64

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has been closely correlated to their excessive noise signature which allows early
detection and consequent retaliatory enemy action.  The industry has therefore been
keenly engaged in research and development programs specifically aimed at the
problem of noise reduction.   However, much of the work has been directed toward
the development of modification concepts applicable  to long-established production
models or economically viable  to production lines.  As almost all of the civil heli-
copter fleet are direct derivations of military models, later production models have
benefited from the noise suppression developments.  Retrofit modifications are generally
not economically feasible for many private operators, although made available by
*u  •  ^  *   18'19
the industry.
            Another approach taken by the industry toward noise alleviation has
been  in educating the private operator in particular methods of operation which
avoid prolonged community noise exposure and  which circumvent the condition of
                                         19
blade-slap noise during descent maneuvers.    These  and other facets of the industry's
awareness of the noise problem relate to  past and immediate production helicopter
types which will tend to dominate the civil  market for the next decade.
            The responsibility for developing noise  suppression techniques for heli-
copters has been firmly implanted in the  manufacturing industry because of the
encompassment of aerodynamic structural design and performance considerations
in the acoustic technology matrix.  The emphasis of past and current programs has
been in the specific area of rotor and propeller noise  reduction because of its
predominance in the acoustic signature of most  V/STOL aircraft,  although significant
attention has also been  given to engine and transmission system quieting.  The latter
is important when it is realized that almost 50 percent of the light utility helicopters
in operation in 1970 were piston-engined and that most of these have unsatisfactory
                                                     18 19
exhaust mufflers as original factory-installed equipment.  '
            An illustration of programs related  to helicopter design is presented in
Figure 2.2-7.  '   '   '    Examples of  the noise reduction benefits attainable by
these approaches are shown in Figures 2.2-8 and 2.2-9, and are indicative of what
                                       65

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  © Lower revolutions per second
  (?) More blades
  (D Large blade area
  (5) Modified blade tip shapes
                                    ©Reduced blade interaction
                                    ©Engine inlet suppression
                                    ©Engine exhaust muffling
                                    ®Cabin insulation improvements
Figure 2.2-7.  Current Design Approaches to Helicopter Noise Reduction
           100
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            80
          ;  70
    60
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8  50
            40
             30
                   Original Design

                   Modified Version

                   Redesigned Version
                100   200   400   700  1000   2000  4000
                      Distance to Helicopter — feet
          Figure  2.2-8.    Effect of Design Changes on  a  Light
               Helicopter Noise Signature (Demonstrated)
                                   66

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             Figure 2.2-9.  Demonstrated Noise Reduction

              of a Heavy-Helicopter Twin-Rotor System
ea
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    70 -
                                                  Unmuffled
                                                        Stack-Mounted Muffler
                                                  Structure-Mounted Muffler
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     200          500       1000      2000

           Distance from Helicopter (ft)



               Figure 2.2-10. Exhaust Noise Suppression

                  of Light Piston-Erigined Helicopters
                                67

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can be expected in future helicopter models designed specifically toward noise goal
objectives.  Major areas of noise reduction study pursued by the industry are discussed
•   *u  F ii   •           u  10-13,19
in the following paragraphs.
            •   Propeller/Rotor Noise Reduction — The most direct and efficient
                methods of propeller and rotor noise reduction are to reduce the
                blade tip speed and reduce either the total load on each blade or
                the load per unit blade area.  There are obvious limits to the
                application of these principles in addition to those of aerodynamic
                stall (which gives a sudden noise increase) and the weight/
                performance requirements for economic operation.  Thus/ most
                research effort has been aimed at deriving more subtle approaches
                to design, whereby the above methods can be implemented and
                improved upon with negligible performance penalty.   Some of the
                more successful of these methods are:
                -  Larger blade area
                -  Increased number of blades
                -  Variable geometry blades (changeable camber in flight)
                -  Modified blade tip shapes
                All of these have either resulted from, or  have been  made practical
                by, combined efforts  in acoustic, aerodynamic and materials research.
                In particular,  the noise reduction potential from increasing the number
                of blades and blade area has been known for quite some time, but this
                approach has only recently become  practical due to the development
                of lightweight construction materials and fabrication techniques.
                Blade tip shape modifications have  undergone extensive investigation
                for both aerodynamic and acoustic benefits, including reduction  of
                blade slap. Helicopter rotor tests indicate that 5 to  8 dB  can be
                achieved by this approach.
                                       68

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Engine Noise Reduction — At ground-idle and in-flight conditions
with noise abatement procedures in operation, the loudest component
sound of a V/STOL aircraft may be its engine noise.  For piston-
powered helicopters,  the exhaust noise is extremely noticeable in the
signature.  Gas turbine engines are distinguishable by high frequency
whine of their compressor stages and by their exhaust when the jet is
used as q propulsive force.  Each of these can be treated by different
types of suppression, from the relatively simple piston-engine  muffler
to the more complex jet-exhaust suppressor.  However, all methods
cause some degradation of the performance-cost ratio of the vehicle,
and consequently the buyer/operator is often reluctant to include
them in his optional equipment list.  The manufacturer/seller is also
reluctant to include them as standard equipment because of the sales
competition within  the industry and his desire to provide the most
economically operable item.  Nevertheless,  the equipment for noise
suppression has been developed, demonstrated, and made available
by the industry and other independent  companies in the form of retro-
fit kits composed  of factory-installed options.  Although much remains
to be done to improve the noise and performance influence of  suppres-
sion devices, an immediate improvement can be obtained if their
usage is required.
The noise reduction currently attainable  by available mufflers for
helicopter piston-engine exhausts is shown in Figure 2.2-10.  '
Stack-mounted units are very lightweight and are designed to  fit
directly onto the  exhaust port of the engine.   The acoustic performance
of these units ranges from relatively poor to moderate, but they are
designed to impose  little penalty on operating costs.  Structure-
mounted types are heavier and more efficient in noise reduction, but
are more expensive and in particular have the greatest detrimental
effect on operating costs.
                       69

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                 Gas turbine (jet) powered helicopters are generally quieter than
                                                                          19
                 their piston-engine counterparts/ as shown in Figure 2.2-11',
                 however their market popularity is restricted by a requirement for
                 specialized fuel.  Again, the main noise problems are associated
                 with their terminal operation rather than their cruise mode.  In
                 this case, both the inlet and exhaust require noise suppression
                 treatment, and absorptive vanes or lining installed within the
                 appropriate ducting has been demonstrated to provide a total
                 reduction of up to 10 dB with a resultant power  loss of about 1  to
                 2 percent.
            The past 5 years have seen a  most significant advancement  in V/STOL
noise control.  Methods  of noise suppression  have been  developed which can, if
applied to new production models and the noisier of the older types, allow the full
development of the V/STOL as a community  service item.  Until  recently, little
attention  has been given to the design of the actual landing site  to alleviate the
noise radiated to nearby residential areas.  In fact,  the tendency of some operators
is to deliberately aim for line-of-sight pads  in order to  advertise their service.  This
practice is highly undesirable from a noise nuisance viewpoint.  Recommended
practices, or even mandatory regulations, should be developed for city heliport
design and construction.
            In summary, the industry is acutely aware of the noise problem and its
relationship to the development of an  expanding market for their products.  It has
been  involved in considerable research and development study (at both  Federal and
industry expense) to find practical methods of reducing  the noise levels of current
and future production line models.  The present situation is that these efforts have
been  significantly successful, but only in terms  of present helicopter usage patterns.
The expected increase in intra-city transport and law-enforcement usage will change
this pattern over the next decade.  This change must be accompanied by further noise
reduction built into the  helicopter and by more  detailed study of urban  helicopter

-------
      90
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      80
      70
     100
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           2000
                                               Distance =  500 feet
                    -2-5
                             5000          10,000
                                 Gross Weight (Ib)
           20,000   30,000

          -20-40	-
                             Approximate Seating Capacity
                                 <\
                                  Turbine-Powered
Distance =  500 feet
            2000
                              5000          10,000

                                  Gross Weight (Ib)
           20,000  30,000
                Figure  2.2-11.  Trend of Helicopter Noise Levels with
                         Gross Weight and Seating Capacity
                                  71

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structures/ location and operating procedures, to ensure that the helicopter fleet
will not impose an unacceptable noise burden on the community it serves.
STOL Aircraft
            The STOL industry has a tentatively-defined noise goal to meet to
ensure its command of the commercial aviation market by 1985.    This  goal is
being approached by intensive research and development of suitable propulsion and
lift concepts,  some of which have been described in Section 2.2.2.  The main
difference between the VTOL and STOL industries is that the latter must include
noise as a major parameter in their conceptual design studies, whereas the pre-
dominant objective of the VTOL (helicopter) industry is to reduce the noise of their
established design models.
2.2.5       Noise  Reduction Potential
VTOL  Aircraft
            The most immediate problem for the VTOL industry is to further develop its
noise suppression technology to make it economically acceptable to the  commercial
and private operator.  With the increasing usage of helicopters within the urban
service system, it can be expected that community reaction to the  noise intrusion
will also increase and force legislation of operational characteristics  to  be developed
and imposed.  It has been demonstrated that significant noise suppression can be
installed on current design concepts and therefore it is practical to consider that the
helicopter can become compatible with community usage.  However,  the result can
only be achieved by incorporating noise reduction methodology into vehicles produced
for the urban-user market as a standard procedure.  The potential for  future helicopter
(VTOL) noise  reduction is summarized  in Table 2.2-1.
STOL Aircraft
            The long term future of the interurban STOL aviation economy depends on
the development of the larger (80 to 150 passenger) STOL bus.  Current projections
indicate that with present technology the 95 PNdB goal will not be met at the 500 foot
                                       72

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                                    Table 2.2-1
                  Estimated Noise Reduction Potential for Helicopters
Time Period
Short Term Potential
Utilizing Available
Production Methods
Long Term Potential
Utilizing Current
Industry Trends
Long Term Potential
Utilizing Demonstrated
or Advanced Technology
Noise Reduction, dB^1)
Heavy
Transport
Helicopters
0

10

10

Light and
Medium
Turbi ne- Powered
Helicopters
' 5 '

15 '

17
*
Light Piston-
Powered
Helicopters
10

10

20

Noise reduction relative to typical current noise levels in dB(A) <
at 1000 feet.
         o
distance.  This would mean that a large section of residential area around STQL ports

would be subjected to unsatisfactory noise intrusion levels.  Further, many quiet sub-

urban communities under the STOL flight path would be exposed to excessive noise

unless the aircraft cruise altitude were increased enough to achieve compatible ground

noise levels.  The economic tradeoffs between source noise reduction and higher than

optimum airspace altitudes must receive careful study.
                                       73

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2.3         General Aviation Aircraft
2.3.1       Introduction
            The term "general aviation" refers to all civilian aviation activity other
than that of the commercial  air carriers. Within this broad definition, general aviation
includes a wide variety of aircraft uses.   The following use categories may be con-
 .,    ,1, 2
sidered:
            •    Business Aviation — This is the largest single category of general
                 aviation in terms of total aircraft hours flown. It includes all aircraft
                 used by corporations and individuals for business  transportation.
                 About one-third of the total hours flown by general aviation aircraft
                 fall into this category and these hours are flown by about one-fourth
                 of the registered general aviation  aircraft.
            •    Personal Flying — This covers over half of general aviation aircraft
                 registered in the United States. This category is generally made up
                 of smaller and less expensive aircraft than those in the  business
                 aviation group.
            •    Air Taxi, Charter and Contract Usage — These aircraft are generally
                 considered part of the general aviation fleet.  Also included in this
                 category are small charter aircraft contracted with a flight crew.
            •    Instructional Usage — This category accounts for about one-fourth of
                 the total general aviation aircraft hours flown.  However, in numbers
                 of aircraft,  instructional aircraft comprise only about 11 percent of
                 the total fleet.  Most of these are smaller single-engine types.
            •    Aerial Application,  Industrial and Special Use — This includes air-
                 craft used for agricultural spraying purposes, patrolling, advertising
                 photography, aerial  surveying and equipment testing.   This category
                 is relatively small both in terms of numbers of aircraft and hours flown.
                                        74

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            The use of general  aviation aircraft has grown in the past 10 years from
12 million flight hours to a total of 25.5 million aircraft hours flown in  1970. Equally v
significant,  the composition of the general aviation fleet has changed from a pre-
dominance of small,  single-engine propeller types to a much more complex fleet mix.
Figure 2.3-1 summarizes this fleet mix and provides information on the number of air-
craft operations and typical noise levels produced.
            A conservative picture of the economic impact of general aviation is
obtained from the fact that manufacturers of airframes, power plants  and avionics
employ 23 thousand people and had gross sales in 1970 of about  $375 million. In addi-
                                                                     3
tion,  $240 million of gasoline was utilized by the general aviation fleet.
2.3.2       Source Noise Characteristics
            The noise associated with general aviation propeller aircraft with both
piston  and turbine  engines is produced principally by the propellers. This noise con-
tains a harmonic series of discrete frequency tones, with the dominant fundamental
                                            4
tone typically in the range from 50 to 250 Hz.     Depending on the propeller blade
shape and the propeller operating environment, the second and third harmonic tones
may also have significant levels.  Figure 2.3-2 shows typical noise levels and spectra
                                           4
measured during propeller aircraft operations.   The broadband  and discrete frequency
noise above approximately 250 Hz consists of higher propeller noise harmonics, dis-
crete frequency noise from  the engine and exhaust, and exhaust broadband noise.  The
latter noise  sources may contribute measurably to the total noise generation by some
types of general aviation aircraft, but are generally masked by the propeller noise.
Additional information on the noise generation mechanisms of propellers is contained
in Appendix C.
            The noise characteristics of. jet-powered general aviation aircraft, or
executive jets, are shown in Figure 2.3-3.  Their characteristics are similar to those
of commercial jet aircraft.  Most business jets are powered by pure turbojet or low by-
pass ratio turbofan engines; thus, the jet exhaust is the dominant source of noise.
Since these  engines are much smaller than those used to power commercial  jet aircraft,
                                       75

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         Single-Engine
           Propeller
      • Pleasure
      • Instructional
      • Business
                             General Aviation Aircraft
                                     Multi-Engine
                                       Propeller
                                   •  Pleasure
                                   •  Business •
                                   •  Commercial
                           Executive Jet
                           Corporate Aircraft
                           Business
 o
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|   7°
Z   60
            110,500
                             Numbers in Service (1970)
                       105
                    90
              77
              67
                     76
                        85
                                         17,500
                              Growth of Aircraft Fleet
no,
68,
1
1
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81,
300


i
300




50C









7,
n,
250

17,
800

500


                    60 65 70           60 65 70

                                  Typical Noise Levels
                                        93
80
                                  70
                                        79
         %
                                900
                                                                    900
                                                                 loor—]
                                                              o  .—I   I
                                                             60  65 70
                                                                 97

87
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93
[Takeoff
95
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80
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                  Approach and Takeoff Levels Measured at '1000 feet


              Figure 2.3-1. Characteristics of General Aviation Aircraft

                                          76

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                                                    Exhaust
                      Propeller
Engine
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                     I  I II       I     I
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                                                 Engine/Exhaust
                                                 Ground Noise Level at 1000 Feet
                      —Typical Operation
     50
    1201—
                     81
                                      Frequency in Hertz
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                Contributing Subsources for Typical Aircraft
    Figure 2^3-2.  Noise Levels and Spectra of General Aviation Propeller Aircraft
                                         77

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                          Fan/Compressor
                                                          Jet/Turbine
CO
 I
o
   50
120
100
 80
 60
 40
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                                                1000
                                     Frequency in Hertz
                    89
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             Contributing Subsources for Typical Aircraft
          Figure --'.3-3.  Noise Levels and Spectra of Executive Jet Aircraft
                                        78

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the characteristic frequencies in the jet noise are higher, and also the noise levels are
lower than for the big turbofan engines.
2.3.3       Environmental Noise Characteristics
            The operator or passenger in a general  aviation aircraft is subjected to
noise levels of about 90 dB(A), which is  5 to 15 dB higher than in a commercial jet
aircraft.  Figure 2.3-4 shows a typical interior cabin noise'level for a general avia-
tion propeller aircraft.      This high noise environment is caused by several factors:
          t
           N
            •   The engine  is mounted close to the cabin,  hence the cabin walls are
                exposed to the highest sound pressures generated by the propeller
                without any benefit of attenuation from distance.  This situation is
                aggravated  in conventional twin-engine aircraft.
            •   The dominantly low frequency content of the propeller noise makes
                                i
                conventional fuselage noise insulation techniques rather ineffective.
            •   The small volume within the cabin limits the effect of interior wall
                sound absorption.
            The airport noise impact due to general aviation aircraft noise is quite
small when compared to the impact of commercial aircraft operations.   Figures 2.3-5
and 2.3-6 show  NEF values versus slant  range, respectively for takeoff and landing
operations,  for the average national mix and the number of aircraft that are expected
to utilize a typical general aviation airport.  The lack of significant impact is evident
on noting that the NEF values stay below 30 even at very close ranges and below 20
for relatively short ranges.  Consequently, the vast majority of general aviation air-
ports do not have a serious community noise problem.
            The low level  of impact associated with executive jet aircraft in this
example is due to their relatively small  number of operations, despite their high noise
                                         V.
levels.  However, at several general  aviation airports that have a significantly higher
rate of operation for executive jets than  the national average mix, these aircraft tend
to dominate the  airport noise picture.  This effect is illustrated by the additional
                                        79

-------
                   Propeller
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                                                    -—Typical  Operation
                         100
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Propeller

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Engine and
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.. ,
Total

                 Contributing Subsources for Typical Aircraft
                ly^itt z.J-4.  Interior Cabin Noise Levels and Spectra for

                          General Aviation Propeller Aircraft

                                           80

-------
 0>
I
    20 -
10 -
   -10
   -20
   -30
                                                           Operations per Day
                           Executive Jet (national average)          1
                           Executive Jet (higher proportion)
                           Single-Engine Propeller Aircraft
                           Multi-Engine Propeller Aircraft


                            .i.l	,	,
     10
    240
     23
       200
               400      700      1,000         2,000
                             Distance to Aircraft — Feet
4,000
7,000 10,000
        Figure 2.3-5.  Noise Exposure Forecast Values for an Example of a Representative
                     General Aviation Airport with Daytime Use Only
                                        81

-------
                                           Operations Per Day

          Executive Jet-(National Average)            1

          Executive Jet (Higher Proportion)          10

          Single-Engine Propeller Aircraft          240

       —  Multi-Engine Propeller Aircraft            23
                                 APPROACH
      i    ,   ,  .   ,
400
4000
7000    10,000
                     700    1000         2000

                   Distance to Aircraft — Feet
Figure 2.3-6. Noise Exposure Forecast Values for an Example of a Representative
                       General Aviation Airport with Daytime Use Only
                               82

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business jet curves in Figures 2.3-5 and 2.3-6.  In the future, the proportion of execu-
tive jets in the general aviation aircraft fleet is expected to increase considerably.
Hence, these aircraft may become major noise sources around typical general aviation
airports unless their noise levels are reduced.
            An additional source of aircraft noise at some general aviation airports
consists of the operations of fighter and trainer aircraft of World War II vintage.  These
airplanes are generally very noisy and tend to create noise problems wherever they are
based.  The eventual retirement of these aircraft appears to offer the most satisfactory
means of alleviating this problem.
2.3.4       Industry Efforts in  Noise Reduction
            The great majority of all general aviation aircraft are owned by private
individuals. More than one-half of these  aircraft are used for personal and recreational
flying.  Therefore, the general aviation aircraft industry deals predominantly with a
consumer market similar to that for automobiles or motorcycles.  Competitive confor-
mance requires maximum capacity and performance within the particular price class,
coupled with economy of operation.  The exploitation of technologies such as noise
reduction that bear only indirectly on product desirability are consequently relegated
to secondary levels of importance.  Thus,  the consideration of noise in general aviation
aircraft is geared to competitive objectives within the industry,  rather than to any
desired standards.
            The industry noise objectives have been aimed at quieting the  aircraft
interior in order to provide more comfort to the operator or passenger. The approach
.has been rather cautious and straightforward.  Existing quiet engine  and quiet propeller
technology have been utilized within the constraints of performance, but the main
efforts have been directed at cabin noise insulation.  Again, the progress has  not been
spectacular due to the weight penalties associated with noise-insulating materials and
the governing performance constraints.
            General aviation aircraft are  not at the present time a major source of
noise pollution.  At the hub airports, at which approximately one-half of the aircraft
                                         83

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operate, their noise characteristics are masked by the much noisier commercial aircraft.
The remainder of the aircraft are distributed over more than 11  thousand airports within
                 2
the United States.   With some exceptions, the noise levels at the general aviation
airports have not reached a magnitude at which the environment is severely affected.
Thus, the general aviation industry has not, until  very recently, considered aircraft
noise in terms of the non-participant environment.
            The general aviation fleet has grown rapidly during the last 15 years and
will continue to grow an an accelerated rate until at least 1985.  As is indicated in
Figure 2.3-7, what is more important than the total  growth in the  fleet from noise
considerations is the growing number of multi-engine piston, turboprop and turbojet
                             8
aircraft in the projected fleet.   Hence, the  typical general aviation aircraft will
become noisier.  This factor,  in addition to the increase in the number of aircraft
operations, will lead to an increasing noise pollution potential.
Noise Reduction Programs
            As discussed above, the main effort in noise reduction by the general
aviation industry has been directed toward lowering  the interior cabin noise levels.
This objective has been achieved by combining reduced noise generation at the source
and improved transmission  loss through the cabin walls.   Propeller  and engine noise
reduction have not been actively pursued.  However, as discussed in the V/STOL
Section, the propeller and engine manufacturers have been engaged in the develop-
ment of quiet concepts for military and V/STOL commercial applications, and some of
the results have fed back to the general  aviation industry.  As an example, current
aircraft models generally have three-bladed propellers rather than the old two-bladed
                                                     9
propellers, with a resulting noise reduction of 3 to 5 dB.    This result has been made
possible through materials technology development by the propeller manufacturers
whereby the new propellers weigh less than the older types, despite the increased
                                          \
number of blades.
            Reduction of the interior noise levels  by means of cabin wall insulation
has been the subject of more active participation by the industry.  The typical interior
                                        84

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     150
 S

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 (0 _C
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1     50
Single Engine, Over 3-Place

Single Engine, 1-3 Place

Multi Engine

Turbine/Jet

Other
              1955
         1960
1967
1975
1980
1985
                  Figure 2.3-7.  Number of General Aviation Aircraft

                        with Projections for 1975, 1980 and 1985
                                        85

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noise levels of general aviation aircraft lie in the range of 90 to 105 dB(A).     Some
                                                                              9 "•-
of the new models on the market have corresponding noise levels down to 85 dB(A),
a reduction of 5 to 20 dB of which 5 to 12 dB is due to improved cabin wall insulation.
            The executive jet aircraft are typically much noisier than  propeller-driven
airplanes,  but they constitute such a small percentage of the total  general aviation
fleet that their noise impact has generally been kept within bounds except at some air-
ports which have a much higher than average proportion of jet operations.  However,
                                                                        r
with the projected future growth in the number of executive jets, they may be expected
to cause noise problems at  an increasing number of airports unless their noise levels are
reduced.  The jet engines in use by the executive jet aircraft fleet have been developed
for military purposes, or as smaller versions of early jet engines for the commercial  fleet.
Hence, they tend to be objectionably noisy. Only very recently has the general
aviation industry actively sought more advanced and quieter jet engines for the business
jets.  An example of the noise reduction achieved by substituting an advanced tech-
nology engine (AiResearch TFE-731 turbofan) for  an older type jet engine is presented
in Figure 2.3-8.    This change will reduce the  noise level  generated by the Lear Jet
at the FAA certification position on takeoff from  96 EPNdB to less than 86  EPNdB.
Another example is provided by the Cessna Citation business jet, powered by Pratt &
Whitney JT15D turbofan engines.  FAA certification figures for this aircraft show noise
levels of 76 EPNdB on takeoff and 88 EPNdB on approach at the FAR-36 measurement
positions.il These figures lie 17 and 14 EPNdB respectively,  below the noise levels
stipulated by FAR-36.  An equivalent noise reduction throughout the business jet fleet
would strongly reduce the potential noise impact  of these aircraft.
            With respect to the suppression of the sources of noise in general aviation
aircraft, the industry will, at least in the near future, continue to rely on  the power-
plant and propeller manufacturers for further developments.  These programs are dis-
cussed elsewhere in  this report; propellers and the associated powerplants are evaluated
in the V/STOL Section, and the jet engine programs are discussed under Commercial
Aircraft.
                                        86

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            The general aviation industry's plans for further reduction in the interior
noise levels are formulated in terms of what the expected achievements are, rather
than as desirable objectives.  Disregarding any possible significant reduction in the
   i.
powerplant noise levels, an interior noise level of 75 dB(A) is considered possible
            :            9
within the next  10 years.   This will be achieved by means of improved cabin wall
lining  materials and a more sophisticated evaluation of the critical noise transmission
paths. This level would represent a considerable improvement over the typical noise
levels in the current general  aviation fleet, as shown in Table 2.3-1.
                                    Table 2.3-1
                                                        9
                          Interior Noise Level  Objectives
                                    Interior Noise Levels - dB(A)     Year
          Typical Older Aircraft
          in Current Fleet                    90 - 105
          Current' Production
          Aircraft      .                      83-85                 1971
          Objective for Future
          Aircraft Design                       75                    1981
2.3.5       Noise Reduction Potential
            In order to assess the potential noise reduction in the general aviation
fleet, it is appropriate to establish specific noise reduction objectives.  Figure 2.3-7
shows that by 1985 there may be 316 thousand general aviation aircraft operating
             '8
within the United States.   However, 58 percent of these are expected to be  con-
centrated  within the population hubs, where  in many cases their noise characteristics
will be masked by commercial aircraft operations.  The remainder will be distributed
throughout the suburban and rural  areas served by approximately 11 thousand general
aviation airports.  In the low population density  rural  and outer suburban areas,  the
                                        87

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                 Static Test at Takeoff Power
                   Noise Levels at 400 Feet
30'
                             90
            60
                        120C
                                    150
140     130     12i
110      '110    120     130    140
     Exhaust
                     Approximate
                   Sound Pressure Level
                       in  dB(A)
        CJ610-6
        TFE 731-2
Figure 2.3-8.  Comparison of Noise Levels at Various Angles from
            Engine at Approximately 3000 Ibs Thrust

-------
general aviation airports are generally located sufficiently far away from population
centers that no significant noise impact is expected,  even with the noise levels generated
by the current type aircraft. The potential  noise problem  is thus predominantly associated
with the growth of aircraft operations at major suburban general aviation airports.  Assum-
ing a normal suburban residential area, median daytime outdoor noise level (Leo) of
49 dB(A) and a typical minimum slant range of 500 feet, a single event maximum noise
level of 74 to 79 dB(A) may generally be considered acceptable.  Figure 2.3-9 compares
this range of levels, extrapolated to 1000 feet distance, with the noise levels generated
                                                        4
by a variety of current general aviation  propeller aircraft.   Some light, single-engine
airplanes fall within the  desired range, but generally a suppression of 5 to 15 dB will be
required to meet the suggested criterion. For the business jet aircraft, a suppression of
at least 15 dB will be required over that achieved with the current state-of-the-art, as
demonstrated by the Lear Jet with advanced technplogy turbofan engines (discussed in
Section 2.3.4).
            In order to establish  whether these noise  reduction objectives are realistic,
                 t
propeller aircraft will first be considered.  As  discussed in the V/STOL Section, a
reduction  in engine/exhaust noise of 13  dB is  achievable with  current technology.
Similarly, a realistic objective for propeller noise reduction is approximately 10 dB
over the next 5 years.  Extrapolating these values to  the 1980's, it appears that  a maxi-
mum noise level objective of 68 to 73 dB(A) at 1000 feet for general aviation propeller
aircraft is achievable.
            For business  jet aircraft, the potential quiet airplane is evaluated by con-
sideration of the expected possible noise reduction in commercial jet aircraft.  Extrapo-
lation of the potential noise levels of the commercial quiet jet engine to the  size and
thrust required for the business jet aircraft powerplant yields a level of approximately
75 dB(A) at  1000 feet during takeoff operations, which is within 2 dB of the desired
result.
            It must be emphasized that these noise reduction values refer to new air-
craft only.  The future potential  noise reductions are summarized in Table 2.3-2.
                                        89

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                          Table  2.3-2
       Potential  General Aviation Aircraft Noise Reduction
                                                Future Noise Levels
                          Noise Reduction          at 1000 Feet
                               indB                  dB(A)
Propeller Aircraft              5-15                 68-73
Executive Jet Aircraft
Near Term                      13                     85
Long Term                      23                     75
                                90

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95


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Figure 2.3-9.  Noise Levels Generated by General Aviation Aircraft



                          91                       	

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2.4         Highway Vehicles
2.4.1       Introduction
            Highway vehicles include automobiles, trucks, buses, and maintenance
and utility vehicles.  Motorcycles are treated in the section on Recreation Vehicles.
Traffic studies of highway vehicle usage in typical urban areas show that about 1600 to
2300 trips are made by automobile drivers and passengers every day for every 1000
people, while 200 to 400 truck trips are made for every 1000 people.  Approximately
40 percent to 45 percent of the latter terminate  in residential areas. This urban travel
represents about 52 percent of the estimated 3 billion highway vehicle miles traveled in
1970.  The general characteristics, numbers, growth patterns, and typical noise levels
for highway vehicles are summarized in Figure 2.4-1.  Significant factors relative to
each type of highway vehicle are summarized in the following paragraphs.
            •   Automobiles — Automobiles are the primary mode of transportation in
                the United States and constitute the largest number of highway vehicles.
                From 1950 to 1970, the number of automobiles in use has increased
                from 36 million to 87 million; passenger cars traveled  1000  billion
                miles in  1970.  Automobile  sales, including vehicles, equipment and
                service,  reached $92 billion in 1970.  Approximately 5 million people
                were employed by this industry.
            •   Trucks— The total number of trucks in use has increased from 8.2
                million in  1950 to almost 19 million in 1970. Total truck miles in-
                creased to 206.7 billion in  1969 from 90.5 billion in 1950.  The
                average annual mileage for  all  trucks is over 11,000 miles.  A majority
                of the  total truck operating  hours (194 billion) was in population
                centers,  86 percent of the time in pickup and delivery service, and
                the remainder in long haul service.  Thirty-nine (39) percent of all
                truck miles were on urban streets.
            •   Buses — Highway and city buses accounted for about 27 billion passen-
                ger miles in 1970.  Mileage has been on a slight decline for a number
                                        92

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1
Automobiles
1
• Passenger Cars
• Sports & High
Performance
• Economy & Compact
• Imported
Highway
1

Trucks
1
• Light Trucks
• Medium
• Heavy Duty
Vehicles

1
Utility &
Maintenance
1

1
Buses
1
• Street Sweepers • Highway
• Garbage Compactors • City
• Tree Chippers • School
              87,000,000
                                           Numbers in Operation
 19,000,000
                                                         Estimated 75,000
  400,000
                                Growth of Number of Highway Vehicles
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                         Figure 2.4-1.  Characteristics of Highway Vehicles

                                               93

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                of years, and bus passengers now const!tute 4.2 percent of the com-
                mercial total.  Around 74 percent of the total of 400 thousand buses
                are school  buses and account for about one-half of the total mileage.
                The combination of local and intercity bus lines have carried 5.8
                billion passengers in 1970, for a passenger revenue of $2 billion, and
                have employed 150 thousand people.
            •   Utility and Maintenance Vehicles — The three major types of vehicles
                in this category selected for study are garbage compactors, street
                sweepers, and brush and tree chippers.  It is  estimated that there are
                approximately 75 thousand garbage  compactors, street sweepers, and
                tree and brush chippers  in use in the major cities of the United States.
                Garbage compactors and street sweepers generally operate 40 hours per
                week.  They usually begin operation by 6:00 a.m. and often extend to
                Saturdays to  meet pickup requirements.
2.4.2       Source Noise Characteristics
            The noise levels produced by highway vehicles can be attributed to the
following three major noise generating systems:
            •   rolling stock; tires and gearing
            •   propulsion system:  engine and related accessories
            •   aerodynamic and body
            The noise levels produced by highway vehicles are generally dependent
upon vehicle speed, as illustrated for a number of different vehicle types in Figure
-) A 96-8
2.4-z.
            Figure 2.4-3 illustrates the relative contribution of tire and engine noise
                                                                   9  10
to the overall noise levels of automobiles and trucks at highway speeds.  '     The
small difference between the 65 mph coast and cruise conditions for the automobile
indicates that its noise is generated primarily by the tires.  In fact, tire noise for auto-
mobiles becomes a  significant contribution to overall levels at around 35 mph.    The
                                        94

-------
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                                                       Highway Buses
                                                      Rangs
                                             Passenger Cars
                                   ____ Mean Levels
                             i      i      i      i      i      i      i
         0    To     20     30    40    50    60     70    80


                              Speed - Miles per Hour




    Figure 2.4-2.   Single Vehicle Noise Output as a Function of Vehicle Speed
                                  95

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                                        Diesel Truck

                                        55 mph Cruise
                            Truck - Coasting
                                      i  i  i
                                      Auto

                                     65 mph
50
                    IOO
           1000


Frequency in Hertz
IOOOO
       figure 2.4-3.  Diesel Truck and Automobile Noise at Highway Speeds/

                       Cruise and Coasting (at 50 Feet)

-------
tire noise for trucks begins to become important in the high frequency portion of the
spectrum at speeds of 45 to 50 mph, although even at 55 mph, engine noise controls
the low frequency spectrum.
            Tire noise levels vary by  7 to 10 dB,  depending upon road surface compo-
sition and roughness. Another 5 to 7  dB  variation may be expected for truck tires as a
function of axle load.   In addition, significant variations in noise are found to be a
function of tread design and state of wear.  At constant speed, these variations may
                                    12-14
result in a 20 dB range in  noise levels.
            Figure 2.4-3  also identifies  the segmenf of the noise spectra contributed
by the propulsion system.   This contribution is further defined in Figure 2.4-4, which
compares the typical noise spectra produced by a heavy diesel truck and by an auto-
mobile,  both under maximum acceleration at 35 mph.     The noise characteristics of
propulsion systems may be classified as either acoustic noise radiating directly out of
the engine openings, or as noise produced by internal engine processes which then
radiate from the engine structure.  Figure 2.4-5 illustrates the relative effect of
silencing on overall  engine-generated noise attributable to these two classifications.'"
The unsilenced exhaust noise is seen to overshadow the total of the other noises by 10
to 15 dB in each octave over the entire audible range.  With the exhaust silenced, in-
duction noise is observed to prevail at frequencies below 1000 Hz, whereas noises
radiated from the engine structure control the spectrum above 1000 Hz.
            The third principal source of noise in highway vehicles includes aero-
dynamic turbulence and body rattles. It is generally felt that streamlined designs do
much to reduce the noise contributions of automobiles and buses at highway speeds;
however, application of aerodynamic styling to trucks is not considered practical  due
to servicing requirements.     Body rattles generally reflect the care and maintenance
the vehicle  has received.  These are mainly an annoying factor at low speeds in resi-
dential areas and can be controlled only by routine servicing of the vehicle and
careful loading of the  truck and cargo space.
            The following paragraphs provide a discussion of the characteristics of the
noise generated in trucks,  automobiles, buses and maintenance vehicles.   An analysis
                                        97

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            Illustrating the Effects of Silencing for the Exhaust and the Intake
                                          99

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of the major noise sources for trucks will be provided first, as the characteristics of
these sources are relevant to all types of highway vehicles.  Additional detail on the
most significant of these noise sources is presented in Appendix C.
Trucks
            Gasoline engines power 97.5 percent of the trucks in operation, and the
remaining 2.5 percent are powered by diesel engines.  Diesel  trucks are generally 8
                                                                                 17  18
to 10 dB noisier than gasoline powered trucks and 12 to 18 dB noisier than automobiles. '
The noise output of trucks increases with age, and about 60 percent of operating trucks
are more than 5 years old.   This increase of noise with age is aggravated by the tendency
to overhaul trucks with replacement mufflers or recapped tires which generate higher
noise levels than the original equipment.
            The major contributing subsources of truck noise include the exhaust,
cooling fan,  engine mechanical noise,  intake noise  and tire/roadway noise.  Figure
2.4-6 and Table 2.4-1 depict the relative contribution of these subsources to overall
noise levels, and Figure 2.4-6 presents a range of octave band spectra for typical
                19-21
operating modes.        Following is a discussion of each of these major
  ,        12-14,16,  18, 22-32
subsources.
            •   Exhaust — The noise levels generated by truck  exhaust systems are
                dependent on  factors such as engine type, timing and valve duration,
                induction system, muffler type, muffler size and location in the
                exhaust system,  pipe diameter, dual or single system, and engine
                back-pressure.  The actual noise-generating mechanism is created by
                vibrating columns of gas at high pressure amplitudes which are pro-
                duced by the opening of the exhaust valve. This noise is communi-
                cated directly to the atmosphere.  Additional  exhaust noise is created
                by the direct impingement of these  released gases on the pipes and
                muffler shell. The fundamental and harmonics of engine firing fre-
                quency are the principal components of exhaust noise. At high engine
                                        100

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                  Exhaust-
                                                                 Aerodynamic Noise
Cooling Fan
                                             Typical Range of
                                                Spectra for
                                             Normal Operating
                                                 Modes
                                                              SAE Maximum Noise
                                                             Acceleration to 35 mph
                                                                    92 dB(A)
                                  Highway Speed
                                  (84 dB(A))
                                                Cruise 75 dB(A)
      50
                          100
                                                 1000
10000
                                       Frequency in Hertz
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                        Table 2.4-1

DIESEL TRUCK NOISE COMPONENT CONTRIBUTIONS TO MAXIMUM
           NOISE LEVELS AT 50 FEET FROM VEHICLE
Truck Examples
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
#11
Contributing Subsource
Engine
Mechanical
81
85.5
83
85
83
81
82.5
85
.83
81
83.5
Exhaust
84
81
86
82
83
77
86
82
83
77
82.5
Intake
75
74
80
80
72
70
79
80
72
70
74
Cooling
Fan
82
81
81
83
78.5
82
82
83
78.5
82
78
Total Vehicle
Noise Level
dB(A)
88
87.5
89
89
87
85.5
89.5
89
87
85.5
87
                           102

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speeds,  these individual frequency components are masked by a more
continuous spectrum created by the turbulence noise produced by the
flow of high velocity gases through the exhaust valve.
Cooling Fan— In nearly all applications involving water-cooled
engines, an  axial flow type fan is used to draw cooling air through a
forward-mounted radiator.  In many designs, fan noise approaches the
level of exhaust system noise and is generally considered an important
factor in reducing overall  vehicle levels.
Generally, fan noise is directly related to fan speed.  It has been
shown that fan noise increases at a rate of 2 dB per 100 rpm at speeds
between 1000 and 1500 rpm and at a rate of 1  dB per 100 rpm between
1500 and 2000 rpm.  The noise output is also dependent  upon  tip speed
and configuration, blade design and spacing, and proximity of acces-
sories and other objects which affect airflow.
Intake— Induction system noise is created by the opening and closing
of the inlet valve, starting and stopping the air flow into the  cylinders.
It  is also markedly affected by the flow properties of the exhaust valve
and the exhaust system due to the fact  that during the duration of in-
take and exhaust valve overlap, some exhaust noise is transmitted
through the intake.  Intake noise of supercharged,blower-scavenged
and turbocharged engines is created by the air-compressing process.
It  may be modified by resonant induction systems which can, under
certain  conditions of engine speed and system  length,  amplify intake
noise levels. The intake noise increases with increasing load.  For
diesel engines between no-load and full-load, this increase may range
from 10 to 15 dB, while gasoline engine  intake noise may increase
from 20 to 25 dB.
Engine Noise— Engine-associated noise in internal combustion engines
is  produced by the compression and subsequent combustion process
                            103

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which gives rise to severe gas forces on the pistons and to forces of
mechanical origin, such as those produced by piston-crank operation,
the valve-gear mechanism,  arid various auxiliaries and their drives.
Both types of fluctuating forces produce mechanical vibrations of the
engine structure which in turn  cause all components attached to the
engine to resdnate and radiate noise.
As previously noted,  diesel  engines are typically about 10 dB noisier
than gasoline engines.  This difference results mainly from their different
mechanisms of ignition.  Gasoline  engines initiate combustion with a
spark from which the  flame front gradually spreads throughout the com-
bustion  chamber until the entire  fuel/air charge is burnt. This yields a
smooth blending with the compression.  The diesel engine, however,
relies on a much  higher compression ratio to produce spontaneous com-
bustion  which burns a large volume of fuel/air mixture  rapidly.  This
yields a much more severe and more rapid pressure rise  in the cylinder,
causing more engine vibration  for the diesel engine  in comparison with
the gasoline engine.
Many efforts at quieting diesel engines are aimed at smoothing out this
abrupt pressure rise, either through prechamber combustion chamber
designs or turbocharging (which tends to reduce these abrupt pressure
rises).   However, efforts at reducing diesel engine noise by smoothing
out cylinder pressure  rises are only effective when combustion-excited
noise is greater than mechanical  noise.
At constant speed, diesel engines show only slight reduction in noise,
with reduction in load due to the high compression pressure even under
no-load.   Gasoline engines, however, show a substantial decrease in
noise output with decreasing load,  due to throttling of the inlet which
yields a large reduction of compression pressure.  Therefore,  the '
change in noise level between no-load and full-load conditions is
                        104

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 rarely more than 3 dB for a diesel engine, but can be as high as  10 dB
 for gasoline engines.  In addition, compression ignition in diesel
 engines produces their characteristic ''knock" which is  associated w,ith
 a broad peak of noise in the frequency range from 800 to 2000 Hz.
 Engine speed also affects engine noise output.  At low  speeds under
 full load,  the gasoline engine is quieter than the diesel;  however, the
 noise from, gasoline engines increases much more rapidly with increasing
•engine speed than  from diesels (45 dB per tenfold increase in engine
 speed versus 30 dB for diesels).  Hence at high speed, the noise  levels
 of both diesel and gasoline engines are of the same order of magnitude
 for the same horsepower.
 Tires — Truck tire noise presents the major obstacle in limiting overall
 vehicle noise at speeds above 50 mph, since at this speed tire noise
 often becomes  the dominant noise-producing source on  heavy duty trucks.
 Typical noise levels from truck tires at 50 mph range from 75 dB(A) for
 "low noise" tread designs to over 90 dB(A)  for "high noise, level"  tires.
 Figure 2.4-7 illustrates the noise output of various truck  tire tread con-
 figurations over the normal speed range of interest.  The major offender
 is the standard cross-bar design used by the vast majority of trucks on
 their drive wheels.  These tires may produce levels in the 80 to
 85 dB(A) range when new, but their noise increases with  wear as much
 as 10 dB in the half-worn condition.  This increase is attributable to a
 change in  the tread curvature resulting from wear.  Cross-bar retreads
 pose an even greater problem as  their noise level can be  as much as
 95 dB(A) at 50 feet when operated at 55 mph in,the half-worn condition.
 Despite their noise, cross-bar retreads are very popular for economical
 reasons and each tire is recapped an average of two to  three times.
 They wear roughly twice as long as the continual rib automobile  type
 design tires and exhibit superior  dry and wet traction performance.
                        105

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              60
                                                      New Retread
                                                      1/2 Worn Retread
                          1/2 Worn Crossbar
                                                      New Crossbar
                          New Rib
                          35535655
                          •i«^«0^M^0


                          New Rib
                                                      Passenger Car
                                                      (Typical)
        Figure 2.4-7.   Effect of Various Tires Mounted on the Drive Axle.
                Loaded Single Chassis Vehicle Operating on
                 Concrete Road Surface (Levels at 50 Feet)
                                 106

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                Tire manufacturers state that recapped tires are generally much noisier
                than are new tires because of tread design.  Current new tread designs
                are optimized on  the basis of both  traction and noise output.   However,
                most recap tire molds are 5 years old or more and do not reflect the
                newer thinking in quiet tread designs such as randomized tread element
                size and spacing variations.  These older molds become a critical noise
                factor when one considers that well over half the truck tires on the road
                today are  retreads.
                Axle loading is also a major factor in the amount of noise generated by
                tires.  Retread tires exhibit the most predominant dependence  upon load.
                One example indicates a decrease of 15 dB resulting when  load per tire
                was reduced from 4500 to 1240 Ibs. The explanation is that with the
                tire unloaded, the sides of the retread do not contact the road surface,
                hence the cups in the tread cannot seal against the road surface and
                compress small pockets of air.
                New and half-worn cross-bar tires also produce more noise with in-
                creasing load.  The explanation follows that with increasing load, the
                tread pattern is compressed, hence more of the load is  carried on the
                outer sections of the tread.
                The rib type tire designs are generally independent of loading due to
                their uniform tread design accross the tire cross-section.
                Variations in road surface also significantly affect tire noise generation.
                Here again, retread tires exhibit the most dependence  on this  variable,
                with the most noise generated on smooth  road surfaces.  Differences
                have been observed experimentally to be of the order of 8 dB at speeds
                of40to50mph.
Automobiles
           While not as noisy as trucks, buses and motorcycles, the total contribution
of automobiles to the noise environment is significant due to the very large number in
                                        107

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operation. Approximately 70 percent of automobiles on the road in 1970 were over 3

years old, the average age being about 5-1/2 years.  Vehicles over 2 years old tend

to produce higher noise levels (2 to 3 dB) under most operating conditions,  due to

deterioration of exhaust silencer performance and the response of the vehicle to pave-
               Q
ment roughness.   Like trucks, the noise produced by individual automobiles is a

function of several subsource contributions — exhaust, cooling fan, intake, tires,
                                                                           !
engine and transmission noise and aerodynamic noise.

            Figure 2.4-8 illustrates the relative contributions of these major subsources

of noise to the overall noise levels and shows typical octave band spectra for various
                           f f\ J OO
automobile operating modes. '  '    Following is a discussion of each of these

subsources.12-14,21,24,34-36



          I  • ,    Exhaust — For most automobiles, exhaust noise constitutes  the pre-

           i I     dominant noise source for normal operation at speeds below about

                 35 tq 45 mph, depending upon the condition and design of the

                 exhaust system. Above this speed range,  in many cases tire noise

                 becomes equally significant.  While exhaust noise does not create a

                 significant interior noise problem, certain objectionable periodic
                I                                                             :
                 tones may be audible inside the car.                           '

            •   I Intake — Intake noise in automobiles constitutes a minor problem in

                 achieving current and projected automobile noise requirements, arid

                 the noise control, principles are well understood by automotive

                 engineers.  Underhood space is sufficient  to allow air cleaners large

                 enough  to achieve adequate silencing with minimal air restriction.

            •    Fan  Noise — In some cases, the intensity of fan noise is almost equal

                 with exhaust noise.   The parameters which  govern fan noise

                 generation are  essentially the same as those related to  trucks. More

                 work has been done in  the passenger car area to reduce noise in the

                 passenger compartment, hence quiet fans have been desirable for some

                 time.
                                         108

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        Aerodynamic
            Noise
                                                          Intake
   Exhaust
   100
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            •   Tire Noise — Tire noise in passenger cars presents much  less of a
                problem than in trucks.  The principal reason for this is that standard
                automobile  tires do not employ the cross-bar tread design. For com-
                parative purposes, Figure 2.4-7 includes the noise characteristics of
                a typical rib-type passenger car tire.   As can be observed, its noise
                level at 50  to 60 mph can be as much as 25 dB  less than the worst truck
                tires.  Snow tires on automobiles are similar in design to truck tires
                and produce high noise levels on the order of 85 dB(A) at highway
                speeds.  At highway speeds and at rated load,  current automobile
                tires produ'ce levels on  the order of 65 to 75 dB(A).  In  most new auto-
                mobiles, these are the controlling noise sources at the higher speeds.
            •   Engine Noise— Nearly all passenger cars  utilize four-cycle gasoline
                powered engines which for the most part (imported and compact  vehicles
                excepted) normally operate at a fraction of their rated horsepower out-
                put.  Consequently, engine mechanical noise is a minor problem to the
                observer.  In addition,  automobile engines are well  shielded on all
                sides; therefore little noise is radiated directly out to the observer.
                Most attention to engine/transmission noise is focused on reduction of
                interior noise levels.  Extensive noise attenuation treatment work is
                      i
                conducted on the majority of U.S. cars to reduce engine noise trans-
                mission into the passenger compartment.
Buses
            Although trucks  and buses share many basic design characteristics and some
common components, buses are generally quieter due to their increased packaging space,
which allows larger  mufflers, and their enclosed engine compartment. Typical noise
spectra for buses at highway  speeds are shown in Figure 2.4-9.   At highway speeds,
passenger buses exhibit noise levels primarily in the range of 80 to 87 dB(A) at
50 feet,  principally due to tire noise.   One of the most annoying noises produced by
city buses is heard by the person standing at the curb while a bus pulls away.  As the
                                       110

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                         ..-»'---
                                    Standing Start Drive Away
                                   Measured from Curb (4-6 feet).
                                           (94 dB(A»
                                  60-69 mph
                                  (at 50 feet)
                               50-59 mph
                               (at 50 feet)
                        100
                                                1000
5    I 0 000
                                     Frequency in Hertz
              Figure 2,4-9.   Typical Octave Band Spectra for Highway Buses
                                      111

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bus passes the person,  its noise level increases until it reaches a maximum of well  above
90 dB(A) as the engine intake grille passes.  This noise has a startling effect because of
                                  37
its sudden onset and very high level.
Utility and Maintenance Vehicles
            Utility and maintenance vehicles share many common elements with trucks.
The chassis elements are essentially identical to heavy and medium trucks, hence the
noise output at most speeds is quite similar.  The major distinction lies in the type of
auxiliary functions these vehicles perform.  A typical octave band spectra is presented
in Figure 2.4-10 for a garbage compactor during the compacting operation. °
2.4.3      Environmental Noise Characteristics
            Noise from vehicular traffic generally establishes the residual noise levels
(defined in Section 2.1) in most urban and suburban communities.  This residual noise
level varies throughout the day, based on the average density of noise sources in a given
          39
community.    In the immediate vicinity of a major arterial or freeway,  the noise  level
is much higher.  Its actual value is dependent upon traffic flow rate, average vehicle
speed, distance to the traffic lane and the ratio of trucks to automobiles on the highway.
For a typical 4-lane freeway, average daytime traffic flow rates can be of the order of
6 to 10 thousand vehicles per hour.  For this condition, the median noise level beyond
100 feet from  the flowing traffic is  equivalent to a continuous line of noise sources.
            Under this condition, the average noise level  varies in the manner shown
in Figure 2.4-11.  This level increases 3 dB for every doubling of traffic flow rate,
6 dB for every doubling of vehicle velocity, and decreases approximately 3 dB for
every doubling of distance from the freeway centerline.    At distances of the order
of 500 to 1000 feet from the  freeway, the decrease in noise level with distance
generally ceases, as the freeway traffic noise becomes equal to ambient level in the
neighborhood.
            Superimposed on this median traffic noise level are the intrusive or single-
event noises from individual  noisy trucks, cars and motorcycles.  These are normally
                                       112

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15 to 25 dB above the residual noise levels on neighborhood streets.  However,  at the
high traffic flow rates typical for freeways, these individual single events are barely
distinguishable from the overall roar of the total traffic flow.  During nighttime hours
on major interstate freeways, the percentage  of trucks is often much higher than on
typical  freeway systems, and truck noise dominates the traffic noise levels.
            In  a rural or "quiet" suburban community located well away from major
highways,  the normal ambient is 10 to 15 dB  lower than in urban areas, and the passby
of a noisy car will momentarily increase the noise level by  as much as 40 dB above
                 39
the ambient (L0(~).    A noise intrusion of similar magnitude can also be  created by
garbage compactors and street sweepers that begin their rounds at 6:00 a.m.
Interior Noise Levels
            Because most noise reduction in current automobiles has been created for
passenger comfort, a special discussion is warranted on the  subject of interior noise
levels.  Figure 2.4-12 shows a  representative range of automobile interior noise
                        40 41
spectra  at highway speeds.   '     At the upper end of the range is a  popular import.
while the lower end represents a medium-size standard domestic passenger car.  The
noise levels in  the smaller import tend to be higher because of less sound  treatment in
the body, less resilient tires, and stiffer suspension systems.
            Generally, the interior noise levels increase with speed, with the noise
of domestic passenger cars increasing at about 2.5 dB per 10 mph, while the noise in
sports cars and  small  imports increases at a higher rate— up to 5 dB per 10 mph.  At
35 mph  on an asphalt road, the typical interior noise levels range from 64 to 73 dB(A).
Typical  noise levels at 60 mph inside automobiles at highway speeds range from 63 to
82 dB(A) on concrete with windows  closed. Air conditioners add at least 5 dB to the
                                                                        40  42  43
overall  interior noise level, depending on operating mode and vehicle speed.   '   '
            Open windows generally increase noise levels 5 to 15 dB, depending on
the "closed window" noise  level, aerodynamic design and the combination of windows
which are opened.  A particularly annoying Helmholtz resonant condition can be
created in some vehicles by opening just one  side window.  Noise levels  at this
                                       115

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                                                      Domestic Sedan at 70 mph
                                                      (72 dB(A))
                                                      Popular Economy Import- at-
                                                      70 mph (82 dB(A))
                                                      Range of 15 cars
60
50
     40
                        100
                                            1000

                                 Frequency in Hertz
I 0 000
         Figure 2.4-12.  Range of Typical Interior Noise Levels for Domestic
                   and Imported Passenger Cars at Highway Speeds
                                       116

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resonance may be well  in excess of 100 dB(A).  This resonance usually occurs at a
specific speed and often may be stopped by opening an opposite window a very small
       40
amount.
            Buses, by virtue of their rear engine design and adequate allowance  for
interior sound package treatment, provide generally acceptable interior noise levels
in the range of 72 to 80 dB(A). However, the interior noise in trucks ranges up to
100 dB(A) for the largest and noisiest trucks.  These higher levels may be excessive
in terms of a potential hazzard of hearing  loss.
2.4.4       Industry Efforts Toward Noise  Reduction
            The  highway vehicle industry  is strongly committed to the development of
vehicles intended for specific segments of  the consumer public.  Each vehicle model
is manufactured with a particular performance goal or  overall  image in mind. This
image ranges from a luxury vehicle, wherein  a quiet car is desired by the consumer, to
a performance vehicle which generally exhibits as high a noise level as is legally
allowed to provide the consumer with a sense  of power.  Considerable technical effort
has been  expended for many years to obtain the "proper sound" for each automobile
design.                                                        ,
            At its infancy in the early  1900's, the automotive industry  found it neces-
sary to equip its  engines with mufflers when the noise of the "horseless carriage".
frightened horses on the road.  Cities and  towns began to require mufflers on cars in
the 1920's and the automobile  muffler has  improved significantly since that time.
            Trucks, utility and maintenance vehicles, and buses are generally manu-
factured to individual customer specifications which place major emphasis on perfor-
mance, operating economy and initial cost.   The customers in this industry often
associate noise with better economy and more power; hence there has been little  cus-
tomer pressure to reduce truck  noise, although individual cities and  towns have begun
to demand quieter maintenance vehicles and buses.  In the late 1950's, recognition
that exterior truck noise was causing problems led the  Society of Automotive Engineers
(SAE) to develop a truck noise measurement standard and to recommend a maximum
                                        117

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exterior loudness level of 125 sones at 50 feet.  This standard, including the recom-
mended maximum level,  was voluntarily adopted by the major producers of trucks and
resulted in a reduction in the noise of the larger trucks.  More recently, this standard
has formed the basis for the measurement of truck noise by new state legislation and
regulations.  The manufacturers are committed to meet the exterior noise goals of this
new state noise legislation.  However,  the accomplishment of this commitment is
greatly complicated by the fact that the new vehicle manufacturer faces a number of
differing noise laws and measurement standards throughout the country,  and different
time deadlines for achieving various amounts of noise reduction.  In general, manu-
facturers have been faced with very short time constraints and have been essentially
forced to exploit the "band-aid" type of problem solution,  without having adequate
time to incorporate the new requirements into a basic redesign.  This approach is
generally wasteful of effort and costly to the consumer.  It is preferable for the manu-
facturer to have a single set of regulations which are technically and economically
achievable and which  contain a time schedule compatible with the basic design, proto-
type, test and production tooling timeframe.  This approach generally will achieve the
best overall design in respect to both vehicle  performance and ultimate  cost to the
consumer.
            An additional factor which influences the industry commitment is pending
legislation in other areas of concern to manufacturers which include safety, emissions
and, of late  in the trucking industry, horsepower/ton considerations which may greatly
affect powerplant and  chassis designs.
            The industry employs qualified noise control engineers who  haye extensive
experience in solving all  types of vehicle noise problems to satisfy market requirements.
They are geared to solve problems in new models within very tight schedule constraints
prior to start of production.  Many companies incorporate large noise control staffs
which have at their disposal sophisticated laboratory facilities and computer assisted
analysis equipment. The analyses are highly refined and are geared toward problem
area definition and comparison of relative improvements in problem areas.
                                        118

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            Though most of the principles of noise generation in highway vehicles are
w«ll understood, incorporation of advanced acoustic technology proceeds slowly for a
number of reasons, the foremost being that the engineers are almost always dealing
with a basic design which  is in production. Any new refinement to a specific model
may require modification to  the original basic design and must be compatible with all
design; and production constraints.
            A further consideration in the application of acoustic technology is that a
majority of the components in a motor vehicle are supplied by outside specialty product
vendors who do not have direct responsibility for the performance of the total end
product.   The net result of this aspect is that  many manufacturers are now compelled
to supervise the design of these auxiliary components or to produce many of them to
insure that the total system will be compatible in  terms of function and desired acousti-
cal performance.  A good example of this is the cooling system on  heavy trucks, where-
in the entire cooling system  must now be engineered by the vehicle manufacturer to
achieve adequate engine cooling,  together with reduced transmission of engine
                                             24  25 44
mechanical noise and reduced cooling fan noise.   '   '     The increased require-
quirements for system design which tend to exceed the technical scope  and capability
of the specialist vendors may lead to major changes in the historical purchasing
pattern of the entire industry.
            One final  aspect which impedes application of advanced acoustic tech-
nology is the high  use factor associated with highway vehicles and the.very severe
economic/durability constraints on the manufacturer. Extensive and time-consuming
highway durability test programs always precede introduction of any modifications to
today's vehicles,  as illustrated by the typical engineering/development/production
timing schedule shown in Figure 2.4-13.
2.4.5       Noise Reduction Potential
            Figure 2.4-14 illustrates the present ranges of noise levels for highway
vehicles under both maximum noise conditions (SAE test method) and highway cruise
conditions.  It summarizes noise reduction potentials deemed  achievable in the near
                                       119

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                 A Typical New Diesel Engine Design
                      and Development Program*
£
'>
Engineering Acti
Detail
Design
Single
Cylinder
Lab Tests
1
Further Lab
Development
Testing
Toolina
i
1

Engineering
Prototype
Development
and Test
i
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Durability
' Fleet Usage
i i
          12
24
    36
Months
48
60
Based essentially on minor modifications (such as displacement increase)
of an existing engine series.
       Figure 2.4-13,. Typical Industry Production/Timing Schedule
                           120

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Current
Levels
I
Short-term
Potential

Long-term
Potential
 I
Cfc
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 E
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     90
    80
    70
    60
SAE
Test Method
Highway
Speed
                                     35 mph
                                     Accel.
                               Highway
                               Speed
35 mph
Accel.
Highway
Speed
Normal
Operation
                       Trucks
                                        Automobiles
                                                City & Highway
                                                     Buses
                            Utility
                           - and
                                                                                                      Maintenance
                       Figure 2.4-14.  Effect of Potential Noise Reduction for Highway Vehicles

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future for existing vehicle concepts with current technology, and long term potentials
which should result from further research and development efforts.  These noise reduction
potentials are based on an extensive analysis of the subsources of vehicle noise, and '
assume continuing advancement in the applicable noise reduction technology.  For most
vehicles at highway speeds,  the long term potential  is limited by tire noise which  is
inadequately understood at present.   Further noise reduction, particularly at  high  speeds,
requires successful research and development efforts  in tires. At low speeds,  further
reduction may require considerable effort in advancement in engine design and muffler
technology, and for large  vehicles possibly a change from the conventional reciprocating
engine to new devices such as the gas turbine for propulsive power.  The following para-
graphs discuss current and  projected noise reduction  activities of the various segments of
the highway vehicle industry.
Trucks
            Historically, many new trucks were sold without mufflers in their exhaust
system and with little or no attempt to minimize cooling fan and engine noise levels.
Such noise reduction simply was not in keeping with the customer's request for maximum
performance and economy  of operation.  However, heavy diesel trucks are now recog-
nized as the loudest single category of highway vehicles. A recent statistical study  on
traffic noise shows the average noise level at highway speeds of tractor trailers to  fall
in the 85 to 90 dB(A) range.   Considerable effort has been expended on the part  of
industry in attempting to quiet these machines.  One particular program currently  under-
way involves a joint effort between the California Division of Highways and the Inter-
                              44
national Harvester Corporation.    Their goal  is to silence a standard heavy-duty diesel-
powered vehicle as much as is feasible through application of current acoustic technology.
Their stated goal  is 83 dB(A) at 50 feet,  but they are attempting to achieve lower
levels.  While program costs are not available, the project has been in progress for the
past 6 months and is expected to continue for another 3 to 6 months.
            The average heavy diesel truck will probably run over 500,000 miles  in  its'
lifetime.  Over this time period, many of the components will  be replaced due to  wear
                                        122

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or be modified to meet individual operator needs.  The net result of this long-term
usage is that after a year or two, the noise characteristics of many heavy trucks is
altered significantly.   The widespread usage of retread tires and modified exhaust
                                                   13 35
systems contribute to even higher overall truck levels.  '
            Figure 2.4-15 illustrates the potential noise reduction of the major sub-
sources of truck noise.  The potential  for reduction of noise generated by these sub-
                         12-14, 16, 18, 22-24,  27, 29-31, 33, 44-47
sources is discussed below.
            •    Exhaust System — In achieving reductions in the noise produced by
                heavy trucks,  a foremost consideration must be the exhaust system.
                The effect of adequate exhaust silencing treatment alone, under maxi-
                mum noise output conditions, can provide a gross overall noise reduc-
                tion of at least 10  to 15 dB, bringing the over 100 dB(A) unmuffled
                offenders down to the 90 dB(A) range.  It is considered that a
                feasible goal for the near-term in exhaust noise for all  trucks appears
                to be in the range  of 80 dB(A) measured at 50 feet,  (In some instances
                a power loss may result.)
                The current state-of-the-art in muffler technology, which relies on
                large muffler volumes to obtain adequate silencing with low back-
                pressures, will  allow approximately 18 to 20 dB attenuation through a
                muffler alone.  When greater reduction values are sought, noise
                radiation from the  pipe and muffler  casing becomes a significant
                factor.  In one program,  where greater exhaust noise reduction was
                required,  the exhaust pipe diameter was reduced from 4 inches to
                3-1/2 inches, yielding a noise reduction of the order of 25 dB with
                a typical diesel engine and muffler. This reduction  in  diameter,  how-
                ever, could lead to an increase in back-pressure of approximately
                40 percent. Some turbo-charged diesel engines (exhaust turbine-
                driven supercharger) may meet current  legal noise restrictions without
                the use of mufflers. These devices, like mufflers, extract energy
                                        123

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                                                                                 HIGHWAY

                                                                                   SPEED  '
                                                                                                             Current

                                                                                                             Levels
                                                                                                       Short-term

                                                                                                       Potential

                                                                                                       Levels



                                                                                                       Long-term

                                                                                                       Potential

                                                                                                       Levels
                   Figure 2.4-15.  Effect of Potential Noise Reduction for Diesel Trucks

-------
from the stream of exhaust gases.  Further research into exhaust
system designs, or allowance for more muffler space  in new truck
designs, could produce additional exhaust noise reduction  for future
vehicles without drastically increasing engine back-pressure, although
in the interim some increased back-pressure and the  associated power
loss may have to be accepted to achieve significantly reduced levels.
It would appear that exhaust levels in the 70 to 75 dB(A) range should
be feasible in the  longer term.
Cooling Fan — The standard method of reducing fan noise is to utilize
a larger fan running at a slower speed to produce essentially  the same
air flow.  In many cases,  this solution necessitates a larger radiator at
a definite cost and weight penalty.  The extent to which this technique
may be  applied is, of course, limited by the overall  radiator size which
is of concern for driver visibility. Thermostatically-controlled fan
release  clutches are also  successful  in greatly reducing fan noise,  but
are only effective at highway cruising speeds where  a sufficient cooling
air flow is provided by the vehicle speed.
A major consideration in the design of engine cooling fan systems is to
minimize the horsepower requirements of the fan itself,  which consumes
from 5 to 11 percent of total engine horsepower.  Larger fans, or
increased cooling capacity requirements resulting  from application  of/:,
engine shielding and enclosure  will have a marked effect on  fan horse-
power losses and hence performance  and economy.
Substantial development is required in the area of total  engine system
cooling and related heat transfer in order to provide a more refined
solution to this problem.   Acoustic technology for reduction of fan
noise  developed for the noise control of aircraft can  be implemented;
however, additional applied research and experimentation  will be
required before estimates of expected performance are possible.
                           125

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Certain manufacturers are now instituting internal research activities
aimed at development of new concepts in engine cooling.  Based on
analysis of existing programs, fan noise levels in the low 70 dB(A)
range are a reasonable future expectation for low speed truck operation.
Intake — Silencers are readily available which achieve reduced levels by
utilization of a design which incorporates an expansion or plenum
chamber to reflect noise back toward the engine.  The amount of
silencing achieved by these devices is a function of air cleaner size
and location in the induction system, the optimum being the center of
the air intake system.  The frequency range of attenuation generally
depends on location and air cleaner length; larger air cleaners atten-
uate lower frequencies.  The most effective air cleaner/silencer
designs currently available utilize an absorbent packed construction
for high frequency absorption and incorporate a Helmholtz resonator
into their designs for attenuation of frequencies below 600 Hz.   Feasible
near-term potential  for  intake noise levels fall in the 70 to 75 dB(A)
range.
The major considerations in  implementing these designs are packaging
the silencer and minimizing the amount of performance loss due to
increased restriction in  air flow. One manufacturer suggests that
approximately 2.5,  3 and 8 percent power losses  result from each
additional  inch of mercury restriction for two-cycle blower scavenged
diesel, four-cycle naturally aspirated diesel and gasoline engines,
respectively.  It is believed that further overall  engine development
in this area will aid in reducing intake contribution to the 68 to
70 dB(A) range in the long term.
Engine Noise — Reducing the total mechanical and  engine-generated
noise output is a critical problem facing truck manufacturers.  Most
current efforts by U.S.  industry in reducing engine noise have involved
                          126

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acoustic shielding and encapsulation of the engine and transmission.
These methods have met with little success, primarily due to engine
cooling problems and  increased servicing costs.  Reduction in the
diesel engine mechanical noise output appears limited to the general
range of 81 to 84 dB(A)  measured at 50 feet (see Table 2.4-1).
Further, the current trend in engine design is to make power plants
lighter and to extract more power; this exaggerates the noise
problem.
Substantial research has been conducted by Priede in  England on the
subject of engine design.  His work has established that by certain
radical changes  in design of the engine structure, engine noise levels
can be reduced by 10 dB.   The effect of these changes has been
demonstrated in  a research  engine with resultant 7 to 8 dB noise
reduction.  The  techniques involved adding more crankshaft main
bearings to reduce crank vibration amplitudes and stiffen the engine
structure, reducing maximum combustion pressure, closer tolerance
to reduce piston slap and remounting accessories on the cylinder
head (because of its stiffness,  the cylinder head exhibits low vibration
amplitudes and hence transmits little vibratory energy to accessories).
In addition, all  valve covers and engine cover plates were heavily
damped and an isolated  crankshaft pulley was used which incorporated
damping rubber between the hub and rim to reduce noise radiation.
The American manufacturers generally support Priede's work, but feel
at the present time these techniques are only minimally effective and
are presently impractical from cost and servicing standpoints.  The
basic problem in implementing these concepts is one of proving
durability.
The research  efforts of Priede and others could be the basis for a long-
term goal in engine noise levels to be  in the 72 to 76 dB(A) range
                           127

-------
(based on reduction  levels achieved with experimental engines).
The combined result of these noise reduction efforts for all component
sources is a potential reduction of total truck noise, measured under
current SAE maximum noise tests at 50 feet,  to the 74 to 80 dB(A)
range in the longer term.
A consideration in assessing long-term goals  for truck noise reduction
lies in the realm of incorporating power plants other than conventional
reciprocating  internal combustion engines.  Much effort  has been
expended on the part of  industry in attempting to utilize the gas turbine
engine effectively in heavy duty truck applications.  The technology
exists for quieting turbine engines to a high degree of efficiency,
although widespread application of turbines in the next 10 years is
not anticipated unless significant breakthroughs in certain key design
areas occur.  However,  the gas turbine may  eventually provide a
major breakthrough in truck engine noise reduction.
Tires — At speeds greater than 45 to  50 mph,  total truck noise levels
are affected by tire  noise.  Obviously (from  Figure 2.2.4-7), one
way to reduce these levels is to outlaw the present design cross-bar
design tires and not  allow retreads of this design.  This action would
probably  reduce truck tire noise levels at highway speeds by as much
as 12 to 15 dB.  However, as the cross-bar tires exhibit superior .
wear and traction characteristics over the alternative automobile-
type rib tire designs, this change might have a significant impact on
operating cost and safety.  Therefore, it is reasonable to assume that
current levels reflect the maximum reduction that can be achieved
within economical and safety constraints with current technology.
Further research into tire noise generation and the parameters of tire
design is  needed to achieve levels of 74 to 76 dB(A) at highway speed.
In addition, as has been pointed out in Section 2, tire/roadway noise
                           128

-------
                is greatly influenced by pavement surface characteristics; consequently,
                the burden of reducing tire noise levels should be studied jointly by
                the tire manufacturers and those responsible for highway design.
Automobiles
            Substantial noise reduction is currently incorporated into the majority of
automobiles.  Much of this noise reduction is directed at reducing interior noise levels,
and successful industry efforts have been rewarded by increased sales of those vehicles
which emphasize quiet ride and  passenger comfort. One automobile manufacturer has
advertised that —
            "In  the last 5 years, the noise level in American cities has risen over
            20 percent.  In the  last 5 years,  sales of the very quiet  (manufacturer's
                                                    48
            brand name) have risen over 160 percent."
This passenger car model, and other American passenger cars in the $3000 and up
category, typically exhibit interior noise  levels at highway speeds on the order of 63
to 70 dB(A) with the windows up and the air-conditioner off,  With the air-conditioner
on, the levels are usually increased by at least 5 dB.  The automotive engineers who
develop air conditioning systems feel the customer associates air conditioning fan noise
with cooling — quiet air conditioning fans are not popular.
            Studies of the exterior noise levels of passenger cars, measured under
various normal operating conditions along freeways, city streets and rural roads, show
the noise of the  newest vehicles is slightly less than that of older vehicles.  For
example,  a recent statistical study, conducted by the California Highway Patrol,
obtained extensive noise data listed by manufacturer for models "1964 and earlier,"
and "1965 and later." In nearly all operational modes, the newer and older vehicles
exhibited  the same statistical average noise level fora given operational  mode. Also,
the vehicles of the various manufacturers exhibited identical average exterior levels.
An exception were Volkswagens of "1965  and later" which were 1  dB noisier than  the
rest.   (Volkswagen represents 55 percent of all imports on the road.) Subsequent
studies have been conducted which distinguish between "1968 and older"  vehicles,
                                       129

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 and "1969 and newer."  The newer cars in these studies average around 2 to 3 dB
                                                      o
 quieter than earlier models under most operational modes.
             Further silencing efforts in passenger cars, as in trucks, must be accom-
 plished in the exhaust system. In general, incorporation of a  dual muffler exhaust
 system will yield more noise reduction than the  more economical single exhaust system.
 This is largely due to the principle relating exhaust silencing to muffler volume.  Many
 current 1971 model passenger cars now produce  levels approaching 80 dB(A) at 50 feet
 in the maximum noise tests when the test vehicle is fitted with a dual muffler system.
 For one manufacturer, this system raises the price of the car by an estimated $30.00
                                            33
 over that of a car with  a single exhaust system.
             However, most major automobile manufacturers have stated that they will
 be  incorporating catalytic conversion muffler systems to meet the 1975 emissions
 standards.  It is anticipated that these systems will increase gas temperatures in the
 exhaust system by a significant amount in many  applications and hence necessitate
 larger muffler volumes to achieve current noise  levels.  The use of the dual exhaust
 systems mentioned above will now become considerably more expensive due to the
 requirement of dual converters. Also, packaging of muffler units is a  critical con-
 sideration in automobile design, and in most cases the addition of extra mufflers would
.necessitate redesign of the vehicle underbody.  This change will undoubtedly also
 require the use of larger radiators,  fan shrouding and larger fans.  The net result will
 probably be a requirement for a great amount of effort to maintain current fan and
   ,,.,',  24,33,34
 exhaust noise levels.
             As has been stated earlier, under normal operating modes  the automobile
 probably sets the majority of the ambient noise  levels in communities.  Hence, any
 major.reduction in automobile noise will have a significant effect on the ambient noise
 environment.  It would appear that levels around 68 to 70  dB(A) under cruise con-
 ditions at all legal speeds are potentially possible for automobiles.   However, at 60
 to 70 mph, the levels are highly influenced by tire noise,  and hence cannot be achieved
 without further research and development. Thus,  less potential noise reduction is
                                        130

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anticipated at highway speeds in comparison with that expected for 35 mph maximum
acceleration,  as shown in Figure 2.4-14.
            It is questionable whether or not the current SAE new car noise certification
                    49
test for vehicle noise  is a totally reliable measure of automobile noise output, since
a very small percentage of actual driving time is spent at full throttle acceleration.  It
is felt  that to further reduce new vehicle noise levels,  more attention must be paid
their normal operating modes and future noise legislation must be geared in this direction.
Buses
            Most noise reduction in buses has resulted from the desire to provide more
passenger comfort.  Buses utilize essentially the same propulsion systems as heavy trucks,
but by virtue of their designs, which allow for larger mufflers,  quieter tires and
enclosed engines, are much less a noise problem.
            As an example of silencing  existing highway vehicles,  a major manu-
facturer has developed a "retrofit" exhaust and noise emission reduction package  for
diesel-powered buses. The package includes modified fuel injectors and a large and
rerouted  exhaust muffler which  now incorporates a reactor to provide further odor and
emission  control. In addition,  the package includes a more effective air-cleaner/
silencer unit and a modified engine mounting system which reduces noise by isolating
the engine from the bus chassis. This system will  provide up to 10 dB reduction in noise
levels  as well  as providing significant reduction in exhaust emissions, smoke and odor.
The cost  of this conversion is $373.00 when installed on  new coaches;  however, to
convert a used bus runs up to $1300.00 for materials, with an average of 160 manhours
                       33 50  51
required  for installation.   '  '     Clearly from this example, further effort into the
area of developing economical  "retrofit" noise reduction packages for long-life vehicles
would  appear to be  feasible and warranted and not solely limited to bus applications
but heavy trucks as  well.
            It is believed that further efforts toward aerodynamic styling will  aid in
reducing aerodynamic noise at highway  speeds.  Further  reduction at highway speeds
will be dependent upon newly-designed "quiet" tires.  It is estimated that the noise at
                                       131

-------
50 feet from both city and highway buses can be reduced to levels of 74 to 76 dB(A)
under both acceleration and highway speed conditions in the long  term.
Utility and Maintenance Vehicles
            Utility and maintenance vehicles are a breed apart from the rest of high-
way vehicle types.  The only common elements are their chassis and propulsion systems.
These vehicles are most often operated at low road speeds in lower gear ranges.  As
many of these vehicles are diesel powered, they tend as a group to produce high noise
levels even at low speed.  These vehicles are normally  muffled, but little attention
has been paid to noise associated with the auxiliary functions they perform.
            Certain manufacturers have developed quiet utility vehicles and market
them on a limited basis.   One excellent example is the  "quiet refuse truck" developed
by General Motors for the State of New York.  In addition  to larger mufflers and a
silenced air cleaner, numerous additional engine seals were utilized along with a
"quiet" cooling fan  and "quiet" tread tires.  The refuse packer itself was quieted by
isolating the hydraulic valves and lines, cushioning certain components and damping
the body panels.  Typical noise levels at 50 feet were reduced  from approximately
87 dB(A) during the  packing cycle to 80 dB(A).  It is  estimated that these modifications
                                                  33 50 51 52
added about $3000 to the price of the complete unit.
            Thus,  auxiliary functions performed by these vehicles are amenable to
noise reduction treatments.  It is estimated that the refuse packing function can be
reduced in noise level to  the 76 to 78 dB(A) range in  the medium to long term. The
noise levels of street sweepers and other similar function vehicles  should also be able
to be reduced to a level of 70 to 75 dB(A) in the long term.
                                       132

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2.5         Rail Systems
2.5.1       Introduction
            Rail systems are used for a variety of applications, including long distance
freight and passenger trains, commuter trains and rapid transit trains.  These applications
have required development of specialized vehicle systems which differ significantly in
their noise characteristics.  In discussing the problem of noise in rail systems,  it is con-
                                          1-3
venient to consider the two following groups:
            •   Railroads — including locomotive-propelled freight, long distance
                passenger and commuter trains, as well as high-speed intercity trains.
                This industry reported $12 billion in operating revenues in 1970, and
                employed 566 thousand trained personnel.   Railroad passenger traffic
                has steadily declined during  the past 20 years to  a figure of 283 million
                passengers carried 11  billion revenue passenger miles in  1970, approxi-
                mately one-third of those traveled in 1950.  However,  freight ton-
                mi ies have increased during this period from 590  billion  to 776 billion.
                Manufacturers of railroad equipment made $2 billion worth of shipments
                and employed 50 thousand people in 1970.
            •   Rail Rapid Transit Systems — including subway and elevated systems,
                surface stretching railways and trolley lines.  Intracity rail transit has
                declined since  1950 from 907 million to 480 million revenue passenger
                miles.  This segment of the rail industry reported $1.7 billion in
                operating revenue for 1970 and employed 138 thousand trained per-
                sonnel.  This system transported approximately 2.1 billion passengers
                in 1970.
The characteristics of rail systems  are summarized in Figure 2.5-1.
                                        133

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                                         Rai I  Systems
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                          Figure 2.5-1.   Characteristics of Rail Systems
                                                134

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2.5.2       Source Noise Characteristics
Railroads
            Noise in railroad systems can be separated into the contributions of two
basic sources, the locomotives and the train vehicles which the locomotives haul.  '
            •   Locomotives— The total number of locomotives in service in the
                United States was slightly over 27 thousand at the beginning of 1971.
                Of these, 99 percent were diesel-electric locomotives, and the
                majority of the remainder were electric. Approximately one-half of
                the locomotives are used for main line haulage and are generally
                powered by engines of 1800 horsepower and greater.   Lower powered
                locomotives are used for short-haul trains and as switchers in the
                railroad yards.
                The major source of noise in this group is the  diesel-electric loco-
                motive.  Typical noise levels under various load conditions and speeds
                are shown in Figure 2.5-2.  The propulsion system includes a diesel
                engine, usually 8- to 16-cylinder, that drives an electrical generator.
                This generator in turn provides power to traction motors on each axle
                of the locomotive.  The diesel engine is water-cooled and thus requires
                a radiator and associated cooling fans, situated in the roof of;the loco-
                motive.  Dynamic braking is used to slow the locomotive and train at
                higher speeds, and is accomplished by disconnecting the traction  motors
                from the main generator, using them as generators.  The high electrical
                currents that result are passed through heavy duty resistors which are
                cooled with the use of separate fans in the roof of the locomotive.
                The sources of noise in a moving diesel-electric locomotive are,  in
                approximate order of contribution to the overall noise level:
                -  diesel exhaust muffler
                -  diesel engine and surrounding casing, including the air intake  and
                   turbocharger (if any)
                -  cooling fans
                                       135

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          Figure 2.5-2. Wayside Noise Levels and Spectra of Railroad Equipment


                                           136

-------
-  wheel/rail interaction


-  electrical generator


An additional source of noise is the siren or horn, which produces noise


levels 10 to 20 dB greater than that 'from the other sources.  This is not


a source that is operated continuously, however (30 times per hour on  a


typical run), and is a necessary operational safety feature causing it to


be excluded from the above list.


The electric locomotive draws electrical power from a catenary. This


electrical power is converted for application to the traction motors by


means of transformer rectifiers and smoothing reactors.  The braking is


similar to that described for the diesel-electric locomotive, with the


exception that blowers are used in place of fans.  The major noise


sources from the electric locomotive are as follows:
                  ;                      I
-  cooling blowers


-  wheel/rail interaction


-  electric traction motors


The electric locomotive produces most noise when braking from high


speeds, the increase in noise over that of normal  operation being due to


the operation of the  dynamic brake resistor cooling blowers.   Braking


from high speeds is normally an operation that is  confined to rural


areas, so the noise impact  is not severe.  If this operation is ignored,


the electric locomotive is considerably quieter than its diesel-electric


counterpart, as shown in Figure 2.5-2.


Train Vehicles— The other main noise source associated with railroad


trains is that of the vehicles being hauled.  Typical wayside noise
                                             t

levels for freight and passenger cars are shown in Figure 2.5-2.  Freight


and passenger cars have no propulsion system of their own, so that the


exterior noise produced is due mainly to the interaction between the


wheels and the rails. The  magnitude of the noise depends heavily on
                         137

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the condition of the wheels and track, whether or not the track is
welded,  and on the type of vehicle suspension.  Modern passenger
vehicles with auxiliary hydraulic suspension systems in addition to the
normal springs can be 5 to 10 dB quieter than the older type with
springs alone.  However, most  freight cars have the simple spring
suspension.  Additional noise can be  produced by empty boxcars with
loose chains and vibrating sections.
The noise inside passenger vehicles is also partly due to the wheel/rail
interaction.  Typical interior noise levels are shown in  Figure 2.5-3.
This noise is produced in two ways.  First, there is broadband noise due
to the inherent roughness both in the  wheels and the rails. At high
speeds, variations on the order of a few thousandths of an inch are suf-
ficient to-produce high noise levels.  Secondly, there is the impact of
the wheels as they pass over the rail joints, producing the familiar
"clickety-clack."  There are two paths by which this track noise
reaches the passenger.  First, there is the direct mechanical  path from
the wheels through the suspension and hence to the car body. The
resulting vibration of the body radiates sound to the interior of the car.
Secondly, there is the airborne path from the track through the car
body and windows.  This  latter path becomes more important when the
train is passing through cuttings and tunnels. The introduction of the
welded track eliminates impact noise, leaving the broadband track
noise.  At present, only about 10 percent of the nation's railroad tracks
are of the welded type,  but the amount of welded track is being
increased at the rate of 3000 miles per year as the older sectional type
requires replacement.  In addition to the  track noise, interior passenger
car noise is created by the air conditioning system.  This is the typical
broadband."rushing" noise emanating from the exit and  return grilles,
usually in the roof of the car.
                        138

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               Figure 2.5-3.  Train Vehicle Interior Noise Levels and Spectra

                                          139

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                 In suburban areas, manyiof the commuter trains consist of multiple-' -
                 unit electric car systems in which the motors on all cars in the train
                 may be operated from the lead car.  Many of these systems consist of
                 modern, high-speed equipment in which noise level criteria  were con-
                 sidered during the design and construction.  If the wheels and track are
                 in good condition, the interior noise levels of these vehicles is often
                 dependent on the air conditioning system.  Figure 2.5-3 shows the con-
             1    tribution of track and air conditioning noise to the total noise level of •
                 a modern high-speed suburban rail car.
            i     One other major source of noise  from railroad operations is produced
                 in retarder yards where freight trains are assembled.  The individual
                 freight cars are allowed to  roll along the selected track and are braked
                 automatically or manually before they strike the remainder of the train.
                 The braking mechanism consists of a steel rail that is pressed against
                 the wheel  flange, producing a high-pitched sound at a level that can
                 exceed 120 dB(A) at  50 feet.
Rapid Transit Systems
            At rhe beginning of 197], there were 15 rail rapid transit systems in the
United States.  Of these, 7 were subway and elevated, 4 were solely surface and 4
provided inter-urban surface transportation.  All of these rapid transit systems use
electric multiple-unit rail cars,  designed for fast  loading and unloading of passengers.
A minimum amount of seating is provided since the average trip length is between 3 and
5 miles.  Consequently, in  rush hours  the number  of passengers standing can easily
exceed those seated by a factor of three or greater.  Ease of entrance and exit requires
many doors which are wide  enough for these operations to be conducted simultaneously.
In addition, to obtain good general visibility, large-sized windows are utilized.
Efficient operation of a transit train also requires  that the cars be lightweight so as to
reduce the overall load to be hauled,  the time required for acceleration, and the
motor size and power.  All  these factors result in  vehicles that are inferior to railroad
                                        140

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passenger cars as far as acoustic insulation is concerned. Suspension systems universally
contain steel springs, additional cushioning being provided by either rubber pads or air
cushioning systems.
            There presently exists a wide mix of vehicles in operation in terms of age
and condition.  The older type of vehicles that still operate on all existing systems in
general,have a poorer suspension system than those more recently introduced.  There is
also a definite requirement to use air-conditioned vehicles  that allow all windows to be
permanently sealed;  These improvements have enabled the modern vehicle to be a
significant improvement over the older type as far as noise and comfort are concerned.
            The electrical power for rapid transit trains is collected by means of a shoe
from a third rail and is applied to traction motors, one for each axle of the vehicle.
The motors drive the axles through a gearing system.  Most  systems use compressed air
braking systems, the exception being the  Chicago Transit Authority which uses all
electric braking.
            In addition to the electrical power required for propulsion,  power is also
required for door operation, lights, fans,  heaters and a host of other utilities.   Since
the power required for those utilities  differs from the type picked up externally,
it is usual to include  batteries together with a motor alternator to provide ac  power
and a motor generator set to charge the batteries.  The motor alternator,is used con-
tinuously, whereas the motor generator and air compressor work only when required.
Air conditioning is provided by means of fans and cooling systems. The  lack of space
under the vehicle dictates that this system be small.  This means a high pressure system
is required to obtain the necessary air flow, which in turn results in high interior noise
levels as the air passes through the vents.  All  the electrical motor systems are situated
underneath the vehicle and require a passage of forced air over them both for cooling
and dirt removal.  Air fans or blowers are therefore required to provide the necessary
air flow, and these are often operated continuously.
            The major noise sources associated with rapid transit systems are, in order
of their contribution to the overall level, as follows:
                                       141

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            •   wheel/rail interaction
            •   propulsion system
            •   auxiliary equipment
Typical ranges of wayside noise levels from rapid transit vehicles, together with the
contribution from the various individual noise sources, are shown in Figure 2.5-4. '
            The main source of noise is the interaction between the wheels and rails.
This source  is  more serious in rapid transit systems than in rail systems because the tracks
are subject  to a much higher amount of wear.  Unevenness in the track is produced by flat
spots in the vehicle wheels and by  heavy braking as the train enters the station.  Once this
unevenness  is  initiated, the track continues to deteriorate with further passage of trains.
                                                      ;
            Another wheel/rail interaction occurs at small radius curves in the track,
where the difference in speeds between wheels on the same axle and the rubbing  action
of the wheel flange on the rail can produce a severe squeal.  This source may increase
the normal track noise level by 10  dB or greater, the increase occurring  mainly at dis-
   * r        -   15~]7
crete frequencies.
            The noise from a rapid transit system is complicated, however, because  of
the effect of elements not totally connected with the vehicles.  First, there is the pro-
nounced effect of tunnels in subway systems.  The surfaces of tunnels are hard and
acoustically very reflective.  Hence,  the noise from the sources outlined above is now
effectively  being radiated into a reverberant enclosure.  It is thus possible to obtain
much higher noise levels  (as much as 10 dB greater)  than those out of tunnels.  This
effect is also found in below-ground subway stations which tend to be fairly reverberant.
Noise levels inside rapid transit  rail vehicles above and below ground are shown  in
_.     0 _  -  18-23
Figure 2.5-5.
            Secondly, there is the effect of aerial structures where the track  is supported
by concrete and/or steel  frameworks above the surrounding city. The track on these
structures is less rigid than it would be at grade level on a solid foundation.   Therefore,
noise levels 2 to 5 dB higher can be expected due to increased vibration not only of
the track but sometimes of the structure itself.  In some  aerial structures, there is a
                                        142

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                     Figure 2.5-5.  Subway Noise Levels and Spectra

                                          144

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direct airborne path from the underside of the train to the ground below.  In these cases,
extremely high noise levels can be experienced.
            Finally, there is the effect of different types of track systems. Although
reports vary on this subject, it appears that both the type of rail fastener used and the
type of  trackbed are significant as far as wayside and interior noise are concerned.
For example, the highly reflective concrete trackbed produces higher exterior and
interior vehicle noise levels than does the tie and ballast which  is  less reflective.
Similarly, variations of up to  5 dB can be obtained by the use of different rail
         12 24
fasteners.  '
            Street and trolley cars still operate in Boston, San Francisco and
Philadelphia and other cities, in some cases in a dual operation  with subway systems.
External noise levels vary in the case of streetcars between the  old and the new type
                                                         25
of PCC  cars, the range  being  approximately 68 to 80 dB(A)   at 50 feet under varying
operating conditions, as shown in  Figure 2.5-4. Trolley cars are significantly quieter
in the absence of the wheel/rail noise, producing external  levels in the order of
68 dB(A).  Internal noise levels are similar in trolley cars and in the newer PCC type
of street cars, 77 to 80  dB(A), whereas in the few remaining old street cars the levels
are approximately 5 dB  greater.
2.5.3       Environmental Noise Characteristics
            The noise levels experienced by people who live in  communities adjacent
to these systems depend upon the distance from the tracks as depicted  in Figure 2.5-6
for various types of trains. In this figure,  the  majority of train types  are included in a
single band of estimated noise levels varying with distance  from  the train.  Rapid transit
trains tend to be in the  lower  half of this band, whereas locomotive-hauled trains
(diesel-electric) are in  the upper half.  The length of trains varies from as little as
150 feet in transit systems to over  3000 feet for freight trains.  Consequently, the
duration of the noise for a single passby varies considerably from a few seconds up to
one minute and perhaps longer.
                                       145

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               Figure 2.5-6.  Noise Level as a Function of Distance

                     from Train for Railroad and Rapid Transit
                                    146

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            The noise levels experienced by people on-board the train or by persons
waiting at the station for the train to arrive are in the range 60 to 75 dB(A) on long
distance and intercity passenger trains,  and 72 to 93 dB(A) on rapid transit systems.
Noise levels in subway stations are higher on some systems, lying within the range 76
to 96 dB(A). The range of levels in transit systems encompasses trains both above  and
below ground under many varied conditions  of operation.
            Over 80 percent of the passengers using rail transit systems are carried on
the subway and elevated lines.  The number of passengers in 1970 averaged 4.3 million
per day, the average trip length being 3 to  4 miles and the trip duration 0.2 hours.
On railroad systems — including commuters — 780 thousand  passengers were carried per
day over an average trip length of 38 miles. The trip duration varies widely from
0.5 hours for commuter trains to several hours for intercity trains.
2.5.4       Industry Efforts in Noise Reduction
Rai I roads
            The incorporation of noise-limiting  requirements in the specifications for
new rail vehicles has only recently caused industry to initiate noise abatement programs.
Therefore,  the majority of vehicles in operation today are  not affected by these
programs.  The only requirements that manufacturers must meet in  the specifications
for locomotives concern the noise levels existing in the driver's cab.  As far as wayside
noise from railroad equipment is concerned, a small number of programs  have been
started and are at present in progress.  These mainly concern the noise from diesel-
electric locomotives, but detailed information as to the possible outcome of the pro-
gram is  not available at this time.
            Diesel-electric locomotives have had little noise control applications other
than to  the interior of the cab.  The exhaust system has no muffler, and  the spark
arrestor provides little attenuation.  Since the exhaust is probably the major source of
noise,  it is possible that mufflers could  be designed that would reduce the overall
sound level. In addition,  more substantial or modified casing around the diesel engine,
                                       147

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together with acoustical absorbent material, may well be effective in reducing the
noise from this source.
            More attention has been paid to the noise produced by the passenger
vehicles, both exterior and interior.  The luxury-type railroad cars as well as the
more modern commuter cars hauled by locomotives are equipped with rubber isolation
pads and shock absorbers, in addition to the spring suspension systems common in the
older stock.  The  reduction in wayside noise level  is on the order of  10 dB or greater.
As far as freight cars are concerned, improvements in functional  performance over the
years has had the  effect of reducing the noise level as a by-produ'ct.  There are, how-
ever, no programs in existence for the control of noise  from freight cars.
            The modern high-speed, intercity trains such as the Metroliner and the
TurboTrain that travel at speeds around 100 mph  have been designed to achieve interior
levels in the region of 70 to 74 dB(A)  with air-conditioning equipment running.  These
trains have extensive carpeting, improved door seals, smaller windows (Metroliner)  and
acoustic insulation in th'e ceiling and wall structures.  Wayside noise from the Turbo-
Train propulsion unit at operational power with the train stationary is 82 dB(A) at
        26
50 feet.    In addition, the modern suspension system incorporated in the TurboTrain
should result in lower interior noise levels'than in  the conventional passenger train.
Rapid Transit
            The development of specifications for  rapid transit vehicles is complicated
by the division of responsibilities between the cognizant transit authority and the
manufacturer.  For example,  a typical present-day specification concerns noise levels
produced by propulsion units and auxiliary equipment with the vehicle stationary.  It
does not include the noise produced by the wheel/rail interaction which in most cases
is the major contribution to the overall noise level.  Nor does it take into account the
effect of tunnels upon the interior noise levels in the vehicles.  These factors are the
responsibility of the Rapid Transit Authorities.  Consequently, vehicles built to the
specifications but operated on tracks that are not maintained in a good condition may
therefore generate interior and exterior noise levels well in excess of those stated in
                                         148

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the specifications.  As a result,  both the manufacturer and the customer (in this case
the Rapid Transit Authority)  are required to pursue-separate programs to reduce  the noise
levels.
            Much of the work that has been conducted by transit authorities has been
on systems outside the United States.  The result is that the transit systems in this
country tend to be amongst the noisiest in the world, as shown in Figure 2.5-7.
            The quietest systems in the world are in Berlin, Hamburg and Toronto.  It
is true, of course,  that European countries in particular have placed and still do place
more reliance on rail transportation.  It is therefore natural that research and develop-
ment would  be of greater importance in these countries than in the United States,
where rail passenger travel is on the decline.
            However, investigations have not been neglected in this country.  The
Chicago Transit  Authority (CTA) has conducted many experiments in an attempt to
achieve some reduction in noise levels.  More recently,  New York, San Francisco
and Washington, D.C. also have been particularly concerned with this problem,  and
do plan improved systems for the future.
            A number of noise abatement programs have been conducted in the past,
both by the  equipment manufacturers and by the transit authorities. It was shown in
Section 2.5.2 that there is a wide range of noise levels associated with transit  systems,
and that this exists because of the equipment used, the type of surroundings, and the
degree of track and vehicle maintenance.  The programs conducted by the transit
authorities have been directed naturally enough toward the noise sources most important
for their individual  systems.  The conclusions that will be drawn will therefore  reflect
what could be done now, using current technology, to reduce noise levels in rapid
transit systems.  It is difficult, however, to state overall quantitative conclusions as
to the results of  these programs because of the differences existing between systems.
The following review of noise abatement programs will treat each major source  of
            . ,      t     ....      .,,  8,  12-16, 20,27-29
noise separately, as tar as this is possible.
                                       149

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                                            I  I Foreign Subways
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                          Transit Vehicle Speed — mph
                   Figure 2.5-7. Comparison of Interior Noise

                       Levels in Subway Transit Vehicles
                                    150

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Wheel/Rail Interaction — The noise produced by the impact of the
wheels on the joints of sectional rail is the dominant noise problem
for almost all rail systems.  The most successful approach to  reducing
this noise has been  the use  of continuous welded rail.  Reductions
on the order of 5 dB or greater can be obtained by this method.  More
systems are now incorporating this type of rail during rail  replacement.
The unevenness in the track in the form of corrugations that  are the
major source  of noise in rapid transit systems can be removed by
grinding. However, the track of some systems appears to  be more
susceptible to corrugations  than others due to the differences in rail
used and the  variability in  vehicle wheels and suspension.
In order to reduce the vibration of the wheels and car body when the
vehicle is operating on rough track, the possibility of resilient wheels
has been studied.  The results have not been conclusive due partly to
the varying condition of the track in the different systems on which
resilient wheels have been  tried.  Of the three systems in the world —
Berlin, Hamburg and Toronto — that are considered to be the quietest,
one (Hamburg)  incorporates resilient wheels, the others use the con-
ventional solid wheels.  It  has been confirmed,  however, that the use
of resilient wheels does result in a  reduction of low frequency ground
vibration.  Other wheel treatments include the use of vibration damping
material, sometimes constrained, applied to the truck wheels.  Measure-
ments of track noise from vehicles negotiating curves of various radii
have shown noise level reductions of the wheel squeal  ranging from 5
to greater than 15 dB.  The higher  values of noise reduction are
usually determined  by the noise  levels in a narrow frequency band
covering the  main frequency of squeal.  On a straight track, the
reduction in wayside levels gt 50 feet are on the order of 2 dB.  In
this case, wheel squeal  is not evident and the small reduction in  noise
                        151

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levels is obtained over a wide frequency range.  At curves'of small
radius,  attempts have been made to reduce the severe wheel squeal
by lubricating the track with water,  oil or graphite.  Such systems
have been fairly  successful and have been installed at New York,
Cleveland,  Chicago and elsewhere.
An interesting program conducted by the Chicago Transit Authority
involved the use  of an experimental rubber rail head. This was quite
a successful program in reducing  track noise, but was accompanied by
many practical complications and so was abandoned.
One method of reducing track noise that has been tried in a few cities
(Paris, Montreal  and Mexico City) is to use rubber tired vehicles on a
concrete road bed.  Reports on the effectiveness of these systems vary,
but the general opinion is that the reduction in noise  levels is not
significant when  compared with the noise of the more common steel
wheels on steel rails if these are  in good condition.  It may be con-
cluded, therefore,  that in  the absence of regular maintenance, rubber
tires may result in lower noise levels, although it is reported that they
require a great deal of maintenance effort.  With welded track and
regular maintenance, there is little evidence to indicate the advantage
of rubber tires.   Economically, rubber tire systems tend to be expensive,
since a separate guidance system is required as well as a  backup system
of conventional steel wheels and track which is reverted  to in the event
of a tire failure.  There is, however, one exception to the above
generalization.   The recently opened system in Mexico City is reported
to be one of the quietest in the world, and is considered  to be better
than that of the other two rubber tire systems. One reason put forward
for the  lower noise levels is the use of a ballasted track bed as opposed
to the concrete used in Paris and Montreal, but a final opinion will  have
to wait until a noise measurement program has been conducted.
                        152

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There appears to be substantive noise data to support the use of
ballast between the rails.  The alternative that is often employed is
a concrete slab which forms a good reflector of sound emanating from
the underfloor equipment of the vehicle and the wheel/rail inter-
action.  Ballast provides more absorption and has been shown to
reduce interior noise levels by 3 to 4 dB,  if structure-borne noise is
adequately controlled.  A  similar reduction in exterior noise  level
may be expected if it is dominated  by noise from the propulsion system
or auxiliaries.
Tunnels — The high reflectivity of tunnel surfaces coupled with the
enclosed space results in higher noise levels for  a given source sound
power than it does in open  space.   The sound energy is confined to a
small volume instead of being able  to propagate away  in all directions.
A method of reducing the noise levels in tunnels is to apply acoustical
material  on the surfaces of the tunnel so as to reduce the reflectivity.
This has been tried in Toronto with  the result that the interior vehicle
noise levels were reduced by approximately 10 dB.  Although  this is
a solution for reducing noise, it is not necessarily feasible from an
economic point of view. For example,  there are over 100 million
square feet of tunnel surface area in the New York  subway system
which is  estimated would cost over  $150 million to coat with  an
acpustic  absorbent material.  However, the cost is much less  for under-
ground subway stations, which are extremely reverberant, and the use
of absorbent material can result in noise level reductions in the order
of 10 dB  or more.
Vehicle Body — Noise reaches the vehicle interior by the transmission
of external airborne noise through the body work and by the trans-
mission of structure-borne vibration to the body work and its subsequent
radiation.  An integrated approach is thus required  if interior noise
                        153

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levels are to be reduced.  Above ground, with no nearby reflecting
objects,  most of the interior noise is radiated from the floor structure,
which provides a noise reduction in the range 20 to 30 dB in existing
vehicles.  Eliminating and sealing holes and cracks in the floor and
installing a layer of damping material  has been shown on New York
transit cars to reduce the interior levels  in prototype  cars by approxi-
mately 10 dB.  The amount of reduction  obviously is dependent on the
original  condition of the floor.
A recent trend that substantially reduces interior noise levels is the
introduction  of air conditioning systems in modern transit vehicles.
The older systems in general rely on open windows for ventilation,
resulting in interior  noise levels as high  as 95 dB(A) in some subway
trains.  Closing the  windows can result in a reduction of 10 to 15 dB
in interior noise levels, depending upon the  situation.
Propulsion and Auxiliary Systems — The propulsion system in a rapid
transit car ranks second in the list of sources contributing to the over-
all noise level. This ranking, however, assumes that the wheels and
track are in fair to rough condition.  If ground-welded track and
wheels are used, it is possible for the propulsion  system noise to be of
greatest  significance. Under these conditions, it is possible to achieve
lower wayside noise levels by using an acoustically treated electric
propulsion system with skewed armature slots and a force ventilated
cooling system. The reduction in noise level compared to existing
propulsion units having little noise control treatment  is shown in
             13
Figure 2.5-8.     This figure applies to vehicles  traveling close to
their maximum design speed.  At lower speeds, the noise levels may
be lower than those  indicated.  Again, it must be emphasized that
the track should be welded and  maintained in good condition for these
noise reductions to apply.
                       154

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                                                     100
                Figure 2.5-8.  Noise Levels at 50 Feet from
                 Steel Wheel Transit Vehicles on Tie and
                     Ballast Trackbed for Maximum
                            Vehicle Speed
                                  155

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Electric propulsion units drive the wheels through gears, the gear
ratio varying from system to system,  depending upon the power require-
ment.  For a given vehicle speed, the resulting variation  in motor rpm
among the various systems gives rise to wayside levels that vary as
much  as 10 dB.  High gear ratios are thus important as far as noise
from the propulsion system is concerned.  The application of improved
or additional motor covers plus sound absorbing material,  together
with acoustic treatment of the motor cooling fan ducts, can result in
a 6 dB reduction  in noise level from motor units.  The noise from the
cooling fans  contains pure tones associated with the blade passage
frequency.  Variable spacing of the fan blades makes these pure tones
less distinct and produces a subjectively less annoying sound,  even
though the reduction in noise level is only 1 dB or so.
There are two main types of motor cooling systems — one that sucks air
(self-ventilating), and one that blows air through the motor.   The latter
is preferable from a noise point of view, since noise control techniques
can be applied in the blower ducts.  It does have the disadvantage,
however,  that it  remains in continual operation,, whereas the  self-
ventilating type runs off the motor and hence is not operative in
stations.  Because of the lack of space under the vehicles, it  is not
usually possible to increase the size of the fans and have  a lower flow.,
velocity with an  accompanying reduction in noise level.  The s.ame
comments apply to the cooling systems for the auxiliary equipment on
the vehicle.
Barriers — Since the major noise sources in a rapid transit  vehicle are
situated underneath the  vehicle body, one method of reducing the
wayside noise level that has been tried has  been the installation of a
side barrier. The requirement  for the design of the barrier is that  it
should prevent a line-of-sight  to the underside of the vehicle from
                        156

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                locations where the noise reduction is required. A simple barrier of
                thjs type, placed alongside the track and overlapping the vehicle
                floor by about 6 inches,  can provide a 10 to  12 dB  reduction in noise
                level at 50 feet.
                An alternative  to the installation of a barrier alongside the track,
                which could be extremely expensive,  is to place skirts on the sides of
                the vehicles.  However,  there must be a clearance of a few inches at
                the bottom so as to clear the track; so the noise reduction is only about
                6 dB in this case.  A combination of both types of barrier could result
                in noise reductions in excess of the 10 to 12 dB for  the wayside barrier
                alone.
                Even greater noise reductions (in the order of 15 dB at  ground level)
                can be obtained by placing the track in a cutting.  The amount of the
                reduction depends upon the depth of the cutting and the angle of
                elevation of the sides.
2.5.5       Noise Reduction Potential
            A summary of the effect that the application of current technology could
have on the noise levels produced by the various  sources is given in  Table 2.5-1.  The
railroad and rapid transit authorities,  together with the manufacturers of rail  equipment,
are becoming increasingly aware of the noise problems  associated with rail systems and
are planning a number of future  programs for noise reduction.  In most cases,  however,
the programs are not defined in terms of final goals,  but more  to determine what
reductions can be achieved using current technology.  The following programs are
among  those that are planned:
Railroads
            •    A study of the noise characteristics of diesel-electric locomotives
                with a view toward eventual noise reduction.
            •    The development of a new type of auxiliary generator of electrical
                power or suburban, locomotive-propelled,  commuter trains.
                                       157

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                               Table 2.5-1

        SUMMARY OF THE NOISE REDUCTION POTENTIAL BY APPLYING
           CURRENT TECHNOLOGY TO EXISTING TRANSIT VEHICLES
Existing Condition
Standard track, not
regularly maintained
Concrete trackbed
Bare concrete tunnel
surfaces
Bare concrete station
surfaces
Old type vehicles
using open windows
or vents for
ventilation
Standard doors and
body
Standard steel
wheels
Standard type
vehicles

Standard, noisy pro-
pulsion unit
Modified Condition
Welded track, ground
Ballast trackbed
Strips of absorbent
material at wheel height
Limited absorbent
material on wall sur-
faces and under plat-
form overhang
New type cars with air-
conditioning
Improved door seals,
body gasket holes
plugged, et cetera
Steel wheels with con-
strained damping layer
Installation of a 4 ft.
barrier alongside track
Installation of a skirt on
side of vehicles
Modified unit with
skewed armature slots,
random blower fan
blade spacing, acousti-
cally treated fan ducts
Estimated Noise
Reduction dB
Car
Interior
5-15
0-5
5-10
-
10-15
0-5
5-15
: - ' •••
-
0-5
Car
Exterior
5-15
0
-
5-10
-
-
5-15
10-15
6
5
Note:  The values of noise reduction are estimated for the particular source alone,
       assuming no contributions from other sources. The values therefore cannot
       be added to obtain an overall noise reduction.
                                    158

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           •    Improved suspension system for the TurboTrain which, it is estimated,
                                                                             30
                may reduce interior noise levels from 74 dB(A) to 60 to 65 dB(A).
                Due to the noise from the air-conditioning system, the  noise reduction
                obtained may be less than  this.  The final levels may be in the range
                of 65 to 70 dB(A), depending on the position in the car, unless the
                air-conditioning equipment noise  is reduced.
           •    The replacement of old track by welded track.  About 3 thousand
                miles of track per year are  renewed in this  manner.
Transit Systems
           •    The application of spray-on acoustic absorbent material on the
                ceilings and under the platform  edges, together with noise barriers
                between tracks at a New York subway station.  This is  intended  as a
                demonstration program that is estimated to provide 6 to 7 dB noise
                reduction. The total  cost of this experiment will be about $75 thousand.
           •    The replacement of old transit cars with more modern types incor-
                porating air-conditioning,  door and window seals, rubber suspension
                mounts and vibration damping materials on the body.  It is estimated
                that a 10 dB reduction in interior  noise levels will  result.  This is a
                definite program in New York,  Chicago and San Francisco, and  is a
                trend that is being followed by  most transit  authorities.
           •    The replacement of old track with welded track in many transit
                systems.
           •    The New York City Transit Authority is replacing old track with  a new
                type incorporating a  rubber rail pad.  Previous tests have shown  that
                this provides a more comfortable ride and reduces interior noise levels.
           •    A study to determine whether improved sound insulation of transit
                cars can be achieved without increasing the mass of the car body.
                Along with this is a study to improve door seals.
                                        159

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Design of an integrated heat transfer system for air-conditioning
equipment that uses cooling coils or fans that are operated while
the train is out of the station area.
                        160

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2.6         Ships
2.6.1       Introduction
            The United States merchant fleet consists of approximately 2000 active
vessels of 1000 gross tons or greater.   Of these vessels, about 180 are combination
passenger/cargo type, their average age being over 20 years.  The number of ships
capable of transporting passengers has been  decreasing since 1950, and in this time
only about seven new passenger/cargo ships have been completed by American ship-
yards.  In 1971 the total number of passengers transported by sea from  the United
States to foreign countries was  1 .7 million.   Not all these people, however,  traveled
on U.S. ships.
            In recent years,  the trend toward larger merchant ships constructed of
lighter materials has resulted in an increasing number of excessive shipboard noise
and vibration  problems.  Specifications for the construction of ships tend to be rather
loosely written,  without specific performance requirements for the levels of noise
and vibration. This practice allows the delivery of ships without adequate noise
control, and often makes it difficult to determine the responsibility for any  such
problems that  arise.
2.6.2       Source Noise Characteristics
            Of all the sources of noise in transportation systems, ships are probably
the least important in terms of an environmental impact on the community in general,
although noise problems may  occur on board ship.  There are three principal reasons
why ship noise does not impact the community:
            •   The major sources of noise on a ship are the engine, gears, and
                propeller.  This equipment is all below the water level and/or  is
                enclosed by the structure of the ship,  and most of the sound energy
                generated is radiated into the water.
                                       161

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.••   As far as airborne noise radiation is concerned, the sources of noise
     are the vibrating structure of the ship, the ventilation blowers, and
     the engine exhaust  (funnel) where applicable.  However, the hull
     vibrations are primarily at very low frequencies, and the noise from
     air moving devices  is generally controlled sufficiently to make the
     noise levels on the  deck acceptable for speech communication.
 •   The only time that a ship produces an appreciable wayside noise
     level is when it is under full  power which occurs only when the
     vessel is out at sea.  In ports, ships rarely exceed 5  knots, so wayside
     noise is negligible except for horn blasts which are generally well
     received by people living in  port towns and cities.
                                           345
 The principal sources of shipboard noise are:  ' '
 •   Propulsion  System and Auxiliary Machinery — This includes gearboxes,
     turbogenerators, stabilizers,  etcetera.  The propulsion motors operate
     at a very low rotational  speed compared to that of other transportation
     systems and consequently, the noise produced by the majority of the
     equipment  is predominantly at the low frequencies.  Gearboxes and
     turbines produce noise at the higher frequencies due to gear-tooth
     impact, and are audible in many of the cabins, particularly  those
     located inboard in the vicinity of the engine rooms.
 •   Ventilation Systems— This equipment produces broadband noise
     typical of air conditioning and ventilating units, and is usually
     more obtrusive in tourist sections than  in first class.
 •   Movement  of People — This is mainly impact noise produced  by
     people's footsteps on  the deck above the observer.   It is possible
     for such impacts to  propagate considerable distances as structure-
     borne vibration.
                            162

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            •    Plumbing Noise — This is due to the passage of water through pipes
                and faucets.
            •   Bulkhead Noise — The creaking of bulkheads with the movement of
                the ship,  perhaps caused by wave impact.  The noise is due to  relative
                motion of the bulkhead panels and their supports.
            In addition to these sources of noise,  there are a number of sources  of
structural vibration that can be radiated as airborne  noise from walls and floors, '
including:
            •   Propeller — This is primarily a source of very low frequency vibration
                that can produce rattles  in loose objects in the aft  part of the ship.
            •   Propulsion System — As discussed above.
            •   Wave Impact —  This is more a random than periodic occurrence and
                can be transmitted throughout the ship's structure.
            The noise levels existing in a passenger  ship (20 thousand to 25 thousand
                                                            3  6
gross tonnage) at normal  cruise speed are given in Figure 2.6-1 . '    These vessels
are capable of carrying approximately 1000 passengers.  There is a fairly wide spread
of levels corresponding to first and tourist class accommodations in various areas of
the ship.  In general, the levels  are higher on the lower decks than on the upper decks.
            Little has been done toward changing the noise levels in cabins, except
for installing ventilation systems  which have high speed airflow.  There is, in fact,
a scarcity of data on the individual noise  sources and the levels that they produce
throughout a typical commercial  ship. Some of the problems,  such as impact, plumbing
and bulkhead noise, could be  reduced in magnitude  by using similar techniques  to
those used in buildings.  Although it  is possible to reduce the  noise  from air conditioning
systems using present technology, in many cases this steady state noise masks the inter-
mittent rattling and creaking of the structure which might be otherwise disturbing.  In
addition,  further reduction of  the noise level  might lead to a new  requirement for
better transmission loss between cabins to  recover adequate privacy.
                                      163

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                                          164

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2.6.3      Environmental Noise Characteristics
            As previously stated, the only environment which is significant in an
analysis of shipboard noise is the area within the ship itself. These levels, as shown
in Figure 2.6-1, are generally lower than 65 dB(A),  and appear to have found general
passenger acceptance over the years.
                                      165

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2.7         Recreation Vehicles
2.7.1       Introduction
            Recreation vehicles, as defined herein, include pleasure boats, snow-
mobiles, all-terrain vehicles and motorcycles.  There has been a remarkable growth
in the  number of these vehicles in.the last 20 years.  This growth is a reflection of
the greater amount of leisure time and availability of these vehicles at attractive
prices. Figure 2.7-1 summarizes the general characteristics of this category in terms
of growth patterns and typical  noise levels.  The following  paragraphs discuss pertinent
                                            1-4
aspects of the major vehicles in this category.
            •    Pleasure Boats —  The pleasure boating industry has enjoyed a
                 relatively steady increase in sales over the past 20 years,  from
                 2.8 million outboard motors in use in 1950, to around 7.2 million
                 in use in  1970. There are currently over 8.8 million recreational
                 boats in use in the United States.  Of this number, 627 thousand
                 are  inboard motorboats and 5.2 are outboard motorboats.  The
                 boating industry estimates that over 44 million persons  participated
                 in recreational boating in 1970, and that  $3.4 billion  were spent
                 on retail  sales and services.
            •    Motorcycles— Motorcycles have experienced a remarkable increase
                 in popularity over the last 10 years.  Over 90 percent  of the
                 2.6 million motorcycles in the United States today are used
                 primarily for pleasure and are operated  in many residential
                 and recreational areas.  The number in  use is expected to increase
                 to 9 million by 1985.  Estimates for retail  sales of new motorcycles
                 in 1970 reached  $440 million and used motorcycle sales reached
                 $142 million.  Parts and accessory sales amounted to $155 million
                 for an aggregate of $737 million in sales.   More than 8 thousand
                 people were employed  by motorcycle and  parts manufacturers in 1970.
                                        166

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Motorcycles


      •  Highway < 350 cc
      •  Highway > 350 cc
      •  Off Road
      •  Minicycles
           2,600,000
                                 Recreation Vehicles
                                    Snowmobiles
                       Stock
                       Modified
                                Numbers in Service
                        1,600,000
                                                Pleasure Boats
                                                     •  Outboard
                                                     •  Inboard
                                                          5,850,000
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                                       70
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              Figure  2.7-1.  Characteristics of Recreation Vehicles

                                        167

-------
            •   Snowmobiles — This is one of the faster growing industries in the
                leisure field. Over 600 thousand snowmobiles were sold in the
                1970-71  season in the United  States and Canada, as compared with
                fewer than 10 thousand  in the 1962-63 season.  There are currently
                about 1 .6 million snowmobiles in operation, the majority of which
                are recreation vehicles.  Persons who live on farms own 28.5 per-
                cent of the snowmobiles.  Many farmers and ranchers in the west
                and midwest rely on snowmobiles for feeding and rescuing storm- t
                stranded cattle.  In addition,  foresters and utility  servicemen  often
                use these vehicles to  make their rounds.  Almost 80 percent of (the
                people who own snowmobiles live in rural communities of 25 thousand
                population or less. The average enthusiastic snowmobile owner rides
                about 13 hours per week during the snow season.  Approximate dollar
                volume for the 1970-71 sales season has been estimated at $600 million.
2.7.2       Source Noise Characteristics
            The noise output" of leisure vehicles, although dependent upon speed,  is
primarily a function of the way they are  operated. Though many off-road motorcycles
and some snowmobiles are capable of speeds of 80 to 100 mph, they are most often
operated .in the lower gears at medium to high engine output.  Hence, except when
cruising at constant speeds or coasting downhill,  these vehicles are operated at high
throttle settings and near their maximum noise output.
            The major contributing source of noise from these vehicles is the exhaust.
A high percentage of these vehicles operate solely off-the-road and hence are not
licensed for highway use; therefore, many of the vehicles' exhaust systems are not
silenced.   As a result, these vehicles may create noise levels as high as 100 to
110 dB(A) at 50 feet. '   Pending state  legislation to regulate the noise produced
by off-road machines has  caused manufacturers to reduce the noise of vehicles in
current production to 92 dB(A) at 50 feet.   The noise radiated from intakes and engine
walls is also significant in these vehicles.  Intakes are not generally silenced, and
engines are either partially or totally unshielded.

                                        168

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            The following discussions relate to the various types of vehicles that have
been categorized as recreation vehicles.
Pleasure Boats
            In a recent survey, the maximum noise levels measured for a large number
                                                                       8
of inboard and outboard powered pleasure boats ranged from 65 to 95 dB(A).   The
lower limits of this'range are created by small outboard powered craft (usually 6 to
        ,-.     9   .
10 horsepower).   In a different series of tests, levels exceeding  110 dB(A) at 50 feet
were produced by inboard powered ski boats with unmuffled (dry stack) exhausts.  '
The typical  range for  noise levels produced by pleasure boats (by engine size and type)
is illustrated in Figure 2.7-2.
            Exhausts are generally the principal source of noise for pleasure boats.
On the  fdrger-engined ski boats,  whose design incorporates a completely exposed
engine, intake noise and engine mechanical noise also provide a significant contri-
bution.  As  engine size is reduced, noise  levels are typically lowered; however, in
most cases,  even though exhaust is exited under water,  it is still ;the major noise source.
In the medium and smaller outboard engine sizes, engine mechanical noise and intake
(though acoustically shielded),provide noise output almost equal to the exhaust.
Motorcycles
            The noise produced by motorcycles operating under cruise conditions is
highly dependent on speed.  ; Figure 2.7-3 depicts typical noise levels for various
operating modes. Figure 2.7-4 illustrates a typical range of octave band frequency
spectra  for motorcycles under a variety of operating conditions.  The relative  contri-
butions  of the various subsources'to the overall levels are also shown for  a typical
example.     The contribution of these subsources to the total noise levels are:
            •   Exhaust — The exhaust controls the noise levels of motorcycles.  In
                discussing exhaust system noise, a distinction  must be made between
                2-cycle (primarily imported) and 4-cycle machines. The noise
                spectra are of somewhat different character, with the 2-cycle
                                        169

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            Engine
             Noise
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Exhaust-
                                                        Hull
    120


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                                                           iS
               Outboards
  Inboard
  Ski Boats
                                                                 Other
                                                                Inboards
                                Type of Pleasure Craft
                Figure 2,7-2. Typical  Ranges of Noise Levels Produced by
                     Various Pleasure Boat Types (dB(A) at 50 Feet)
                                    170

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               Figure 2.7-3.   Motorcycle Noise Levels

                    for Various Operating Modes
                                  171

-------
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                                        172

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machines exhibiting more high frequency spectra energy content
and the 4-cycle machines more low frequency content.
A major consideration in engine performance for 4-cycle motorcycle
engines, over a specific rpm range, is exhaust pipe length.  These
machines must, by virtue of their design constraints, emphasize
lightweight,  compact construction.  These requirements are not
directly compatible with the basic principle of 4-cycle muffler
tuning which equates the degree of silencing to gross muffler volume.
i                 i
Performance and economy are directly affected by silencing,  as these
machines rely on low backpressure to achieve competitive horsepower/
weight ratios.
Two-stroke machines present less of an exhaust silencing problem.
They are designed to incorporate an expansion chamber system (which
                                            i
is considered mandatory for 2-cycle performance), in which much of
the acoustic energy is reflected back into the engine.  This principle
is used to advantage in  achieving a supercharging  effect on the com-
bustion mixture as well  as exhaust scavenging of the burned gases.
A well-designed 2-cycle exhaust muffler system will actually increase
power while at the same time reducing noise levels.   This effect
is found in the majority of 2-cycle engine applications with the
exception of maximum output racing models.
Intake — Noise radiated through the intake system is almost equal to
the noise radiated through the exhaust system.  Here again,  performance
and packaging considerations have minimized any  silencing efforts in
this area since both 2-cycle and 4-cycle designs rely on low intake
restriction to achieve their power output requirements.
                        173

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                Engine Mechanical  Noise — Engine mechanical  noise is the source
                of greatest concern  in future reduction of overall levels.  On current
                machines, engine noise is approximately the same order of magnitude
                as intake noise. The concept of acoustic engine enclosures and
                shielding has been considered almost totally impractical for light-
                weight air cooled motorcycles.
                Drive Chain and Tire Noise — Noise levels from these sources appear
                to be low enough to be considered of secondary importance.  However,
                refinements to drive chain design may be warranted when  contributions
                from other sources are reduced by at least  10 dB.
Snowmobiles
            The noise produced by snowmobiles is highly dependent upon theirage.
Current production models produce noise levels in the range of 77 to 86 dB(A) under
maximum noise conditions measured at 50 feet and  105 to 111  dB(A) at the operator
        916
position. '  i   The noise levels from poorly muffled machines  generally range from
90 to 95 dB(A) at 50 feet with racing machines causing levels as high as 105  to
110 dB(A). '    The operator, on a number of machines surveyed,  experienced levels
                                                                               t
in the range of 108 dB(A) under normal cruise conditions.  Figure 2.7-5 shows typical
octave band spectra for snowmobiles for a variety of operating modes,  and presents a
bar chart summary of those components which contribute to the overall noise  levels. '   '
The major contributors are:         i
            •   Exhaust — A dominant source of snowmobile noise is the engine
                exhaust. Design constraints which minimize space and emphasize
                lightweight construction, and customer demands for maximum power
                have restricted the usage of adequate silencing devices.
            •   Engine Mechanical Noise — Another major factor in overall noise
                output of snowmobiles is engine mechanical noise. The lightweight,
                2-cycle, high power design of the snowmobile power plants restricts
                                       174

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                   Engine
               Intake/ Track    NJogies
                                                Range of Spectra
                                                     Over
                                          Typical  Operating Conditions
                                                    at 50 ft
                                       1000

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                  Figure 2.7-5.  Snowmobile Noise

                              175

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                the application of quieting techniques to the internal engine structure,
                and cowling enclosures provide the only suitable and practical means
                for reducing engine noise.
            •   Intake — Most  current snowmobile manufacturers do not silence the
                engine intake.  Unfortunately, the intake is usually directed ahead
                of the operator and contributes significantly to his noise exposure.
                Some sacrifice in engine performance may be required to silence the
                intake system.  However, little work has been done in this area,
                although some  manufacturers are now producing accessory air-cleaner
                units  which aid in reducing  this problem.
Dune Buggies,  ATV's  (All Terrain Vehicles) and Other Off-Road Vehicles
            The principal noise output of the remainder of those vehicles considered
under the "recreation" classification is predominantly from the exhaust.  Because of
the unregulated nature of these  vehicles and their  use, the owners tend to attempt to
achieve maximum power output  through the use of  tuned and straight-through exhaust
(unmuffled) systems.   An example of typical spectra for a VW-powered dune buggy
                                                                  20
with a tuned "megaphone" exhaust system is presented in Figure 2.7-6.     Engine and
intake noise are also quite apparent in these vehicles,.but are on the order of 15 to
20 dB less significant than the exhaust.
2.7.3       Environmental Noise Characteristics
            Except when several recreational vehicles are operating semi-continuously
around motor recreation parks and high usage lakes, they provide only a minor contri-
bution to the steady-state residual noise levels in the areas in which they operate.
However, since the majority of  these vehicles are  operated in remote areas which have
low residual noise levels, they can be heard as intrusive noises at much greater  distances
                                       21
than would be expected in an urban area.
            Power boats are operated (by law) at least 100 feet from shore and usually
well away from other boats, hence minimizing the levels at the shore and local  communrty.
                                        176

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            Mini-bikes/ a particularly annoying noise source in residential communi-
ties, are normally produced with a muffler which reduces their noise levels at 50 feet
                           1 ^ 99
to the  75  to 80 dB(A) range.  '    The problems that arise from the usage of these
machines  (primarily by youngsters not old enough to obtain driver's licenses) stem
mainly from their operation in the proximity of residential dwellings.  The problem is
further aggravated when the stock muffler is removed and replaced by an "expansion
chamber" exhaust system which the owners feel contributes to the power.   The modi-
fied machines are then capable of levels of 85 to 90 dB(A) at 50 feet.2
            The operator of most types of recreation vehicles is usually exposed to
high noise levels for the duration of his ride. Typical levels for snowmobiles range to
as high as  115 dB(A) under full throttle acceleration.  Under cruise condition,  the
                                                       5918
operator's  noise level  is often in the vicinity of 108 dB(A).  '  '     It is  estimated that
the average enthusiastic snowmobile owner  uses his vehicle about 13 hours per week
                       3
during the snow season.  The average duration per ride will probably range from 3 to
4 hours.   It is assumed that this usage pattern is fairly typical for other types of recre-
ation vehicles, including watercraft and motorcycles (90  percent of which are estimated
to be pleasure vehicles).
            The noise levels in outboard motorboats are also generally high. Typical
levels  range from 84 dB(A) for 6 horsepower units to 98 to 105 dB(A) for  125 horsepower
                                                                9
units measured at the driver position under accelerating conditions.  At cruising speeds,
                                                                              23
operator levels on all boat types (inboard and outboard) range from 73 to 96 dB(A).
Operator  levels on  motorcycles also follow this trend of typically high levels with
                                                    13
115 dB(A)  occurring on some unmuffled off-road cycles.
            A factor which should be considered in discussing operator noise exposure
is the use of safety  helmets.  When properly fitted and used, they provide a significant
reduction in noise levels at the operator's ear, as well as providing accident protection.
There is no question that snowmobiles, many motorcycles, and some boats present a
risk of permanent hearing damage to both operator and any passenger. Ear protective
devices should be worn in these cases.
                                        178

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2.7.4       Noise Reduction r- industry Efforts and Potential
            Figure 2.7-7 illustrates the present ranges of noise levels for recreation
vehicles at both the  observer at 50 feet and the operator positions. Also summarized
in this figure are the near-term noise  reduction potentials deemed achievable with
current technology and the long-term noise reduction potentials which must result
from further research and development efforts.
            The recreation vehicle industries have incorporated some rather refined
concepts into their products to achieve current noise levels. The greatest noise reduc-
tion has been accomplished through exhaust system treatment.  Because nearly all
snowmobiles, outboard engines, and a good percentage of motorcycles are powered by
2-stroke engines, a good deal of development and research  has been done in quieting
the exhaust systems on these devices.   The expansion chamber exhaust system, which is
considered essential  for 2-stroke performance,  has been muffled to a high degree with
little loss of horsepower.   '     Engine shielding and isolation  have been developed  to
a great extent on outboard motors and this technology is gradually being applied to
snowmobiles.  Excluding motorcycles, the  industry as a whole has nearly reached the
stage where exhaust treatment has been fully exploited, leaving further reduc-
tion efforts to be aimed towards intake silencing and engine noise itself.  However,
the motorcycle has yet to overcome its design constraints in packaging exhaust systems
of sufficient size to provide greatly improved silencing; therefore, further research is
required to achieve adquate silencing without imposing severe weight and size restrictions.
            In the following paragraphs, current industry efforts in noise reduction and
noise reduction potential will be discussed separately for pleasure boats, motorcycles,
and snowmobiles.
Pleasure Boats
            The outboard motorboat has the longest history of any of the products in
the leisure vehicle field.   The annoyance caused by noise from outboard motors was
recognized by industry long before any legislative bodies began to act to control its
effect.  In the"late 1920's and early 1930's, manufacturers motivated by public pressure
                                       179

-------
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-------
began experimenting with underwater exhaust systems to reduce the noise output of
these devices.  Their success in the late 1940's was one of the factors which led to a
dramatic growth market for motorboats.  By the mid-1950's,  more sophisticated quieting
techniques were being  incorporated, such as extensive  vibration isolation within the
                                                    25 26
engine and acoustically treated cowling on the engine.  '     The outboard engine
has been continually refined up to its present state. The current outboard probably
represents the quietest  application of a 2-stroke engine for its power output on the
market today.
            The largest manufacturer of outboard  engines produces a top-of-the-line
125-horsepower engine that produces maximum noise levels at 50 feet of 81.5 dB(A).
The quietest model is rated at 6 horsepower and produces maximum noise levels of
                    9
64.5 dB(A) at 50 feet.    This same manufacturer feels that because of the company's
efforts in  producing quiet outboards, its percentage of the market has increased
                                                     27
substantially until  it is now the leader in outboard sales.    The major areas of
complaint concerning pleasure boat noise are created by the large inboard-drive ski
boats which incorporate dry stack exhausts (unmuffled and not exited under water).
In addition, many  inboard ski boats also incorporate the automobile "hot rod" tech-
niques in achieving maximum horsepower from their engines.  The engine is fully
exposed, and in addition to unsilenced exhausts,  usually has unsilenced carburetor
intake as well.  These  machines produce noise levels at 50 feet of up to 112 dB(A).
Noise output from  the same  configuration, with underwater exhausts, has been reduced
to around 97 dB(A).    Many states are now moving to prohibit operation of these dry
stack boats.
            More refined inboard designs incorporate a silenced intake system and an
acoustically treated full engine enclosure along with the underwater exhaust mentioned
above.  This type of ski boat will exhibit noise levels in the 85 to 90 dB(A) range at
50 feet.     Smaller engined inboard boats will fall in the 75 to 80 dB(A) noise level
         8,9
category.
                                      181

-------
            For pleasure boats, significant future noise reduction efforts should be
primarily aimed at further reducing operator noise exposure levels.  Crash helmets
are seldom used by participants,  except during race events, hence the noise levels
in these pleasure craft must receive more attention.
            Significant noise reduction can be accomplished in inboard designs due
to the rather advanced state of acoustic enclosure design  for items of this size.  It
is felt that for the majority  of inboard designs, a long-term goal of 76 to  82 dB(A)
is reasonable.  Outboard engines (whose reduction potential is indicated  in Figure 2.7-7
for models  over 25 horsepower) pose a more difficult problem due to their design con-
straints which emphasize high power-to-weight ratios.  It is expected that lower
operator levels for outboard powered craft will only come through further efforts in
intake silencing and either  through revised internal engine design or bulkier engine
enclosures. For outboard powered boats, an examination of current abatement tech-
nology indicates that operator noise levels in the range of 78 to 86 dB(A) constitute
a reasonable long-term potential.  Further, as a  result of efforts to reduce operator
noise exposure,  non-participant  levels at 50 feet should eventually be reduced  to the
range of 70 to 76 dB(A).
Motorcycles
            The motorcycle also has a long history in the leisure field.  Motorcycles,
due to their design constraints of lightweight construction and maximum power output
for a given displacement engine, have long been criticized for their excessive noise.
The average motorcycle rider tends to associate noise with power and performance,
and generally feels it fits the motorcycle "image".  The major manufacturers have
only recently taken steps to change these beliefs.  Now all current production motor-
cycles intended for highway use must comply with state noise legislation.  In addition,
most major manufacturers, under the guidance of the Motorcycle Industry Council,
have agreed to place mufflers on all their off-road motorcycles to limit their noise
output to 92 dB(A) at 50 feet.   The industry is currently in the process of trying to
convince the consumer that noise does not necessarily mean power.  It feels that
                                        182

-------
this is an essential step in preparing the consumer to accept the quieter, new generation
machines that will, necessarily, weigh somewhat more and deliver less horsepower per
cubic inch displacement.
            The noise levels of current production motorcycles cover a fairly wide
range among different manufacturers and among vehicles of varying engine displace-
     28 29
ment.  '     The majority of motorcycles are now meeting the 88 dB(A) maximum noise
specification of various states; however,  a number of the large displacement machines
                                                    29
are unable to meet this criteria in their present designs.    Although the technology
exists to produce quieter motorcycles, achieving further noise reductions will necessitate
some design compromises on a majority of the models.
            The exhaust system is the major  contributor to overall noise levels. Although
exhaust systems .can be designed to reduce this component's contribution to the 75 dB(A)
                                                                  14
range, significant packaging and weight limitations must be overcome.    Also, current
motorcycles do very little to silence their intake systems,  although almost all provide
air cleaner devices.  Silencing on the order of 10 dB is feasible  if moderate restriction
of intake air flow can be tolerated.
            The most critical area yet to be tackled in motorcycle silencing is the
engine and mechanical noise.   Acoustic enclosures have not been found to be practical
solutions on air-cooled engines. A number of attempts have been made at silencing
individual engine noise sources, such as adding damping compound to timing gears,
stiffening primary chain covers, positive oil feed lubrication of cam shaft bearings,
and adding cross ties to the engine cooling fins.  This attempt by one  manufacturer
                                           12
yielded only an average reduction of  1.2 dB.
            Achieving the more restrictive noise level requirements for motorcycles
that are forecast for the next 5  years will require major redesign of numerous compo-
nents.  Specific examples of solutions that may yield beneficial  results include
incorporation of journal rather than roller or ball bearings, timing chains rather
than gears,  more lubrication, stiffer structures and nonresonating materials for non-
functional components.  With these changes will undoubtedly come an unwelcome
                                       183

-------
power loss.  For example/  one manufacturer reduced engine noise levels in laboratory
                                                       12
experiments to 75 dB(A)/ but with a 15 percent power loss.    Cost and weight penalty
figures are not available for this example.
            Figure 2.7-8 gives the spectra of two 750  cc 4-cycle motorcycles of
different manufacture, but tested under identical conditions.  The difference in the
                                               29 30
noise levels produced by the two vehicles is 11  dB.   '     The price of the quiet motor-
cycle  is $1848 as compared to  $1595 for the noisy machine. The quiet vehicle weighs
                                                                            i
440 pounds versus 480 pounds for the noisy model. The relative horsepower ratings are
57 horsepower at 6400 rpm for the quiet machine as compared to 67 horsepower at
8000 rpm for the noisier vehicle.  This example illustrates the  compromises with which
the industry and the consumer are faced in  achieving reduced noise levels with current
technology.
            Motorcycles potentially face severe design modifications if their intruding
effect  upon the ambient noise environment  is to be significantly reduced.  Redesign of
internal engine structure to provide the noise reduction achieved in  laboratory experi-
ments may  be required to achieve a long-term potential of 75 to 80 dB(A) at 50 feet
under maximum noise conditions.  Additional attention must be given the engine intake
system to reach these levels.  It is assumed that technology will advance sufficiently
to provide  quieter intake and exhaust systems with minimized power  loss and reduced
package space requirements.
            Operator levels should be reduced to the 85 to 90 dB(A) range as a result
of the  modifications listed above.   Here again,  the use of protective crash helmets
would  serve to greatly reduce the risk of high operator  noise exposure.
Snowmobiles
            Snowmobiles are a relative newcomer on the  leisure vehicle scene.  Since
their introduction in 1958 as a  low powered,  lightweight,  go-anywhere-?n-the-snow-
type vehicle, they have evolved into a more refined family-type recreation vehicle.
The original concept called for a minimum  of weight coupled with maximum perform-
ance for the engine size.  Hence,  the original snowmobiles possessed unshrouded
                                       184

-------
            Comparison of Two Current Production 750 cc Four-Stroke Motorcycles

                          Tested Under Identical Operating Conditions
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                                             185

-------
engines and unmuffled (or poorly muffled) exhausts.  Their rapid rise in popularity
led to numerous consumer complaints about their excessive noise.  As more vehicles
were produced,  consumers demanded higher and higher horsepower outputs until today,
some snowmobiles are capable of nearly 100 mph.   Their effect on the noise environ-
ment has been compounded in many cases by the fact that some owners remove the
factory-installed muffler systems in an attempt to achieve more power.  In most cases,
this actually results in less power and considerably greater noise.
            The noise  levels of  1971 models at 50 feet generally range from 15 to 20 dB
less than the noise of 1961 models. This reduction clearly indicates the manufacturers'
concern for the problem, and is impressive,  particularly since prior to June 30, 1970,
there were no effective snowmobile noise regulations in effect.  Minnesota was the
first state to require that the noise level of snowmobiles not exceed 86 dB(A) at 50 feet.
Most of this reduction  has resulted from improved exhaust  systems which actually
            .   ,.,     ,    ,        14
improve engine lite and pertormance.
            Exhaust treatments are currently available which utilize an expansion
                                                24
chamber incorporated into a  tuned silencer system.   With this design, much  of the
acoustic energy is reflected back to the exhaust port, where it acts to supercharge the
mixture.  This configuration  also creates a negative pressure pulse  at the exhaust  port
to scavenge the spent gases.  Such systems are more effective  than straight pipes or
mufflers alone, both for noise suppression and  power output.
            Another consideration in muffler design is to place the exhaust exit away
from the operator to reduce his noise exposure.  Exhaust exits  may  be directed down
into the snow or beneath the driver; however, care must be taken to avoid icing up the
tracks and suspension by the  blast of hot exhaust gases.
            Other major considerations in achieving these levels have been in the
areas of intake silencing and engine enclosures.  The cowling configurations on the
different brands of snowmobiles vary quite markedly.  The lighter weight, price-
competitive units generally use a minimal engine shielding, while  the more luxurious
multicylinder units are provided with much better shielding.  The need for adequate
                                       186

-------
engine cooling is a legitimate design constraint and the main argument against engine
enclosure for most vehicle types.  However, the snowmobile, by virtue of the environ-
ment in which it operates,  is most ideally suited to a well-ventilated acoustic
enclosure.  In addition to reducing noise levels to the  distant observer, the engine
enclosure is perhaps the most significant factor in reducing the high noise levels
experienced by the operator.
            Further reduction is undoubtedly obtainable through more refined engine
cooling methods which would allow more complete  engine enclosure,  some design
modifications to allow rerouted intake through silencing devices, and more space
for large volume mufflers. '   '
            The major problem area left to be fully assessed is the operator noise
environment.  While earlier noise levels of 120 dB(A) and greater have been substan-
tially reduced, current models still produce levels at operator position of 105 to
          59.
115 dB(A). '   It is felt that the additional work on intake silencers and engine
enclosures will do much to alleviate this problem.  It is estimated that the current
snow vehicles reflect a cost increase of about 15 percent to obtain their present
noise  levels.
            There are currently pending a number of noise laws which,  if enacted,
will attempt to limit the noise output of snowmobiles at 50 feet to 73 dB(A) in 2 to
3 years.   One manufacturer is currently attempting to develop a machine to comply
with this requirement.  While specific details are not available  concerning the tech-
niques involved in achieving these levels, he has estimated that such reduction will
carry with it a  15 to 30 percent increase in vehicle weight, and a corresponding
                           9
30 percent increase in price.   A number of the smaller manufacturers with limited
or no research and engineering facilities may be unable to meet these requirements.
            One of the major suppliers of mufflers for the snowmobile industry
expressed the opinion  that there exist currently available exhaust treatments which
                               14
provide 30 to 35 dB attenuation.    This means a reduction in the contribution of
the  exhaust .system from approximately 105 dB(A) unmuffled to the 70 dB(A) range.
                                      187

-------
This reduction can be accomplished with minor power  loss but at the expense of some
additional weight and space required for the muffler.
            On the majority of current production snowmobiles, no intake air cleaners
or silencers are used.  It has been shown experimentally that a simple air cleaner
assembly will reduce intake noise by 7 dB without impairing performance.    'It would
appear that further reduction in this area is possible, and reductions of 12 to 15 dB  •
would be feasible with some power loss, thus reducing the intake contribution to
approximately 70 dB(A) at 50 feet.
                                                                       14
            An example cited by one manufacturer is shown in Table 2.7-1.
It is felt that further overall reduction into the 75 dB(A) range is feasible with
improved engine enclosures.

                                    Table 2.7-1
             Example of Further Noise Reduction  Using Existing Technology,       ;
Noise Producing Component
Exhaust
Intake (stock range 77 to
87 dB(A) )
Cooling fan
Track & suspension
Engine/mechanical*

Unmodified

OVERALL
1971 Model
As Produced
(dB(A) at 50 feet)
82
85
(bare stack)
80
72
76
86 dB(A)
With Intake and Exhaust
Treatment
(dB(A) at 50 feet)
70
78
(with silencer)
80
72
76
82 dB(A)
     Test vehicle had production engine cowling in place.
                                       188

-------
            Future snowmobile noise output levels at 50 feet could be reduced to the
70 to 73 dB(A) range by 1980.  This figure assumes significant .advancement in noise
reduction  technology in a number of areas.  The first step is to utilize existing exhaust
                                                                   14
systems, which reduce  exhaust noise levels to the 70 to 75 dB(A) range.    Further
refinement will be required to produce systems that are of reduced size and do not
drastically affect power output. Intake system silencing  should be advanced suffi-
ciently by that time to also provide maximum intake noise levels in  the 70 dB(A) range
without significantly affecting engine performance.  A key area of attenuation will be
in more refined engine cooling and air ducting techniques that will  allow the use of
full engine enclosures, hence reducing this system's contribution to  the 70 dB(A) range.
The last significant system that must be further refined would be the drive track and
suspension system. Current contribution from these elements is now  estimated at
                14
around 72 dB(A).    It would appear that component isolation and slightly refined
design  will achieve adequate noise reduction in  this region.
            It is believed that these noise reduction techniques will greatly aid in
reducing operator noise exposure levels.  Rerouting the intake and shielding the
                                                                20
engine should reduce these levels down to the 88 to 92 dB(A) range.
                                       189

-------
3.0         Devices Powered by Small Internal Combustion Engines


3.1         Introduction

            The noise emanating from equipment powered by small internal combustion

engines is well known to millions of people, particularly those who maintain gardens

or lawns.  The total United States production of these engines was about 10.9 million

units in 1969.  This total includes all engines below 11 horsepower except those used

for boating, automotive and aircraft applications.

            Over 95 percent of these engines are air cooled, single cylinder models.

The vast majority are 4-cycle,  while the 2-cycle version comprises most of the remaining

market.  More than half of the single cylinder engines power the  estimated 17 million

lawnmowers in use today.  The majority of the remaining engines  are used in other lawn

and garden equipment such as leaf blowers, mulchers, tillers, edge trimmers, garden

tractors and snowblowers.  In addition, about 750 thousand chain saw engines and

100 thousand engines for small  loaders, tractors, et cetera, were  produced in 1970,

while agricultural and  industrial usage together account for another 1 .5 million engines.

Generator sets, while not presently employing as  large a number of engines, are an
                                                      1  2
important consideration because of their growing numbers. '

            The categorization of these devices by  usage and typical noise levels is

summarized in Figure 3-1.


3.2         Source Noise Characteristics

Generators

            Of the 100,000 generator sets sold each year in the United States,  most

are used in mobile homes, campers, and large boats, where their  electrical output is

used to power air conditioning, lighting, and other equipment.  These  sets generally

have 3 to 5 kilowatt capacity with a few units producing 8 kilowatts or more.  Engine

size is of the order  of 2.2 horsepower per kilowatt,  often with considerable derating of

the engine for quiet operation so that the generator's noise may be tolerated by users
                                          o
and their neighbors over long periods of use.
                                        190

-------
            Generators
          Battery Chargers
          Air Conditioners
          Auxiliary Power
                                  Internal Combustion
                                       Engines
                                      Lawn Care
                                  • Mowers
                                  • Edgers
                                  • Tillers
                                  • Leaf Blowers
                                  • Snow Blowers
    Other Types
• Chain Saws
• Model Aircraft
    120
    110
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550,000

30,100,000

2,500,000
                                 Typical Noise Levels
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-------
            Figure 3-2 illustrates a typical one-third octave spectrum radiated by
small generators of the 3 to 5 kilowatt size.  The spectrum is characterized by two
peaks, one occurring at the firing frequency, around 40 Hz,  and a second peak about
1000 Hz. This spectrum is characteristic of most types of internal combustion engines.
The low  frequency peak is associated  with the fundamental firing frequency of the
engine.  However, the high frequency peak is generally the most annoying portion  of
the spectrum since it occurs at a frequency where human hearing is most sensitive.
This peak may be attributed to acoustic radiation by the hot  gas bubble leaving the exhaust
with each firing, and to mechanical noise in the engine.  In the example given, the
high frequency noise has been heavily suppressed in comparison with other equipment
having less stringent noise requirements.
Lawn-Care Equipment
            Lawn-care apparatus built in the United States is predominantly equipped
with engines running at 3000 to 36000 rpm.  The characteristic noise spectrum, as
shown in Figure 3-3,  has a double peak, the lower  frequency peak corresponding to
the engine firing frequency and the higher peak occurring from 2 to 3 octaves above
the firing frequency. Additional high noise levels are radiated by  the rotating bjade.
In the case of a rotary mower driven by a 4-cycle engine, the blade passage will be
4 times the firing frequency and will merge with the high frequency engine noise.
Equipment without a rotating blade will generally have other machinery noise of the
same approximate level.
            It can be shown that "A"  scale measurements of  engine noise from this
class of engine is generally  2 or3 decibels below an A scale measurement of the
machinery noise.  However,  the modulation of the high frequency engine noise by the
lower firing  frequency makes the engine noise more audible than the noise  of a rotating
blade or  other machinery.  Thus, even heavy muffling on lawn-care equipment does
not totally eliminate the audibility - or characteristic "putt-putt" - associated with
this modulation.
                                       192

-------
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                  Figure 3-2..  Typical  Noise Characteristics of Generators
                                   193

-------
Exhaust
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                                       (Engine)
                                                               92


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                 Figure 3-3. Typical  Noise Characteristics of Rotary Lawnmpwers
                                       194

-------
Chain Saws
            A typical chain saw, designed for casual use, weighs from 6 to 20 pounds
and has a blade from 1  to 3 feet long.4 The engine produces 5 to 8 horsepower and has
a life expectancy of 1000 to 2000 hours.   In order that a device this powerful may be
made portable, the engine must have a high power-to-weight ratio.
            Fuel consumption,  muffling,  and durability are secondary considerations
even in the industrial machines, as design criteria dictate the use of high speed. A
typical  engine may operate at 9000 rpm at a firing frequency of the same rate, or 150
times per second.  The  engine incorporates a muffler,  typically weighing less than a
pound,  which includes  a spark arrestor to prevent fire.  The very high firing frequency
                                                                                4
brings the direct exhaust noise well within the audible range, as shown  in Figure 3-4.
The broad peak, characteristically found in these engines two octaves above the firing
frequency, occurs  around 1000  Hz, the region of greatest audibility in humans.
            Thus,  the requirement for a small but powerful device has resulted in
designs  in which the engine noise is in the frequency range of greatest audibility, and
the muffler structure is  as light and small  as possible.  This combination results in equip-
ment which produces levels as high as 115 dB(A) at the operator's position, with  levels
                                        4 7
of 83 dB(A) common at  a 50-foot distance. '                      •   •
Model Airplane Engines
            Model airplane engines are normally rated by displacement in cubic inches
and few figures are published in terms of horsepower.  These engines range from 0.029
to 0.20 cubic inch displacement, and may exhibit up to 1 .5 horsepower per cubic inch.
The noise spectra shown in Figure 3-5  were measured on 0.049 cubic:  inch displace-
ment engines which would probably produce 0..06 to 0.08 horsepower.  Model airplane
engines are 2-cycle types, turning at very high rotational speeds, typically 12 to 18
                                                        4
thousand rpm, resulting in a firing frequency above 200 Hz.
            Manufacturers have only recently incorporated any type of muffling.
Figure 3-5 illustrates data taken  on two identical engines of 0.049 cubic inch
displacement. One was equipped with a  muffler and the other was not.  The 200-Hz
                                        195

-------
                                                                    Chain
                                        Engine
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                       Figure 3-4,  Typical Noise Characteristics of Chain Saws



                                           196

-------
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             Figure 3-5*   Measured Noise Characteristics of Muffled
                     and Un muff led Model Airplane Engines
                                  197

-------
firing frequency is in evidence in both cases.  Indeed,  the noise level at the firing
frequency is higher for the muffled engine than for the unmuffled engine.  However,
since the "A"  scale (and the human ear) discriminates against this 200-Hz signal.by
10 decibels, the levels of this frequency are not quite as audible as are similar .levels
between 1000 and 4000 Hz.
            Thus, the unmuffled noise levels at 1200 and 2400 Hz are considerably
more audible when the bareiengine is operated than when the muffled engine is
operated.  Even with muffling, the double peak frequency characteristic is very
much in evidence, but the character of the engine sound has changed from an "angry
mosquito" to something more like a noisy electric motor, while reducing the "A"
scale noise by 12 decibels.
3.3         Environmental Noise Characteristics
            It is characteristic of small internal combustion engines that the equip-
ment being powered  is operated by a single person or is unattended.  The low noise
equipment, such as generators which have been well-muffled,1 operate unattended.
However, the  typical generator is used for supplying power to a camper, mobile home,
or boat, and is built into a metal frame which  also houses the owner and his family.
When its vibrational energy is communicated to this frame, considerable annoyance
may result even though its directly radiated acoustic levels are very low.
            The operator of lawn-care equipment attends the equipment at all times.
Usage is generally during daylight hours in urban and suburban areas.   A given user
will operate a lawnmower for one or two hours per week and may then run an edge
trimmer for approximately one-half hour.  He may continue with a leaf blower to
pick up the clippings and then  use either a garden tractor or tiller in his garden.
During such a  hypothetical day, the operator may be exposed to four or five hours
of noise in the high 80 to low 90 dB(A) range,  depending upon the manufacturer's
dedication to noise control and to the user's maintenance of the equipment.
                                        198

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            Some other lawn-care equipment transports the operator, as in the
popular Hiding mowers or garden tractors.  Here the operator is directly behind
or directly above the engine.  The muffler and intake ports are generally somewhat
closer'to the operator's ear than the 6 feet characteristic of the push-type equipment.
Also/ equipment which can carry the operator generally requires a larger engine than
would be required otherwise.  These two factors  combine to create considerably
higher sound pressures at the operator's ear.  The A-weighted noise level for this
situation generally' ranges from the low to mid-90's, presenting the operator with a
risk of permanent hearing damage when long periods of operation are endured each
day,  or when shorter time periods of operation are endured by a person who is especially
sensitive to hearing damage.
            A third type of engine characterized by high speed and minimal  muffling
is the chain saw.  Operator ear levels for this device may be as high as 115 decibels,
                                                    78
with quieter machines operating near  102 to 103 dB(A). '   Such  levels present a
definite risk of permanent hearing damage,  and use of ear protective devices should be
recommended as a prudent precaution in  the operating instructions and the  labeling
of such equipment.
            The noise of model airplane  engines and other small devices is usually
not of a sufficient level to impose hearing damage risk on the user, during  the short
exposure times of close proximity to the engine.
            A well-built generator will seldom exceed 70 to 72 A-weighted decibels
at a distance of 50 feet when installed in a motor home or other such vehicle.  It will
not generally cause speech interference;  however, when the generator is used during
early  evening and beyond, there may be  considerable interference with sleep and
relaxation to persons nearby.   As the market for these devices expands, they will
become a greater nuisance.  Consequently,  current production units are being
improved as rapidly as technology and cost permit.
                                        199

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            The norHparticipant noise environment generated by lawn-care equip-
ment has at least some 'effect on a large portion of the population in the United States.
This extensive effect is the result of the large numbers of engines being used in this
application in heavily-populated areas.  The equipment generates A-weighted noise
levels in the low 70's at:50 feet and produces some speech interference.  Where any
kind of solid barrier exists between the source and receiver, a decrease of 5 to 15
decibels can be expected. Thus, a solid wooden fence or the house itself will gen-
erally reduce the speech interference to acceptable levels.  In many cases, the lawn-
care equipment will not become a cause of complaint by the non-participant, as long
as its use is restricted when people are sleeping and in early evenings when people
are relaxing on their patios.  In other cases,  where a wire fence or no fence at all
exists, complaints might well be forthcoming. •
           ) The non-participant environment generated by chain saws is fully capable
of causing  speech interference at distances of several hundred feet.   Non-participants
within 25 feet of the chain saw will be exposed to potentially damaging levels, as is
the operator.  The chain saw is not frequently used in areas of heavy population and
is therefore not of frequent concern in the non-participant environment.  When it is
used in populated areas, considerable reaction may be experienced from those exposed
to the noise.  It is probable that a reduction of the noise levels for the operator to
the levels of lawn-care equipment would minimize problems in the non-participant
environment.  However, it must be recognized that a great deal  of study would be
required to accomplish this noise reduction within the cost, weight, and power con-
siderations imposed upon chain saws by their preferred use.
            In all cases of the non-participant environments mentioned, the persons
affected will be in  their homes or at other locations where they have gone for leisure
time activities.  Apartment dwellers are not exempt since the lawns around their
apartments are mowed by  larger, noisier equipment.  Children attend schools where
lawns are mowed,  and even most hospital rooms are within earshot of a lawnmower.
                                        200

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            Generators and chain saws both have a small effect on the general community


since they are used outside populated areas.  Chain saws affect the operator and helper


at levels between 90 pnd 110 dB(A) with the operator receiving the highest levels; When


this equipment is used in  populated areas,  all persons within 500 feet will  generally


be annoyed.  However, duration is short and occurrence is infrequent so that their total


impact is small.  It is estimated that fewer than 5 million people per year will be


adversely affected by these devices.


           Generators affect their half-million owners plus another 1.5  million family


members., In addition,; each generator may annoy two other families,  bringing the total


number of persons affected to 12 million, roughly 5 percent of the population.


            The non-participant environment for model airplanes can range from 78 dB(A)


for nearby planes to 40 or 50 dB(A) at distance.  Audibility is present at distances of


many hundreds of feet.  When  short flights are made during daylight hours, annoyance


is small., When  flying is continuous or is conducted when  people are relaxing outdoors,


annoyance.becomes great.  .    ;•



3.4         Industry Efforts Towards Noise Reduction



            Historically, noise reduction has not been of  primary consideration to the
                                                                i

manufacturers of small internal combustion engines although unmuffled equipment has


not been produced for many years because of buyer resistance to an excessively noisy


product.  Public tolerance, combined with some noise control,  has produced a com-


promise situation between the  consumers and the manufacturers.
            i                    \                '              .       '


            Generally, noise  reduction achieved by the engine manufacturers has


resulted in engines which make somewhat less noise than the equipment they are


designed to  power.  However, equipment manufacturers are not completely convinced


of this conclusion, and tend to attribute the noise of the entire unit to the engine.
                                       201

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This situation is particularly characteristic of the small equipment manufacturer who
purchases the engine from an outside source,  having no involvement with engine
design.  In this category are large numbers of lawn-care equipment units which are
constructed of pressed sheet metal  in production shops around the country.
            Many of the manufacturers of internal combustion engine powered equip-
ment feel that they are being placed in  the difficult position  of being required to meet
several divergent nuisance lawS.   These laws have been promulgated by various
individual cities and towns, where noise restrictions are related to local economic
and social conditions.  This situation is  typified by the experience of the manufacturers
of lawnmowers.  The recently enacted ordinance for the City of Chicago lists a
descending scale  for allowed noise for lawnmowers over the next few years which most
manufacturers interviewed agree is realistic,  and they are working toward compliance
within the allotted time.    However,  in  the recent ordinance enacted by the City
of Minneapolis, the equipment is riot allowed to exceed certain ambient  levels at the
property  line by more than 6 decibels.     Lawn  care equipment is specifically
exempted from  these requirements, but is restricted to operation between the hours of
7:30 a.m. to 9:00 p.m. on weekdays, and 9:00 a.m.  to 9,:30 p.m. on Saturdays,
Sundays, and holidays.   If the  lawn-care  equipment can comply with the specified
ambient requirements, then it may be used during any hours.
            Other cities around the country have ordinances with noise levels as
                                  12
low as 40 dB(A) at the property line.    Although there does  not appear to be a strong
effort to  comply with or enforce this latter ordinance, no manufacturer can  look with
impunity upon such a law, and he might even decide not to market in that area. As
other localities pass noise ordinances, such inequities could proliferate,  making the
manufacturers'  task much more  difficult.
         ,   The extent of noise reduction within the industries supplying small internal
combustion engines has been directly related to  its effect on sales and the existence of
noise ordinances.  With the exception of the small generator industry, public pressure
has not been sufficient to produce significant noise reduction efforts in most of these
devices.
                                      202

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            As a result, noise abatement1 programs have not been consistent.  For
instance, one manufacturer has demonstrated that a small generator, using a 3 horse-
power engine with a vertical  shaft housed within a complete enclosure, may be quieted
to 70 decibels at a position 6 feet from the engine.  If this same treatment were applied
to a  lawnmower, it would achieve an  improvement of approximately 20 dB over most
current production lawnmowers, and would make the engine  quite inaudible in the
presence of a rotating blade.  However,  no serious plans are being made for production
of such a mower because of the high cost of the noise reduction treatment.
            Another manufacturer is presently producing a lawnmower operating at a
noise level of 50 dB(A) at 50 feet. This is some  13 decibels  below the average machine
and is accomplished through the use of a  2-cycle engine with a large muffler, and
cast  frames where pressed steel was previously used.  Only 10 percent of the engines
manufactured in the United Stares are of  the 2-cycle type, so that a changeover to
that  type of engine from the present majority of 4-cycle types would be a very long
and expensive task.  High fuel cost could also create resistance in the marketplace.
            Some manufacturers were  questioned as to the feasibility of producing
                                                                      3
2-cylinder engines for use in lawn-care equipment and other such devices.   This
change from the singles-cylinder engine has the advantage of allowing the  exhaust
pulse from one cylinder  to partially cancel the pulse from the other cylinder. While
many manufacturers admitted the  feasibility of this concept,  estimates of cost for such
engines ran from 30 percent to 50 percent higher than  the single-cylinder engines for
a given horsepower rating.  Such  a penalty would make the  "quiet" engines non-
competitive with the lower-priced models of current design.
            Chain saw manufacturers recognize the existence of a serious noise
problem with their equipment.  The high  power-to-weight ratio necessary in a device
that  must be hand-carried and be  capable of quickly cutting trees and large brush
requires a structure not capable of containing its own noise.   Further, the  noise
produced" by the chain itself is of the order of 100 dB(A) at the operatpr position
and reduction of the engine noise below this level would not reduce total output to
                                         203

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an acceptable level.  In addition, where experimental prototypes have been built
using electric motors to achieve very low engine noise, the more apparent mechanical
noise of the chain gives the impression of a device "ready to fly apart, " causing
operators to resist using it.   Some experimental work is being done to reduce the.
noise of the chain, but cost limitations rapidly become prohibitive when exotic  ,  ,
materials are used to damp the response .of the blade to the chain.
            Considerable engineering work has been expended to make the mufflers
more efficient within weight and size limitations, and some success has rewarded
these efforts.  Sound levels have been reduced to as low as 103 dB(A) by some  special
mechanical devices with power losses of no more than 10 to 12 percent.
            Noise control within the industry served by small internal combustion
engines will be affected  by various laws and ordinances as enacted by the government  ,
bodies concerned.  However, there will always be difficulty in encouraging noise
abatement until  public education advances to the point where the charisma of noise
                1           ,      .              '     :        "'>•.•    •'.-.)••••
is gone. The motorcyclist who  removes his mufflers to obhain more power may well
degrade his performance and still feel he has gained power and status.  He has his
counterpart in the backyard garden.  This man may remove the muffler from his tiller
in order to dig his garden faster (he thinks).  He may not remove his lawnmower muffler,
but as it becomes old and less efficient, he may rationalize that the lessened back
pressure will  tend to compensate for losses of power through aging of other parts of
the engine.
           Whatever the basis for associating loud noise with  productivity, an
educational  program is required  to reduce  public acceptance of noise.  When each
person is convinced that  his contribution to noise  reduction is meaningful, he may
go to the manufacturer of the quietest machine, even if the cost is higher, and may  "
take pride in his accomplishment.  When this happens, as it has in the-small generator
field,  manufacturers will  probably respond decisively toward reduced noise levels.
Interviews have  shown that most manufacturers can respond, but, at the present time
have found little market for quiet products when the public is asked to pay a premium
for the  quiet  product.
                                      204

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3.5
Noise Reduction Potential
            The combined effort by the public in demanding quieter products powered
by internal combustion engines and successful response to this demand by the manu-
facturers, should provide a substantial  decrease in annoyance from this equipment.
This reduction in annoyance of intruding noise from'lawnmowers,  chain saws, et cetera,
will be the principal benefit of a broad noise reduction program for devices powered
by internal combustion engines.   The estimated potential noise  reduction that might be
expected in the future for these devices is summarized in Table 3-1.  The noise
reduction values are relative to current noise levels and are specified in  terms of
potential reductions that can be achieved by the  1975, 1980 and  1985 time periods.
            Full accomplishment  of these noise reductions would  largely  eliminate
annoyance  problems in residential areas associated with use of lawn care equipment.
However, the noise reduction  potential for chain saws using existing technology is
not sufficient to eliminate their annoyance problems or hearing damage risk for
operators.  Further noise' reduction' research is called  for with these unique devices.

                                     Table 3-1
                  Estimated Noise Reduction Potential for Devices    '
                      Powered by Internal Combustion Engines           •,
•>
Source
Lawn Gare Equipment
Chain Saws
Generator Sets
Noise Reduction, d6 *
1975
10
2 '
5
1980
13
2
•7
1985
15
5
17
      *Noise reduction relative to typical current noise  levels in dB(A) at 50 feet.
                                     205

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4.0         ENVIRONMENTAL IMPACT FOR TRANSPORTATION VEHICLES
            AND SMALL INTERNAL COMBUSTION ENGINES
            The preceding chapters have illustrated the nature of the noise character-
istics as well as an estimate of current and future noise reduction potential  for each
major element of the transportation system and for small non-industrial  internal com-
bustion engine  powered devices.  With, this background, one would like to  have an
overall view of the impact of these noise sources on the observer in a community and
on the operator or passenger.  As with any complex situation, several viewpoints are
desirable in order to obtain such an overall perspective.
            First, a simplified overview of the relative contribution of each of the
source categories is provided by comparing their estimated daily outputs of  acoustic
energy.  Next, the sources are compared to estimate their relative contributions to
the outdoor residual noise level in average urban residential areas. Third,  the sources
are reviewed with respect to their individual single event intrusive characteristics,
and their potential impact in terms of community reaction.   Finally, the operator/
passenger noise environment is reviewed with respect to the  potential hazard for
hearing damage and speech interference.   Each of these comparisons is examined in
terms of today's situation and in terms of one possible estimate of the potential change
in the future.  This example of a  possible estimate of future  noise helps to provide
some  insight into potential changes in the relative impact of the various source
categories  that could  be effected with current or advanced technology.
            A detailed discussion of the methods and sources of data used in carrying
out this impact analysis is presented in Appendix B.  Key assumptions utilized are
summarized as  follows.
                                                    J
            •   The impact analysis is based on current figures for the number
                and use pattern of the noise sources as determined from nationwide
                statistical data.   These data, coupled with the definition of
                characteristics of the noise sources, provided the basis for evalu-
                ating noise impact for 1970 in statistically-average communities.
                                       206

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To project- changes in the noise impact to the year 2000, a conservative
model was chosen for growth of the transportation system and growth  in
numbers of internal combustion devices.  Major assumptions for the
model included (a) conservative population growth,of,1.15 percent per
year from 1970 to 1985 and 1.05 percent thereafter, and (b) conserva-
tive estimates for numbers of noise sources with growth rates approaching
estimated urban population growth rates by the year 2000.
The potential change in noise  levels for transportation vehicles and
internal combustion engine devices has been estimated for three
possible options for future noise  reduction:
Option 1 —  No change  in source noise levels after 1970.  This
            represents a base-line condition wherein changes in
            noise impact would  be due only to changes in number
            or use-patterns of the noise sources.
        \          7        '        '
Option 2 —  Estimated noise reduction that would be achieved by
         ;.   extrapolating current  industry trends by the year 1985,
            with no  further reductions thereafter.   This option
            assumes  no new noise  control regulations by local,
            state or  Federal agencies, or any  change in consumer
            demand  for quieter vehicles.
Option 3 —  Example of projected  noise reduction achieved by
            implementation of an  incremental  regulatory program
            to achieve a specified amount of noise reduction by
            the years 1975, 1980, and  1985..  The  criteria used
            for defining these estimates for potential noise reduction
          r under this option example are as follows:
                      207

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                            —  By 1975, what noise reduction could be achieved by
                               reducing levels to those for a typical quieter model
                               now  on the market.
                            —  By 1980, what noise reduction could be achieved
                               that  industry has already demonstrated can be
                               accomplished.
                            -  By 1985, what is a practical limit for the potential
                               noise reduction that could be achieved utilizing, if
                               necessary,  advanced technology.
                 The estimates of potential noise reduction utilized for Option  3
                 are summarized in Table 4-1 for the major transportation categories
                 and in Table 4-2 for Internal Combustion Engine  Devices.
            Due to the very different use-patterns  for transportation vehicles in
contrast to non-industrial stationary internal combustion engine devices, it is desirable
                                                            *
to evaluate their impact separately.  Transportation vehicles are considered first.
4.1         Total Noise Energy Output per Day for Transportation Systems
            A small, but no longer insignificant, byproduct of the growth in  transporta-
tion is the conversion of a tiny fraction of the mechanical energy  expended by  the
industry into sound — normally an unwanted  sound or noise.  For example, to propel
87 million automobiles and 19 million trucks and buses in the United States, an energy
equivalent to approximately 7800 million kilowatt-hours is consumed every 24 hours
— approximately one-third of the total energy consumption in the United States from
all sources of power. Approximately one-millionth of this portion for transportation
is converted into noise.  The amount  of noise energy per day for each element of the
transportation system is a function of its noise  level,  number of units, and number of
hours per day operation.  Thus,  a source category which has high  noise  levels,  but
only a few units  in operation^ can produce the same total noise energy per day as a
source category which has a lower noise level but a very large number of units  in
                                      208

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                    Table 4-1

Example of Potential Noise Reduction for Externally
Radiated Noise for Transportation System Categories
Source
HIGHWAY VEHICLE1
Medium and Heavy Duty Trucks
Utility and Maintenance Vehicles
Light Trucks and Pickups
Highway Buses
City and School Buses
Passenger Cars (Standard)
Sports, Compact, and Import Cars
Motorcycles (Highway)
AIRCRAFT
Commercial —with Turbofan
Engines^
3
General Aviation — Propeller
Heavy Transport He li copters '-
3
Medium Turbine- Powered Helicopters
Light Piston- Powered Helicopters^
RAILWAY1
Locomotives and Trains
Existing Rapid Transit and Trolley Cars
RECREATIONAL VEHICLES1
Snowmobiles
Minicycles and Off-Road Motorcycles
Outboard Motorboats
Inboard Motorboats
Effective Date
1975
3
3
2
3
2
2
6
2

4
0
0
5
10

0
5
10
2
2
5
1980
8
8
5
8
5
4
8
7

7
5
5
12
15

5
10
12
7
4
6
1985
10
10
8
10
8
5
9
10

10
10
10
17
20

8
15
14
10
6
7
1
Relative reduction in average noise levels in dB(A) at 50 feet.
2
Relative reduction in EPNdB at FAR-36 Measurement Position for Takeoff.
3
Relative reduction in EPNdB at 1000 feet from aircraft during takeoff.
                       209

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                                    Table 4-2
                  Estimated Noise Reduction  Potential for Devices
                     Powered by Internal Combustion Engines*

Source
Lawn Care Equipment
Chain Saws
Generator Sets
Effective Dates
1975
10
2
5
1980
13
2
7
1985
15
5
17
* Noise reduction relative to typical current noise levels in dB(A) at 50 feet
operation. Although this energy comparison does not relate directly to impact on
people, it does identify and give some perspective  to the major noise sources.
            Table 4-3 summarizes the estimates of the A-weighted noise energy
generated throughout the  nation during a 24-hour day, by each category of the
transportation system as it exists today.  The top ten transportation categories, as
ranked by their noise energy, constitute 96 percent of the total, and of these, heavy
trucks and 4-engined aircraft alone produce over 50 percent of the noise energy.
            The approximate A-weighted noise energy expended per day has also been
estimated for the year 2000 for most of the surface transportation categories except
aircraft for each of the three options defined above.  The results are summarized  in
Table 4-4.  The estimated value for 1970, specified earlier, is listed in the first
column  for reference.  The  second column, based on Option 1  (no noise reduction),
shows the increase in noise  energy per day due solely to the estimated increase in
number  and usage of sources.  The third and fourth  columns show the estimated trend
in noise energy by the year 2000 for Option 2 (current industry trends) or Option 3
(possible noise regulation).
            With the Option 3 noise reduction program, the noise energy by the
year 2000 for all categories is always less  than 1970 values.  The reduction for
Option  2 relative to Option 1  by the year 2000 reflects the current effort by the
                                      210

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                                  Table 4-3
       Estimated Noise Energy for Transportation System Categories in  1970
Major Category
                                            Noise Energy
                                        (Kilowatt-Hours/Day)
 Aircraft
  Highway
  Vehicles
 Recreational
 Vehicles
 Rail Vehicles
• Commercial — 4-Engine Turbofan
• Commercial — 2- and 3-Engine Turbofan
• General Aviation Aircraft
  Helicopters
• Medium and Heavy Duty Trucks
• Sports, Compact, and Import Cars
• Passenger Cars (Standard)
• Light Trucks and Pickups
• Motorcycles (Highway)
  City and School Buses
  Highway Buses
• Minicycles and Off-Road Motorcycles
  Snowmobiles
  Outboard Motorboats
  Inboard Motorboats
• Locomotives
  Freight Trains
  High Speed Intercity Trains
  Existing Rapid Transit
  Passenger Trains
  Trolley Cars (old)
  Trolley Cars (new)
3,800
  730
  125
   25
5,000
1,000
  800
  500
  250
   20
   12
  800
  120
  100
   40
1,200
   25
    8
    6.3
    0.63
    0.50
    0.08
                                                       Total ~ 15,000
    Top ten categories which each generate at least 125 kilowatt-hours per day.
                                     211

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                              Table 4-4

 Example of Estimated Future Change in Noise Energy for Major Surface
Transportation System Categories with Three Options for Noise Reduction


Source
HIGHWAY VEHICLES
Medium and Heavy Duty Trucks
Sports, Compact, and Import Cars
Passenger Cars (standard)
Light Trucks and Pickups
Motorcycles (Highway)
City and School Buses
Highway Buses
RECREATION VEHICLES
Minicycles & Off-Road Motorcycles
Snowmobiles
Outboard Motorboats
, Inboard Motorboats
RAIL VEHICLES
Locomotives
Existing Rapid Transit
Noise Energy in Kilowatt-Hours/Day
1970



5,000
1,000
800
500
250
20
12

800
120
100
40

1,200
6

- — : —
1

10,000
2,500
1,200
1,000
800
20
12

2,500
400
160
63

1,200
10
NA — Not available.
*Option 1 — No noise reduction.
2 — Estimated Industry trend in noise reduction.
3 — Example of possible Incremental program of Noise
2000
Option* 	
2

4,000
1,600
800
400
320
8
5

NA
NA
NA
NA

1,200
6.3

Regulation.
/

3

800
250
400
160
80
3
1.2

250
16
40
12

200
0.5


                                 212

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various industries to achieve a quieter product, while the additional reduction indicated
for Option 3 shows the significant additional benefit that could be obtained, through
noise regulation.                                   ..-.•••
            These values of noise energy provide a rough indication of change in the
relative magnitude of potential noise  impact from transportation vehicles.  By the
year 2000 the  noise energy values in Table 4-4 indicate a 100 percent increase from
those in 1970 if no further action were taken to reduce noise (Option 1).  Assuming
        V.
current industry trends are continued (Option 2), there is little significant change in
estimated  noise energy indicated by the year 2000.  Thus, the estimated noise reduction
just offsets the  increase in numbers of vehicles.  However, by implementation of a
positive regulatory program (Option 3 example),  the aggregate noise energy per day
for these sources in the year 2000 might be approximately 78 percent less than the
current,amount.
4.2         Contribution of Transportation System Components to the Residual
            Background Noise Level in an Average Community
            As discussed in Reference 2, the residual noise  level  in a community is
the slowly changing nonidentifiable background  noise which is "always there" when-
ever one listens carefully outside the  home.  This residual noise level is originated
by all forms of traffic moving throughout the community, and the large number and
variety of stationary sources in a community, such as dispersed industrial plants or
multiple air conditioning systems. The method for predicting this residual noise  level
is discussed in Appendix B.
            Table 4-5 summarizes the estimated  daytime residual  noise levels for-
1970 for each  significant type of highway vehicle that operates in an average urban
community. It is apparent that automobiles and  light trucks are the principal sources"
which control  the contribution to the  residual noise level from transportation sources.
            The average residual level was also predicted with the same technique
for the years 1950 and 1960.   The estimated values for the typical urban community are:
           »                                                .
            •    For 1950 - Daytime Residual Level (L9Q) « 45 dB(A)   '.              .
            •    For 1960- Daytime Residual Level (L9Q) «46 dB(A)
                                      213

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                                    Table 4-5
             Predicted Contributions to Daytime Residual Noise Levels
            By Highway Vehicles for a Typical  Urban Community in 1970
Source
Passenger Cars (Standard)
Sports, Compact, and Import Cars
Light Trucks and Pickups
Medium and Heavy Duty Trucks
Motorcycles (Highway)
City Buses
Approximate
Source Density
Units/Square Mile
~ 50
- 20
- 20
- 1.5
~ 1
- 0.8
Residual Noise Level
dB(A)
43
41
42
33
18
15
ITotal (All Vehicles) 47 dB(A)
            These estimates indicate an increase over 10 years of approximately one dB
in the residual  level O-Q/\)-  This conclusion is consistent with the available measure-
ments which are summarized in Reference 2.  Although these estimated values for the
residual level are certainly no more accurate than ±3dB, they agree very well with
the available data and clearly indicate the prime sources of the residual noise in a
                        2
typical urban community.
            Although the average  residual level 0-9f.) in an urban community may not
have changed significantly over the past two decades,  the residual noise  level  in any
given neighborhood may have changed.  Such change is expected in neighborhoods
where the land use has changed  or where new service arterials (highway or freeway)
have been developed.   Thus,  the development of rural  land into suburban communities
has increased the residual level, as has the construction of a freeway through an
existing fully developed community.
            The same model for  estimating residual noise levels for 1970 has been
applied to forecast trends for 1985 and 2000 as a function of the noise reduction options
                                       214

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for highway vehicles only.  The result of this projection, including the estimated
residual levels for 1950 and I960, is shown in Figure 4-1.  The trend for Option 1
is clearly an upper bound, and indicates an additional growth of about 2.5 dB in
the residual level  in an average community by the year 2000 due  solely to growth
in the number and density of the noise sources.  The lowest line (for the Option  3
example)  represents the cumulative effect of achieving the 3-step noise reduction
values summarized in Table 4-1.  It estimates a  net reduction in average residual
noise level of 5 dB relative to today by the year 2000,  whereas little change is
forecast by the year 2000 for the projection of current industry trends (Option 2).
              %
            In summary, therefore, if no further action were taken to reduce noise
levels of highway vehicles, the residual noise level  in an average urban residential
community would be expected to increase an additional 2 to  3 dB by the year 2000
over today's  levels.  On the other hand, a positive program of noise reduction for
highway vehicles could prevent such an increase and achieve a desirable and reason-
able reduction in average .residuaI noise levels of about 5 dB over the next 30 years,
not including any  additional noise reductions to be achieved after 1985.
4.3        Relative Annoyance Potential of Intruding Single Event Noise
           As discussed in Reference 2, the reaction of a community to excessive
noise is the summation of annoyance from successive intruding single event noises such
as aircraft flyovers or many cars driving by.  It is desirable, therefore, to rank trans-
portation noise sources according to their noise levels at a fixed distance, or, as
illustrated in Figure 4-2, define the distance from the source within which the single
event noise is greater than a specific value.
            Two measures of the noise  level are  useful for this comparison; the maxi-
mum noise level which occurs when the vehicle passes by, and the single event noise
exposure level (SENEL)* which integrates the A-weighted noise throughout the entire
passby. This latter measure accounts for both noise level and duration, both  of which
have been found to be factors in annoyance.  An SEN EL of 72 dB has been chosen  as
  See Appendix B for definition.
                                       215

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    50
<,
CO
    48
-  46
 0)
 d>
'5


1  44

 O
 o
O 42
                                  Option 1
                            (No Noise Reduction)
                                                            Option 2   _
                                                          (Current Trend)
                                                            Full
                                                            Effects of
                                                            Limits
                         Option 3 Example
                 (Effect of Regulatory Limits Set in
                       1975, 1980 and 1985)
                                          Dates of
                                        Introduction
                                          of  Limits
                                           Option 3
                                       m
   40
     1950
                  1960
1970
1980
1990
2000
     Figure 4-1,     Estimated Long-Term Trend in Outdoor Residual Noise
              Levels in a Typical Residential  Urban Community
                                      216

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          Single
          Event   A
          Noise  T
          Level
                                                             Noise Level
                                                              Generally
                                                             Acceptable
                                                              S89.
                                                 i Noise Level
                                                 ' Potentially
                                                  Annoying
Figure 4-2.  Decay of Noise Level with Distance from Single Source
            Defines Relative Bounds of Annoyance Zone
                              217

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the reference value for comparing the distances required between a receiver and each
of the various sources if the sources are to be judged equally annoying.  This SENEL
value is approximately that experienced at a distance of 50 feet from a residential
street when a standard passenger car passes.   In subjective tests with  motor vehicles '
of all types, this SENEL value has been found to be a dividing line betv/een  "quiet"
and  'acceptable", and is approximately 10 dB below the dividing  line between
                         2 3
'acceptable "and "noisy". '   In these tests, the effective duration of the vehicle
noise was approximately one second, so that the maximum noise level during the pass-
by was numerically equal  to the SENEL.  Thus the maximum noise  level found 'accept-
able" ranged between  72 and  82 dB(A), which brackets the sound level of one's own
voice as measured at the ear.   This "self voice level" has been suggested as a possible
annoyance reference level.
            Table 4-6 summarizes typical values for maximum noise levels  and SENEL
values at a representative distance for transportation sources. The table also lists the
distance within which  the SENEL exceeds a fixed  level of 72 dB.  Examination of the
various  categories in Table 4-6 clearly shows that aircraft are obviously the outstanding
source of annoying sounds.  However,  heavy trucks, highway buses, trains and rapid
transit vehicles,  which normally operate along restricted traffic routes, will also be a
distinct source of intrusion — potentially affecting more people. This noise intrusion of
single events is more severe in communities where the residual noise level  is inherently
low.  For example, in a rural  or  "quiet" suburban community located well  away from
major highways,  the residual noise level is 10 to 15 dB lower than in  urban areas, and
the passby of a noisy sportscar at night may momentarily increase the  noise level by as
much as 40 dB.  Similarly, during the nighttime near a  major highway, noise intrusion
from single trucks is readily apparent due to the lower density of automobile traffic.
            Recreational vehicles operating on land are in a class by themselves.  .
Their high noise  levels, wide  usage  in both residential and recreational areas, and  the
rapid increase in their number have all  contributed to the current concern  regarding
noise pollution from these devices.  The growth pattern is particularly significant, as
indicated in Figure 4-3, which also illustrates the growth pattern of other  consumer
devices operated by internal combustion engines.
                                       218

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                                  Table 4-6

Comparison of Major Surface Transportation System Categories According to Typical
      Maximum Noise  Levels, Single  Event Noise  Exposure Levels  (SENEL),
         and the Distance Within Which the SENEL is Greater than 72 dB
Category
AIRCRAFT
Commercial — 4-Engine
Turbofan
Commercial — 2rEngine
Turbofan
Helicopters
General Aviation Aircraft
HIGHWAY VEHICLES
Medium and Heavy Duty
Trucks
Motorcycles (Highway)
Utility and Maintenance
Vehicles
Highway Buses
Sports Cars (etc.)
City and School Buses
Light Trucks and Pickups
Passenger Cars (Standard)
RAIL VEHICLES
Freight and Passenger Trains
Existing Rapid Transit
Trolley Cars (Old)
Trolley Cars (New)
RECREATIONAL VEHICLES
Off-Road Motorcycles
Snowmobiles
Inboard Motorboats
Outboard Motorboats
Typical Single Event Levels
Distance
Feet

1000

1000

1000
1000

50

50
50

50
50
50
50
50

50
50
50
50

50
50
50
50
A-Weighted
Noise Levels1
dB re:
20 |jN/m2

103

96

77
83

84 (88)

82 (88)
82 (88)

82 (86)
75 (86)
73 (85)
72 (86)
69 (84)

94
86
80
68

85
85
8.0
80
SENEL
dB re:
20 MN/m2
and 1 sec

111

104

87
96

87

85
85

83
78
78
75
72

114
96
83
71

90
90
85
85
Distance2 '
for SEN EL
Less Than
72 dB
Feet

>8000

>8000

>2000
>2000

700

540
540

540
170
120
100
50

>2000
480
260
40

750
750
400
400
 Values inside parentheses are typical for maximum acceleration. All other
 values are normal cruising speeds. Variations of  5 dB can be expected.
 without shielding loss.
                                     219

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  1970
o I960
o>
  1950
        0
          Legend:

         Gas Powered Lawnmowers

         Motorboats

         Motorcycles

         Chain Saws

         Snowmobiles
     10
Number of Units
  (in millions)
20
     Figure 4-3.     Approximate Growth of a Few Types of Noisy Recreational
         Vehicles and Outdoor Home Equipment.  There were Negligibly
                   Few Gas Powered Lawnmowers, Chain Saws
                           and Snowmobiles in 1950
                                   220

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            The noise intrusion of water craft is generally regarded to be fairly low,
particularly since power boats are legally required to be at least 100 feet from shore
when operating at high  speed, thus minimizing their impact in local communities.
            Looking ahead, the potential change in annoyance or intrusiveness of
single events from surface transportation vehicles can be roughly evaluated by applying
the potential noise reductions listed earlier in Table 4-1. This noise reduction also
can be translated into a reduction of the spatial extent of potentially annoying single
event levels by applying the following approximate corrections to the fourth column of
Table 4-6.
            Noise Reduction                Correction  Factor for SENEL
            (From Table 4-1)                   Distance (Table 4-6)
                 OdB                                  1
                 2                                     0.7
                 4                                     0.5
                 6               ,0.4
                 8                                     0.3
                 10                                     0.2
            Applying the full potential noise reduction limits suggested in Table 4-1
for 1985, a substantial decrease in the annoyance would  be achieved for most of the
transportation categories.   For example, with the exception of motorcycles and main-
tenance trucks, the vehicles commonly operating on urban streets would .tend to have
SENEL values less than  72 dB at 50 feet — a typical distance between a street and a
residence.
4.4         Overall  Assessment of Noise Impact by the Transportation System on
            Non-Participants
            As suggested above,  the cumulative effect of the repeated occurrence of
intruding noises will  place a different emphasis on individual transportation system
categories than is obtained by considering only a single event.  The land area within
a Communify Noise Equivalent Level  (CNEL) of 65, as defined in Reference 2, is
utilized to obtain a minimum estimate of the  integrated noise impact for major urban
                                      221

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highway systems and airport operations — the most important elements of the transporta-
tion system with respect to noise impacted areas. The general method for estimating
noise impact contours around airports has been briefly described in Section 2.1.  A
summary of the method for estimating noise impact contours near highways is presented
in Appendix  B.
            The noise impacted land within a Noise Exposure Forecast (NEF) 30 con-
tour for airport operations throughout the nation in  1970 was 1450 square miles.   This
                                                  2
NEF value is essentially equivalent to a CNEL  of 65.  Therefore, for comparison, a
CNEL of 65 was chosen as the outer boundary of noise impacted land near major urban
highways.  Calculations of the area enclosed between an effective  "right of way"
boundary and the CNEL 65 boundary for freeways,  major arterials and collector streets
gave a total  impacted area of 540 square miles. This area was  associated with free-
ways only, since the distance to the CNEL 65 boundary for the other types of roads
was less than their effective right of way distance.  Thus, the estimated noise
impacted land within a CNEL 65 boundary for the two major transportation systems as
of 1970 was approximately:
                       Highways      ~ 545 square miles
                       Airports        ~1450 square miles
                       Total          ~1995 square miles
            It should be emphasized that both of these estimates include land area
which has compatible land use, as well as  land area which does not.  If it is assumed
that the  land use is similar to the average urban use,  then the population density in
1970 would be approximately 5 thousand people per square mile. Thus, approximately
10 million people could be living  in the noise impacted areas defined by this criterion.
However, the expected reaction of a residential urban community to a noise intrusion
                                                              2
which produced a CNEL of 65 would be "widespread complaints."  Therefore, this
choice of a criterion for the contour boundary is conservative and the total impact for
both commercial airports and freeways is certainly greater.
                                       222

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            Furthermore, the criterion value for widespread complaints is a function
of the residual  noise level in the community.  Consequently, a more accurate figure
of noise impact would require assessing  the number of people actually  living within
the CNEL 65 boundary in urban residential areas, plus the number of people within
the CNEL 60 boundaries in normal suburban areas and the number within the
CNEL 55 boundary in quiet suburban and rural areas.  These lower CNEL boundary
values account for the lower values expected for the residual noise levels in the
quieter areas — thus allowing for an equal amount of relative noise intrusion  for each
type of residential community,  as discussed in Reference 2.  Accounting for  the
factors, it  is conservative to estimate that at least 10 to 20 million individuals are  .
impacted by these two types of noise intrusion.
            The noise impacted land near rapid  transit lines was  not included in this
analysis as there are only 386 miles of electric railway  lines compared to about 9200
miles of urban freeways.  This fact, combined with the  effect of  intermittent operation
along rapid transit lines compared to the steady  noise levels along freeways, indicates
noise impacted land for the former will  be much less.
            Because helicopter flight route patterns are essentially random at present,
it is practically impossible to define their noise  impact  in terms of land area or  popu-
lation. A sustained public reaction has not materialized, despite the  intrusive  nature
                                                                 «
of the sound, probably because of the irregularity of this usage pattern.  However,
widespread complaints have arisen due to air taxi services in New York and  police
operations in Los Angeles.
            The airport noise impact due to general aviation aircraft operations is
quite small when compared to the impact of commercial jet  aircraft operations.  This
is due primarily to the lower noise levels for general aviation aircraft and to the fact
that most of the airports are located in outlying  sparsely populated areas, or the air-
ports are sufficiently large that NEF 30 contours do not enclose significant residential
areas. However, at some general aviation airports that have a high rate of operations
for  executive jets, a significant amount of residential land may be impacted by their
noise. The amount of land area involved is not  known.
                                      223

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            To indicate past and future trends, the total impacted land area near free-
ways and airports has been estimated from 1955 to the year 2000.  The resulting values,
given in Table 4-7 represent the incompatible land area lying within a Community
Noise  Equivalent Level (CNEL) of 65.  Future projections of noise impacted land
have considered the effect of implementing  the noise reduction options discussed at
the beginning of this chapter.  Thus, estimates of noise impacted land areas are given
for 1985 and the year 2000 for both  Option  2 (values in parentheses) and Option 3
examples.  A marked reduction in impact is achieved by the  latter.  For Option  3,
the estimated noise impacted land near airports is reduced by 88 percent from the 1970
value of 1995 square miles to 240 square miles.   Based on a CNEL 65 boundary,  noise
impacted land near freeways is reduced to zero by the year 2000 on the assumption of
a net noise reduction by vehicles and freeway noise barriers of about 5 dB beyond
today's values.
            These changes in land area, based on very conservative criteria for the
noise impact boundary, correspond to an increase from  a minimum of about 10 million
people  impacted today to about 17 million by the year 2000 assuming no further regu-
latory action (Option 2).  Alternately, the estimated number of people impacted (based
on this  criterion) could be reduced by  the year 2000 to no more than 1.2 million with
a positive regulatory program to achieve further noise reduction for aircraft, highway
vehicles and freeways.  It is particularly important to note that the effect of imposing
the noise limits on aircraft .by FAR-36  is already showing at least a "holding action"
         ;           .           ' - -           .            ' '
on noise impact around airports.  However,  without any similar policy for highway
vehicles at the national level, the potential growth in  noise impact near freeways is
severe.
            These results must be viewed with extreme  caution.  First, they are based
on a widespread complaint boundary which may or may not be deemed publicly
acceptable.  Second, they do not count the additional impacted area in communities
with lower residual noise levels.  Third,  they do not account for the effect of lowering
the future residual noise levels.  For example, the  5 dB reduction of average residual
                                      224

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                          Table 4-7

Summary of Estimated Noise Impacted Land (Within CNEL65 Contour)
 Near Airports and Freeways from 1955 to the Year 2000 with Future
        Estimates Based on Option 2 (Values in Parentheses)
                      and Option 3 Examples

1955
1960
1965
1970
1985
2000
Impacted Land Area —Square Miles
Near Airports
~ 20
200
760
1450
780 (870)*
240 (1210)
Near Freeways
8
75
285
545
400 (1470)*
0 (2050)
Total
28
275
1045
1995
1180 (2340)*
240 (3260)
*Number in parentheses is the estimated impact area if no further regulatory
action is taken (Option 2). It assumes FAR Part 36 remains in force for
aircraft, no new limits established for highway vehicle noise, and no change
in existing freeway design concepts to increase noise reduction. Numbers
outside of parentheses assume FAR-36 minus 10 dB for aircraft and additional
combined noise reduction for freeways and highway vehicles of 3 dB by 1985
and 5 dB by the year 2000.
                             225

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noise level estimated for Option 3 (see Figure 4-1) would require a 5 dB reduction in
the level of intruding noises just to maintain the status quo.  In this instance, a CNEL
60 in the year 2000 would be equivalent in terms of predicted community reaction to
a CNEL 65 today.  On the other hand, the interpretation of the results does not account
for the  long term 30 year evolution of land use  patterns which undoubtedly will occur.
For example, one of the principal reasons why railroads are not generally considered
a major community noise problem  today, is  that, for the most part, the land use around
railroads has slowly evolved to compatible usage over the past 30 to 60 years.  The
extent to which this factor will  offset the previous factors is  unknown.
            Estimates have been made of the  relative cost-effectiveness of alternate
methods for reducing noise impacted  land.  For  airports, reduction of noise at the
source (i.e., quieter engines) has been shown to be clearly more cost-effective than
reducing impact by land acquisition.  Continued progress to reduce jet aircraft noise
should remain a first priority for Federal action  on noise pollution. For freeways,
improvement of design to increase noise reduction with barriers  is more cost-effective
by about 2 to 1 over land acquisition.  Vehicle noise reduction is probably least cost-
effective for reducing  freeway noise  impact only, but it gives other benefits for the
total urban population.  Thus, a balanced approach for reducing noise  impact for the
highway transportation system should emphasize both vehicle noise reduction and
improved freeway design.
4.5         Impact on Participant or Passengers in Transportation Systems
            The two significant effects of noise for participants or passengers in trans-
portation systems are (a) potential hearing damage from excessive noise exposure, and
(b) interference with speech communication for  passengers.
Potential Hearing Damage
            The potential hazard  with respect to hearing damage for all categories of
the transportation system is summarized in Figure 4-4 in terms of an equivalent 8-hour
exposure level.   This equivalent level is determined from the actual passenger noise
                                      226

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                                                                    Average
                                                                            Maximum
      Highway Vehicles (Typical Hours Use Per Day)
          Motorcycles (Highway) (1)
          Medium and Heavy Duty Trucks (4)
          Highway Buses  (4)
          Utility and Maintenance Vehicles  (1)
          Light trucks and Pickups (1.5)
          City and School Buses (2)
          Passenger Cars-All  Types (1)

      Aircraft
          Light Piston-Powered Helicopters  (2)
          Commercial - Propeller (1.4)
          General Aviation — Propeller (1)
          Commercial —2- and 3-Engine Turbofan  (1.4)
          Heavy Transport Helicopters  (0.5)
          Medium Turbine-Powered Helicopters  (0.5)
          Commercial —4-Engine Turbofan (1.4)
          Commercial — Widebody (1 .4)
          General Aviation — Executive Jet  (0.5)

      Rail Vehicles
3ay)


g
IE
153



anfl.4) 171
I
X
T
Iso
[so
77 |85
^5 	 J85
3 ]s
|80
75
.
I 84
75 87
75 87
Iso
i
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95
95

8


90



     Existing Rapid Transit  (1.5)
     Trolley Cars  (1.5)
     Passenger Trains  (6)
     High Speed Intercity  (2)

Recreational Vehicles   (Typical)
     Snowmobiles  (2)
     Minicycles and Off-Road Motorcycles  (2)
     Inboard and Outboard Motorboats  (2)
                                     I	I
                                          50
                                              60
                                                          65
                                                                              Occupational
                                                                              Safety and
                                                                              Health Act
                                                                              Criteria
70
80
90
                                                    Equivalent 8-Hour Exposure Level, dB(A)
Figure 4-4.   Potential Hearing Damage Contributions from Transportation System Categories
       in Terms of Equivalent 8-Hour Exposure Levels, for Passengers or Operators
                                         227

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exposure using the same rule for trading off time of exposure and level that is utilized
in the Occupational Safety and Health Act.  The estimated equivalent 8-hour exposure
levels of five of the transportation categories exceed the Occupational Safety and
Health Act criteria for an equivalent 8-hour day.  In each case, even though  the
number of days of exposure  per year is much less than in a working year,  noise protec-
tion for the operator's ear is highly desirable.  In addition, many of the other  sources,
including all those  exceeding an equivalent 8-hour exposure level  of 80 dB(A) are
potentially hazardous  to some indivuals, particularly in combination with their expo-
sure to other noise environments.  A proper evaluation  of hearing damage risk  for the
individual must account for this cumulative effect of his entire daily exposure  to all
potentially harmful noises.   Consequently, efforts should be made to reduce this noise
to minimize its potential hazard for hearing damage.
            The effect of implementing the potential noise reduction outlined  in Table
4-1 for transportation  vehicles would be a substantial reduction of  this risk of hearing
damage.
            Speech  interference criteria specify maximum desirable noise levels at the
listener's ear as a function of talker-listener separation for effective normal speech
communication.  Table 4-8 summarizes typical talker-listener separation distances in
various transportation  systems and corresponding maximum desired noise levels  to mini-
mize speech interference at these distances.
            Comparing the  last two  columns, average internal  levels for the principal
passenger-carrying transportation categories generally fall within the desired limits to
avoid speech interference.  V/STOL rotary-wing aircraft are a  notable exception for
which internal noise levels  are generally much higher than desired for effective speech
communication.
            It should be noted that a lower bound can exist for  internal sound  levels
inside multiple passenger vehicles based on speech privacy requirements. While setting
minimum levels is not  necessarily desirable for short-haul rapid  transit vehicles or buses
                                       228

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 used daily by commuters, long-haul passenger vehicles such as aircraft with close seat
 spacing are potential candidates for minimum levels based on speech privacy.
                                   Table 4-8
     Typical Passenger Separation Distances and Speech Interference Criteria
                 Compared to Average Internal Noise Levels for
                        Major Transportation Categories

Passenger Cars
Buses
Passenger Trains
Rapid Transit Cars
Aircraft (Fixed Wing)
V/STOL Aircraft
Talker- Listener
Separation
Feet
1.6 To 2. 8
1 to 1.7
1 to 1.7
1 to 1.7
1.1 to 1.7
1.1 to 1.7
Speech
Interference
Limits*
dB(A)
73 to 79
79 to 85
79 to 85
79 to 85
79 to 84 '
79 to 84
Average
Internal Noise
Levels
dB(A)
78
82
68 to 70
82
82 to 83
90 to 93
  * Maximum noise levels to allow speech communication with expected voice level
    at specified talker-listener separation distances.
            A comparison of the average  interior levels listed in Table 4-8 with speech
privacy criteria shows that aircraft and rapid transit vehicles tend to meet  this "minimum"
level  requirement for a typical seat pitch  distance.  However, internal levels for auto-
mobiles, buses and passenger trains generally fall below speech  privacy criterion levels
for typical seat-to-seat distances.  Reduction of minimum levels required for speech
privacy can be achieved only be  increasing the seat spacing or increasing  the barrier
attenuation of sound between seats.
            In summary, the impact of internal noise levels on current commercial
passenger vehicles appears to be minimal, with the exception  of V/STOL propeller or
rotary-wing aircraft.  For the latter,  internal levels tend to be excessive according to
both speech interference and potential hearing  damage criteria.  Noise levels for
                                       229

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operators of heavy trucks, motorcycles and most gas engine-powered recreational
vehicles are excessive and should be reduced to avoid potential hearing damage risks.
4.6         Environmental Impact for Internal Combustion Engine Devices
            As indicated earlier in Figure 4-3, various labor-saving devices powered
by internal combustion engines are a rapidly growing source of intrusive noise in many
communities.
            The principal characteristics of internal combustion engines as sources of
potential noise impact are summarized in Table 4-9 using the same parameters presented
earlier for transportation vehicles.  In general, these devices are not significant
contributors to average residual noise levels  in urban areas.  However, the relative
annoyance of  most of the garden care equipment tends to be high.  This is due to the
long duration  of noise for these  sources.   This leads to a Single Everit Noise Exposure
Level much greater than the approximate annoyance threshold of 727dB at a distance
of 50 feet, a typical  neighbor-to-neighbor distance.  Clearly, further noise reduction
for these devices is desirable.  Similarly, a distinct local increase in the residual level
in rural or wilderness areas  may be experienced at  distances up to one mile from such
devices as chainsaws.  As a result,  they constitute a persistent source of annoyance for
persons seeking the solitude of wilderness areas.  In addition, use of chain saws can
result in equivalent 8-hour exposure  levels of 83 to 90 dB(A) for the operator, indicating
the desirability of hearing protection for operators.
Potential Change in Noise Impact of Internal Combustion Engine Devices
            The future growth in numbers of  these devices is difficult to forecast
accurately due to the lack of detailed data on their current usage.  Such devices often
have a short life span and,  since they are seldom registered in any systematic way, the
accuracy of future growth projections is  questionable.  The past growth of some of
these devices  has been spectacular, as shown in Figure 4-3.  However, once the device
has completed its basic market penetrati9n, its growth rate should be  expected to slow
down to that-of the general economy. Therefore, one can at least expect a general
upward trend in their utilization as convenient and normally effective labor-saving
                                       230

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                                                         Table 4-9
                              Summary of Noise Impact Characteristics of Internal Combustion Engines
Source
Lawn Mowers
Garden Tractors
Chain Saws
Snow Blowers
Lawn Edgers
Model Aircraft
Leaf Blowers
Generators
Tillers
A-Weighted(1)
Noise Energy
KiJowatt-Hrs
Day
63
63
40
40
16
12
3.2
0.8
0,4
Typical A-Weighted
Noise Level
at 50 Feet
dB(A)
74
78
82
84
78
.78. -
76
71
70
Typical
SENEL(4)at,
50 Feet
and 1 sec
111
N/A
118
120
111
108
106
—
106
• " (2)
8-Hr Exposure
Level
dB(A)
Average
74
N/A
85
61
67
70(3>
67
-.
72
Maximum
82
N/A
95
75
75
79(3)
75
-
80
Typical
Exposure
Time
Hours
1.5
N/A
1
1
1/2
1/4
1/4
•
1
(1) Based, on estimates of the total number of units in operation per day.
(2) Equivalent level for evaluation of relative hearing damage risk.
(3) During engine trimming operation.
(4) See Appendix B for definition of SEN EL.
CO

-------
devices which will always be in demand.  This clearly represents an upward trend in
their noise intrusion  potential.
            The combined effort by the public  in demanding quieter products powered
byinternal combustion engines and successful response to this demand by the manu-
facturers, should provide a substantial decrease in annoyance from this equipment.
This reduction in annoyance  of intruding noise  from lawn mowers, chain saws, et
cetera, will be the principal benefit of a broad noise reduction, program for devices
powered by  internal  combustion engines.  The estimated potential noise reduction that
might be expected in the future for some of  these devices has been summarized earlier
in Table 4-2.  The noise reduction values were relative to current noise levels and
were specified in terms  of potential reductions  that could be achieved by the 1975,,
1980 and 1985 time  periods (i.e., Option 3).
            Full accomplishment of these noise reductions would largely eliminate
annoyance problems  in residential areas associated with use of lawn care equipment.
However, the noise  reduction potential for chain saws using .existing technology is not
sufficient to eliminate their annoyance problems or hearing damage risk for operators.
Further noise reduction  research is called for with these unique devices.    .
                                      232

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5.0         CONCLUSIONS AND RECOMMENDATIONS
            The data and discussions presented in this report have attempted to sum-
marize many aspects of a very complex environmental problem.  The manufacturing  and
transportation industries involved are a major segment of our national economy.  Further,
the transportation industry provides the essential service which enables the remainder of
our economy to function.  Unfortunately, noise is a byproduct of these industries.  Thus,
the majority of the sources discussed in this report contribute to noise'.pollution.
            Highway vehicles are responsible for the outdoor residual  noise level in our
communities, as'well as for freeway noise.  Aircraft are responsible for the noise in the
vicinity of airports.   Recreation vehicles are responsible for disturbing noise in the
remote wilderness areas, and lawn care equipment is responsible for excessive noise in
the neighborhood.  In addition, some of the sources in each of :these general categories
represent a potential  hazard of hearing damage and most of the sources are often respon-
sible for single-event noise intrusion in residential neighborhoods.  Consequently^ there
are a variety of noise problems to be examined and solved within acceptable economic,
technical and social constraints.        '.,...              .     -
            It will be a very difficult  task to solve all of the major noise problems in
the environment within these constraints.   Such a task requires development of national
noise goals, cause-and-effect noise system models, and economical and technical
feasibility analyses which are beyond the scope of this report. However, the data pre-
sented  in this report forms a necessary  point of departure and suggests several useful
directions for accomplishing the much  needed task of controlling our noise environment
for the benefit of our entire population.
            This chapter presents the initial conclusions from  this work, including the
total impact on people of the noise sources discussed herein, industry's need for public
guidance if it is to successfully implement  noise reduction,  and an  identification of
possible priorities for Federal action.  It also contains a brief summary of major recom-
mendations for the development of noise measurement standards, noise reduction
demonstration projects, and research programs.
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5.1         Noise  Impact on People
            The noise of each of the source categories in this report has been evaluated
in Chapter 4, with reference to its potential impact.  This evaluation, together with the
                                                  1  o
analysis of the effect of noise in companion reports, '  provides a basis for assessing the
impact of the noise of the source categories on the population of this country. This
assessment is  made for (1) continuous outdoor noise sources which interfere with speech,
(2) other noises resulting in community  reaction and annoyance, and  (3) noise which may
be potentially hazardous to hearing.
Continuous Outdoor Noise which Interferes with Speech
            The noise environment is primarily a product of man and his machine.  It
consists of an all-pervasive and non-specific residual  noise, to  which are added both
constant and intermittent intrusive noises. The  residual noise level in urban residential
communities  is generally the integrated result of the noise  from  traffic on streets and.
highways, principally automobiles and  light trucks in  the daytime, and including
heavier trucks at night.   The daytime outdoor residual noise levels vary widely with
the type of community and can be grouped into the following approximate ranges:
            •   wilderness and rural             16-35 dB(A)
            •   suburban residential            36 - 45 dB(A)
         •  •   urban residential               46 - 55 dB(A)
            •   very noisy urban residential     g.,   _,.  IR/A\
                and downtown city
            Residual noise levels in suburban and rural areas do not appear to interfere
with speech communication at distances compatible with normal use of patios and back-
yards and often provides beneficial masking for speech .privacy.  However, some inter-
ference with  outdoor speech is found  in urban residential communities, and considerable
continuous interference is found in the very noisy urban and downtown city areas.  Thus,
f-he use of outdoor space for conversation  is effectively denied to an estimated 5 to
10 million people who reside in  very  noisy urban areas.
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            The backyards,  patios and balconies facing an urban freeway are similarly
rendered useless on a continuous basis, except when traffic is very light in the early
morning hours.  Although windows are kept closed in many dwelling units adjacent to
freeways to keep out the noise, the level inside the dwelling may still be too high for
relaxed-conversation.  An estimated 2.5 to 5 million people living near freeways are
impacted significantly  by this intrusive noise source.  Probably another 7 to  14 million
people are impacted to a lesser degree by the noise from traffic on the 96 thousand
miles of major arterial  roads in  urban communities.
            Thus,  the combination of continuous daytime noise pollution caused  by
traffic on city streets,  major arterials and freeways impairs the utility of the patios,
porches and yards outside the dwelling units of approximately 7 to 14 percent of  the
total population.  The  analysis  of Chapter 4 suggests that this situation will grow worse
by the year 2000,  unless the noise from automobiles and trucks is reduced.  However,
it could be improved by about 5 dB if noise reductions of 5 and 10 dB for automobiles
and trucks, respectively, were  accomplished by the 1985 time period.  Such a reduc-
tion  in the residual noise level  should not destroy speech privacy in suburban areas and
would improve the situation  in the higher noise level urban areas.  However, it  would
need to be supplemented by  better land use planning and design of freeways and
arterials to solve current and future noise problems.
Other Noises  Resulting in Community Reaction  and Annoyance
            Adverse community reaction may be expected when the energy equivalent
                                                        2
level of an intruding noise exceeds the residual noise level.   The degree of reaction
depends primarily on the amount of the excess,  and secondarily on additional factors
such as season, personal attitude, and characteristics of the noise.  For example, wide-
spread complaints may  generally be expected when the energy equivalent level exceeds
the residual level by approximately 17 dB,  and vigorous community action when  the
excess is approximately 33 dB.  For these two values, the approximate percentage of
the affected residents who are "very much annoyed" was found in one survey to be 37
and 87 percent,  respectively.  The impact of several forms of noise pollution, including
                                        235

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intermittent noise from multiple single events such as aircraft overflights, infrequent
diesel trucks on the highway, and the use of lawn care equipment, is often most
effectively evaluated in terms of community reaction.
        :    The most outstanding national problem which can be defined in these terms
is the impact of aircraft noise.  It is conservatively estimated that the number of .people
living in areas where aircraft noise exceeds the level required to generate widespread
complaints is 7.5 million.  This estimate assumes that all of the  people affected live in
residential urban communities.  A more realistic estimate, including the people affected
by aircraft noise who live in quiet and normal suburban communities, is 15 million.
Most of the people impacted experience noise levels which interfere with speech/ TV.
enjoyment,  and indoor and outdoor speech communication every time an aircraft passes,,
and are often awakened or disturbed during sleep.
            This has been a most difficult problem to splye because i;t, jgrew to enormous
proportions in only a few.years, with no technically or economically feasible means
available for its solution.  Partial solutions of the noise psoblems of fixed-wing aircraft
are now available.   These solutions have resulted from Federal action  to regulate noise.
and the incorporation of new noise reduction technology, which meets or. exceeds the
Federal  standards^ into.new aircraft.   However, an additional 10 dB of noise reduction^
over that achieved to date must be obtained through future technological research and
development; otherwise, the problem cannot be solved for the remainder of this century
withoutia massive alteration, in land use near airports or the development of an entire
new airport system well removed from urban areas. Realization,  of this additional noise
reduction through technical advance and Federal regulation,  together with effective
procedures for implementing  compatible land use planning should effect a solution
through the year 2000.
                                                       -,•••'                      t
            In addition to the people  impacted by aircraft noise,  there are uncounted
                                                  •  .. • •        j       •'
millions who are annoyed by sources such as:  motorcycles, minicycles and sportscars
                                                                  i
operated in a noisy manner on residential streets; dunebuggies,  chainsaws and snow-
                                >           .             .    i               i
mobiles operating in the wilderness; power lawnmowers,  edge clippers and snowblowers
                                         236

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operated by a neighbor on Sunday morning; and heavy trucks transporting freight at
night.  The single event noise exposure levels of almost every noise source category
examined in this report can be classified as noisy when the source is operated in the
urban residential environment.  The principal  exception is the automobile in its normal
operation oh a residential street,  although automobiles, particularly sportscars  and
small imported compact cars, are judged noisy when operated with unnecessarily high
acceleration.           '
            The number of people who experience intermittent Interference with speech  •
and are otherwise annoyed by one or more of these sources at various times, probably
include at least 75 percent of the population.  However,  the degree of lasting  annoyance,
and its accompanying'probable community reaction, depends critically on the number'of
times the source'operates per day, the time of day that it  operates, people's attitude
                                   2
toward the source, and other factors.   There is no simple way of quantifying the magni-
tude of the overall impact in these terms since, unlike the airport or other industrial
noise problems, there has been no centralized focal point for citizen expression.   There-
fore, perhaps the best indicator of the true community reaction is the significant incre'ase
of political  activity by citizens operating through all levels of government to attempt to
reduce the noise output of most of these sources through governmental regulation.
            If the noise reductions selected in the Option 3-example of Chapter 4 were
achieved by 1985, most of these noise sources would be expected to be judged  accept-
able when operated properly  in the appropriate land use areas. However, considerable
technical development is required to achieve this result with production hardware, and
local operational and noise regulations will be required to ensure proper operation and
restriction to appropriate land use areas.
Noise Which May  be Potentially Hazardous with Respect to Hearing Damage
            There  is a  long history of occupational  noise environments  which have
resulted in hearing impairment of various degrees for some of the working population.
For the most part,  workers are now protected from such hazard through  Federal  enforce-
ment of the provisions in the  Occupational Health and Safety Act.
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            However, there are also many occasions where people may be exposed to
potentially hazardous noise in a non-occupational, environment. The more significant
of these potential hazardous noise exposures for the sources in this report are summarized
in Table 5-1.  The equivalent 8-hour exposure level for these sources,  on any day of
use, was estimated in Chapter 4 to exceed 80 dB(A).  Although the average person who
is infrequently exposed to such noises will not necessarily suffer permanent hearing
damage,  frequent exposure to any one or several of these noises, or infrequent exposure
in combination with  industrial noise,  will increase the risk of incurring permanent
hearing impairment.
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                                  Table 5-1

          Approximate Number of People (Operators and Passengers) in
              Non-Occupational Situations Exposed to Potentially
              Hazardous Noise with Respect to Hearing Damage from
                           Various Significant Sources
Source
Snowmobiles
Chain Saws
Motorcycles
Motorboats (over 45 HP)
Light Utility Helicopters
General Aviation Aircraft
Commercial Propeller Aircraft
Internal Combustion Lawnmowers
and other Noisy Lawn Care
Equipment
Trucks (Personal Use)
Highway Buses
Subways
Noise Level in dB(A)
"Average**
108
100
95
95
94
90
88
87

85
82
80
Maximum
112
110
110
105
100
103
100
95

100
90
93
Approximate Number
of People
In Millions
1.60
2.50
3.00
8.80
0.05
.0.30
5.00
23.00

5.00
2.00
2.15
**
 Although average use of any one of these devices by itself may not produce
 permanent hearing impairment, exposure to this noise in combination, or
 together with occupational noise will increase the risk of incurring permanent
 hearing impairment.
k
 Average refers to the average noise level for devices of various manufacture
 and model type.
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Summary
            These data show that approximately 22 to 44 million people have lost part
of the utility of their dwellings and yards due to noise pollution from traffic and aircraft,
and an even larger number of people are frequently subjected to intermittent speech
interferences and annoyance from most of the sources considered in this report.   Further-
more, some of these people, and others, are exposed to potentially hazardous noise,
principally when operating or riding in  noisy devices. Although the number exposed
to potentially hazardous noise cannot be accurately assessed, since the people enumer-
ated in Table 5-1 are not additive, a total of 30 million people might  be a reasonable
estimate.
            Thus, noise pollution from these sources appears to impact at least
50 million people,  or 25 percent of the population.   Roughly one-half of this total
impact is a potential health hazard, and the remaining one-half is anlinfringement  on
the ability to converse  in the home environment.  When the number of people who have
occasional interference with speech as a result of intruding single  event noise sources
is included, the total number of people impacted probably rises to the  order of 75 per-
cent of the population.  These percentages clearly show the need for action to reduce
the number of devices which have potentially hazardous noise and are  used by the
public,  and to reduce the outdoor noises which interfere with the quality of life.
5.2         Interaction Between Public and Industry
            Much of the strength of the nation's economy, and the accompanying high
standard of living,  resulted from technical innovation and  its utilization by industry in
the development of new and better machines which fulfill people's needs.  By-and-
large, the performance criteria for these machines are defined in terms of the useful
work which they will accomplish and the value of this work with respect to its cost.
The success of any  new product is determined in the market place, primarily in terms
of the potential economic value of the product to the customer relative to its total
cost,  including both initial and operating costs.
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            In the case of acoustical devices such as musical  instruments, hi-fi sets
and speech communication equipment, sound characteristics are a primary performance
criterion.  However,  for the other devices, noise is generally an unwanted  byproduct
which is not associated with the primary performance criteria.  Only when a need for
less noise is articulated, through customer preference or public action, does noise
become one of the primary performance criteria.  The information feedback process
from the public to industry generally takes many  years and often presents a conflicting
set of needs. .For example, the purchasers of devices such as motorcycles, sportscars,
trucks and power lawnmowers often consider noise as a positive indicator of high per-
formance.  For the same reasons, the owners of many types of devices purposely operate
them in their noisiest mode or modify them by  removing their mufflers  for "added power."
In such  cases, where the consumer and public  interests diverge, industry responds to the
consumer until the offended public articulates its requirements.
            One of the best examples of the possible long term noise accommodation
among industry, public and the market place is the standard American passenger car.
In its sixty-year history, it has evolved from a noisy, sputtering, crude, low-powered
vehicle to a relatively quiet,  efficient, high-powered vehicle.  Mufflers were installed
before World War I to prevent scaring horses,  and thus win a wider acceptance in the
market place.  In the 1920's,  cities  and towns set regulations requiring that all cars be
muffled, primarily to ensure that owners retained the mufflers supplied with the vehicle
in good working order.  Without further action in the public sector, industry has made
continuous progress toward quieting the automobile interior to gain wider acceptability
in the market place, and in so doing has also attained reasonably acceptable exterior
noise levels for individual automobiles.
            Thus, although the market place provides industry with sufficient infor-
mation to act in the national interest in the primary performance and cost aspects of its
products, it does not necessarily provide such  information about secondary performance
factors such as noise'.  Consequently, unless the public articulates its requirements  for
noise,  industry has  little basis for establishing noise criteria and developing products
which meet these criteria.
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            During the last few years, various governmental bodies have begun to express
the public concern by developing and implementing noise regulations for various sources.
With the exception of aircraft noise, where the Federal Government has begun to act/
many of the remaining sources are being subjected to a series of separated, uncoordinated
and often conflicting regulations.  Actions by the public, as well as the data presented
in this report, give clear evidence of the need for noise reduction.  However, if industry
is to make an  effective response  in controlling the noise of its products, it must have
clear and consistent guidance.  Only the Federal Government can fulfill this role.
5.3         Federal Action to Reduce Source Noise
            Most of the sources discussed in this report have additional  noise reduction
potential  which can be attained  with application of today's technology. In many cases,
these potential improvements will probably be sufficient to control noise pollution in the
public interest. However,  in some cases, including aircraft engines,-tires and chain-
saws, present  technology is clearly insufficient to provide adequate noise control, and
research is necessary.  In either  case, the eventual reduction of noise pollution in the
nation requires establishment of a balanced set of noise goals which will enable priorities
to be set for systematic exploitation of existing technology and development of new
technology.
            Together with these  goals, source noise standards and the implementation of
regulations must be promulgated  to give industry a definite set of performance criteria
for all of its products which  are capable of causing noise pollution.  Such standards
should have time scales for achievement which are consistent with  industrial design,
prototype test and production cycles to encourage the most economical and effective
incorporation  of noise performance criteria into the total design of the product.
            Regulations should cover at least all the sources which were shown in this
report to be responsible for the significant noise pollution. High priority should be
given to the sources which may constitute a potential  hazard for hearing.  This includes
most of the recreational vehicles, internal combustion powered lawn care equipment
and some transportation vehicles, as presented in Table 5-1.  In addition, high priority
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should be given to all types of aircraft and large highway vehicles which are associated
with the airport and freeway noise problems, and to the other elements of city traffic,
so that the people living in major cities will eventually be able to enjoy relaxed con-
versation outdoors.  Finally, high priority should be given to the lawn care equipment
and recreational vehicles which cause unnecessary intrusion, intermittent interference
with speech, and annoyance. Without an effective noise regulatory program,  today's
noise pollution problems will grow in size and impact an ever-increasing number of
people.
5.4         Recommendations for Noise Reduction
            Specific recommendations for programs to reduce the overall noise pollution
of transportation systems and internal combustion engine devices are summarized in the
following paragraphs.  These recommendations are provided in four general  groups in
approximate descending order of priority within  each group.  The  four types of programs
and their basic objectives are:
            •   Demonstration  Programs — Provide a clearly visible (or really audible)
                demonstration of the application of existing technology to noise reduc-
                tion for a particular category.   Economic practicality shall be con-
                sidered but shall not be a firm  constraint.
            •   Research  Programs — Carry out  applied or basic research to develop new
                technology required to define the ultimate noise reduction potential
                available beyond existing technology or achieve economically practical
                methods for utilizing existing technology, where adequate.
            •   Measurement Standards Programs — Develop, in conjunction with industry
                and professional organizations, effective procedures for noise certifica-
                tion of all categories of the transportation system not currently covered
                by Federal noise standards.
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            •   Noise Certification Programs — Develop national standards for maximum
                noise levels of major transportation vehicles (similar conceptually to
                FAR Part 36) and internal combustion engine devices so that manufac-
                turers can plan product development for noise control on a uniform
                basis.  Control on usage  relative to community noise abatement should
                be retained by local state, county and city governments.
Several criteria  have been  used to establish the approximate priority for the recommended
programs.  These criteria include:
            •   Action to reduce potential hearing damage risk to passengers or non-
                commercial operators of transportation vehicles or internal combustion
                engine devices.
            •   Action to reduce the noise impacted land area near airports and major
                urban highways.
            •   Action to reduce the annoyance from noise of increasing numbers of
                vehicles or ICE devices which generate higher noise levels.
Demonstration Programs
            •   Commercial Aircraft — Continue Federal commitments to the full range
                of aircraft  noise reduction programs.  Commercial jet aircraft are and
                will  continue to be for the foreseeable future the major source of noise
                pollution in urban communities.  Reduction of this noise impact will
                require vigorous pursuit by the Federal government, in conjunction with
                aircraft engine and airframe manufacturers of the .currently planned
                demonstration programs.  These include:
                     The  "Quiet Engine" Program (NASA Lewis/General Electric)
                     Development of flightworthy nacelle retrofit packages  (FAA/Boeing)
                                       244

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     Prototype 150-passenger STOL aircraft to meet 95 EPNdB at
     500 feet (NASA  Program anticipated)
     Small engine noise reduction program  (WPAFB/AiResearch)
Establish a program to demonstrate maximum noise reduction potential
within the present state of the art for helicopters  intended for law
enforcement and other general governmental  functions.
General Aviation Aircraft — A major program should be formed at the
Federal level to demonstrate the optimum state of the art in reducing
propeller and engine  noise for general aviation aircraft. The projected
growth of the general aviation fleet over the next 20 years is sufficient
to indicate that the growth innumberand operation of urban general
aviation airports will  provide another source  of significant  noise impact
for urban populations  unless counteracting action is taken to minimize
any increase in noise  pollution  corresponding to the growth  in the gen-
eral  aviation fleet.
Demonstration of very significant noise reductions for executive jet
aircraft is now being  made by some manufacturers. Further demonstra-
tion  and implementation of this noise reduction should be fostered by
strict enforcement of  FAR Part 36 for all  new or modified aircraft
requiring a new flight certification.
Highway Vehicles — Noise levels of new passenger cars are  generally
being limited by existing or proposed limits imposed by state law.  No
specific  Federally-funded demonstration  program  is considered necessary
at this time for such vehicles.  However, tire noise presents a major
obstacle to further substantial reduction of automobile noise and
requires a separate high priority effort.
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Noise levels for new trucks are also being partially limited by state laws.
However, a demonstration program is recommended to foster industry
competition to achieve substantial additional reduction in truck noise
levels. Excluding tire noise, truck  noise can be reduced substantially
within the present state of the art.  The principal objective of this
demonstration program would be to define this state-of-the-art limit
with due consideration given to economic practicality.  The results of
the program would provide a baseline for establishing  research goals
to improve the state of the art.
Noise levels for trucks generally increase with age.  A demonstration
program is recommended to define an optimum concept for truck over-
haul which combines practical noise reduction concepts with optimum
performance objectives to extend the economic  life of the truck while
minimizing :ts noise signature.
Sufficient demonstrations have been made of potential reduction in
tire noise to indicate that an extensive research program is required
to advance the state of the art.
A program to demonstrate practical noise reduction retrofit packages
for existing utility and maintenance trucks (such as garbage trucks)
would provide a basis  for achieving  compliance with desired reduction
in annoyance  from these vehicles.
Recreation Vehicles — The motorcycle is the primary source of noise
pollution  from recreation vehicles.  A program to demonstrate "quiet
motorcycles" for both  highway and off-highway use is recommended.
This could take the form of an industry competition to achieve the maxi-
mum practical noise reduction within the present state of the art.
An educational program for the potential user should be part of this
effort to motivate the  motorcyclist to employ a quiet muffler for all
recreational uses.
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                Stringent reductions  in noise from snowmobiles are imposed by state
                laws now in existence or proposed.  It is felt that compliance with
                these regulations will effectively demonstrate noise reduction potential
                (within the current state of the art) for these vehicles.
                A related program would provide a demonstration of an acceptable
                compromise between noise reduction and performance for high-
                powered pleasure boats  used for ski-towing.
            •   Rapid Transit Vehicles — Substantial improvements have been made in
                reducing noise for several different rapid transit systems.  However,
                there is a real need to bring together into one program, a demonstra-
                tion of the  best noise reduction features of all these systems — in other
                words, demonstrate the  best noise reduction available with a rapid
                tranit system designed with noise reduction as a  principal  constraint.
            •   Internal Combustion  Engine  Devices — A demonstration program is
                recommended to achieve substantially lower noise levels for lawn
                mowers and chain saws.  This might take the form of an industry
                competition and would have the objective of defining practical  limits
                for  noise reduction within the  current state of the art, thus  leading to
                research goals for improving this state of the art.
Research Programs
            •   Commercial Aircraft — Increased research on:
                     Fan/compressor noise
                -    Core engine noise
                     Supersonic jet engine noise reduction
                     Advanced technology quiet aircraft
                     V/STOL propulsion systems.
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General  Aviation Aircraft
     Basic research on propeller noise should be pursued by propeller
     manufacturers .
     Pursue improved  concepts in engine muffler designs for reciprocat-
     ing and turboshaft propeller aircraft.
     Develop optimum lightweight methods for cabin noise treatment
     of general aviation aircraft.
     Develop "quiet" turbofan engines specifically designed for mission
     requirements of executive jet aircraft.
Highway Vehicles
     Conduct a broad  ranging research program on tire noise reduction.
     Objectives should include, but not be limited to, overcoming the
                                                         K
     current economic and safety constraints of quiet recap tires  for the
     trucking industry.
     Advanced  technology research for quieting of truck noise with
     emphasis on overall system design tradeoff problems involving intake
     noise reduction versus engine block cooling concepts, engine casing
     enclosure techniques  versus engine compartment cooling require-
     ments, exhaust noise  reduction versus exhaust pressure effects on
     engine performance.
     Basic and applied research on noise reduction potential for  new
     types of truck engines such as turboshaft drive, unique engine cycles
     (i.e., Wankel engine), or turbocharged two or four cycle diesel
     engines instead of roots-type blowers for diesels.
     Basic and applied research on quieting of transit buses.  Research
     objectives to emphasize reduction in wayside noise of engine
     intake experienced by bystanders as bus departs; and elimination
     of brake squeal.
                       248

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    Applied research program to establish improved methods for
    evaluating noise levels generated by highway vehicle traffic.
    Study should include models for evaluating residual noise levels
    as well as noise impact areas near freeways as a function of free-
    way noise reduction design features.
Recreation  Vehicles
-   Wide ranging research program directed toward development of
    lightweight muffler designs adaptable to motorcycles, minicycles,
    snowmobiles, etc.  Program should  include full exploration  of
    advanced materials and acoustics technology to achieve  optimum
    performance with design constraints for these vehicles.
         t         .     '      -  '
-   Applied research program to overcome systems problems in achiev-
       • . ' *\            ...                         -     »
    ing additional  noise reduction for gasoline-powered recreational
    vehicles. Approaches should reflect new technology or utilization
    of new techniques to reduce engine intake and engine casing noise
    on the assumption that the engine muffler program will be suffi-
    ciently successful so as to make these sources dominant.
Rail Transit Vehicles and Ships
    Conduct analysis of future noise impact from high speed above
    ground, ground surface and below ground rapid transit systems
    that may be developed over the next  15 to 25 years in major urban
    areas.  Srudy to include evaluation of probable transportation
    demands and the noise impact generated by alternate methods for
    meeting this demand.                             :
    Conduct similar study for potential  noise impact for high speed
    water transportation systems such as surface effect machines or
    hydrofoils that may be included in  significant numbers in future
    urban transportation systems.
                        249

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                     Depending on results of above programs, conduct advanced
                     research on noise reduction techniques applicable to urban rapid
                     transit systems for which a significant growth in noise impact is
                     predicted.
            •   Devices Powered by  Small Internal Combustion Engines
                     Adopt noise  reduction research results or objectives for recreation
                     vehicles to requirements for low-cost engine design constraints of
                     lawn care and yard maintenance equipment. Particular attention
                     to be paid to reducing noise of chain saws and  lawn mowers with
                     the use of advanced technology.
Measurement Standards and Noise Certification  Limits
            •   Commercial Aviation
                     Continue utilization and periodic  updating of FAR Part 36 for
                     noise certification of commercial aircraft.
                     Establish  comparable standards for STOL and VTOL aircraft.
            •   General Aviation Aircraft
                     Continue development of noise certification  limits and measure-
                     ment' techniques for all categories of general aviation aircraft.
            •   Highway Vehicles
                     Update existing industry measurement standards for highway
                     vehicles (such as the SAE method) to reflect more realistic
                     operating conditions  for the vehicle and measurement procedures
                     more readily adaptable to local agency enforcement.
                     Develop standard techniques for noise measurement of individual
                     components on trucks and cars to provide  a uniform basis for noise
                     control at the manufacturers level.  Particular  emphasis should be
                                       250

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    placed on engine intake air and cooling components as well as
    tires.  Specification of limits for these components should be the
    responsibility of manufacturers who must meet total  system noise
    limits imposed by local or Federal  government agencies.
    Develop a noise measurement procedure and outline potential
    noise certification limits for vehicles at highway speeds (50 mph
    or greater) which fairly accounts for the influence of tire noise.
Recreation Vehicles
    Develop national standards for noise measurement techniques and
    minimum noise levels for all classes of recreation vehicles with
    emphasis on motorcycles.
Devices Powered by Small Internal Combustion Engines
    Standardize, at  the national level, measurement techniques
    and noise certification limits for newly manufactured internal
    combustion engine devices such  as lawn mowers and chain saws.
    Establish minimum standards for noise certification of portable
    generators to be used for mobile homes.
                       251

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REFERENCES - 1.0  Introduction
      "Report to the President and Congress on Noise, " U.S. Environmental
      Protection Agency, December 31, 1971.
                                    252

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REFERENCES-2.0  Transportation Systems


1.    Statistical Abstract of the United States 1970,, Bureau of Census, U.S.
      Department of Commerce.

2.    1969 Statistical  Supplement to the Survey of Current Business,  Bureau of
      Census,  U.S. Department of Commerce.

3.    Auto Facts, Automobile Manufacturers Association, Inc.,  Detroit, Michigan,
      WT

4.    Air Transport  1971, Air Transport Association of America,  Washington,  D.C.

5.    70-71 Transit Fact Book, American Transit Association, Washington, D.C.

6.    Leisure Time Product  Noise, Sub Council  Report, National Industrial
      Pollution Control Council, May 1971.
                                    253

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REFERENCES-2.1  Commercial Aircraft


 1.    Statistical Abstract of the United States 1970, Bureau of Census,  U.S.
       Department of Commerce.

 2.    Air Transport 1971, The Air Transport Association of America, Washington,
       D.C., 20036.

 3.    "Aviation Week and Space Technology Forecast and Inventory Issue,"
       Aviation Week and Space Technology, March 8, 1971.

 4.    McPike, Ad., "Community Noise Levels of the DC-10 Aircraft, "  Paper
       5957, McDonnell-Douglas, Long Beach, California,  1971.

 5.    Sperry,  W.C., "Information Brief on  Estimated Maximum Noise Levels of the
       Existing Turbojet/Fan Airplanes," Report on Agenda Item 1, International
       Civil Aviation Organization Committee on Aircraft Noise (CAN), Montreal,
       Canada, September 28-October 2, 1970.

 6.    Sperry,  W.C., "Information Brief on  Boeing 747 Noise Characteristics,"
       Federal  Aviation Administration Briefing, September 23,  1970.

 7.    Bishop,  D.E. and Horonjeff, R.D., "Procedures  for Developing Noise
       Exposure Forecast Areas for Aircraft Flight Operations,"  FAA DS-67-10,
       Federal  Aviation Administration, August 1967.

 8.    Bishop,  D.Eoand  Horonjeff, R. D., "Noise Exposure Forecast Contours for
       Aircraft Noise Tradeoff Studies at Three Major Airports, "FAA-NO-07-7,
       Federal  Aviation Administration, July 1970.

 9.    Bray, D.E., "Noise Environments in Public Transportation," 81st Meeting of
       The Acoustical Society of America, Washington, D.C., April 21, 1971.

10.    Gebhardt, G.T., "Acoustical Design Features of Boeing Model 727,"
       Journal  of Aircraft,  Vol. 2, No. 4, July/August 1965.

11.    McPike, A.L., "Cabin Sound Pressure Levels During Cruise of the DC-8 with
       JT3C-6 Engines,"  Report No.  SM-23966, McDonnell-Douglas,  Long Beach,
       California, May 1960.

12.    Anon.,  "Cruise Flight Cabin Acoustics, DC-9, Nos 23 and 28,"  TM-DC9-4132,
       McDonnell-Douglas, Long Beach, California, July 1966.
                                      254

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13.    Aircraft Noise Staff, The Boeing Company, private conference, August 1971.

14.    Wyle Laboratories, (unpublished data),

15.    Higgins, T.,  Federal Aviation Administration, private telecon, August  1971.

16.    Hubbard, H.H., "The Nature of the Sonic-Boom Problem," 70th Meeting of
       The Acoustical Society of America, St.  Louis, Missouri, November 3-6,
       1965.

17.    Kryter, K.D., "Sonic Booms from Supersonic Transports,"  Science, Vol. 163,
       January 24, 1969.

18.    Wyle Laboratories Research Staff, "Community Noise,"  WR 71-17, Office of
       Noise Abatement and Control,  Environmental Protection Agency, Washington,
       D.C.,  November 1971.

19.    Supporting  Papers, DOT  TST-10-5 and NASA SP-266, Joint DOT-NASA
       Civil Aviation Research and Development Policy Study,  Department of
       Transportation and National Aeronautics and Space Administration, March
       1971.

20.    Bishop, D.E.  and Simpson,  M.A., "Noise Exposure Forecast Contours for
       1967, 1970 and 1975 Operation at Selected Airports,"  FAA-NO-70-8,
       Federal Aviation Administration, September  1970.

21.    Wyle Laboratories Research Staff, "Palmdale Intercontinental Airport Study of
       Noise Attenuation Requirements for Palmdale Schools and Residences Based on
       Noise Contours Projected for the 1985 Time Period,"  Department of Airports,
       Los Angeles, California, July 1971.

22.    "NASA Acoustically Treated Nacelle Program," NASA SP-220, National
       Aeronautics and Space Administration, September 1971.

23.    Kramer, J.J., "The NASA Quiet Engine," NASA TM-X-67884, National
       Aeronautics and Space Administration, September 1971.

24.    Pendley,  R.E.,  "The Integration of Quiet Engines with Subsonic Transport
       Aircraft," NASA CR-72548, National Aeronautics and Space Administration,
       August 1969.

25.    Copeland, W.L., et al,  "Noise Measurement Evaluations of Various Takeoff-
       Climbout Profiles of a  Four-Engine Turbojet Transport Airplane,"  NASA TN
       D-3715, National Aeronautics and Space Administration, July  1966.
                                      255

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26.    Quigley,  H.C., et al, "Flight Simulation Investigations of Method for
       Implementing Noise Abatement Landing Approaches," NASA TN D-5781,
       National Aeronautics and Space Administration, May 1970.

27.    Zalovcik, J.A.,  "NASA Research on Noise - Abatement Approach for
       Multiengine Jet Transport Aircraft," NASA TN D-4044, National Aero-
       nautics and Space Administration, April 1967.

28.    Russell, R.E. and Kester, J.D.,  "Aircraft Noise.  Its Source and Reduction,"
       Society of Automotive Engineers — Department of Transportation Conference
       on Aircraft and the  Environment, Washington, D.C., February 8-10, 1971.

29.    FAA Request for Proposal WASS-1 (DC), Federal Aviation Administration,
       1970.

30.    Acoustics  Research Staff, National Aeronautics and Space Administration,
       Lewis Research  Center, private conference,  August 1971.

31.    Yaffee, M.L.,  "NASA Building STOL Transports," Aviation Week and Space
       Technology, September 13, 1971.

32.    Aerodynamics Staff,  National Aeronautics and Space Administration, Ames
       Research Center, private conference, August 1971.

33.    Aviation Forecasts,  Fiscal Years  1970- 1981, Federal Aviation Administration,
       January 1970.

34.    Report of the Department of Transportation Air Traffic Control Advisory
       Committee,  Department of Transportation, Washington, D.C., December 1969.
                                     256

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REFERENCES -2.2  V/STOL Aviation
 1.    Jagger, D.H. and Kemp, E.D.G., "The Potential and Development of V/STOL
       Intercity Airlines, " Aircraft Engineering, Vol. 42, No. 1, 1970.
                                                                     t
 2.    "Study of Aircraft in Short Haul Transportation Systems, " NASA  CR-986,
       National Aeronautics and Space Administration, 1968.

 3.    Metygar, F.B. and Foley, W.M., "STOL Aircraft Noise Certification - A
       Rational Approach, " SAE No. 700325, Society of Automotive Engineers,
       April  1970.

 4.    Snodgrass, I.C., "Position Paper on STOL Noise Rules, " Aerospace Industries
       Association of America, Washington,  D.D., May 27, 1970.

 5.    Directory of Helicopter Operations in the United States and Canada 1971,
       Aerospace Industries Association of America, Washington, D.C.

 6.    "Aviation Week and Space Technology Forecast and Inventory Issue, "
       Aviation Week and Space Technology, March 8, 1971.

 7.    Statistical Abstract of the United States 1970,  Bureau of Census,  U.S.
       Department of Commerce"

 8.    Air Transport 1971,  The Air Transport Association  of America, Washington,
       D.C., 20036.

 9.    Supporting Papers,  DOT TST-10-5 and NASA SP-266, Joint DOT-NASA Civil
       Aviation Research and Development Policy Study, Department of Transportation
       and National Aeronautics and Space Administration, March 1971.

10.    Bell Helicopter Company, private correspondence, August 1971.

11.    Hamilton Standard Division,  United Aircraft Corporation,  private correspond-
       ence, August 1971.

12.    Sikorsky Aircraft, United Aircraft Corporation, private correspondence,
       August 1971.

13.    The Boeing Company,  Vertol Division, private correspondence, August 1971.
                                     257

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14.    Wyle Laboratories  (unpublished data).

15.    Yaffee, M.L., "NASA Building STOL Transports, " Aviation Week and
       Space Technology/ September 137 1971.

16.    Rosen, G., "Prop-Fan —A High Thrust, Low Noise Propulsor, " Society of
       Automotive Engineers, National Air Transportation  Meeting, Atlanta, Georgia,
       May 10-13, 1971.

17.    Jane's All  The World's Aircraft  1970.

18.    Holmes, D.R. and  Cox, C.R., "Noise Reduction Possibilities fora  Light
       Helicopter, " Society of Automotive Engineers National Aeronautic  and Space
       Engineering and Manufacturing Meeting, Los Angeles, California, October
       6-10, 1969.

19.    "Flying Neighborly- Hot to Operate the Light  Helicopter More Quietly, "
       Bell  Helicopter Company, Fort Worth, Texas.

20.    Duke, F.H. and Hooper, W.E.,  "The Boeing Model 347 Advanced  Technology
       Helicopter Program, " 27th Annual National V/STOL Forum of the American
       Helicopter Society, Washington, D.C., May 1971.
                                    258

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REFERENCES -2.3   General Aviation Aircraft
 1.    Statistical Abstract of the United States 1970, Bureau of Census,  U.S.
       Department of Commerce.

 2.    Air Transport 1971, The Air Transport Association of America, Washington,
       D.C., 20036.

 3.    General Aviation Manufacturers Association of America, Washington, D.C.,
       private telecon, August 1971.

 4,    Adcock,  B.D. and Ollerhead,  J.B., "Effective  Perceived Noise Level
       Evaluated for STOL and Other Aircraft Sounds, " FAA-NO-70-5, Federal
       Aviation  Administration, May 1970.

 5.    Tobias, J.V., "Noise in Light Twin-Engine Aircraft, " Sound and Vibration,
       September 1969.

 6.    Tobias, J.V., "Cockpit Noise Intensity;  Fifteen Single Engine Light Aircraft, "
       FAA AM  68-21, Federal Aviation Administration, September 1968.

 7.    Tobias, J.V., "Cockpit Noise Intensity:  Eleven Twin-Engine Light Aircraft, "
       FAA AM-68-25, Federal Aviation Administration, October 1968.

 8.    The Magnitude and Economic Impact of General Aviation, 1968-1980, Speas
       Association, Aero Publications, Manhasset, New York,  1970.

 9.    Piper Aircraft Corporation,  private conference, August 1971.

10.    Acoustics Group, AiResearch Manufacturing Company, Phoenix, Arizona,
       (unpublished data).

11.    Woolsey, J.P.,  "Operators, FAA Seek Jet Noise Solution, " Aviation Week
       and Space Technology, September 20,  1971.
                                    259

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REFERENCES -2.4 Highway Vehicles
 1.    Auto Facts, Automobile Manufacturers Association,  Inc., Detroit, Michigan,
       T97T

 2.     "Automotive News,  1971 Almanac, " Automotive News, Detroit, Michigan,
       April 1971.

 3.    American Trucking Trends 1970-71, Departments of Research and Transport
       Economics and  Public Relations, American Trucking  Association, Inc.
       Washington, D.C.                                                    ,

 4.    '70 - '71  Transit Fact Book, American Transit Association, Washington, D.C.

 5.    Cities of Los Angeles,  Long Beach, Torrance and Culver City, California,
       private  telecons, September 1971.

 6.    "Statistical  Study of Traffic Noise, " National Research Council of Canada,
       Division of  Physics,  Ottawa, Canada, 1970.

 7.    "Passenger Car Noise Survey, " California Highway  Patrol, January 1970.

 8.    Little, R.A., California Highway Patrol, private correspondence, August 1971.

 9.    Wyle Laboratories "Traffic  Noise" (unpublished data).

10.    Galloway, W.J., Clark, W.E. and Kerrick, U.S.., "Highway Noise:  Measure-
       ment Simulation and Mixed Reactions, "  NCHRP Report 78, Highway Research
       Board, National Academy of Sciences,  1969.

11.    RoK. Hillquist, Standards Engineer, General  Motors Company, private
       conference, September 1971.                  <

12.    Leasure, W.A., Jr.,  "Truck Tire Noise — Results of a  Field Measurement
       Program, " Purdue Noise Control Conference, Purdue University, July 14-16,
       1971.

13.    Tetlow, D., "Truck  Tire Noise, " Sound and Vibration, August 1971.

T4.    Leasure, W.A., Jr., et al, "Interim Progress Report of Research Activity —
       Truck Tire Noise Investigation,"  NBS Report  10567, National  Bureau of
       Standards, April 1971.
                                      260

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15.    Wyle Laboratories, "Truck Noise" (unpublished data).

16.    Austen, A.E. and  Priede,  T., "Origins of Diesel Engine Noise," Proceedings
       of the Symposium on Engine Noise and Noise Suppression, London, England,
       October 24, 1958, The Institute of Mechanical Engineers, London,  England.

17.    Dickerson, D.O. (Editor),  "Transportation Noise Pollution:  Control and
       Abatement, " NASA Contract NGT 47-003-028, National Aeronautics and
       Space Administration, Langley Research Center and Old  Dominion University,
       Summer 1970.

18.    Soroka, W.W. and Chien,  C.F., "Automotive Piston-Engine Noise and Its
       Reduction -A  Literature Survey, " SAE No. 690452, Society of Automotive
       Engineers  Midyear Meeting, Chicago, Illinois, May 19-23,  1969.

19.    Wyle Laboratories,"Truck Tire Noise" (unpublished data).

20.    "The Noise Trucks Make, " American Trucking Association, Inc., Washington,
       D.C., September  1964.

21.    "Noise  Measurements of Motorcycles and  Trucks, " Automobile Manufacturers
       Association, Inc., Detroit, Michigan, June 1971.

22.    Engineering Representatives, Stempco Manufacturing Co., Longview, Texas,
       private  conference, August 1971.

23.    "Sources of Truck Noise, "Acoustic Technical Bulletin No. 20,  Donaldson
       Company,  Inc., Minneapolis, Minnesota, December 1970.

24.    Engineering Representatives, Ford Motor Company, private correspondence,
       August  1971.

25.    "Submission of Caterpillar Tractor Company, " Regional Hearing on Transportation
       Noise (Highway),  Chicago,  Illinois, Office of Noise Abatement and Control,
       Environmental  Protection Agency, Washington, D.C., July 28,  1971.

26.    Millard, R.S.  (Editor), "A Review of Road Traffic  Noise - The Working  Group
       on Research into Road  Traffic Noise, " LR  357, Road Research Laboratory,
       Crowthorne, England, 1970.

27.    "Donaldson SBM Intake Silencer— Product Technical Information, " Donaldson
       Company,  Inc., Minneapolis, Minnesota, July 1968.
                                    261

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28.    Hempel, R.E., "Does Turbocharging Increase Diesel Engine Noise? —
       Observations on the Generation,  Emission and Reduction of Diesel Engine
       Noise," SAE No.  680406, Society of Automotive Engineers Midyear Meeting,
       Detroit, Michigan, May 1968.

29.    Priede, T., "Noise of Internal Combustion Engines," Paper C-2,  National
       Physical Laboratory Symposium No. 12, England, July 1961.

30.    Mr. S.A. Lippmann, Uniroyal Tire Company, Detroit, Michigan,  private
       conference, July 1971.

31.    Engineering Representatives,  Firestone Tire and Rubber Company, Akron,
       Ohio, private conference, July 1971.

32.    Hayden, R. E., "Roadside Noise for the Interaction of a Rolling Tire with the
       Road Surface," Purdue Noise Control Conference, Purdue University/
       July  14-16, 1971.

33.    "Submission of General  Motors Company,"  Regional Hearing on Transportation
       Noise (Highway),  Chicago, Illinois, Office of Noise Abatement and Control,
       Environmental Protection Agency, Washington, D.C., July 28,  1971.

34.    Engineering Representatives, Automotive  Division,. Anv.in Industries, Columbus,
       Indiana, private conference,  July 1971.

35.    Groening, J.A.,  "Characteristics and Control of .Gar/ Truckand Bus Noise,"
       Purdue Noise Control  Conference, Purdue University, July 14-16, 1971.

36.    Wiener, P.M., "Experimental Study of the Airborne Noise Generated by
       Passenger Automobiles," Noise Control, July/August 1960.

37.    Wyle Laboratories, "Bus Noise" (unpublished data).         .

38.    Wyle Laboratories, "Garbage Compactor Noise" (unpublished data).

39.    "Study on the Effect of  Noise Pollution, Section  on Community Noise,"
       Office of Noise Abatement and Control,  Environmental  Protection Agency,
       Washington,  D.C., October  1971.

40.    Wyle Laboratories, "Automobile Interior Noise Levels" (unpublished data).

41.    Solomon, L. and Underwood, J.,  "Interior Automotive Noise Measurements
       Under Various Operating Conditions," Journal of the Acoustical Society of
       America, Vol.  49, 1971.
                                      262

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42.    "More on Interior Car Noise," Noise Measurement, The General Radio
       Company, Spring 1971.
    f  : .-.  •         '        -                            .
43.    Ford, R.D., Hughes, G.M. and Sanders,  D.J., "The Measurement of Noise
       Inside Cars," Applied Acoustics, January  1970.
      i>-.         -     :    :'.                   •:  •
44.    Engineering  Representatives,  International Harvester Company, private
       conference,  August 1971.

45.    Rowley, D., Manager,  Acoustics Section, Donaldson Company, Inc.,
       Minneapolis, Minnesota, private telecon, August 1971.

46.    "Comments on Traffic Noise Reduction,"  Society of Automotive Engineers
       Vehicle Sound Level Committee, Detroit,  Michigan,  September 1971.

47.    Priede, T.,  Stockman,  E.S., Bonora, A., and Zimmerman, K., "Cut
       Engine Noise Three Ways," Journal of the Society of Automotive Engineers,
       April  1970.
      '•..'»'"•        •      '
48.    Magazine Advertisement, Time, Ford Motor Company, July 1971.

49.    "Sound Levels for Passenger Cars and Light Trucks," SAE J986a, Society
       of Automotive Engineers Standard.

50.    Starkman, E.S., Vice President, Environmental Activities  Staff, General
       Motors Company, private correspondence, August 1971.

51.    "A Proposal  to Reduce Exhaust Emissions and Decrease Vehicle Noise from
       Existing Diesel Coaches," Truck and Coach Division, General Motors Company,
       December 1970.

52.    Kelly, K., "CMC Offers Quiet Refuse Truck," Automotive News,
       February 22, 1971.
                                     263

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REFERENCES-2.5  Rails/stems
 1.    Yearbook of Railroad Facts, Association of American Railroads, Chicago,
       Illinois,  1971.

 2.    Statistical Abstract of the United States 1970, Bureau of Census,
       U.S.  Department of Commerce

 3.    70-71 Transit Fact Book, American Transit Association, Washington, D.C.

 4.    Embleton, T.F.W. and Thiessen, G.J., "Train Noises and Use of Adjacent
       Land," Sound:  Its Uses and Control, January/February 1962.

 5.    Locomotive Engineering Department, General Electric Company,  private
       conference, July 1971.

 6.    "The Visibility  and Audibility of Trains Approaching Rail-Highway Grade
       Crossings,"  FRA-RP-71-1, Federal  Railroad Administration, May 197.1,

 7.    Bray, D.C.,  "Noise Environments in Public Transportation," Joint American
       Society of Civil Engineers - American Society of Mechanical Engineers
       Transportation Engineering Meeting, Seattle, Washington,  1971.

 8.    Advanced Technology Industrial Systems Group, Rohr Corporation, private
       conference, August 1971.

 9.    St. Louis Car Division, General Steel Industries, private conference, July
       1971.

10.    Kendall, H.C., "Noise Studies in Retarder Yards," Railway Systems
       Control/Vol. 2, No. 7,  1971.

11.    Blazier, W.E.,\Jr., et al, "Chicago Urban Noise Study,  Phase I, Noise in
       the Urban Environment,"  The City of Chicago Department of Environmental
       Control,  Chicago, Illinois, November  1970.
                                    i
12,    "Acoustic Studies,"  Technical Report No. 8, San Francisco Bay Area Rapid
       Transit District, San Francisco, California,  June 1968.

13.    Wilson, G.P.,  "Noise and Vibration Characteristics of High Speed Transit
       Vehicles," Office of Noise Abatement ancj Control, Environmental Protection
       Agency,  Washington, D.C., June 1971.
                                         264

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14.    Wilson, G.P.,  "Environmental Features and Advantages of Rapid Transit
       Systems," Institute of Electrical and Electronic Engineers,  Region Six
       Conference, May 1971.

15.    Kirschner, F.,  "Control of Railroad  Wheel Screech Noise," 6th International
       Congress on Acoustics,  Tokyo, Japan,  August 1968.

16.    Research Center, B.F.  Goodrich Company, private correspondence, August
       1971.

17.    Bender, E.K. and Hirtle, P.W.,  "The Acoustic Treatment of Stations to
       Alleviate Wheel-Squeal Noise," Prepared under Contract No. CS-009 for
       Massachusetts Bay Transit Authority, Boston,  Massachusetts, October 1970.

18.    Kramer, M.  and Richards, A., "Data on New York City  Subway Noise,"
       (unpublished data), Sunset Park Family Health Center, Brooklyn, New York.

19.    Botsford, J.H., "Damage Risk," Transportation Noises -r A symposium on
       Acceptability Criteria, Chalupnik, J.D.  (Editor), University of Washington
       Press, 1970.
        1  i                                                 •
20.    Northwood,  T. D., "Rail Vehicle Noise>" Research Paper  No. 155, Division
       of Building Research, National Research  Council,  Ottawa, Canada, 1963.

21.    Harris, C.M. and Aitken, B.H., "Noise in Subway, Cars, " Sound'and
       Vibration, February 1971.

22.    Davis, E.W., et'al,  "Comparison of Noise and Vibration Levels  in Rapid
       Transit Vehicle  Systems,"  National  Capitol Transportation Agency,   <
       Washington, D.C., April 1964.

23.    Bender, E.K., et al, "Noise Generated  by Subways above Ground and in
       Stations," Report No.  OST-ONA-70-1, Office of Noise Abatement and
       Control, Environmental  Protection Agency, Washington, D.C., January 1970.

24.    "Aerial  Structure and Rail Support Methods,". Technical  .Report No. 11,
       San Francisco Bay Area Rapid  Transit District, San Francisco, California, 1968.

25.    Bonvallet, G.L., "Levels and Spectra  of Transportation Vehicle  Noise,"
       Journal  of the Acoustical Society of America, Vol. 22, No. 2, 1950.

26.    Wyle Laboratories (unpublished data).
                                    265

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27.    Engineering Department, Chicago Transit Authority, private conference,
       July 1971.

28.    Franken, P. A,, et al, "Chicago Urban Noise Study, Phases III and IV,
       Noise Control Technology, Federal Aid for Noise Abatement, Noise Control
       Program Recommendations," The City of Chicago Department of Environ-
       mental Control, Chicago, Illinois, November 1970.

29.    New York Transit Authority, private correspondence, August 1971.

30.    Land Systems, Sikorsky Aircraft, private correspondence, August 1971.
                                    266

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REFERENCES-2.6  Ships
 1.    Statistical Abstract of the United States 1970,  Bureau of Census, U.S.
       Department of Commerce.

 2.    Air Transport  1971, The Air Transport Association of America, Washington, D.C.,
       20036.

 3.    Shearer,  K.,  "Ambient Sound Measurements on Two Passenger Ships and an Oil
       Tanker, " Report No. 424, British Shipbuilding Research Association,  1962.

 4.    Conn,  R.,  "Noise Levels in the Engine Room and Bridge of Merchant  Ships,"
       Report  No. NS  121,  British Ship Research Association, 1966.

 5.    Hagan, R., and Babcock,  G., 'Shipboard Vibration Problems and Their
       Solutions," Noise Control, p. 36, July 1959.

 6.    Hagan, A.f and Hammer,  N., "Shipboard Noise and Vibration From  a
       Habitobility Viewpoint, " Marine Technology,  January 1969.
                                    267

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REFERENCES -2.7 Recreation Vehicles,
 1.     Leisure Time FVoduct Noise/ Sub Council Report,  National •Industrial
        Pollution Control Council, May 1971.

 2.     Dickerson, D.O. (Editor), "Transportation Noise  Pollution: Control and
        Abatement," NASA Contract NGT 47-003-028, National Aeronautics
        and Space Administration,  Langley Research Center,  and Old Dominion •
        University,  Summer, 1970.

 3.     "A Continuing Market Analysis of Snowmobile. Owners,"  Snow Goer, .1971
                           »                        i          ''•",•••
 4.     Boating 1970, Marketing Department of the Boating Industry Association,
        The Outboard Boating Club of America and the National Association of
        Engine and Boat'Manufacturers.             .                     -7>

 5.     "Snowmobile Noise, Its Sources, Hazards and  Control, " APS-477,
        Division of Physics, National  Research Council of Canada,  Ottawa,
        Canada, 1970.
                           i            .        •          _•')>•
 6.     Harrison, R.,  Acoustical Engineer,  U. S.  Department of Agriculture,
        Testimony before the California Assembly Committee  on Natural Resources
        and Conservation, April 2, 1971.                      .:
         •  •          t          •    .  •   ,           •.'•-•••..'• ,£r1 .
 7.     "Resolution to Control Noise," Motorcycle Industry Council,  Inc.,
        April  14, 1971.

 8.     Campbell, R.A., "A Survey of Passby Noise from Boqts," Sound and
        Vibration, September 1969.        .

 9.     Lincoln, R.H., Manager, (Environmental Engineering, Outboard Marine
        Corporation, Milwaukee,  Wisconsin.  Private  correspondence,    ,     i
        August 23,  1971.
                     ; j,       '
 10.     Tests conducted by the State of California, Resources Agency,  Department
        of Parks and Recreation, Millerton Lake State  Recreation Area,
       W.J.  Reinhardt,, Area Manager, May 19,  1971 and July 21, 1971.
           . •  ,            .   '        '      '     -i          -.•'.',
 11.     Campbell, R. A., "Noise  Levels During an Outboard  Boat Race, "
        Veterans Administration Hospital,  Miami,  Florida, July 1970.

 12.     Engineering  Representatives, Birmingham Small Arms  Corporation.
        Private correspondence, August 27,  1971.
                                       268

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13.    Wyle  Laboratories, "Motorcycle Operator Noise Levels" (unpublished data).

14.    Rowley, D.,  Manager, Acoustics Section, Donaldson Company,  Inc.,
       Minneapolis,  Minnesota.  Private telecon, August 1971.

15.    "Power of Silence", Cycle News, Western Edition, Vol.  VIII, No. 43,
       November 10, 1970.

16.    Engineering Representatives, Harley Davidson Motor Co., Inc.,
       Milwaukee, Wisconsin.  Private conference, September 1971.

17.    Hoene, J.V., "Snowmobiles and Noise", International Snowmobile •
       Industry Association, Minneapolis,  Minnesota, 1970.
           t  .                              !        '   •
18.    Nesbitt, John F.,  Engineering Director, International Snowmobile  '
       Industry Association.  Private correspondence, August 1971.

19.    Foster, L.W., "Snowmobile — Safety and Ecology",  Twin Cities Section,
       Society of Automotive Engineers, Minneapolis, Minnesota', May 1971.
                                                                     i  .
20.    Wyle  Laboratories  "Dune Buggy Noise Levels" (unpublished data).

21.    Harrison, R., "Study of Sound Propagation and Annoyance under Forest-
       Conditions",  Project Record ED and T 1768, U.S.  Department of Agri-
       culture, Forest Service, Equipment  Development Center,  December 1970.

22.    Wyle  Laboratories, "Motorcycle Noise" (unpublished data).

23.    Campbell, R.A., "A Survey of Noise Levels On Board Pleasure Boats",
       Veterans Administration Hospital, Miami, Florida, 1970.

24.    "Mufflers and Exhaust Systems (for Snowmobiles)", Bulletin 1200-154,
       Donaldson Company, Inc., Minneapolis,-Minnesota,  March 1971.     (

25.    Conover, W.C.,  "Noise Control of Outboard Motors", Noise Control,
       March 1955..                                                  ~~

26.    Kueny,  D.F., and Boerma, M.J.,  "A Modern Outboard  Design — Johnson
       and Evinrude  50  HP", SAE No. 710580,  Society of Automotive  Engineers
       Midyear Meeting,  Montreal,  Canada, June 1971 .
                                   269

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27.   Engineering Representatives,  Outboard Marine Corporation, Milwaukee,
      Wisconsin.  Private conference, August 1971.

28.   Handle/,  W.C., "Noise Level Studies of Motorcycles in Bermuda",
      Noise Control, July 1959.

29.   "Motorcycle Noise Test Procedure Evaluation", California Highway
      Patrol, January  1971.

30.   Little, R.A.,  California Highway Patrol.  Private conference, September 1971

31.   Snowmobile Safety, Laws Section Conservation 55 — Mufflers, State of
      Minnesota,  1969-1970.

32.   Hiraboyashi, T., "Noise and the Snowmobile, " Purdue Noise Control
      Conference, Purdue University, July 1971.                          ..
                                     270

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/'REFERENCES — 3.0  Devices Powered by Small Internal Combustion Engines


  1.    Industrial Report/  Bureau of Census, U.S. Department of Commerce,  1963-1969.

  2.    Moody's Industrials, 1971.

  3.    Kohler  Company,  Kohler, Wisconsin and Onan Corporation, Minneapolis,
        Minnesota.  Private conference, August 1971.

  4.    Wyle Laboratories (unpublished data).

  5.    Nelson Muffler Corporation, Stoughton, Wisconsin, private conference,  ;
        August  1971.

  6.    McCulloch Corporation, Los Angeles,  California,  private conference, July 1971

  7.    Leisure Time Product Noise, Sub Council Report, National Industrial Pollution
        Control Council, May 1971.

  8.    Outboard Marine Company, Milwaukee, Wisconsin, private conference,
        August  1971.

  9.    Rettinger, M., "Noise Level Reductions of Barriers. l! Noise Control,
        September 1957.

 10.    Noise Ordinance, City of Chicago, Illinois.

 11. •   Noise Ordinance, City of Minneapolis,  Minnesota.

 12.    Noise Ordinance, City of Costa Mesa, California.
                                        271

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REFERENCES —4.0  Environmental Impact for Transportation Vehicles and
                   Small Internal Combustion  Engines
 1,    Statistical Abstract of the United States 1970, Bureau of Census, U.S.
       Department of Commerce.  '.                                     -{
                                                                      i
 2.    "Study on the Effect of Noise Pollution, Section on Community Noise,"
       Office of Noise Abatement and Control, Environmental Protection Agency,.
       Washington,  D.C., October 1971.

 3.    Mills,  C.H.G. and Robinson,  D.W., "The Subjective Rating of Motor
       Vehicle Noise,"  The Engineer, pp.  1070-1075, June 30,  1961.

 4.    vonGierke,  Dr. H.E., Director, Biodynamics Bionics Division, 6,570th
       Aerospace Medical Research Laboratory, Wright Patterson Air Force Base,
       private conference, September  1971.

 5.    George,  R.W., et al,  "Jet Aircraft, A Growing Pollution  Source,"
       Journal of the Air Pollution Control Association, pp.  847-855,
       November 19, 1969.

 6.    Miller, J.D., "The Effects of Noise on the Quality of Human  Life,"
       Central Institute for the Deaf,  1971.

 7.    Webster, J., "SIL—Past, Present, and Future,"  Sound and Vibration,
       pp. 22-26, August 1969.
                                     272

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REFERENCES- 5.0 Conclusions and Recommendations
1.    Miller, J., "Effects of Noise on People, " Central Institute for the Deaf,
      to be published by the Environmental Protection Agency, Washington, D.C.,
      November 1971.

2.    Wyle Laboratories Research Staff, "Community Noise, " WR 71-17, Office of
      Noise Abatement and Control, Environmental Protection Agency, Washington,
      D.C., November 1971.
                                    273

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     NOISE FROM TRANSPORTATION
    SYSTEMS, RECREATION VEHICLES
    AND DEVICES POWERED BY SMALL
    INTERNAL COMBUSTION ENGINES
             APPENDICES


A    MEASUREMENT STANDARDS
B    METHODOLOGY FOR IMPACT ANALYSIS

C    NOISE GENERATOR CHARACTERISTICS

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                                 APPENDIX  A
                          MEASUREMENT STANDARDS

            In this appendix, several typical measurement standards relevant to the
categories of Transportation Systems and Devices Powered by Internal Combustion
Engines are summarized. The purpose of this discussion is to provide insight into the
procedures used to obtain the standard levels contained in the body of this report.
However, it is not all-inclusive since an analysis of every standard applicable to
these categories is beyond the scope  of this appendix.
            The purpose of a noise measurement standard is to establish a practical
formal procedure for determining the noise output of a device under realistic and
repeatable operating conditions.
            In some  instances,  measurement standards may be created  by civil  agen-
cies whereby they are set forth  as a basis for verifying that the noise output of a
device falls within specified legal limits.  The  FAR-36 specification for certification
of jet aircraft contains such a measurement standard.  The new-vehicle noise
measurement procedure  utilized by the California Highway Patrol is another example.
            Voluntary measurement standards may also be created by manufacturers'
associations, professional societies, or other member bodies of the American National
Standards Institute. In these instances, the purpose  of the standard is to establish a
common measurement basis  which may be utilized by manufacturers and users through-
out the nation.  It also  serves as a guide to groups with a peripheral involvement in
the product,  such as subcontractors and distributors, as to the basis for measurement
on the completed system.  This  type of standard is typified by the SAE standards for
measuremenfs on commercial vehicles, automobiles, and other types of internal com-
bustion engine powered equipment.  These voluntary measurement standards may
frequently be incorporated  into government regulations and ordinances which specify
maximum noise levels for various devices. An example is SAE Standard J192 for
snowmobiles, which  is utilized  by a number  of states as the basis for legislation of
                                      A-1

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maximum snowmobile noise.  Although  a number of the voluntary measurement
standards have gained fairly wide acceptance in industry and government, they
generally have not been developed for regulatory use.  Therefore, the quantities
measured and  the operating procedures utilized may not be appropriate for regu-
lation of noise at the source.
            For example, the State of California adopted SAE Standard J986a as
a noise  test compliance method for automobiles.  This approach has been criticized
because it  penalizes certain vehicles by rating them in a maximum noise-producing
mode which, in a  large percentage of cases, does not typify normal operation. As
a result, luxury American automobiles with 400 to 500 cubic inch displacement
engines have difficulty  passing the full-throttle acceleration noise test, w.hereas
small imports and sports cars have  little difficulty.  Yet in use, the luxury vehicle
is generally considered  acceptably quiet, whereas the smaller car often is not so
judged.  This  inequity results  from the fact that the luxury automobile normally
operates at only a fraction of  its potential power, whereas the small  low~powered
vehicle normally operates near maximum power.  This situation exemplifies the
case of  a standard, designed to serve as a common measurement basis, being
incorrectly applied to noise regulation.
            The principal noise source categories analyzed in this report are
summarized in Table A-l,  with a listing of the major measurement standards which
apply to these categories.  As can be observed, a number of these categories are
not covered by any specific measurement or regulatory standards.
            Following Table A-l are brief descriptions of the test methods incor-
porated in  the standards and the recommended noise levels produced under these
operating conditions.  In addition, because of its significance as the first noise
standard promulgated by the Federal Government, the FAR Part 36 Noise Standard
for Aircraft Type Certification is presented in its entirety at the conclusion of this
appendix.  This certification standard demonstrates the detail and complexity
required in some standards, and appropriate sections of it may serve as a model
for future standards.
                                       A-2

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                                  Table A-1
                Summary of Major Noise Measurement Standards
Category
General Aviation
Aircraft
i '.
V/STOL:
Business Jets
Subsonic Commercial
Aircraft
Trains
Passenger Cars and
Light Trucks
GVW < 6000 pounds
Trucks and Buses
GVW > 6000 pounds
Motorcylces
Snowmobiles
Pleasure Boats
Other Devices
Powered by I/C
Engines, Lawn
Mowers, etc.
Applicable Noise Measurement Standard — Observer
None
X

X



X







X




FAR1
Part
36



X
X














ISO2
R362







X


X

X






CHP3
Article
10







X


X

X






SAE4
J331
Proposed












X






SAE
J366










X








SAE
J986a







X











SAE
J192













X





SAE
J952b















X



'Federal Aviation Regulation.
"International Organization for Standardization,
 California Highway  Patrol.
 Society of Automotive Engineers.
                                      A-3

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Title:

Originator:
Noise Source:
Purpose:
Measurement
Location:
Procedure:
Maximum
Noise Ljmits:
FAR 36 -  NOISE STANDARDS: AIRCRAFT TYPE CERTIFICATION
Issued  Novembers, 1969, last revision November 24, 1969    .:
Federal Aviation Agency
Subsonic Transport and Turbojet Powered Aircraft
FAR-36 is an FAA procedure for flight certification of all subsonic
transport and turbojet aircraft.  It establishes maximum allowable
noise  levels for new aircraft and a standardized procedure for
their measurement.
Landing — 1 nautical mile from threshold, directly under the
aircraft path,
Takeoff- 3.5 nautical miles from brake release, directly
under the  aircraft path, and
Sideline - at the location of maximum noise along a line parallel
to and at a distance of 0.35 nautical miles from the runway center-
line, for,aircraft which have four or more engines; and 0.25 nau-
tical miles from the runway centerline, for aircraft which have
three or fewer engines.
Appropriate measurement instrumentation is set up at the specified
locations.  A series of takeoffs and landings are made by the air-
craft to be certified,  in accordance with prescribed engine power
and flight profiles. This procedure is performed with the aircraft
operating  at maximum gross takeoff weight.  Noise data taken
during this procedure  is subsequently analyzed  for compliance
with the specified limits.
The noise  limits of this regulation are set forth  in terms of Effective
Perceived Noise Levels and gross takeoff weight.  For landing and
sideline, these levels range from 102 EPNdB to 108 EPNdB.  For
takeoff, the  levels range from 93  EPNdB to  108 EPNdB.
                                      A-4

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Other
Requirements:
Additional specifications are set forth relating to the measurement;
instrumentation, weather conditions, flight profiles, test aircraft
operating conditions, and the appropriate technique for calcula-
ting EPNdB.
Title:
       ;' M
         e  '
Originator:

Noise Source:

Purpose:
Measurement
Location:
Procedure:
ISO RECOMMENDATION R362 - MEASUREMENT OF NOISE
EMITTED  BY VEHICLES - First  Edition, February, 1964.
International Organization for Standardization
Motor  Vehicles
Establishes a procedure for measurement of the maximum exterior
noise level  for motor vehicles,  consistent with normal driving
conditions,  and is capable of giving easily repeatable results.
Should consist  of an  extensive flat  open space of some 50  meters
radius, of which the  central  20 meters  would consist of concrete
or asphalt paving =
j^
Locate microphone  7.5 meters from  the centerline of the vehicle
path.  Approach microphone  in  low gear  range (generally second
gear) at  50 kph, or 3/4  maximum  rated engine rpm, or 3/4  maxi-
mum engine speed permitted by governor,  whichever is lowest.
At  a point  10  meters ahead of  microphone, accelerate fully  and
hold at full throttle until the vehicle  is 10 meters beyond  the
microphone.
Recommended
Maximum  Level:
No recommendations  made.

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Title:

Originator:
Noise Source:
Purpose:
Measurement
Location:

Procedure:
SAE J192 - EXTERIOR SOUND  LEVEL  FOR SNOWMOBILES
Approved September 1970.
Society of Automotive Engineers
New Snowmobiles
Provides a procedure for measurement of maximum exterior sound
level for snowmobiles.
Test site to be flat open space, free of large reflecting objects
within  100 feet of either the vehicle or the microphone.
Locate microphone 50 feet from the centerline of the vehicle path,
Vehicle operated on grass (3-inch height).  Accelerate fully from
standing start such that maximum  rated  engine rpm is achieved
25 feet ahead of the microphone.  Hold this maximum rpm until
50 feet beyond microphone.
Recommended
Maximum  Level:  82 +2 dB(A) at 50 feet.
Title!

Originator:
Noise Source:
Purpose:,
Measurement
Location:

Procedure:
SAE J331 - PROPOSED - SOUND  LEVELS FOR MOTORCYCLES
Draft No. 5, April 30, 1971
Society of Automotive Engineers
Motorcycles
Establishes a procedure for determining maximum sound levels
for all classes of motorcycles.
Test site shall be a flat open space, free of large reflecting objects
within 100 feet of either the vehicle or the microphone.
Locate microphone 50 feet from the centerline of the vehicle
path.  Motorcycle  usually operated in  low gear. Approach
                                      A-6

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Recommended
Maximum Level:
microphone at 2/3 maximum rated engine rpm. At a point of at
least 25 feet ahead of microphone, accelerate fully to achieve
maximum rate engine rpm at a point between 15 and 25 feet past
the microphone.
Recommended dB(A)* for motorcycles manufactured after
January 1, 1972:
                                              1972
    Engine Displacement
      170 cc and less
      171 cc - 300 cc
      More than 300 cc
                    *With an additional allowance of +2 dB
1973
1974
86
90
92
83
87
89
80
84
86
Title:

Originator:
Noise Source:
Purpose:
Measurement
Location:

Procedure:
Recommended
Maximum Level:
SAE  J366- EXTERIOR SOUND LEVEL FOR HEAVY TRUCKS
AND BUSES - Approved July 1969.
Society of Automotive Engineers
Trucks and Buses over 6000  pounds  G'VW
Establishes the method for measuring the maximum exterior
sound level for highway motor trucks, truck tractors and buses.
Test  site shall be flat open  space,  free of large  reflecting
objects within 100 feet of either the vehicle or the  microphone.
Locate microphone 50 feet from the centerline of the vehicle path.
Approach microphone in a gear ratio selected such that at a point
50 feet ahead of the microphone, the vehicle is at no higher than
2/3 the maximum rated or governed engine speed.  Accelerate fully
such that maximum rated engine rpm is achieved between 10 and
100 feet beyond microphone and without exceeding 35 mph at
end point.

88 +2dB(A)at50feet.
                                      A-7

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Title:


Originator:

Noise Source:

Purpose:
Measurement
Location:


Procedure:
SAEJ952b-SOUND  LEVELS  FOR  ENGINE  POWERED EQUIPMENT
Approved May 1966, Last Revised January 1969.

Society of Automotive Engineers

Engine Powered Equipment

Establishes procedure for measuring maximum sound levels for

engine powered equipment.

Test site shall consist of a flat open area, free of large reflecting

objects within 100 feet of either the-microphone or the test specimen.

Locate microphone 50 feet from the test specimen.  Operate equip-

ment at the combination of load and-speed which produces maximum

sound level without violating the  manufacturer's operating
specification.
Recommended
Maximum Levels:
                 Type of Equipment
                                          Maximum Sound Level
                                            dB(A) at 50 feet*
                                          (A-Weighting Network)
     1.   Construction and industrial machinery

     2.   Engine powered equipment of 5 hp or less intended
         for use in residential areas at frequent intervals

     3.   Engine powered equipment exceeding 5 hp but not
         greater than 20 hp intended for use in residential
         areas at frequent intervals

     4.   Engine powered commercial equipment of 20 hp
         or less intended for infrequent use in a residential
         area
                                                   70

                                                   78



                                                   88
    5.   Farm and light industrial tractors
     *An additional 2 dB allowance over the sound level limits is recommended to
      provide for variations in test site, vehicle operation, temperature gradients,
      wind velocity gradients, test equipment, and inherent differences in nominally
      identical  vehicles.
                                    A-8

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Title:

Originator:
Noise Source:
Purpose:
Measurement
Location:

Procedure:
Recommended
Maximum
Levels:
SAE J986a - SOUND LEVEL FOR PASSENGER CARS AND LIGHT
TRUCKS - Approved July,  1967; Last Revised January, 1969
Society of Automotive Engineers
Passenger Cars and Light Trucks (of 6000 GVW or less)
Provides a method for determining the maximum sound level for
passenger cars and  light trucks.
Test area to be flat open space, free of large reflecting objects,
within 100 feet of either the vehicle or the microphone.
Locate microphone 50 feet from the centerline of the vehicle path.
Approach microphone at 30 mph in a low gear range.  At a point
25 feet ahead of microphone,  accelerate at wide open throttle such
that maximum  rated rpm is  achieved 25 feet beyond microphone.

86 + 2 dB(A) at 50  feet.
                                     A-9

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Title:


Originator:
Noise Source:
Purpose:
Measurement
Location:
Operating
Conditions:
CALIFORNIA  ADMINISTRATIVE CODE, TITLE B, CHAPTER 2,
SUBCHAPTER 4, ARTICLE  10,  VEHICLE NOISE MEASUREMENT
February 15,  1968.
Department of California  Highway  Patrol
All new motor vehicles offered  for sale in the State of California.
Three categories of motor vehicles are defined:  (1) trucks and buses
with gross weight greater than 6000 pounds; (2) trucks, buses, and
passenger cars with gross weight under 6000 pounds; and (3) motor-
cycles.
Establishes procedures for implementation of Section 27160 of the
California Vehicle Code which  is concerned with limits on noise
output of new motor vehicles offered for sale in the State of California,
Open area, free of reflecting surfaces within a 100-foot radius of the
microphone and within 100 feet of the center!ine of the path of the
vehicle from the point where the throttle is opened to the  point where
the throttle is closed.
Vehicles are operated along a path 50 feet distant from, and at
right angles to, the measurement microphone.
Category 1  (Truck and Buses >6000 pounds GVW):  Operate vehicle
under conditions of grade,  load, acceleration, deacceleration and
gear selection to achieve maximum noise at a speed of up  to 35 mph.
Category 2 (Light Truck,  Passenger Cars; GVW  <6000 pounds):
Operate vehicle in a  low gear range.  Approach microphone at
30 mph, accelerate fully at a point 25 feet ahead of microphone
and continue to 100 feet beyond microphone or a point at  which
maximum rated engine rpm  is reached.
Category 3 (Motorcycles):  Motorcycle driven in second gear at
constant speed corresponding to 60 percent of maximum rated engine
rpm.  Accelerate full at a point 25 feet ahead of microphone.
                                       A-10

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 Noise Limits:   New Vehicles offered for sale in California: *
                              Manufactured Prior to
                                January 1, 1973
                :per California Vehicle Code
                                     Manufactured After
                                      January 1, 1973
Category 1
Category 2
Category 3
88 dB(A)
86
88
86 dB(A)
84
86
Title:


Originator:
Noise Source:

Purpose:
Measurement
Location:
Operating
Conditions:
CALIFORNIA ADMINISTRATIVE CODE, TITLE 13, CHAPTER 2,
SUBCHAPTER 4, ARTICLE 10, VEHICLE NOISE MEASUREMENTS,
February 15,  1968.
Department of California  Highway Patrol
Motor vehicles and combinations of vehicles subject to registration
when operated on California  highways.
Establishes procedures for implementation of Section 23130 of the
California Vehicle Code which is concerned with limits on noise
output of motor vehicles operated on all  California highways.
Open area, free of large  reflecting surfaces within a 100-foot
radius of the microphone and within a 100-foot radius of the point
on the centerline of the path of the vehicle nearest the microphone.
Sound level readings are recorded on vehicles which are in lanes
of travel whose centerlines are at or beyond 50 feet from the
microphone position.
                                      A-ll

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Noise Limits*:                                       Speed Limit of    Speed Limit of
                                                    35 mph or less   more than 35 mph
                  1.   Motorcycles and motor vehicles
                      of 6000  GVW or more
                       (a) Before 1 January 1973       88  dB(A)         90  dB(A)
                       (b) After 1 January 1973        86               90
                 2.   All other motor vehicles           82               86
      *  per California Vehicle Code
        (with an additional allowance of +2 dB)
                                      A-12.

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    PART 36—NOISE STANDARDS:
   AIRCRAFT TYPE  CERTIFICATION
            Subparl A—General
 Bee. -
 S6.1    Applicability.
 36.2    Special retroactive requiremente.
 S6JS    Compatibility  with airworthiness
          requirements.
 36.5    Limitation a! part.
  Subpart B—Noise Measurement and Evaluation
 3C.JO1  Nofee measurement.
 36.1O3  Noise evaluation.
           Subporf C—Noise Limits
 86.201  Noise llmltB.
            Subparl D (Reserved!
            Subparl E IReservedl
            Subpart f IReservedl
 Svbpart G—Operating Information and Airplane
              Flight Manual
 36 J501 Procedures and other Information.
 S6J581 Airplane Flight Manual.
 Appendix  A—Aircraft  noise measurement
             under $ 36.1O1   .
 Appendix  B—Aircraft noise evaluation under
             i 36.103
 Appendix  C—Noise levels for subsonic trans-
             port category and turbojet pow-
             ered airplanes under S 36.201
   AUTHORITY : The  provisions of this Part 36
 Issued under sees.  313(a), 601. 603, and 611
 of the Federal Aviation Act of 1958; 49 U.S.C.
 1354, 1421, 1423, and 1431 and sec. 6(c) of
 the Department of Transportation Act; 49
 U.S.C. 1655 (C),

          Subpart A—General

 g 36.1 Applicability.

   
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           A—AIBCBAFT NOISE  MEASOSEMENT
               UNDER ! 36.101

   Section A38.1  Mrtse certification test and
measurement conditions—(a)  General. This
section   prescribes   the   conditions  under
wblcn noise type certlflcatlon tests must be
conducted and tbe measureuieui. procedures
that must be used to  measure  the  noise
made by  the aircraft for which  the test Is
conducted.
   (b) General teat conditions. (1) Tests to
show compliance with established noise type
certlflcatlon levels must consist  of a  series
of takeoffs and landings during which meas-
urements must  be taken at the measuring
points defined In Appendix C of this part.
Tbe sideline noise measurements  must also
be made  at symmetrical locations on each
Bide  of  the runway. On each test  takeoff.
simultaneous measurements must be  made
at  tbe sideline  measuring  points on both
sides of the runway  and also  at the takeoff
flyover measuring point. If the height of  the
ground at each measuring point differs from
that of the nearest point on the runway by
more than 20 feet, corrections  must be made
as defined In 5 A38.3(d)  of  this appendix.
   (2) Locations  for  measuring noise  from
an aircraft In  flight  must be surrounded by
relatively flat terrain  having no excessive
Bound  absorption characteristics such   as
might be caused by thick, matted, or  tall
grass, shrubs,  or wooded areas. No obstruc-
tions which significantly  Influence the sound
field from the aircraft may exist within a
conical space above  the  measurement posi-
tion, the cone being  denned by an axis nor-
mal to the ground and by a half-angle  75*
from tbls axis.
   (3) The tests  must  be carried out under
the following  weather conditions':
   (1) No  rain or other precipitation.
   (Jl) Relative humidity not higher than
90 percent or  lower  than 30 percent.
   (Ill)   Ambient  temperature  not   above
88*  F. and not  below 41*  P. at  10 meters
above ground.
   (IT) Airport reported  wind  not above 10
knots and crosswlnd component not  above
6  knots at 10 meters above ground.
   (v) No temperature Inversion  or anoma-
lous wind conditions  that would significantly
affect tbo noise level  of the  aircraft  when
the noise Is recorded  at the measuring points
defined In Appendix  C of this part.
   (c) Aircraft testing procedures. (1) The
aircraft testing procedures and noise meas-
urements must be conducted  and processed
In en approved  manner to yield the noise
evaluation measure  designated as Effective
Perceived Noise  Level. EPNL, In units of
EPNdB, as described In  Appendix B of this
part.
   (2) The aircraft height and lateral posl-
. tlon relative  to  the extended centerllne of
the runway must be determined by a method
Independent of  normal  flight Instrumenta-
tion such as radar tracking,  theodolite  trl-
angulatlon, or  photographic  scaling  tech-
niques to be approved by the FAA.
   (3) Tbe aircraft position along the flight
path must be related  to the  noise recorded
at tbe noise measurement locations by means
of synchronizing signals. The position of the
aircraft  must be  recorded relative to  the
runway  from a  point at least  4 nautical
miles from threshold  to touchdown  during
the approach  and at least  6  nautical miles
from the start of roll during the takeoff.
   (4) The takeoff test may be conducted at
a weight  different from  the maximum take-
 off weight at which  noise certification 1ft re-
quested If the necessary EPNL  correction does
 not  exceed 2 EPNdB.  The  approach  test
 may be  conducted at a weight different from
 tbe maximum landing weight  at which noise
 certlflcatlon Is requested provided the neces-
 sary EPNL correction  does  not exceed  1
 EPNdB. Approved data may  be used to  deter-
 mine the variation of EPNL with weight for
 both takeoff and  approach tcr.t conditions.
   (5) The takeoff test must meet  the con-
 ditions of 5 C36.7 of Appendix C of this part.
   (6) The approach test must be conducted
 with the aircraft stabilized and following a
 ft* :*-0.5*  approach angle  and must meet the
 conditions of § C36.9.
   (d) Measurements. (1) Position and per-
 formance data required to  make  the cor-
 rections  referred  to  In  !A36.3(c)  of this
 appendix must be automatically recorded at
 an approved sampling rate. Measuring equip-
 ment must be approved by the PAA.
   (2) Position and performance  data must
 be corrected,  by the methods outlined In
 5 A36.3(d)  of this appendix to standard pres-
 sure at sea level, an ambient temperature of
 77' P.. a relative humidity of 70 percent, and
 Eero wind.
   (3) Acoustic data must be corrected by the
 methods of 5A36.3(d) of  this appendix to
 standard pressure at sea level, an  ambient
 temperature of 77"  P., and  a relative humid-
 ity of 70 percent.  Acoustic data corrections
 must also be made for a mlnlmuu distance
.D_f_370_feet between the aircraft's approach
 path and the approach  measuring point, a
 takeoff   path  vertically  above  the  flyover
 measuring point and for differences of more
 than 20  feet In elevation of measuring loca-
 tions relative to the elevation of the nearest
 point of the  runway.
   (4) The airport tower or another facility
 must be approved for use as the location at
 which measurements of atmospheric param-
 eters are  representative  of  those  condi-
 tions existing over the geographical area In
 which aircraft noise measurements are made.
 However, the surfac wind velocity and tem-
 perature must be measured near the  micro-
 phone at the approach,  sideline, and take-
 off measurement locations, and the  tests are
 not  acceptable unless the conditions con-
 form to  § A36.1(b) (3) of this appendix.
   (5) Enough  sideline  measurement sta-
 tions must be used during tests so  that the
 maximum sideline noise Is  clearly  denned
 with respect to location and level.
  Section A3S.2   Measurement of  aircraft
 noise received on the ground—(a)  General.
 (1)  These measurements provide the data
 for determining one-third octave band noise
 produced by aircraft during  testing proce-
 dures, at specific observation stations, as a
 function of time.
   (2) Methods for determination of the dis-
 tance form the observation stations  to the
 aircraft   Include   theodolite  trlangulatlon
 techniques, scaling aircraft  dimensions  on
 photographs   made  as  the  aircraft flies
 directly  over  the measurement points, radar
 altimeters, and radar tracking systems. The
 method  used must be approved.
   (3) Sound  pressure  level  data  for noise
 type certlflcatlon purposes must be  obtained
 with approved  acoustical equipment and
 measurement practices.
   (b) Measurement system. (1) The acousti-
 cal  measurement  system  must  consist of
 approved equipment  equivalent  to the
 following:
   (1) A  microphone system with frequency
 response compatible with measurement and
 analysis  system accuracy as stated  In para-
 graph (c) of this section.
   (11) Tripods or similar  microphone mount-
 Ings  that  minimize Interference  with  the
 sound being measured.
   (ill) Recording  and  reproducing  equip-
 ment characteristics, frequency response, and
 dynamic range compatible with the response
 and  accuracy requirements of paragraph (c)
 of this section.
   (Iv) Acoustic calibrators using sine wave
 or broadband noise of known sound pressure
 level. If  broadband noise Is used, the signal
 must be described In terms  of Its average
 end  maximum rms value for a nonoverlood
 signal level.
   (v) Analysis equipment with the response
 and accuracy requirements of paragraph (d)
 of this section.
   (c) Sensing,  recording, and reproducing
 equipment. (1)  The sound produced by the
 aircraft shall be recorded in such a way that
 the complete Information, time history In-
 cluded, Is retained. A magnetic tape recorder
 Is acceptable.
   (2) The characteristics of the system must
 comply with  the recommendations given In
 International Electrotechnlcal  Commission
 (IEC) Publication No. 179 with regard to the
 sections concerning microphone and ampli-
 fier  characteristics. The text and  specifica-
 tions of IEC Publication  No.  179  entitled:
 "Precision Sound Level Meters" are Incorpo-
 rated by reference  Into  this  part and are
 made a part  hereof as provided In 6 U.S.C.
 552(a)(l)  and  1  CFR Part ,20. This pub-
 lication was published In  1965 by the  Bureau
 Central de la Commission Electrotechnlque
 Internationale located at 1. rue de  Varembe,
 Geneva. Switzerland, and copies may be pur-
 chased at that place. Copies of this publica-
 tion  are  available  for examination  at  the
 DOT Library. Federal  Office Building  10A
 Branch and at the Office of Noise Abatement
 both located at  Headquarters, Federal Avia-
 tion Administration, 800 Independence Ave-
 nue, Washington, D.C. Moreover,  copies of
 this publication are available  for  examina-
 tion  at the  Regional  Offices  of the FAA.
 Furthermore, a  historic,  official file  will be
 maintained by the Office, of Noise Abatement
 and will contain any  changes  made  to  this
 publication.
   (3)  The response of the complete  system
 to  a sensibly plane progressive sinusoidal
 wave of constant amplitude must He within
 the tolerance limits specified  In IEC Publica-
 tion No. 179, over the  frequency range 45 to
 11.200 Hz.
   (4) If limitations of the  dynamic range
 of the  equipment  make  It necessary, high
 frequency  preemphasls must  he added to
 the recording channel  with the converse de-
 emphasis on playback.  The   preemphasls
 must be applied such that the Instantaneous
 recorded sound  pressure  level  of the noise
 signal between 800 and 11,200 Hz  does  not
 vary more than 20 dB between the maximum
 and  minimum one-third octave bands.
   (5) The equipment must  be acoustically
 calibrated using facilities  for acoustic free-
 field calibration and electronically calibrated
 as stated  in  paragraph (d) of this section.
   (6) A windscreen must be employed with
 the microphone during ail measurements of
 aircraft noise when the  wind  speed Is In
 excess of 8 knots.  Corrections  for any  In-
 sertion  loss produced by the windscreen, as
 a function of frequency, must be applied to
 the measured data  and the corrections  ap-
 plied must be reported.
  (d) Analysis equipment. (1) A frequency
 analysis of the acoustical signal shall be per-
 formed using one-third octave niters comply-
 ing with the recommendations given In  In-
 ternational   Electrotechnlcal   Commission
 (IEC) Publication No. 225. The text and spec-
 ifications  of  IEC publication  No.  225  en-
 titled "Octave. Half-Octnve and Third-Oc-
tave Band Filters Intended for the Analysis
of Sounds and Vibrations" arc Incorporated
 by reference Into this  part and are made a
 part hereof as provided In 5 U.S.C. 552 (a) (1)
 and  1 CFR Part 20. This publication was
published In  1968 by the Bureau Central de
la Commission  Electrotechnlque  Interna-
tionale located at 1.  rue de Varembe. Geneva,
Switzerland, and copies may be purchased
at that place.-Copies of this publication  are
available for  examination at the Office  of
Noise Abatement and  at  the DOT Library,
Federal Office  Building 10A Branch  both lo-
cated at Headquarters. Federal  Aviation Ad-
ministration, • 800  Independence  Avenue,.
Washington.  D.C. Moreover,  copies of .this
publication are available for examination ait
the Regional OSlces of the FAA. Furthermore
                                                            -   12  -
                                                                 A-14

-------
 a historic, official file will be maintained by
 ttoe Office of Noise Abatement and will con-
 tain any changes made to this publication.
    (2) A act of 24 consecutive one-third oc-
 tave filters must be used. The first filter of
 tbo £6i rnuct be centered c.t a gcsmetrtc n;can
 frequency of 50 Hz and the last of 10 kHz.
    (3) The  analyzer Indicating device must
 be analog, digital, or a combination of both.
 The preferred sequence of signal processing
 Is:
    (I)  Squaring the one-third octave filter
 outputs;
    (II) Averaging or Integrating; and
    (Ul) Linear to logarithmic conversion.

 The Indicating device must have a minimum
 crest factor capacity of 3 and shall measure.
 within a tolerance of ±l.OdB, the true root-
 mean-square  (rms)  level of the signal In
 each of  the 24 one-third octave bands. If
 other than a true rms device la utilized, It
 must be calibrated for nonslnusoldal signals
 and time varying levels. The calibration must
 provide  means  for converting the  output
 levels to true rms values.
    (4) The dynamic response of the  analyzer
. to input signals of both full-scale and 20
 dB less than full-scale amplitude, shall con-
. form to  the following two requirement*:
    (1)  When a sinusoidal pulse of 0.6-second
 duration at the geometrical mean frequency
 of each one-third octave band Is  applied to
 tbe Input, the  maximum output value shall
 read 4 dB±l dB less than the value obtained
 for  a steady state sinusoidal  signal of  the
 same frequency and amplitude.
    (ii) The  maximum output  value shall ex-
 ceed the final steady state value by 0.5 ±0.6
 dB when a steady state sinusoidal signal at
. tbe geometrical mean frequency of each one-
 third octave band is suddenly applied to tbe
. analyzer input and held constant.
    (6)  A  single value of the rms level must
 be provided every 0.5 ±0.01 second for each
 of tbe 24 one-third octave bands. The levels
 from all of the 24 one-third  octave bands
 must  be  obtained within a  50-m!!!!second
 period. No more than 6 milliseconds of data
 from any 0.5-second period may be excluded
 from the measurement.
    (6)  The  amplitude   resolution  of  the
 analyzer  must be at least 0.25 dB.
    (7)  Each output level  from the analyzer
 must be accurate within ±1.0 dB with  re-
 spect to the input signal, after all systematic
 errors have been eliminated. Tbe total sys-
 tematic errors for each of the output levels
 must not exceed ±3 dB. For contiguous filter
 systems,  the systematic correction between
 adjacent one-third octave channels may not
 exceed 4  dB.
    (8) The dynamic range capability of  the
 analyzer  for display of a single aircraft noise
 event must  be at least 55 dB in terms of  the
 difference between full-scale  output level
 and the maximum noise level of the analyzer
 equipment.
    (0) The  complete electronic system must
 be subjected to a frequency and amplitude
 electrical calibration by the use of sinusoidal
 or broadband signals at frequencies covering
 the range of 45 to 11.200 Hz,  and  of known
 amplitudes covering the range of signal levels
 furnished by the microphone. If broadband
 signals are used, they must be described In
 terms  of their  average and maximum rms
 values for a nonoverload signal level.
    (e) Noise measurement procedures.  (1)
 Tbe  microphones must be oriented  so that
 the  maximum  sound  received  arrives  as
 nearly as reasonable in  the direction  for
 which the microphones  are calibrated. The
 microphones must  be  placed  so  that their
 sensing elements are approximately  4 feet
 above ground.
   (2) Immediately  prior to and  after each
 test, a recorded acoustic  calibration of the
 system must be made in the field with an
 acoustic calibrator for tho two purposes of
 chocking  system sensitivity and providing
 an  acoustic reference level  for the  analysis
 of the sound level data.
   (3) For the purpose of minimizing equip-
 ment or  operator  error, field  calibrations
 must be supplemented with the use  of  an
 insert voltage device to place a known  signal
 at the input of the microphone, just prior
 to and  after recording aircraft noise data,
   (4) The ambient notso.  Including both
 acoustical  background  and  electrical noise
 of the  measurement system, must  be  re-
 corded and determined in the test area with
 the system gain set at  levels which will  be
 used for aircraft noise measurements. .
   Section  A36.3  Reporting   and correcting
 measured data—(a) General. Data represent-
 ing physical measurements or corrections to
 measured data  must be recorded in perma-
 nent form and appended to the record except
 that corrections to measurements for normal
 equipment response deviations need not  be
 reported. All other corrections must be  ap-
 proved.  Estimates must be made of the indi-
 vidual errors Inherent In each of the opera-
 tions  employed In obtaining tbe final data.
   (b) Data reporting.  (1)   Measured and
 corrected sound pressure levels must be pre-
' sented  in  one-third  octave  band  levels
 obtained  with  equipment   conforming  to
 the standards  described in  9 A36.2  of this
 appendix.
   (2) The type of equipment used for  meas-
 urement and analysts of all acoustic aircraft
 performance and meteorological data  must be
 reported.
   (3) The  following  atmospheric  environ-,
 mental data, measured at hourly Intervals or
 less during the test period at the observation
 points prescribed  in  5 A36.1 (d) (4)  of this
 appendix, must be reported:
   (1)  Air temperature in degrees Fahrenheit
 and relative humidity in percent.
   (11) Maximum,  minimum, and  average
 wind in knots and their direction.
   (Hi) Atmospheric pressure In Inches  of
 Mercury.
   (4)  Comments on looal topography, ground
 cover, and  events that might Interfere with
 sound recordings must be reported.
   (6)  The  following aircraft information
 must be reported:
   (1)  Type, model, and  serial numbers (If
 any) of aircraft and engines.
   (II) Dross dimensions of aircraft  and lo-
 cation of engines.
   (Ill) Aircraft gross weight  for each test
 run.
   (Iv) Aircraft configuration such  as flap
 and landing gear positions.
   (v) Airspeed in knots.
   (vi) Engine performance in pounds of net
 thrust, engine pressure ratios, jet exit tem-
 peratures,  and  fan  or  compressor  shaft
 rev./mln. as recorded by cockpit Instruments
 and  manufacturer's data.
   (vll) Aircraft  height  in feet determined
 by a method Independent of  cockpit instru-
 mentation such as radar tracking theodolite
 trlangulatlon,   or   approved  photographic
 techniques.
   (6)  Aircraft speed and position and engine
 performance parameters must be recorded
 at an approved sampling rate sufficient to cor-
 rect to the noise type certification reference
 conditions  prescribed in 8 A36.3(c)  of this
 appendix.  Lateral  position  relative  to the
 extended centerllne of the runway, configu-
 ration, and  gross weight must be reported.
   (c)  Noise type certification reference con-
 ditions—(1) Meteorological conditions. Air-
 craft position and performance data and the
 noise  measurements must be  corrected  to
 the  following noise type certification refer-
 ence atmospheric conditions:
   (o)  Sea level pressure of 2116 psf  (78 cm
 mercury),
  (b) Ambient   temperature  of   77*   P.
(ISA + 10'C.).
  (c) Relative humidity of 70 percent,
  (d)  Zero wind.
  (2) Aircraft conditions. Tho reference con-
dition for takeoff lo the maximum weight e'-
cept as provided In 5 36.1681 (b).
  The reference conditions for approach are:
  (a) Design landing weight, except as pro-
vided in i 30.1681 (1>),
  (b)  Approach angle of 3 *,
  (c) Aircraft height of 370 feet above noise
measuring station.     •	
  (d) Data corrections. (1)  The noise data
must be corrected to the noise type certifi-
cation  reference  conditions as  stated  In
§ A3B.3(c) of  this  appendix. Tho measured
atmospheric  conditions must be  those ob-
tained in accordance with SA36.1(d)(4)  of
this appendix. Atmospheric  attenuation of
sound requirements are given in 5 A36.6 of
this appendix.
  (2) The measured  flight  path  must  be
corrected by an  amount equal to  the dif-
ference between the  applicant's  predicted
flight paths for the test conditions and for
the  noise type  certification reference  con-
ditions. Necessary corrections relating to air-
craft flight path  or performance may be de-
rlvnd from approved  data other  than cer-
tification test data. The flight path correction •
procedure for approach noise must be made
with reference to a fixed aircraft height of
370 feet and a glide angle of 3'. The effective
perceived noise level correction must be less
than 2 EPNdB to allow for:
  (a) The aircraft not  passing  vertically
above the measuring point.
  (b)  The difference between  370 feet and
the  actual minimum  distance of the air-
craft's ILS antenna from the  approach meas-
uring points.
  (c) The difference between the actual ap-
proach angle and 8'.
Detailed correction requirements  are  given
in 5 A36.6 of this appendix.
  (3) If aircraft  sound pressure levels  do
not  exceed the  background  sound  pressure
levels by at  least 10  dB in any  one-third
ootavo band,  approved corrections  for  tbe
contribution  of  background  sound  pressure
levels to observed sound pressure levels must
be applied.
  (e) Validity of results.  (1)  The  test re-
sults must produce three  average EPNL val-
ues and  their 90 percent confidence limits,
each being the arithmetic average of the cor-
rected acoustical measurements for all valid
test runs at the takeoff, approach, and side-
line measuring points, respectively.  If more
than one acoustic measurement  system Is
used at  any  single measurement  location
(such as for the symmetrical sideline meas-
uring points), the resulting data for each test
run  must be averaged as a single measure-
ment.
  (2) The minimum sample size acceptable
for each of the three certification measuring
points is six. The samples  must  be  large
enough to establish statistically for each of
the  three average noise  type certification
levels a 90 percent confidence limit not ex-
ceeding ±1.5 EPNdB. No test result may  be
omitted  from  the average  process unless
otherwise specified by tbe FAA.
  (3) The average EPNL values and  their
90 percent confidence limits obtained by the
foregoing process  must be those  by which
the  noise performance  of the aircraft  Is
assessed against the noise type certification
criteria, and  must be  reported.
  Section A36.4  Symbols  and units—(a)
General.  The symbols  used  In Appendixes
A and B of  this part have the  following
meanings.
                                                          -  13  -
                                                                A-15

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   Symbol      Unit
                                  Meaning
 ant	
 cuo	dB	
 d	BOC	





 D	dB	



 EPNL	EPNdB..






 f(0orfl_..t H«	


 F(i.k)	dB	





 h	dB	



 H	%....	


 th the presence of dis-
   crete free of f^ownd Pressure Lerel.
  The chnnpc in level between
  Adjacent one-third octave
  band sound pressure levels
  at the i-th hand for the k-th
  instant of time.
Change in Slope of Sound
  Pressure tevcl.
Adjusted Slope of Sound Pres-
  sure Ijfpfl. The change in
  level between adjacent
  adjusted one-third octave
  band  sound pressure levels
  at the i-tli band for the k-tb
  instant of time.
Average Slope of Sound Pres~
  ture Jsvcl.
Sound  Pressure Level. The
  sound pressure level at any
  instant of time that occurs
  inaspcciRed frequency range.
Noy DitcnrUinulty Coordinate.
  The SPL value of the inter-
  section point of the straight
  Hnos representing the varia-
  tion of SPL with lop n.
Noy Intercept. The intercepts
  on the S PL-axis of the
  straight lines representing
  the variation of SPL with
  log n.
Sound  Pressure T*eoel. The
  sound pressure level at the
  k-th instant of time that
  occurs In the i-th one-third
  octave bund.
Adjusted Sound Pressure Level.
  The-flrst approximation to
  background level in the i-th
  one-third octave band for
  the k-th Instant of time.
Background Sound Pressure
  Lerel. The final approxima-
  tion to background level in
  the i-th one-third octave
  band  for the k-th instant
  of time.
Maximum Sound Pressure
  Level. The sound pressure
  level that occurs in the 1-th
  one-third octave band of
  the spectrum for PNLTM.
Corrected Maximum Sound
  Pressure Lerel. The sound
  pressure level that occurs in
  the i-th one-third octave
  band of the spectrum for
  PNLTM corrected for
  atmospheric sound absorp-
  tion.
Elapted Time. The length of
  time measured from a
  reference r,ero.
Time Limit. The beginning
  and end of the significant
  noise time history defined
  by h.
Time Increment. The equal
  increments of time for which
  PNL(k) and PNLT(lc) are
  calculated.
Nonnalifir.ft Time Conftant.
  The length of time used as
.  a reference in the Integration
  method for computing
  duration corrections.
Temperature. The ambient
  atmospheric temperature.
Tat Atmospheric Absorption.
  The atmospheric attenua-
  tion of sound that occurs In
  the 1-th one-third octave
  band for the measured at-
  mospheric temperature and
  relative humidity.
                                                                                                                   Symbol
                                                                                                                               Unit
                                                                                                                                                 Meaning
                                                                 . dB/fpet
                                                                 . dB/IOOO
                                                                    feet.
                                                      O	
           . degrees--.
           . decrees...
           . dcprecs,
           . degrees.
                                                                 . decrees..
                                                                 . degrees...
                       Reference Atmospheric Absorp-
                        tion. The atmospheric at-
                        tenuation of sound tlmt oc-
                        curs in the t-th one-third
                        octnvc band for the reference
                        atmospheric temperature
                        and relative humidity,
                     .  First Constant Climb Antfe.
                     .  Sfcrmd Constant Climb Angle.  '
                       Thriift CuflHict Anglct. The
                        anplcs defining the points
                        on the takeoff flight path at  "
                        which thrust reduction is
                        started and ended respeo-   ',
                        tivcly.
                     .. Approach Angle.
                     .  To.kroff Koisc Anglf. The angle
                        between the flight path and
                        noise path for takeoff opera- •
                        tion. It is Identical for both  ;
                        measured and corrected
                        flight paths.
X	degrees	Approach  Noise Angle. The
                        ancle between the flight
                        path and the noise path for
                        approach operation. It is
                        idenlical for !>oth measured •
                        find corrected flight paths.
Al	EPNdB..  P^LT Correct ion. The correc-
                        tion to ho added to the
                        EPNL calculated from
                        measured data to account   .<
                        for noise level changes due  1
                        to differences in atmospheric
                        absorption and noise ]«ith
                        length between reference    '
                        nnQ test conditions.        I
A2	EPNdB..  A'oiw Path Duration Cwrcc-   •
                        (inn. The correction to be   1
                        added to the EPNL calcu-  j
                        la ted from measured data to [
                        account for noise level      i
                        changes due to the noise    i
                        duration because of differ-  j
                        cnces in flyover altitude    !
                        between reference and test
                        condition.                 j
                       Weight Correction. The onrrec- *
                        tion to he added to the      i
                        EPNL calculated from     !
                        measured data to account   ]
                        for noise level clianpcs du*  j
                        to differences between maxi-
                        mum and test aircraft
                        weights.
            EPNdB. .  Approach Anale Corredinn.
                        The correction to be added
                        to the EPNL calculated
                        from measured daUv to
                        account for noise level
                        changes due to differences
                        between 3* and the test.
                                                                                                                 A3	EPNdB..
 AAB.
 AjS_.__
 Ay....
                        approach angle.
           . feet.       Takeoff Profile Changes. The
           . degrees.     changes in the basic param-
           . degrees.     eters defining the takeoff
           . degrees.     profile due to differences
           ; degrees.     between reference and test
                        conditions.
  FLIGHT PROFILE  IDENTIFICATION POSITIONS

 Position               Description
 A	Start of takeoff roll.
 B	Liftoff.
 C	Start of first constant climb.
 D	Start of thrust reduction.
 E	Start of second constant climb.
 EC	Start of second constant climb  on
               corrected flight path.        •     '
 P;	End of  noise  certification takeoff
               flight path.
 Fc	  End of second constant climb  on
               corrected night path.
 O_,	Start  of  noise  certification ap-
               proach flight path.
 Or	Start  of  noise  certification ap-1
-Nt_x          proach on reference flight path.
 H->	Posltl6n on   approach  path  dl-j
"''            rectly above   noise  measuring!
               station.                            i
 I	Start of level off.                     :
 Ir	Start of level  off on reference ap-;
               proach flight path.                :
 J	Touchdown.
 K-_	Takeoff noise measuring  station.
 L.	S:dcl!no  nclGC nicsGurlng  ctatlca
               (not on  flight track).
                                                                         -   14   -
                                                                               A-16

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      rUGHT PROFILE IDENTIFICATION
           POSITIONS— Continued
Petition             Description
M__... __  End  of noise  type  certification
             takeoff flight track.
N __ - _____  Approach noise measuring station.
O. _______  Threshold  of  approach  end  of
                                                     FMOOT PBOPILE DISTANCES—Continued
S
p ________ Start  of noise  type certification
             approach flight track.
Q ______ .. Position   on   measured  takeoff
             night  path  corresponding  to
             PNLTM at station K.
Qc _______ Position   on   corrected  takeoff
             flight  path  corresponding  to
             PNLTM at statlon.K.
B_ _______ Position   on   measured  takeoff
             flight path nearest to station K.
He _______ Position   on   corrected  takeoff
             flight path nearest to station K.
           Position  on  measured  approach
             flight  path  corresponding  to
             PNLTM at station N.
Sr _______ Position  on  reference  approach
             flight  path   corresponding  to
             PNLTM at station N.
T ________ Position  on  measured  approach
             flight path nearest to station N.
Tr _______ Position  on  reference  approach
             flight path nearest to station N.
X ________ Position   on   measured  takeoff
             flight  path   corresponding  to
             PNLTM at station L.

           FUOHT PROFILE DISTANCES
. Distance     Unit
                            Meaning
AB	feet	


AK	fcet	




AM	feet	
 KQ.	
KR..


•ERo.


LX..


NH.


N8..


NBr.


NT..


NTr
   ... feet	


   ....'feet	


   .... feet	


   .... feet..	


   .... feet	


   ..... feet	


   .... feet	


   ....feet	


   	fort	


	 feet.......
 -ON	feet	
                    Length of Takeoff Roll. The
                     distance along the runway
                     between the start of takeoff
                     roll and lirt on.
                    Takeoff Measurement Distance.
                     The distance from the start
                     of roll to the takeoff noise
                     measurement station alone
                     the extended ccntcrline
                     of the runway.
                    Takeoff Flight Track Distance.
                     The distance from the Start
                     of roll to the takeoff flight
                     track position along the
                     cxtented ccntcrlino of the
                     runway for which the
                     position of the aircraft
                     need no longer bo recorded.
                    Measured Takeoff Noise Path.
                     The distance from station
                     K to tho measured aircraft
                     position Q.
                    Corrected Takeoff Noise Path.
                     The distance from station
                     K to the corrected aircraft
                     position Qc.
                    Measured'Takeoff Minimum
                     IHttance. The distance from
                     station K to point R on the
                     measured fllpht path.
                    Corrected Takeoff Minimum
                     Distance. The distance from
                     station K to point Uc on
                     the corrected flight path.
                    Measured Sideline Noise Path.
                     The distance from station
                     L to the measured aircraft
                     position X.
                    Aircraft Approach  Height. The
                     vortical distance between
                     the aircraft and the ap*
                     proach measuring station.
                    Measured Approach Noise
                     Path. Tho distance from
                     station N to the  measured
                     aircraft position S.
                    Reference Approach Noise
                     Path. Tho distance from sta-
                     tion N to the reference air-
                     craft position Sr.
                    Measured Approach Minimum
                     Distance. The distance from
                     station N to point T on the
                     measured flight path.
                    Reference Approach Minimum
                     Distance. Tho distance from
                     station N to point Tr on the
                     corrected flight path; It
                     equals 3(3'.) foot.
                    Approach Measurement Dls~
                     tance. Tho distance from the
                     runway threshold to the ap-
                     proach measurement station
                     along the extended centw-
                     llae of the runway.
                                                   Symbol
                                                              Unit
                                                                             Meaning
OP..	feet	Approach Flight Track Dis-
                     tance. The distance from the
                     runway threshold to tho ap*
                     proech flight tract position
                     along tho extended center-
                     lino of the runway for which
                     the position of the aircraft
                    • need uo longer be recorded.

Section  A36.5   Atmospheric attenuation of
sound—(a)  General. The  atmospheric  at-
tenuation of sound must be determined In
accordance  with the  curves  of  Figure  15
presented In SAE ARP 866 or by the simplified
procedure presented below. SAE ARP 866  is
a  publication entitled:  "Standard  Values of
Atmospheric Absorption  as  a  Function of
Temperature  and   Humidity  for Use  In
Evaluating Aircraft Flyover  Noise" and  the
recommendations presented  therein are In-
corporated by reference Into this Part  and
are made a part hereof as provided In 5 U.S.C.
522(a)(l) and 1 CFR Part 20. This publica-
tion  was published on August 31, 1964. by
the Society of Automotive  Engineers,  Inc.,
located at 2 Pennsylvania Plaza, New  York,
N.Y.  10001,  and copies may  be  purchased
at that   place.  Copies  of  this  publica-
tion  are  available  for  examination at  the
DOT  Library.  Federal  Office  Building  10A
Branch and  at the Office of Noise Abatement
both  located at  Headquarters, Federal  Avia-
tion Administration. 800 Independence Ave-
nue,  Washington, D.C. Moreover,  copies of
this publication are available for  examina-
tion at the Regional Offices of the FAA. Fur-
thermore, a historic,  official  file will  be
maintained by the Office of Noise Abatement
 and  win contain any changes made  to  this
 publication.    '
   (b) Reference  conditions.  For the refer-
 ence atmospheric conditions  of  temperature
 and  relative humidity equal to Tl' V. and 70
 percent, respectively, and for nil other con-
 ditions of temperature and relative humidity
 where their product Is equal to or  greater
 than 4,000, the sound absorption must be ex-
 pressed by the following equation:

          alo' = n/500 (dB/l,OOOft.)
 alo'  Is the  atmospheric attenuation of sound
 that occurs  In  the  1-th  one-third   octave
 band for  tho reference atmospheric  condi-
 tions and  fl  Is the  geometrical mean  fre-
 quency for the 1-th  one-third octave band.
   (c) Nonre/crence conditions.  (1)  For all
 atmospheric conditions of temperature  and
 relative humidity  where  their  product  Is
 equal to or less than 4.000, the rel.itlonshlp
 between sound absorption, frequency, tem-
 perature,  and  humidity  must be expressed
 by the following  equation:

    500 olVfl = (2/3) ((11/2) - (HT/1,000) ]
 al' Is the  atmospheric attenuation  of sound
 that occurs  In  the  1-th  one-third   octave
 band for  a relative humidity of H percent
 and  a temperature of T' Fahrenheit.
   (2) Figure  Al  graphically Illustrates the
 simplified relationship. The second equation
 represents  the Inclined line  which is valid
 for all values  of HT up to and Including
 4,000. For all values of 4.000 and greater, the
 horizontal  line,  represented by  the  first
 equation,  Is valid. The minimum, reference.
 and  maximum values of humidity and tem-
 perature are Indicated In Figure Al.
                                                               njlii
                                                                      I
                                                            —   H=30%
                                                                  T = 41°F


                                                                                ,,,,!,„,
                                                              IJI
                                                                                                            H=70%
                          1 Ji
                                                                                                                                     = 86°F
                                                                             HUMIDITYX TEMPERATURE, HT/IOOO, % °F

                                                                 FIGURE Al.  SIMPLIFIED RELATIONSHIP BETWEEN ATMOSPHERIC
                                                                             SOUND ATTENUATION, FREQUENCY, HUMIDITY,
                                                                             AND TEMPERATURE.
Section  A36.8  Detailed  correction   proce-
dures—(a) General. If tho noise type certifi-
cation test  conditions arc not equal  to  the
noise certification  reference  conditions,  ap-
propriate positive corrections must be made
to the EPNL  calculated from the measured
data. Differences between  reference and test
conditions which lead to positive corrections
can result from the following:
  (1) Atmospheric absorption of sound un-
der test conditions greater than reference,
  (2) Test  flight  path at  higher altitude
than reference, and
  (3) Test weight  less than  maximum.
Negative  corrections  arc  permitted  If   the
atmospheric absorption of sound under  test
conditions  Is less than reference and also
If the test"TirgTirpal;rr-rg-a'ra~rewCT-BlttUide
than reference.
   The takeoff test flight path can occur at a
higher altitude  than reference If the meteor-
ological  conditions  permit  superior  aero-
dynamic  performance  ("cold  day"  effect).
Conversely, the  "hot day" effect can  cause
the  takeoff test  flight  path  to occur at a
lower  altitude than reference. The approach
test flight path can occur at either higher
or lower  altitudes than reference Irrespec-
tive of the meteorological  conditions.
   The correction procedures presented In the
following discussion consist  of  one or more
of five possible  values added  algebraically to
                                                             -   3.5  -
                                                                  A-17

-------
the EPNL calculated as If the tests were con-
ducted completely under the noise type certi-
fication reference conditions. The flight pro-
files must be determined for both takeoff and
approach, and for both  reference  and test
conditions. The test procedures require noise
and flight path recordings with a  synchro-
nized time signal from which the test profile
can  be  delineated, Including  the  aircraft
position for which PNLTM is observed at the
noise  measuring station. For takeoff, a flight
profile corrected to reference conditions may
be derived from manufacturer's data, and for
approach, the reference profile Is known.
  The noise paths from  the aircraft to the
noise  mcasxirtng  station  corresponding  to
PNLTM  are determined  for both  the test
and reference profiles. The SPL values In the
spectrum of PNLTM are then  corrected for
the effects of:
  (1) Change    In    atmospheric   sound
absorption,
  (2) Atmospheric sound absorption on the
change In noise path length,
  (3) Inverse square  law on the change In
noise path length.

The corrected  values  of  SPL are then con-
verted to PNLT from which is subtracted
PNLTM. The difference represents the correc-
tion to be added algebraically  to  the  EPNL
calculated from  the measured data.
  The minimum distances from  both the
test and reference profiles to the noise meas-
uring  station  are calculated and xised  to
determine a noise duration  correction due
to the change In the altitude of aircraft fly-
over.  The duration correction is added  alge-
braically to the  EPNL calculated from the
measured data.
  Prom approved data In the form  of curves
or tables giving the variation of EPNL with
takeoff weight and also for landing weight,
corrections  are  determined  to be added to
the EPNL calculated from the measured data
to  account for noise  level  changes due to
differences between maximum  and test air-
craft weights.
  Prom approved data In the form  of curves
or tables giving  the variation of EPNL with
approach angle,  corrections  are determined
to be added algebraically to the EPNL cal-
culated  from measured data to account for
noise level changes  due  to differences be-
tween 3° and the test approach angle.
   (b)  Takeoff profiles. Figure A2  Illustrates
a typical takeoff profile. The aircraft begins
the takeolf roll at point  A, lifts off at point
B, and Initiates  the  first  constant climb at
point C at an angle 0. The noise abatement
thrust  cutback  Is started at point  D  and
completed o.t point E  where the second con-
stant climb Is denned by the angle 8 (usu-
ally expressed In terms  of the gradient In
per cent).
   The  end  of  the noise  type  certification
takeoff flight path Is  represented by aircraft
position P  whose vertical projection on the
flight track  (extended centerllne of the run-
way) Is point M. The position of the aircraft
must  be recorded for a distance AM  of at
least 6  nautical  miles.
   Position K Is  the takeoff noise  measuring
station whose distance AK Is specified as 3.5
nautical miles. Position L Is the sideline noise
measuring  station located on a line parallel
to and a specified distance from the runway
centerllne where the noise level during take-
off  Is greatest.
  The takeoff profile Is defined by the fol-
lowing five  parameters:  AD.  the  length  of
takeoff roll; p. the first constant climb angle;
•y. the second constant climb  angle;  and
£ and (. the thrust cutback angles. These five
parameters are functions of the aircraft per-
formance and  weight and  the atmospheric
conditions of  temperature,  pressure,  and
wind velocity and direction. If the test con-
ditions arc not equal to the reference condi-
tions, the corresponding test and  reference
profile parameters will be different as shown
In Figure A3. The profile parameter changes.
Identified as  AAB. AS, Aa, A*, and A<. can
be  derived  from  the manufacturer's  data
(approved by the FAA) and can  be used to
define  the  flight profile corrected to  the
reference conditions. The  relationships be-
tween  the measured and  corrected takeoff
flight profiles can then be used to determine
.the corrections, which If positive, must  be
applied   to the EPNL calculated from  the
measured data.
  NOTE:  Under reference atmospheric  con-
ditions and with maximum takeoff weight,
the gradient of the  second constant  climb
angle,  Q, Is specified to be not less than 4
percent.  However, the actual gradient will
depend   upon  the test atmospheric  condi-
tions,  assuming  maximum takeoff weight
and  the  parameters characterizing  engine
performance  are  constant (rpm. epr, or any
other parameter used by the pilot).
  Figure A4 Illustrates portions of the meas-
ured and corrected .takeoff flight paths In-
cluding the significant geometrical relation-
ships  Influencing  sound   propagation. EP
represents the  measured   second  constant
flight path  with climb  angle -y,  and  EcFc
represents the  corrected  second  constant
flight path at reduced altitude and with re-
duced climb angle Q—AJJ.
  Position Q represents the aircraft location
on the measured takeolf flight path for which
jfflLTTvjC 'lsj .observed jit the  noise  measTTfTng
station K/and Qc'ls the corresponding posi-
tion on the corrected flight path. The meas-
ured and corrected noise propagation  paths
are KQ  and KQc. respectively,  which  form
the same angle 9 with their flight paths.
  Position R represents  the point on the
measured  takeoff flight  path  nearest the
noise measuring station  K, and  Re IB the
corresponding  position  on  the  corrected
flight path.  The minimum distance to the
measured and  corrected  flight paths are In-
dicated  by  the lines KH and KRc, respec-
tively, which are  normal to their flight paths.
   (c) Approach,  profiles.  Figure  A5  Illus-
trates a  typical approach profile. The begin-
ning of the noise type certification approach
profile Is represented by aircraft  position O
whose vertical projection on the  flight track
 (extended centerllne of the runway) Is point
P. The position of the aircraft  must be  re-
corded  for a distance OP from the runway
threshold O  of at least 4 nautical miles.
   The aircraft approaches  at an angle  u,
passes vertically over the  noise  measuring
station N at a height of NH, begins the level
off at position I, and touches down at posi-
tion J.  The distance ON IB  specified as  1.0
nautical mile.
  The approach profile Is defined by the ap-
proach angle i> and the height NH which are
functions of the aircraft operating conditions
controlled by  the pilot. If the measured ap-
proach  profile parameters are different  from
the corresponding reference approach param-'
eters (3* nnd  370 feet, respectively, as shown
In Figure A6), corrections. If positive,  must
be applied to  the EPNL  calculated from the
measured data.
  Flgu.-e A7 Illustrates portions of the meas-
ured and  reference  approach flight  paths
Including the significant geometrical  rela-
tionships Influencing  sound  propagation.
CI  represents the  measured approach  path
with approach angle 17, and  Grlr represents
the  reference  approach flight path at lower
altitude and  approach  angle of  3'.
  Position S represents the aircraft location
on  the  measured approach  flight path  for
which PNLTM Is observed at the noise meas-
uring station  N, and Sr Is the corresponding
position on  the reference  approach  night
path.  The  measured and  corrected  nolsa
propagation paths  are NS and NSr. respec-
tively,  which  form the  same angle X  with
their flight paths.
  Position T  represents  the point on the
measured approach flight path nearest 'the
.noise measuring station N. and Tr Is the
corresponding point on  the reference ap-
proach  flight  path. The  minimum distances
to the  measured and reference flight paths
are  Indicated by the lines NT and  NTr,  re-
spectively, which are normal to  their flight
paths.
  NOTE: The  reference approach flight path
Is defined by ij = 3° and NH = 370 feet.  Con-
sequently, NTr can also be defined; NTr = 369
feet to the nearest  foot and Is, therefore. '
considered  to  be  one  of  the  reference
parameters.
  (d) PNLT corrections. Whenever  the am-
bient  atmospheric  conditions of  tempera-
ture and relative humidity  differ from the
reference conditions (77° P. and 70 percent.
respectively)  and  whenever the measured
takeoff  and approach flight paths differ from
the  corrected and reference flight paths  re-
spectively, It  may  b- necessary or desirable
to apply corrections to the EPNL values cal-
culated from the  measured  data.  If the
corrections   are required,  they  must  bo
calculated as described below.
  Referring to the takeoff flight  path shown
In Figure A4, the  spectrum of PLNTM ob-
served  at station K. for  the aircraft at po-
sition  Q, Is decomposed Into Its Individual
SPLI values.  A set of  corrected  values  are
then computed as follows:
                       -alo) KQ
                  +alo (KQ-KQc)
                  +20 log 
-------
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SLOi1*/ pfcWs length.
  TSie (xrrsc'-ii.  vBltur; of .?°Lio  are  them
converted to  PNX/T  o^r, t uorrnctlon  term
calculatedtis follows:

            i i = PHI/*- - .vHi/n :

wfaKi ysTM'ezents *.ne cnrr'sitto  to be added
afc.:^ ViM i'.Sj  t3 tiie  E.1 K"> -j.?  :.!at
-------
A

L
3.5 N.M.

K M
6 N.M. MINIMUM

        FIGURE A2. MEASURED TAKEOFF PROFILE.
                                     MEASURED
                                     FLIGHT
                                     PATH
        AAB
       FIGURE A3, COMPARISON OF MEASURED AND
                 CORRECTED TAKEOFF PROFILES.
                     -  18  -
                         A-20

-------
>
                                    MEASURED
                                    FLIGHT
                                    PATH
Q
                 FIGURE A4. TAKEOFF PROFILE CHARACTERISTICS
                            INFLUENCING SOUND PROPAGATION.
                   FIGURE A5.  MEASURED APPROACH PROFILE.
MEASURED
APPROACH
PATH
                                                                           REFERENCE
                                                                           APPROACH
                                                                           PATH          370'
                                                                                               N

                                                                              FIGURE A6. COMPARISON OF MEASURED AND
                                                                                        CORRECTED APPROACH PROFILES.
                                                   MEASURED
                                                   APPROACH
                                                   PATH
                                                    REFERENCE
                                                    APPROACH
                                                    PATH
                                                                            FIGURE A7. APPROACH PROFILE CHARACTERISTICS
                                                                                      INFLUENCING SOUND PROPAGATION.

-------
  EPNil
                      TEST
MAXIMUM
               AIRCRAFT TAKEOFF WEIGHT

       FIGURE A8. TAKEOFF WEIGHT CORRECTION FOR
                 EPNL AT 3.5 NAUTICAL MILES
                 FROM BRAKE RELEASE.
EPML
                             TEST
   MAXIMUM
                  AIRCRAFT LANDING WEIGHT

      FIGURE A9. APPROACH WEIGHT CORRECTION
                  FOR EPNL AT 1.0 NAUTICAL MILE
                  FROM RUNWAY THRESHOLD.
                      - 20 -
                       A-22

-------
  EPNL
                                                                           A 4
                           ANGLE OF APPROACH, 1

           FIGURE A10. APPROACH ANGLE CORRECTION FOR
                           EPNL AT 1.0 NAUTICAL MILE
                           FROM RUNWAY THRESHOLD.
  APPENDIX B—AIRCRAFT NOISE EVALUATION
              XJNPEB {36.103

  Section B36.1  General; The procedures In
this appendix must be used to determine the
•noise  evaluation quantity designated  as
'effective  perceived noise level, EPNL, under
i 36.103.  These procedures, which use  the
physical properties of noise measured as pre-
scribed by Appendix A  of this part, consist
of the following:
  (a) Tlie  24 one-third octave  bands  of
eound pressure level  are converted to  per-
ceived noisiness by means of a noy table. The
noy values are combined and then converted
to  Instantaneous  perceived   noise  levels,
PNL(k).
  (b) A tone correction factor, C(k), Is cal-
culated for each spectrum to account for the
subjective response to the presence  of the
maximum tone.
  (c) The tone correction factor Is added to
the perceived noise level to obtain tone cor-
rected perceived  noise levels,  PNLT(k), at
each one-half second Increment of time. The
Instantaneous values of tone  corrected per-
                                           ceived noise level are  noted with respect to
                                           time and the maximum value, PNLTM,  Is
                                           determined.

                                                   PNLT(k) = PNL(k) +C(k)

                                             (d)  A duration correction factor, D,  is
                                           computed by Integration under the curve of
                                           tone corrected  perceived noise level  versus
                                           time.
                                             (e)  Effective perceived noise level, Et>NL, Is
                                           determined by the algebraic sum of the maxi-
                                           mum tone corrected perceived noise level and
                                           the duration correction factor.

                                                      EPNL = PNLTM + D

                                             Section B36.2 Perceived noise level. In-
                                           Btantaneous perceived noise  levels, PNL(k) ,
                                           must be calculated from Instantaneous one-
                                           third  octave band sound pressure  levels,
                                           BPL(l.fe), as  follows:
                                             Step 1. Convert  each  one-third  octave
                                           band SPL(l.k),  from BO  to 10,001) Hz, to per-
                                           ceived  noisiness, n(l,k),  by  reference  "to
                                           Table Bl, or to the mathematical formulation
                                           of the noy table given In  5 B36.7 of this
                                           appendix.
                                             Step 2. Combine the perceived  noisiness
                                           values,  n(l.k),  found  In step  1  by the
                                           following formula:
                                           N(k)=n(k>+0.15
                                                                              n(l, k)
where n(k) Is the largest of the 24 values of
n(l,k)  and  N(k)  Is  the total  perceived
noisiness.
  Step 3. Convert the total perceived noisi-
ness, N(k) , Into perceived noise level, PNL(k) ,
by the following formula:

       PNL(k) =40.0+335 log N(k)

which Is plotted In Figure Bl. PNL(k)  may
also  bp obtained by choosing N(k) In  the
1,000 Hz column of Table pi and then read-.
Ing  the  Corresponding value of BPL(lJc)
which, at 1,000 Hz, equals FNL(k) .
                                                     -  21   -
                                                            A-23

-------
SPL
dB
            One-Third Octave Band Center Frequencies f, HZ

90  O   »»*»12S94»I00150JU«»JOO
                                         <»  wo io» u»  iioo  »«
      Table Bl.
             Perceived Noisiness
             (NOYs) as a  Function
             of Sound Pressure
             L'evel.
                                  -  22  -
                                          A-24

-------
 5100
   80
               .llllll
                  I'l i i
                                 1

                                                         1
                                                                        '  ' J '  "±
I                  10                 100
                          fatal Perceived Nolilnesi, N, noys.
 Figure Jl.  Perceived Nolle Level os o Function of Noy».
                                                              1000
                                                                                 10000
  Section B36.3  Correction for spectral Ir-
repularttiei. Noise having pronounced Irreg-
ularities In the spectrum (for example, dis-
crete frequency components or tones), must
be adjusted by the correction factor C(k)
calculated as follows:        '          '
  Step 1. Starting with the corrected sound
pressure level  In the 80 Hz one-third octave
band  (band   number  3).   calculate  the
changes In Bound pressure level (or "slopes"):
In the  remainder of  the  one-third octave
bands as follows:    '
      s(3JE)=no value
           ) =SPL(4.k) -SPL(3Jc)
            =8PL(IJc) -
                              -1) JtJ
      6(24*) =SPL(24Jc) — SPL(23,k)
  Step  2. Encircle the value of the  slope,
»(l,k),  where  the absolute  value of  the
change In slope  Is greater than S; that Is,
where.
        |As(l, k)|=|s(l, k)-st(i-l), k)|>6.
  Step  3. (a)  If the encircled value of the
(lope s(l,k)  Is  positive  and  algebraically
greater than the slope s[(l—l),k), encircle
8PL(1*).
  '(b) If the encircled valuevrf the slope B(ljc)
                                       Is zero or negative and the elope s[l—l
                                       Is positive, encircle (SPL[(1-1) ,k])
                                          (c) For all other cases, no sound pressure
                                       level value Is to be encircled.
                                         Step 4. Omit all SPL(l,k) encircled In Step
                                       3 'and compute  new sound pressure  levels
                                       SPL'(i,k) as follows:
                                          (a) For nonenclrcled sound pressure levels,
                                       let the new sound pressure levels equal the
                                       original sound pressure levels,

                                                   SPL'(l.kJ=SPL(l,k)

                                          (b) For encircled sound pressure levels In
                                       bands 1-23, let the new sound pressure level
                                       equal the arithmetic average of the preceding
                                       and following  sound pressure  levels,

                                           BPI/(l.k)=(M)[SPL[a-l),k)+8PMa+l),k]]
                                          (c) If the  sound, pressure  level In  the
                                       highest frequency band (1=24) is encircled,
                                       let the new sound pressure level  In  that
                                       band equal                                 ;

                                             SPL'(24Jc) =SPL(23,k) +s(23,k).

                                         Step 5. Recompute new slopes s' (l,k), In-
                                       cluding one for an Imaginary 25-th band, as
                                       follows: i
                                           8'(3.k)=s'(4,k)
                                           s'(4,k)=SPI/(4.k)-SPI/(3,k)
                                                                                              8' (24, k) =SPI/(24. *) _SPL'(23, k)
                                                                                              e'(25.k)=s>(24. k)
                                                                                            Step  S. For 1 from 3 to 23,  compute the
                                                                                          arithmetic  average of  the three  adjacent
                                                                                          slopes as follows:
                                                                                                            ,
                                                                                       Step 7. Compute  final adjusted one-third
                                                                                     octave-band  sound  pressure levels,  SPL"
                                                                                     (l,k) , by beginning with band number 3 and
                                                                                    •proceeding to band number 24 as follows:

                                                                                     8PL"(3i k) =SPL(3, k)
                                                                                     SPL"(4,k)=SPL"(3.k)+5(3,k)
  SPL"(24, k) =SPL"(23, k) +s(23. k)
  Step  8.  Calculate the  differences, F(1JO,
between the original and  the adjusted sound
pressure levels as follows:   .

      •'  F(l.k) =SPL(l,k) — SPL"(l,k»
and note only values greater than zero.
  Step B. For each of the  24 one-third octave
•bands, determine tone correction factors from
the  sound pressure level differences F(l,k)
and Table B2.                  '    '
  Step 10. Designate the  largest of the tone
correction  factors, determined In Step 8, as
C(k). An  example  of the  tone correction
procedure  la given In Table. B3..
  Tone  corrected   perceived   noise  levels
PNI/T(k) are determined  by adding the C(k)
values to corresponding PNL(k)  values, that
is,        ;
         PNLT(k) =PNL(k) +C(k)
  For any 1-th one-third octave band, at any
k-th Increment of time,'  for which  the tone
correction  factor Is suspected to result from
something other than (or In addition to) an
actual  tone   (or any  spectral  Irregularity
other than aircraft noise), an additional
analysis may be made  using a  niter with a
bandwidth narrower than  one-third of an
octave. If the  narrow band  analysis  cor-
roborates that suspicion, then a revised value
for  the  background sound pressure level,
8PIi"(l,k), may be  determined from  'the
analysis and used to compute a revised tone
correction  factor, F(l,k),  for that particular
one-third octave band.
                                                        -  23   -
                                                             A-25

-------
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                                                                                 Table B3.  Example of Tone Correction
                                                                                            for a Turbofaa Sngine

-------
,,.Scctlon B36.4  Maximum tone  corrected
perceived noise  level.  The maximum  tone
corrected perceived noise level,  PNLTM, IB
the maximum calculated value at the tone
corrected perceived noise level, FNLT(k), cal-
culated In accordance with th? procefU'tw of
I B36.3 ol this Appendix. Figure B2 Is an ex-
ample of a flyover nojse time history  where
the  maximum value  Is  clearly indicated.
Half-second  time Intervals,  At,  are  small
                              enough to obtain a satisfactory noise time
                              history.
                                If there are no pronounced Irregularities In
                              the spectrum, then the procedure of ! D36.8
                              of this Appendix would bo redundant since
                              PNIjT(k)   would  tx>  identically  equal  to
                              PNL(k). For this case, PNLTM would be the
                              maximum  value of PNL(k) and would equal
                              PNLM.
  "5-
   > TJ
   8 ss
  « s
  13
             PNLTM
                  t(0
                                   Flyover Time  t, ice,

         figure B2.   Example of Perceived Noise Level Corrected
                       for Tones as  a Function of Aircraft  Flyover
                       Time
                                                           t(2)
  Section  B36.5  Duration  correction.  The
duration correction factor D Is determined
by the Integration technique denned by the
expression:
P"' ant [PNLT/10] dtT^PNLTM
 1(1)              J
D-101og
where T Is  a normalizing time  constant,
PNLTM Is the maximum value of PNLT, and
t(l) and t(2) are the limits of the significant
noise time history.
  Since PNLT  Is calculated from  measured
values of 8PL, there will, In general, be no
•obvious equation for PNLT as a function of
time. Consequently, the equation can be re- .
written with a summation sign Instead of an
Integral sign as follows:

D- 10 log Fu/T) £ AtanttPNLT(k)/10]l-PNLTM

where At Is the length of the equal incre-
ments of tune  for which PNLT(k) Is calcu-
lated and  d Is the  time Interval  to  the
nearest 1.0 second during which PNLT(k) Is
within a specified value, h, of PNLTM.
  Half-second time Intervals for At are small
enough to obtain a satisfactory history of the
perceived noise level. A shorter time Interval
may be selected by  the applicant provided
aproved limits  and constants are used..
  The following values for T, At, and h, must
be used in calculating D :

               T=10sec,
              At=0.6 sec, and
               h=10dB.
Tldng the above values, the equation for D
becomes
  D-10 Ipg f-E'ant [PNLT(k)/10]"j-PNLTM-13

where the  Integer d  Is the  duration  time
defined  by the points that are 10 dB less
than PNLTM.
  If the 10 dB-down points fall between cal-
culated. PNLT(k) values  (the  usual case),
the applicable limits for the duration  time
must be chosen from  the PNLT(k) values
closest to PNLTM—10. For those cases  with
more than  one peak  value of PNLT(k), the
applicable limits must be chosen to yield the
largest possible value for the duration  time.
  If the value of  PNLT(k) at the 10 dB-
down points Is 90 PNdB or less, the value of
d may be taken as the time Interval between
the initial and the  final  times for which
PNLT(k) equals 90  PNdB.
  Section   B36.6  Effective perceived   noise
level. The total  subjective effect of an air-
craft  flyover  Is designated "effective  per-
ceived noise level," EPNL, and Is  equal to
the algebraic sum of the maximum value of
the  tone   corrected  perceived  noise   level,
PNLTM,  and  the  duration  correction,  D.
That is,
            EPNL=PNLTM+ D
where PNLTM and D are  calculated under
55B36.4 and B30.6 of this appendix.
  The above equation  can be rewritten by
substituting the equation for D from 5 B36.5
of this appendix, that is,

    EPNL=101og F£ ant[PNLT(k)/10l"]-13

  Section B36.7  Mathematical formulation
of nay tables. The relationship between sound
                                             pressure level and poroeived noisiness given
                                             In Table Bl Is illustrated in Figure B3. The
                                             Variation of 8PL with log n for a given one-
                                             third octave band can be expressed by either
                                             one or two straight lines depending upon the
                                             frequency range. Figure B3(a) Illustrates the
                                             double line case  for frequencies  below «X»
                                             Hz. and above 6,300 Hz and  Figure B3(b)
                                             Illustrates the single line case for'all other
                                             frequencies.
                                               The important aspects of the mathematical.
                                             formulation are:
                                               1. the slopes of the •straight lines, p(b)
                                             andp(c),
                                               2. the Intercepts of the lines on the 8PL-
                                             axls, SPL(b), and BPL(c), and
                                               3. the coordinates of  the discontinuity,
                                             8PL(a),andlogn(a).
                                               The equations are as follows:
                                             Case 1. Figure B3 (a) f <400 Hz.
                                                                f > 6300 Hz.
                                                                                             SPL(a) =-
                                                                                                     p(c)SPL(b) -p(b)SPL(c)
                                                                                                logn(ft)=-
                                                                                                            p(c)-p(b)
                                                                                                          8PL(c) —SPL(b)
                                                                                               p(b) -p(c)
                                                                             (a)  SPL(b)£BPI/g8PI«(a).
                                                                                            8PL-SPL(b)
                                                                                                   n=ant-
                                                                                                              P(b)
                                                                                           (b)  SPL >8PL(a).
                                                                                                          SPL-SPL(c)
                                                                                                   n=ant-
                      P(c)
  (c) 06300 Hz.
          _M(b)6PL(b)-M(c)SPL(c)
                   M(b) -M(c)
                                                                                 .   _ M(b)M(c) tSPL(c) -.8PL(b) 1
                                                                             log n(a,      .    M(c)_M(b)

                                                                             (a)  SPL(b) <, SPL £ SPL(a) .
                                                                               n=ant M(b) [SPL— SPL(b) ]
                                                                             (b)  SPLgSPL(a).
                                                                               n = ant M(c) |SPL— SPL(c) 1

                                                                             (c)  0SPL(c).
                                                                          I        n=antM(c)[SPL— SPL(c)J
                                                                          I   (b)  logn>0.
                                                                            Table B4 lists the values of the Important
                                                                           constants  necessary   to  calculate  sound
                                                                           pressure level  as a function  of  perceived
                                                                           noisiness.
                                                          -  25  -
                                                            A-27

-------
                     1
                     J
                         SPL (a)
                         SPL(b)
                         SPL(c)
    f  -£  400 HZ
    f  5* 6300 HZ
                                                               log n(«)
                                                   Log  Perceived Noisiness,  log n
K)
00
                     v>
                      %
                     *S
                     "5
                      3
                     V)
                          SPL(c)
400 a^ f-=£6300 HZ

         (b)
                                                    Log Perceived Noisiness,  log  n

                                  Figure  B3.   Sound Pressure Level as a function of Noys.
Bond
(i)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
f
HZ
50
63
80
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
6300
8000
10000
M(b)
0.043478
0.040570
0.036831
II
0.035336
0.033333
II
0.032051
0.030675
-
-
-
-
-
-
-
-
-
-
_
-
-
0.042285
II
SPL
(b)
dB
64
60
56
53
51
48
46
44
42
-
-
-
-
-
-
-
-
_
-
-
-
-
37
41
SPL
(a)
dB
91.0
85.9
87.3
79.9
79.8
76.0
74.0
74.9
94.6
.
-
-
-
• -
-
-
-

_
_
-
-
44.3
50.7
M(c)
0.030103
"
11
H
"
"
11
11
"
"
"
11
"
11
"
0.029960
"
it
»
••
"
"
H
11
SPL
(<=)
dB
52
51
49
47
46
45
43
42
41
40
»
"
"
11
38
34
32
30
29
II
30
31
3<
37
                                                                                                            Table B4.    Corsfants for Mathematically Formulated NOY Values
 APPENDIX C—NOISE LEVELS  TOR  SUBSONIC
   TRANSPOHT   CATEGORY   AND    TURBOJET
   POWERED  AIRPLANES  UNDER  { 36.201

   Section  C36.1  Noise  measurement  and
 evaluation.  Compliance with  this appendix
 must be shown with noise levels measured
 and evaluated as prescribed, respectively, by
 Appendix A and Appendix B of this part, or
 under approved equivalent procedures.
   Section  C36.3  Noise  measuring  points.
 Compliance with  the  noise level standards
 of { C36.5 must be shown—
|  (a) For  takeoff, at  a point 3.5 nautical
 miles from the start of the takeoff roll on the
 extended centerllne of the runway;
J  (b) For  approach, at a point  l nautical
 mile  from  the  threshold on  the extended
 centerllne of the  runway:  and
   (c) For the sideline, at the point, on a line
 parallel to and 0.25 nautical miles from the
 extended centerllne of the runway,  where
the noise level after liftoff Is greatest, except
that,  for  airplanes  powered by  more than
three turbojet engines, this distance must
be 0.35 nautical  miles.
  Socuon  
-------
  (b) Tradeoff. The noise levels In paragraph
(a) may be exceeded  at one  or  two  of th«
measuring points prescribed In  § CSC.3. If—
  (1) The  sum  of the  exceedances  Is not
greater than 3 EPNdB;
  (2) No  exceedance  Is  greater  than  2
EPNdB; and
  (3) The exceedances are completely offset
by  reductions  at other  required measuring
points.
  (c) Prior  applications.  For  applications
made before December 1, 1969. for airplanes
powered by more than  three turbojet engines
with bypass ratios of two or more, the value
prescribed In paragraph (b)(l)  of this sec-
tion may not exceed 5 EPNdB and the value
prescribed In paragraph.(b) (2)  of this sec-
tion may not exceed 3 EPNdB.
  Section C36.7  Takeoff test conditions, (a)
This section applies to all takeoffs conducted
In showing compliance with this part.
  (b) Takeoff power or thrust must be xised
from the start  of the  takeoff  to the point
at which an  altitude  of  at least 1.000 feet
above the runway .Is  reached, except that,
for airplanes powered by more than three tur-
bojet engines, this altitude must not be less
tnan 700 feel.
  (c) Upon  reaching  the altitude  specified
In paragraph {b)  of this section, the power
or thrust may  not be reduced below  that
power or thrust that will provide level flight
with one engine Inoperative, or below  that
power or thrust that will maintain a climb
gradient of  at least  4 percent, whichever
power or thrust Is greater.
  (d) A speed of at least V2 + 10 knots must
be attained as soon as  practicable after lift-
off, and must be maintained throughout the
takeoff noise test.
  (e) A constant takeoff configuration, se-
lected by the applicant, must be maintained
throughout the takeoff noise test.
  Section  C36.9  Approach test  conditions.
(a) 'nils section  applies to all  approaches
conducted In showing compliance with this
part.
  (b) The airplane's configuration must be
that specified by the applicant.
  (c) The  approaches  must be  conducted
with  a  steady glide angle of 3' ±0.5' and
must be continued to a normal touchdown
with  no alrframe  configuration  change.
  (d) A steady approach  speed  of not  less
than  1.30 V. + 10 knots must be established
and maintained over the approach measuring
point.
  (e) All engines must be operating at ap-
proximately the  same power or  thrust, and
must be operating at not less than the power
or thrust required for the maximum allow-
able nap setting.

[P.R. Doc. 69-13368; Filed, Nov. 17, 1969;
                8:08 a.m.]
                                      (As  published  in_the  Federal  Register
                                        /34F.R.   18355/ on  Nov.  18,  1969)
                                                         -  27  -
                               (Pbge 28 is blank)
                                                           A-29

-------
 Title  14—AERONAUTICS  AND

               SPACE
Chapter I—Federal Aviafion Adminis-
tration, Department of Transportation
       [Docket No. 9993; Amdt. 38-1J

   PART  36—NOISE STANDARDS:
   AIRCRAFT TYPE CERTIFICATION

   Approach Noise Test Conditions

   This amendment  changes 'the type
certification approach noise test condi-
tions for subsonic transport category air-
planes and for subsonic turbojet powered
airplanes regardless of category. The pur-
pose of this amendment is to insure that
the approach noise type certification test
(1) Is conducted with the same  airplane
configuration  as  that used during air-
worthiness type  certification; and (2)
does not result in noise levels less than
those  that will  be  generated by the
airplane in normal  operation.
   Parfc-36, Noise standards: Aircraft type
certification was issued by the Adminis-
trator on November 3,  1969, and will be
effective on December 1,  1969. Section
C36.9 of Appendix C of that part contains
the  test  conditions applicable  to  all
approaches conducted in showing com-
pliance  with  Part  36. That  section
contains  two  provisions  that  require
amendment  when   Part  36  becomes
effective.
   First, paragraph (b) of section C36.9
currently  provides  that the airplane's
configuration must be "that specified by
the applicant." It now  appears that this
language could be regarded as permitting"
the  applicant  to  specify configurations
that are not the same  as those used in
showing  compliance with  the  landing
requirements in the airworthiness regu-
lations. This result is not intended. While
the general requirement of compatibility
between  noise and airworthiness type
certification test  conditions and proce-
dures includes approach noise test condi-
tions  and  procedures, it  is  believed
advisable  to  remove any question that
may  be  caused  by section C36.9(b).'
Therefore, that paragraph is amended to
specifically provide, in part,  that the air-
plane's  configuration  during  the  ap-
proach noise test must be "that used in
showing  compliance  with  the landing
requirements in the airworthiness regu-
lations constituting the type certification
basis of the airplane."
  Second, paragraph (e) of section C36.9
currently  provides that the  aooroach
noise test must be conducted with engines
operating at not less than the "power or
thrust required for the maximum allow-
able flap  setting." The  intent of  this
provision is to ensure that the noise gen-
erated  during the approach noise type
certification test  will not  be  less than
that later generated by the airplane in
normal  operation. However,  configura-
tion aspects other than flaps may affect
the noise of the airplane. In addition,
there is no need  to specify a particular-
power  or thrust  once a  specified con-
figuration is  identified  since  section
C36.9 also specifies the glide angle and
minimum approach speed, requires  that
both be "steady,"  and requires that tne
approach be  continued  to  a  normal
touchdown with no configuration change.
In  the light of the above, it is believed
that the  objective of ensuring that  ap-
proaches  made later in normal  opera-
tion will not be noisier than the published
noise levels of the airplane can be more
effectively achieved by providing, in sec-
tion C36.9(b),  that "if more than  one
configuration  is used  in  showing com-
pliance with the landing requirements in
the airworthiness regulations  constitut-
ing the type certification basis of the air-
plane,  the  configuration  that is most
critical from a noise standpoint must be
used"  in showing compliance  with the
approach noise requirements of Part 36.
This  amendment  is necessary to ensure
 that the  approach noise levels generated
 by the airplane during type certification
 will be representative of approach noise
 levels generated in normal operations.
   This amendment is issued in full con-
 sideration of  comments  received  with
 respect to Notice 69-1, issued on Janu-
 ary 3, 1969 (34 F.R. 453), including con-
 sideration of economic data submitted
 by affected aircraft manufacturers and
 operators, and has been determined to be
 economically reasonable, technologically
 practicable, and appropriate to the air-
 craft to  which it applies.
    Pursuant to section 611 of the Federal
 Aviation Act of 1958 (49 U.S.C. 1431) the
 Administrator  has  consulted with the
Secretary of Transportation concerning
the matters contained herein, prior to the
adoption of this amendment.
  Like Part 36, which becomes effective
on December 1. 1969, this amendment to
that part applies to airplanes now near-
ing the completion of the type certifica-
tion process. Therefore, it is essential that
this amendment become effective on the
same date as Part 36. Therefore, I hereby
find that notice and public procedure, in
addition  to that  already  provided by
Notice 69-1, is impracticable. In addition,
I find, for the reasons stated above, that
good cause exists for making this amend-
ment effective on less than 30 days notice
after publication thereof in the  FEDERAL
REGISTER.
  In consideration of the foregoing, sec-
tion C36.9 of  Appendix  C of Part 36 of
the Federal Aviation Regulations which
becomes  effective on December  1, 1969,
is amended, effective on that date, to read
as follows:
  Section C30.9 Approach, teat  conditions.
(a) This  section  applies to all  approaches
conducted In showing  compliance with this
part.
  (b)  The airplane's configuration  must be
that used In showing  compliance  with the
landing requirements  In the airworthiness
regulations constituting the type  certifica-
tion basis of the airplane. If more than one
configuration Is used In showing compliance
with the  landing requirements In the air-
worthiness regulations constituting the type
certification basis of the airplane,  the con-
figuration that  Is  most critical from a  noise
standpoint must be  used.
  (c)  The approaches must be conducted.
with a steady  glide angle or 3 *±0.5* and
must be continued to a normal  touchdown
with no airframe configuration change.
  (d)  A steady approach  speed of not less
than 1.30V,-)10 knots must be established
and maintained over the approach measur-
ing point.
  (e)  All engines must be operating at ap-
proximately the same  power or thrust.

 (Sees. 313(a), 601, 603, 611, Federal Aviation
Act of 1958; 49 U.S.C. 1354, 1421, 1423,  1431;
sec. 6(c), Department of Transportation Act,
49 U.S.C. 1655(c))

  Issued in Washington, D.C., on Novem-
ber 21. 1969.
                     J. H. SHAFFER,
                      Administrator.

 IP.B. Doc. 69-14010;  Piled, Nov. 21,  1969;
               11:63 a.m.)
                                     (As  published in the Federal Register
                                      /34F.R.  1881^7 on Nov.  25,   1969)
                                                    -  29  -
                           (Page 30 Is blank)
                                                         A-30

-------
 Title  14—AERONAUTICS AND

              SPACE
Chapter I—.Federal Aviation AdTHni*-
 fralion, Department of Transportation
     '      [Docket No. 9337}
   PART 36—NOISE  STANDARDS:
   AIRCRAFT TYPE CERTIFICATION
             Corrections
  The following corrections are hereby
made to the preamble and regulatory
material of.new Part 36—Noise Stand-
ards: Aircraft Type Certification, which
was published  in the FEDERAL REGISTER
on Tuesday, November 18, 1969 (34 F.R.
18355-18379):
  (1) On page 18360 of the preamble,
the  word  "noise"  was  Inadvertently
omitted  from  the  statement,  in  the
right-hand column, second paragraph,
that 58 21.93(b) and 3C.KO will insure
that noise reduction technology suffi-
cient to achieve Appendix C limits must
be  applied "before further  aircraft
growth can occur." The  quoted words
are  hereby corrected  to read  "before
further aircraft noise growth can occur."
  (2) On page 18364, paragraph (a) of
§36.2 contains a typographical error In

  In 571.181  (34  P.R.  4637), the New
Bern. N.C., transition area is amended
hereby corrected to read: "5 36.201 (b)
and (cHl)."
  (3)  On page 18379, paragraph (e) of
8 C36.7 is not correct as it now stands,
and this paragraph is hereby corrected
to read as follows:
  Section C36.7 Takeoff test conditions. • • •
  (e) A constant takeoff  configuration, se-
lected by the applicant, must be maintained
throughout the takeoff  noise test,  except
that the landing gear may be retracted.

  Issued in Washington, D.C., on Novem-
ber 24,1969.
                   J.  H. SHAFFER,
                      Adminstrator.

(FJEt. Doc. 09-14169: Filed, NOT.  28,  1969:
              8:45 a.m.)
                                  (As published in the  Federal Register
                                    /34 F.R.  1902J7 on Nov. 29,  1969)
                                                    -  31  -
                                                       A-31

-------
                                   APPENDIX B
                    METHODOLOGY FOR IMPACT ANALYSIS

This appendix summarizes the various analytical models and supporting data used in
Chapter 4 for evaluating impact of noise from transportation vehicles and from internal
combustion engine devices.  Emphasis is placed on the former category as the primary
source of noise  impact in most communities today.  Specifically, this appendix summa-
rizes each of the following approaches used for evaluating noise  impact.
            •    total noise energy
            •    residual noise levels
            •    single event noise levels  for major transportation noise sources as a
                function of distance
            •    noise impacted land areas around  freeways and airports
            •    noise impact on operators or passengers of transportation vehicles
                and internal combustion engine devices.
            In addition, a brief glossary of key terminology is presented at the end of
this appendix.
B. 1         Total Noise Energy
            The total A-weighted noise energy produced on an average day by each
noise source category was estimated in order to provide one simple way of ranking the
potential noise  impact of each category. Categories with higher noise levels which
exist in greater numbers and are used more hours per day will  tend to rank highest  in
terms of their noise energy.  The noise energy for a given category,  such as standard
passenger automobiles, was estimated by the following expression:
            E    = 10~3 N • T • W ,   kilowatt-hours/day                      (1)
where       . .         .    .     ,
            N   = total number of units
            T    = Average hours per day  usage
            W   = approximate A-weighted noise  power, watts
                                        B-l

-------
and
                     W
            10 log 	^r  -  LA  +  20 log  R  +  7.5    dB re 10    watts
                    1Q-13      A
where
            L-A   = typical  A-weighted noise level in dB(A) at a reference distance
                   R  (in feet).
                    o
            The  four input  parameters required for this calculation (N,-T, L.  and R )
                                                                        ^\      O
are summarized in Table B-l for all of the categories considered  under transportation
vehicles and internal combustion engine devices. The values for number of units and
usage shown are based on estimated figures for 1970 compiled from available statistical
data.       Where up-to-date figures were not available for 1970, linear extrapolations
were made based on available data, or where necessary, engineering estimates made of
probable values.
            For ground transportation vehicles, the  "typical A-weighted noise levels"
correspond to average values at a 50-foot distance for the  type of vehicle under normal
operating conditions at typical speeds.  For aircraft, the noise levels correspond to
values at a  slant  distance to the aircraft of 1000 feet and hours of usage were based on
estimates of the duration of landing and takeoff operations in  the vicinity of airports.
Estimates of noise levels were based on the noise level data for all categories cited
earlier in Chapters 2 and 3.
            For projections of noise energy to the year 2000,  extrapolations in usage
were made on the basis of historical trends.  For example, Figure B-l(a) illustrates the
past trends  in passenger-miles of urban  travel by various transportation vehicles.  These
figures have been obtained  from published data — or estimated from information on
                                            I _ f o
vehicle-miles and average passenger loading.    '   They  clearly show the marked
increase in  travel by the average citizen — primarily by increase in personal travel in
the passenger automobile.
            This  general  increase in mobility is summarized in Figure B-l(b) which
shows the total urban passenger miles per urban population for all the transportation
                                         B-2

-------
               Table B-l

Parameters Used to Define Noise Energy
      for Each Category in  1970

Category
AIRCRAFT (Takeoff Only)
4- Engine Turbofan
i
2- and 3-Engine Turbofan
General Aviation
Helicopters
HIGHWAY VEHICLES
i
Medium and Heavy Duty Trucks
Sports, Compact and Import
Cars -;,
Passenger Cars (Standard)
Light Trucks and Pickups
Motorcycles (Highway)
City and School Buses
Highway Buses .
RECREATIONAL VEHICLES
Minicycles, Off-Road
Motorcycles
Snowmobiles
Outboard Motorboats
Inboard AAotorboats

N 1
Number

894
1174
128,900
16

3.64M2
23 M
64 M
15.3 M
2.6M
0.38 M
.02 M

1 M
1.6M
5.2M
.65M
T
Average Use
Hours/Day

0.23
O.I3
0.0173
6

4
1
1
1.5
0.5
2
4

1
0.2
. .05
.5
LA
Noise Level
dB(A)

103
96
77
83

84
75
69
72
82
73
83

88
85
75
80
R
;o
Distance
ft

1000




1000

50
-









50

50





50
                 B-3

-------
Table B-l (Continued)

Category
RAIL VEHICLES
Locomotives
Freight Trains
High Speed Intercity Trains
Existing Rapid Transit Trains
Passenger Trains
Trolley Cars, (Old)
Trolley Cars (New)
INTERNAL COMBUSTION
ENGINE DEVICES
Lawn Mowers
Garden Tractors
Chain Saws
Snow Blowers
Lawn Edgers
Model Aircraft
Leaf Blowers
Generators
Tillers
N
Number

27,100
10,000
2800
21,000
185
300
1200


17M
5M
2.5 M
0.8 M
3.3 M
1 M
0.5 M
0.55M
3.5M
T
Average Use
Hours/Day

12
5
6
0.5
12
12
12


0.1
.15
.05
.1
.05
.05
.1
.1
.01
LA
Noise Level
dB(A)

94
85
85
87
83
'80 ! .
66
.

74
78
83
85
78
78
76
70
69
RO
Distance
Feet

50





50


50








 Compiled from Ref. 1-4
 M = millions
 Estimated hours per day while operating on and near airports and noise level is greater
 than 80 dB(A).
                                          B-4

-------
     1000
 o
 CO
 I
 t/i
 0)
 ID
 D)
 £
      100
       10
                                                                  ,  I
          _ a)  Passenger Miles
                                      Automobile
               City'Bus and Trolley
                                     Trucks (Estimated
                                         , Personal Use)
          	X
                                          Surface Rail and Subway
                               Motorcycles
                                (Estimate)
         1930        1940         1950         1960
                                        Year
                                       1970
                                      1980
a) c   :
ro o ^
    o
  v. O
            b) Total Urban Passenger Miles Per Year
               Normalized by Urban Population
         1930
                                          I
1940
1950         1960
      Year
1970
                        Figure B-rl.  Growth in Urban Travel
               (Compiled or Estimated from Data in References 1-6, 9)
                                       B-5

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modes shown In Figure B-l(a).  Figures B-2(a) and B-2(b) show the same information
for intercity travel.   This upward trend In passenger travel per capita is due primarily
to the increase in numbers of vehicles  per capita and not miles traveled per year by
each vehicle.  The past trend in these two statistics is summarized for highway vehicles
in Table B-2 which shows that the mileage per vehicle has not increased markedly in
the last 20 years, while numbers of automobiles and trucks per capita has increased
substantially.
            Projections of the number  of vehicles to the year 2000 was therefore
made by extrapolation of the trend in number of vehicles per person from Table  B-2
taking  into account the decrease  in rate of growth so that the rate approached the
population growth rate by the year 2000.  The population growth  to the year 2000
was based on the most conservative projection (Series D) made by the Bureau of the
Census in 1968, which is in general agreement with 1970 census figures.
            Similar projections were made for the  change in numbers of internal
combustion engine devices to the year 2000.  Results of these projections for several
of the categories are  shown  in Figure B-3.  It was  assumed that the average number
of hours of usage per  day of each of the categories will not change significantly.
Changes in typical noise  levels to the  year 2000 were made on the basis of the three
future noise reduction options, discussed in  Chapter 4, which were then applied to
the base-line noise levels for  1970.
            While the resulting estimates of noise  energy (see Tables 4-3 and 4-4
in Chapter 4) are subject to appreciable error, they are considered sufficiently
reliable for the purpose of rank-ordering the general magnitude of noise generated
by each category.
B.2         Residual  Noise  Levels
            The residual noise level in any area is generated by all forms of traffic
moving  in and around the community,  and by the large number and variety of dis-
persed  stationary sources.  The magnitude of the residual noise level in a given
community has been shown to vary only slowly if at all in a community with stable
                                        B-6

-------
   1000
    100
I

 I
 I/I
 
 0)
     10
        -  a)  Passenger Miles
                                        Automobile
                                 Rail
—VHi
                   Highway Bus
                                     Private        ..
                                     Flying ~N  .V'
              Airline
                                                 -Trucks
                       /       x"**"  /'  (Estimated Personal Use)

                     /    •/.   /
                     ^--^/'     V	I	I
       1930        1940        1950         1960
                                     Year
                                                1970
                                                            1980
H
"5.
 0) O
 ?8
 a> r~,
 85 "
3.
   b) Total  Intercity Passenger Miles Per
      Year Normalized by Total  Population
                                 I
                               I
                                      I
1930        1940        1950        1960
                             Year
                                                1970
                                                                  1980
                Figure B-2.  Growth in Domestic Intercity Travel
             (Compiled or Estimated from Data in References 1-6, 9)
                                     B-7

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                                        Table 8-2
           Trends in Highway Vehicles per 1000 persons and Mileage per Year
1
Vehicle
Passenger Cars
Light Trucks and Pickups
Medium and Heavy
Duty Trucks
City Buses
Highway Buses
Vehicles per 1000 Persons Mileage per Year
1950
'268
46
10.6
0.38
0.097
1960
341
53
12.7
0.27
0.070
1970
426
75
17.8
0.24
0.075
1950
9078
10,7762
53,833
20,910
65,41 13
1960
9474
10,5802
59; 590
'"-.'. '••»
• -t- • .
16,004
65,567s
1968
9507
11,5702
68,303
14,122
58,4233
1
 Compiled from Reference 1
 Average Mileage for all types of trucks which are dominated by  light trucks.
 Average mileage for intercity motor carriers.
                                          B-8

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400
                      *Number of units x 10
  1950
1960
1970
1980
1990
2000
           Figure B-3.  Growth Trends for Population and Numbers
                 of Several Major Noise Sources Considered
                 for the Noise Impact Analysis.  (Compiled and
                 Projected from data in  References I/  2, and 6)
                                   B-9

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land-use patterns.  It has also been shown that this residual noise level is a key
foundation for evaluation of a community's reaction to intruding noise.
            An available model for community noise has therefore been modified to
                                           12
provide estimates of this residual noise  level.    As illustrated conceptual/ in
Figure B-4, the model assumes that discrete sources of noise in a community can be
replaced by a distribution of noise sources with a uniform density n throughout the
community.  The model provides an estimate of the quasi-steady state residual noise
level (L90) in terms of four basic parameters:
         .   •   The reference A-weighted noise level for each source, LA,
                at a reference distance.
            •   The reference distance R .
                                        o
            •   The excess attenuation of sound over and above that due to
                spherical spreading of the sound, and
            •   The density n of the distributed sources in number of sources
                per unit area.
            The relationship between the residual noise level predicted by  this model
and the reference  noise level  for each contributing source (assumed constant) can be
defined as follows:  For the distribution of discrete sources shown on the left sede of
Figure B-4, the effective boundary of influence for one source is defined by a circle
with an area equal to the area of one of the 6-sided cells bounding each such sourcec
The radius  R of this equivalent circle can be shown to be equal to l/V^n  where
n is the number of sources per unit area.  The noise from the local source within this
zone is considered identifiable as a local intruding noise and is not included as part
of the  residual noise.  The  latter is made up, then, of the summation of noise from all
the other sources outside this local zone so that the residual noise level, expressed
                                        B-10

-------
 Uniformly Distributed
 Sources of Community
Noise
Equivalent Continuous
Distribution of Sources
Excluding Locally Intruding
                   Source Density  n
                   (Units per square mile)
        B-4.  Model for Residual Noise Level (Excluding Local Source)
                             B-11

-------
                                      2    12
in terms of the mean square pressure  P., , is:

where
            P        =   mean square reference pressure of each source at the
                         reference distance R
                                            o
          ,  R.        =   distance from  observer at the center of the local zone
             '            ,  *u  -th
                         to the i   source            .
            m        =   the excess attenuation loss coefficient per unit distance
            s.        =   local shielding loss between observer and i  source.

            By replacing the distribution of discrete sources with a continuous distri-
bution and integrating from the outer radius R of the "local zone" out to infinity to
sum up the contribution of all but the local source to the residual noise level, one
can express  this level (LOQ) in  decibel form as
            L90      =    LA +  10 log  LE/ MJ  + 10 log n + 20 log -o " S " 66>5/
                          dB re: 20 fjN/m2                                     (3)

where                                                  .        ,
            L»       =    Reference A-weighted noise level of each  source at the
                          R  in feet
                          o
                          CO
                          s*
            c  /v\   —    /   -mR
            E' (x)   -    /  e     dR
                                                                               13
                          the exponential integral of the first kind of argument X
                                        B-12

-------
                                 = 0.686 a

            a        =   attenuation  loss coefficient in dB/1000 feet
            n        =   density of sources per square mile
            S        =   average shielding loss between observer and
                         surrounding  noise sources, dB.
            The relationship predicted by this expression  for the residual noise level
relative to the reference noise level L, of a source at a distance of 50 feet is shown
in Figure B-5 for a range of values of the excess attenuation coefficient and zero
shielding loss.  A typical  minimum value of excess attenuation rate, due to air
                                                                             14 15
absorption only, for ground transportation sources is about 1 - 2 dB per 1000 feet.  '
These are approximate values for the effective attenuation.rate when applied to the
overall A-weighted noise  level and are based on recently revised models for air
absorption.   '   '    These are considered more accurate for predicting losses at low
                                          19  20
frequencies than earlier prediction methods.  '     The additional shielding loss
due to diffraction or reflection by buildings between the sources and the observer
                               21 22
has been found to be about 6 dB.   '    Substantially higher values of shielding loss
(10 - 15 dB) have been reported from horizontal propagation tests of warning sirens
over communities; however, these higher values do not appear to be entirely appli-
                                               23
cable for predicting shielding loss of traffic noise.
            The source density n is estimated by the product:
            n =  P .  r • F • T/24
Where P is the population density, r  is the number of sources per person,  F is  the
fractional usage in the type of community being considered,  and T is the number of
operating hours per 24-hour day.  The  primary objective in applying this model  is to
illustrate the approximate contribution to the residual noise level by transportation
sources.  Average values for these parameters were chosen, therefore, to represent
the source density and usage in a typical urban community.  On this basis,  the
average urban population  density for 1970 was assumed to be 5000 persons per
                                        B-13

-------
      +10
 CO
O
10
JJ
 a>
 u
 §
oo
      -10  -
-3   -20  -
 a
 tn
 
-------
square mile.   While there has been a progressive decrease in the average population
density of urbanized areas over the last 20 to 30 years due to urban sprawl,  the rate
of this decrease  is slowing down and is being counteracted by  the growth of apartment
                          1 24
dwellings in close-in areas. '    Thus, for purposes of projection of noise impact in
the future, it was considered reasonable to assume that the average urban population
density remained constant.  The number of sources per person was assumed equal to the
total number operating in the nation, divided by  the total population (see Table B-2
and Figure B-3). Only sources operating  on roads and highways were considered for
estimating ambient levels.   Normally, the other transportation sources do not contribute
significantly to the urban residual noise environments.  Estimates of the fractional usage
in an urban  community and operating time for each source were made on the basis of
available information on urban highway usage. The resulting  estimates of the usage
and density of operating sources per square mile for the years  1970, 1985 and 2000
are summarized in Table B-3.   Note that  the projected increase in source density from
1985 to the year 2000 is slight due to the  assumed trend of number of sources per  capita
approaching a constant by the year 2000.
            The estimated trends in the daytime residual noise level in a typical  urban
residential area, based on this model, have been shown in Figure 4-1 in Chapter 4.
For 1970 conditions, the three most significant contributing sources for this  residual
noise level are:
            •    Passenger Cars (All Types)      45 dB(A)
            •    Light Trucks and Pickups        42 dB(A)
            •    Heavy and Medium Trucks      33 dB(A)
                    Total                      47 dB(A)
            During nighttime the contribution by passenger cars and light trucks will
decrease substantially, but the contribution by heavy trucks tends to remain nearly
constant.  This is illustrated by Figure B-6 which  shows the hourly and daily traffic
                                           25
flow rates on intercity highways in California.     Since this intercity travel normally
involves travel on urban freeways,  the contribution by trucks to the residual noise'
                                        B-15

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                                Table B-3
       Summary of Estimates of Density of Operating Highway Vehicles
                 in  Urban Residential Areas from 1970-2000
Source
Passenger Cars
(Standard)
Sports, Compact
and Import Cars
Light Trucks and
Pick-ups
Medium and Heavy
Duty Trucks
Motorcycles
(Highway)
City Buses
Fractional
Use in
Urban1
Areas
80
80
60
10
80
100
Operating
Time
Hours
Per Day
1
1
1.5
4
1
2
Operating Source Density2
Units/Square Mile
1970
50
20
20
1.5
1
0.8
1985
62
26
23
1.8
2.3
0.7
2000
65
30
25
2.0
2.5
0.6
Use in urban residential communities.
Assuming constant population density at 5000 people/square mile.
                                   B-16

-------
1.000
    12
                          10   12    2
                           Hour of the Day
                                                         12
14,000
13,000
0)
TO
g 12,000
0)
11,000
^^
• ^
" 10,000
s
§ 9,000
O 8,000
*.
O
^ 7,000
.i? 6,000
14-
*~ 5,000
•g "'t100
-^ 3,000
2,000
1,000
0




\
\








^





A

^





^^



All

A
$
All





^-*



Veh

—
X
Veh




Tru
-^
Tru


cle:
//
//
//
//
//
//
/
i

cle:




cks
	 ^
:ks


67



57




>7

i7



S'
\









^



\
\
^








/
SMTWTFSSM

     Dny of the Week
           Figure B-6.   Hourly and  Daily Variations in Intercity Highway Traffic on
            Major California Intercity Highways.  Expressed in Terms of Vehicles
                         Per 10,000 Annual Average Daily Traffic.
                    Data Shown for 1957 and 1967.  (From Reference 25)
                                            B-17

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level does not vary as much during a 24-hour period as the contribution from automobiles.
The net result is an estimated 5 to  10 dB(A) decrease at night in the residual  noise level.
However,  the type of truck which  tends to dominate the nighttime residual noise level
is the heavy duty transport truck — particularly the 5-axle type. This is illustrated in
Figure B-7 by the hourly variation in percent distribution of truck types by number of.
                                           25
axles observed on major California highways.    Heavy-duty 5-axle trucks clearly domi-
nate intercity truck traffic during the nighttime.  The same pattern can be expected for
truck traffic mix on the major urban  freeways.
            During the daytime, the hourly mix of urban vehicle traffic will tend to
vary during the day as indicated in Figure B-8.  This is a composite estimate of the
urban traffic mix based on known statistics on vehicle miles in urban areas of automo-
biles and trucks, and on detailed samples of hourly  mix of these vehicles in  typical
            2.9
urban areas.
            The detailed mix for truck traffic during the daytime in urban areas can be
estimated from the data  in Tables B-4,  B-5,  and B-6.  The first table shows  the per-
centage  distribution by truck size for three ranges of trip lengths ranging from local
(urban or farm) to long haul (greater than 200 miles). Table B-5 shows the distribution
by type of trip for the same range of truck sizes, while Table B-6 indicates the distri-
bution of truck trips in urban areas according to the type of land use at the starting
and termination points.
            The variation in population density and vehicles per capita will  obviously
vary from city to city from the typical  values used here for estimating the residual
noise level.  Figure B-9 illustrates the general distribution of central city population
                                                                                1 9
density according to 1960 census data for the 128 largest cities in the United States.  '
This shows two general trends in population density. It is generally higher for cities
with a higher total population and, as  indicated by the four lines characterizing
regional  areas,  is higher for older  regions. This is simply reflecting  the fact that the
population of a geographically  fixed urban land area tends to increase gradually with
time.  Automobile and truck ownership, on the other hand,  tends to  decrease with
                                         B-18

-------
_
 u
 O>
 u
£
o
 
-------
    o

   w-

    E


   _X



   5




   I
   M-
    o

    c
    0)
    o
    o
10



 9



 8



 7



 6



 5



 4



 3



 2



 1



 0
          12
                                             Total
                       8^10   12
8    10   12
                      A.M.
                                             P.M.
Figure B-8.  Typical Hourly Distribution of Total. Daily Urban Vehicle Traffic

                  (Based on data from References 2 and 9)
                                  B-20

-------
                         Table B-4
  Distribution of Annual Truck Vehicle-Miles According to
       Truck Size and Type of Trip (From Reference 9)

Type of Trip
Local (Urban or Farm)
Intermediate (<200 miles)
Long Haul £>200 miles)
1
Total -All Trips
Percent by Truck Type
(Gross Weight)
<1 0,000
Pounds
66.8
27.8
5.9
i
54.5
10-26,000
Pounds
2i.2
20.8
4.3
18.4
> 26, 000
Pounds
7.0
42.7
79.0
20.9

Miscellaneous
5.0
8.7
10.8
6.2

Total
100$
100$
100$
100$
                        Table B-5
Distribution of Type of Truck Travel According to Truck Size
                    (From Reference 9)      ,
Type of Trip
Local
Intermediate
Long Haul
Total
Truck Size (Gross Weight)
<1 0,000
Pounds
87.7
11.1
1.2
100$
10-26,000
Pounds
75.1
22.6
2.3
100$
> 26, 000
Pounds
21.4
40.0
39.0
100$
Total
All Trucks
68
21
11
100$
                          B-21

-------
                                      Table B-6
          Distribution of Truck Trips by Urban Land Use at Start and End of Trip
                                  (From Reference 9)
^^^^ To
From ^^"^^^^
Residential
Non-Residential
Total
Residential
24.1
18.0
42.1
Non-Residential
16.8
41.1
57.9
Total
40.9
59.1
100$
population or population density as indicated in Figures B-10 and B-ll respectively.
This is a reflection of the greater use of urban mass transit in crowded older cities.
The net effect on predictions of residual noise level in urban areas will be a trend to
make the density of highway vehicle sources more nearly constant and roughly inde-
pendent  of city size.
            Finally, as an  indication of the sensitivity of the residual noise  level to
changes  in the input parameters,  the effect of changes in the estimated density of the
operating sources is illustrated by the following alternate cases:
                                                                   Change in
                                                              Residual Noise  Level
                                                                     dB(A)
                 Increase density of heavy trucks by factor of 4
                 Increase passenger car density by factor of 2
                 Increase density of all sources by factor of 2
                 Increase passenger car density by factor of 4
+2
+4
+5
+8
                                        B-22

-------
   28
S
   24
   20


   16


   12
S!   4
          I    I  I  I  I I I 11      I    I
                                                  i   i   i  i i i i i i
              i  i  i i T'l-V-i""    i    i  i  i  i 111 i
                                                  i    i  I  I i  i l i i	I
                       IOO.OO9               I MILLION

                              POPULATION OF URBANIZED AREA
     Figure B-9.  Central City Population Density as Related to
                      Urbanized Area Population
                         (From Reference 1, 9)
               100
               80
               60
               40
               20
                  TWOORMORE CARS
                                                                   ONE CAR'
                                                                  - NO CARS
                               I960 POPULATION DENSITY
                           ' PERSONS PER SO. MILE (IN THOUSANDS)
12          16

      J
       Figure B-10.  Effect of Central  City Population Density
                      on Automobile Availability
                           (From Reference 9)
                                  B-23

-------
   140
   120
 £  100
 o
 S2
o
o
o
    80
 a  60
    40
    20
     0
       -1     |    —T


    •  Western Cifies


    ©  Eastern Cifies
                                               	Q_©	
I
I
I
      20      50    100    2        5   1000    2

                      Area Population (Thousands)
                            5   10,000
            Figure B-ll.  Registered Trucks/Capita, 1963-65

                           (From Reference 9)
                                 B-24

-------
B.3         Single Event Noise Levels-for Major Transportation Noise Sources as a
            Function of Distance
            The evaluation of relative annoyance of single events, presented in
Section 4.3, required prediction of single event noise levels as a function of distance
from the source.  This was carried for both measures of single event levels utilized as
follows:
Maximum A-Weighted  Noise Level
            The reference octave band spectrum for each source of a  fixed distance
(50 feet for surface vehicles — 1000 fe t for  aircraft) was used as a baseline for pre-
dicting the decrease  in octave band levels at greater  distances using atmospheric
            i
absorption  loss coefficients and ground absorption loss values from  References 14 and 15.
The attenuated levels at octave band  were then recombined after applying the
A-weighting convection to the spectrum to define the new A-weighted noise levels.
Typical results of this process are illustrated in Figure B-120
Single Event Noise Exposure Level (SENEL)
            The SENEL for a single event can be expressed as the  sum of its maximum
noise level and an effective duration  correction  factor.  The effective duration of noise
for moving sources is a function of the distance from the source (R) and its velocity (V).
For surface vehicles  such as automo biles and trucks,  the SENEL can  be  roughly approxi-
mated as follows:
        '   SENEL «  LA(R) + 10 logj"| ^-  , dB re 20 MN/m2 and 1 second
(4)
 See glossary of terms at end of this Appendix for definition.
                                       B-25

-------
     100
      90
^E   80
 o
 CN
  £
 co
  o

  o
  0)
  at
      70
     60
  M^



 ^  50
      40
      30
         20
                                                                        2-Engine Turbofan

                                                                           (Takeoff)
                                      Passenger

                                       Car
50        100      200          500      1000



                        Distance in Feet
2000
5000    10,000
                        Figure B-12.     Variation in Typical Noise Levels vs Distance

                                 For Several Transportation System Categories
                                                B-26

-------
where
            L.(R)  = A-weighted noise level at the distance R
                R  = Distance in feet
                V  = Speed of the vehicle in ft/sec
            For trains,  the duration of the passby noise is essentially equal to the
passby duration  (train length/speed) within a distance R equal to L/ir where L is
the train length.  Thus, within this range, the second term in Equation (4) is replaced
with 10 log  L/V  . At greater distances, Equation (4) is used since the long train
(line) source begins to act like a point source at these  distances.
            For aircraft,  SEN EL values were predicted in the same manner used
for predicting Effective Perceived Noise Levels (EPNL) as a function of slant
distance io me aircraft. 0/27.28  TUS jotter time-Integrated measures of single-
event noise are  used for evaluating noise impact near airports due to aircraft
operations.
                                       B-27

-------
B.4        Noise Impacted Land Areas Around Freeways and Airports.
            As indicated above, the methodology for evaluating noise impact near air-
ports is well developed and fully documented by examples such as in Reference 29.  The
index used for evaluating the noise impact is the noise exposure forecast (NEF) which is
a measure of the composite time-integrated noise exposure on the ground due to aircraft
operations.  The evaluation of noise impacted land area for the total transportation
system dictated the need to apply a similar methodology to highways.  The index of
noise impact utilized in this case is the community noise equivalent level (CNEL).
This composite measure of noise, defined in the Glossary at the end of this Appendix,
utilizes A-weighted noise levels as a basic measure of noise magnitude.
            As for the NEF scale,  a CNEL value accounts for the time-integrated
single-event noise level (expressed by an SENEL),  the number of single events in a
24-hour day and, by weighting factors,  the time of day in which these single events
occur.  These weightings approximate the increased sensitivity of a community to
                                                     27
intrusive noise during the evening and nighttime periods.    This composite scale can
be used in the same way as the  NEF scale to predict reaction of a community to an
accumulation of intrusive noises.     The CNEL value at a given point.can be approxi-
mated by:
            CNEL  »  SENEL  +   10 log Np  - 49.4dB                       (5)
where
            SENEL   =  average SENEL for each single event
            N_       =  weighted number of single events equal to Nn + 3 N_ + 10 N
     ND/  N_, N^.  =  number of single events during the daytime (7:00 a.m. -
                       7:00 p.m.), evening (7:00 p.m. - 10:00 p.m.), and nighttime
                       (10:00 p.m.  -7:00 a.m.), respectively.
            For analysis of the CNEL near freeways, an average SENEL is selected for
each type of vehicle, using Equation (4), along with corresponding figures for the
number of vehicles passing by during each of the three time periods.  The total CNEL
for this traffic mix is the logarithmic (or energy) summation of the CNEL values for
                                       B-28

-------
each type of vehicle.  Typical  SEN EL values for each type of highway vehicle at a
reference distance of 50 feet have been specified in Table 4-6 of Chapter 4.  The
SENEL at other distances was computed in the manner explained in Section B.3.
            Close to a freeway, the propagation loss for the maximum noise level
decreases according to the inverse square law of distance R  from  the source (i.e.,
     2
- 1/R ).  However, the time-integrated measure of the single event (SENEL) includes
a correction for duration which increases directly as the distance  R.  The net result is
that the SENEL decreases according  to a first power law with distance from the
vehicle.
            This is exactly equivalent to other analytical models for predicting noise
near highways, which show that for high traffic volumes (roughly greater than 1000
vehicles per hour), where the traffic noise can be treated as a line source, the average
noise  level near the freeway decreases according to the first power of the distance from
               30 31
the traffic lane.   '     The average A-weighted noise  levels (L,-r\) predicted by these
latter models, for a wide range of traffic volumes and average vehicle speeds, are shown
in Figure  B=13.  In this figure, the change in slope of the curves with traffic flow rate
is due to the change in character of the noise as traffic  volume increases.  For low flow
rates, each vehicle is heard as  an isolated single event  as it passes by.  For high flow
rates, the stream of traffic is heard as a nearly continuous quasi-steady state noise
with only minor fluctuations due to the particular traffic mix at any instant.
            For evaluation of noise  impact on all types of urban roads,  the following
additional parameters were required beyond  those already described:
            •    Mileage on each type of road
            •    Typical vehicle speed by road type
            •    Typical traffic flow rates
            •    Typical road right-of-way
These parameters are defined in Table B-7 for 1970 road conditions.
                                       B-29

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co
I
CO
o
          80
           70
     CN
      Z
       a.
      o
      (N


       £
      CQ

-------
                                 Table B-7

              Highway Mileage and Estimated Average Highway
                       Speeds for Urban Areas in 1970
Freeway

Major Arterial

Minor Arterial

Collector

Local


Notes
Mileage
Miles
9, 160
38,535
46,991
43,970
351,300
2
Typical
Speed
mph
55
40
40
30
25
3
Typical
Flow Rates
Vehicles/Hr
1,980
735
365
157
43
Typical
Right-of-Way
(No. of Lanes)
Feet
200
175
160
150
125
(8)
(6)
(5)
(4)
(2)
1   For urban areas in 1968 from Reference 32.

2   Estimated based on typical free traffic flow.

3   Computed average (see text).

4   Estimated effective value based on 12 feet per lane and 50-foot setback to
    nearest residence from edge of roadway.
                                   B-31

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Effect of Vehicle Speed
            Varying the average vehicle speed has two effects.  The average maximum
noise level for most highway vehicles increases approximately according to the cube
                    o i  o o *\A
of the vehicle speed.   '   '    Although  noise levels of heavy (diesel) trucks  increases
less with speed, due to their small contribution to the total highway noise impact,
the cube rule for vehicle speed was assumed for all vehicles.
            The second influence of vehicle speed is that it changes duration of a
single event and hence the SENEL, as indicated by Equation (4).  The net result is
that the average SEN EL for each type of vehicle  varies by the square of the vehicle
speed, as indicated by the following correction factor:
                   AS  =   20 log  -,  dB                               (6)

Forty (40) mph  is used as the nominal  reference speed corresponding to the reference
SENEL at 50 feet for each  type of vehicle.
Effect of Traffic Flow Rates
            The average traffic flow rates  Q listed in Table B-7 for each road type
were based on an average value computed by:

                   ~       Vehicle - Miles per day       ...   /,
                   U  =  -rrrc - ^ — 75 — jrm — ^r r vehicles/nr
                           (17 hours) x (Road Mileage)

This provides a highly smoothed average flow rate based on total national figures for
                                                                   32
traffic volume, road mileage, and an average "traffic day" of 17 hours.   (See
Figure B-8.)  Actual flow rates on many urban freeways will be substantially greater
than this.  However, to counterbalance this unconservative assumption, it was
assumed, when evaluating  the noise impacted area near freeways, that the entire
length of the freeway was adjacent to residential land.
            The weighted number of single events  Np required for computation of
the CNEL was substantially greater than the actual daily total. Using typical hourly
                                       B-32

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rates of urban traffic, such as indicated in Figure B-8, and the weighting factors for
time of day indicated for Equation (5), the weighted total number of events (vehicles)
was 2.2 to 3  times the actual daily total.  For conservatism, a factor of 3 times the
daily total was used for this analysis.
Additional Factors for Freeway  Impact Analysis
           An average shielding loss of 3 dB was used to approximately account for
the attenuation effect of barriers at the edge of freeways.  In fact, freeway noise can
be changed substantially (up to 10 to 15 dB), depending on the design of barriers and
                     31  35
elevation of the road.  '     The value of 3 dB was considered a reasonable average
for the wide range of freeway design conditions that exist.
           No attempt is made to account  for the effect  of changes in road grade or
conditions of the road surface on traffic noise.  Both of these factors can be significant
                     31
in specific situations..
           The effect of varying distances  from an observer to each lane of traffic
on a multi-lane highway with two-way traffic was accounted for by a single correction
factor to allow computations of noise impact to be based on an equivalent single-lane
flow of traffic.
           The nearest residence to all highways was assumed to be 50 feet from the
edge of the roadway.  The width of the roadway itself was assumed to be 12 feet for
each lane, with an average number of  lanes varying with  road type (as indicated in
Table B-7).  Thus, effective right-of-way was equal to the road width plus a 50-foot
set-back on each side.
Noise  Impacted Land Area
           As discussed in Section 4.4 of the text, a criterion value of CNEL = 65
was selected  as the outer boundary of the noise impacted area.  The area involved for e
each type of  road was equal to:
                         A  =  2  [d-dRl  .   L/5280, sq. mi.                (7)
                                      B-33

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where
            d   =  distance in feet from "equivalent single lane" of traffic to
                   position of CNEL =65 contour
            dD  =  distance in feet from this lane (positioned at center of traffic
             K
                   flow closest to observer) to the edge of the effective  right-of-way
            L   =  total mileage for this type of road, miles.
The resulting predictions of noise impacted land area for highways in  1970  has been
presented in Section 4.4 of the main text.   For a criterion value of CNEL =65, it
was found that only freeways contributed to the estimated noise impact area.  As dis-
cussed in Section 4.4, a lower CNEL criterion would be appropriate in some areas
which have a  lower residual noise level.  However, since all land adjacent to the
freeways was assumed to be residential, the noise impacted areas estimated are con-
sidered  reasonable for ranking the relative contribution of freeways to noise impacted
land of the transportation system.
Future Programs
            The growth of freeway mileage has been very rapid over the  past 20 years.
However, the growth has slowed down to a current rate of about 5 to  7 percent per
year.  The initial rapid growth was responding to the urban expansion in  the 1950's
and the need for improved travel facilities. The marked effect of freeway develop-
ment on urban travel efficiency is illustrated in  Figure B-14. This shows the change
in the 30-minute radius driving time in Los Angeles for three time periods — 1937,
before freeways  were available or urban growth  had occurred;  1953, when  there were
only 45 miles of freeway in the city; and 1966,  when the freeway system had expanded
                   36 37
to about 340 miles.   '      The largest radius (shortest travel time) obviously occurs
for the  latter period, while the smallest radius  (longest driving time) occurred in 1953
during the beginning phases of urban expansion.
            Continued expansion of the freeway system in urban areas is  expected to
follow the trends indicated by  Figures  B-15 and B-16.  The first shows the relationship
                                                                           32
between mileage per capita of various types of urban roads and city population.
                                       B-34

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CD
CO
Seventh Street
  Broadway
                 X/C/C/C
                         Pacific Ocean
                         Figure B-14. Radius of 30-Minute Driving Time to Downtown Los Angeles
                                                (From Reference 36)

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 0_
 O
eff
8
     10
                                                                 Local
 a>
 a>
£  1.0
I
   0.1
                                                                Average for:
                                                                  o Major Arterials
                                                                  o Minor Arterials
                                                                  o Collector

                                                                Freeways
   0.05
     100,000      250,000      500,000     1 Million      2.5 Million
                                         City Population
                     Figure B-15.  Urban Street Mileage Versus City Population
                                       (From Reference 32)
                                               B-36

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0)
0)
III
u-
o

-------
The nearly constant values of highway mileage per capita fora wide range in city
population is clearly evident.  Note,  however, that the largest number of miles per
capita occurs for all types of roads for the largest cities.  Figure B-16 shows  that there
is a very high correlation between freeway mileage and passenger vehicle ownership,
with a slight trend  toward fewer miles  per vehicle for larger cities.
            Thus, for projection to the year 2000, it was assumed that freeway miles
would increase in direct proportion to  automobile ownership in urban areas.  (See
Figure B-3.)
            There has been a small progressive increase in average vehicle speeds
                                                                                38
over main rural highways in the last 30 years, amounting to about 1 percent per year.
                                                 24
Engine horsepower  has also progressively increased.   However, neither of these
effects were considered in forecasting  trends in highway noise in the future.  There
are, in fact, data to indicate that individual vehicles have become progressively
                                                           34
quieter, which would tend to counteract the preceding effects.
            Considering that most freeway systems are currently operating near
capacity, flow rates were assumed to remain essentially constant.  Based on the pre-
ceding assumptions and methods,  predictions of noise impacted land for urban highways
for the years 1985 and 2000 were made for several options of noise reduction for high-
way vehicles.  The results have been presented in Table 4-7.
            Urban  traffic on freeways  is predicted to continue to create the only
significant noise  impacted land areas.   This is due to the inherently high volume of
traffic flow carried on freeways as compared to all other types of urban streets.  As
indicated in Figure B-17, even though freeways constitute only about 2 percent of the
road mileage in a typical urban area,  they handle 21 percent of the vehicle-miles —
as much as all of the traffic on local streets.
                                       B-38

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                            Collector Streets
                                                  Local Streets
                                                  71$miles of street
                                                  21$ vehicle miles
                       Minor Arterials
              Major Arterials
              Freeways
               2% miles
              21$ vehicle miles
             20     30      40      50      60      70     80
               Cumulative Percentage of Miles of Urban Streets
Figure B-17.  Cumulative Urban Street Mileage Versus Cumulative
    Vehicle  Miles Served in a Typical Urbanized Community''
                              B-39

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B.5         Noise Impact on Operators or Passengers of Transportation Vehicles and
            Infernal Combustion  Engines                          .
            The two effects considered in evaluating noise impact on operators or  .
passengers were potential hearing damage risk and speech communication.  To rank the
various sources in terms of potential hearing damage risk, the actual noise  exposure for
a typical  operator or passenger was converted to an equivalent 8-hour A-weighted
noise exposure level  L(8 hr) with the following expression:

            L(8hr) - LA +  16.7 log (T/8), dB(A)                             (8)

            L.   =  A-weighted noise level at the operator's ear
            T    =  typical exposure time in hours
This is essentially equivalent to the  "5 dB per doubling of time" rule that is used in
the Occupational Safety and Health Act for defining allowable noise exposures for
employees.  The equivalent 8-hour exposure levels estimated in this way have been
presented in Figure 4-4 for transportation vehicles and in Table 4-9 for internal
combustion engine devices, along with corresponding exposure times.
            Impact of transportation systems on speech communication for passengers
                                                            39
was evaluated primarily  in terms  of speech interference effects.     Criteria  for the
latter are specified in  terms of the allowable background noise level as a function of
talker-listener separation distance to prevent interference with significant continuous
speech communication.  The criteria allow for the tendency of a talker to  raise his
voice level as noise level increases above about 55 dB(A).
            Conversely, the same criteria for negligible speech interference can also
be used along with data  on normal voice level to estimate the minimum levels desired
in multi-passenger commercial vehicles to provide speech privacy.  That is,  a  lower
bound exists for the desired noise level in such passenger vehicles so that a private
conversation cannot be overheard by adjacent passengers.  This minimum internal noise
level can be lowered only by decreasing talker-listener separation, or increasing the
                                       B-40

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propagation loss between the talker-listener pair and an observer with a sound barrier.
The criteria for speech privacy is based on maintaining an articulation index (AI) less
                                              40
than 0.05 for the undesired communication path.
            Table B-8 summarizes these two criteria for the major passenger vehicles
and is based on the specified typical talker-listener separation distances.  In general,
most transportation vehicles meet these two criteria with the exception of multi-
passenger helicopters, which are generally too noisy,and city or highway buses, which
generally have internal levels lower than allowed for speech privacy between adjacent
seats.
B.6         Glossary of Terminology
Sound Pressure Level  (SPL)
            The sound pressure level,  in decibels  (dB), of a sound Is 20 times the
logarithm to the base of 10 of the ratio of the pressure of this sound to the reference
pressure.  For the  purpose of this report, the  reference pressure shall be 20 micro-
newtons/square meter  (2 x 10   microbar).
Noise Level (NL)
            Noise level,  in decibels,  is an A-weighted sound  pressure level as
measured using the slow dynamic characteristic for sound level meters specified  in
ANSI SI.4-1971,  American National  Standard Specification for Sound Level Meters.
The A-weighting characteristic modifies the frequency response of the measuring
instrument to account approximately for the frequency characteristics of the human
                                                                 -4
ear.  The reference pressure is 20 micronewtons/square meter (2 x 10   microbar).
Single Event Noise Exposure  Level  (SENEL)
            The single event noise  exposure level, in decibels, is the level of the
time-integrated A-weighted squared sound pressure during a given event based on
reference pressure of 20 micronewtons  per square meter and  reference duration of
one second.
                                       B-41

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                                 Table B-8

       Criterion Noise Levels for Speech Interference and Speech Privacy
                    in Transportation Vehicles in Terms of
                         A-Weighted Noise Levels
                        Maximum for No             Minimum for
                        Speech Interference          Speech Privacy

                        Talker-
                        Listener 9           Observer.      Barrier Loss
       Vehicle          Distance            Distance      0    5 dB    lOdB
                           Feet     dB(A)     Feet             dB(A)


Buses,  Trains            1-1.7      79-85   2.25-2.7   90-93  84-86  76-79

Commercial Jet Aircraft
  -Short Haul           1.1-1.3    82-84   2.7-3.1     89-90  82-84  74-,76

Commercial Jet Aircraft                         •
  - Long  Haul           1.2-1.7    79-83   3.0-3.3     88-89  81-89  74-75
 For communicating voice (Reference 39).
2
 Typical range of side-by-side seat spacing — 5 inches.
3
 Typical range of front-to-back seat pitch.

4
 Excess loss by barrier or voice directivity.
                                    B-42

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Daily Community Noise Equivalent Level (CNEL)
            Community noise equivalent level, in decibels, represents the average
daytime noise level during a 24-hour day, adjusted  to an equivalent level to account
for the lower tolerance of people to noise during evening and nighttime periods
relative to the daytime period.  Community noise equivalent level is calculated from
the hourly noise levels by the following:
       CNEL  =  10 log
  t.,
antllog
                         antilog           +   ,0
HNLD
  To"
 Where
        HNLD are the hourly noise levels for the period 0700 -  1900 hours;
        HNLE are the hourly noise levels for the period 1900 - 2200 hours;
        HNLN are the hourly noise levels for the period 2200 - 0700 hours;
 and     y     means summation.
Hourly Noise Level (HNL)
            The hourly noise level, in decibels, is the average (on an energy basis)
noise level during a particular hour.   Hourly noise level is determined by sub-
tracting 35.6 decibels (equal to 10 loglo 3600) from the level of the time-integrated
A-weighted squared sound pressure measured during  the particular hour.
                                      B-43

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Residual Noise Level
            The temporal pattern of an A-weighted noise level measurement of com-
munity noise is generally characterized by two features.  The first is the variation in
peak levels caused by street traffic, aircraft, and other single event noises.  The
second feature is that noise level characterized by a fairly steady lower level upon
which are superimposed increased  levels of the single events. This fairly constant
lower level is called residual noise level.  The continuous noise one hears in the
backyard at night when no single source can be identified and which seems to come
from 'bll around" is  an  example of residual  noise.
                                       B-44

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                                 REFERENCES
B-l.   Statistical Abstract of the United States 1970, Bureau of Census, U.S.
       Department of Commerce.

B-2.   1969 Statistical Supplement to the Survey of Current Business,  Bureau of
       Census, U.S. Department of Commerce.

B-3.   Auto Facts, Automobile Manufacturers Association, Inc.,  Detroit, Michigan,
       1971.

B-4.   Air Transport 1971, Air Transport Association of Amercia,  Washington,  D.C.

B-5.   70-71 Transit Fact Book, American Transit Association, Washington,  D.C.

B-6.   Leisure Time Product  Noise, Sub Council Report,  National Industrial
       Pollution Control Council, May 1971.

B-7.   "Joint DOT-NASA Civil Aviation Research and Development Policy Study,"
       supporting papers, Department of Transportation and  National Aeronautics
       and Space Administration, Washington, D.C.,  March 1971.

B-8.   Transportation and Parking for Tomorrow's Cities,  Wilbur Smith and
       Associates, New Haven, Connecticut, 1966.

B-9.   Smith,  Wilbur and Associates, "Motor Trucks in the Metropolis, "Automobile
       Manufacturer'slAssociation, Detroit, Michigan, August 1969.

B-10.  Ganz, A.  "Emerging Patterns of Urban Growth and  Travel, V
       Massachusetts Institute of Technology, Department of City and Regional
       Planning, January 1968.

B-ll.  "Study on the Effect of Noise Pollution,  Section on Community Noise,"
       Office of Noise Abatement and Control, Environmental Protection Agency,
       Washington, D.C., October 1971.

B-12.  Shaw, E.A.G.,  "Theoretical Model for Steady State Urban Noise,"  77th
       Meeting of the Acoustical  Society of America,  Philadelphia, Pennsylvania,
       April 9, 1969.
                                     B-45

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B-13.    Abramowitz, M. and Stegun, I.A. (editor), "Handbook of Mathematical
         Functions with Formulas, Graphs and Mathematical Tables," National
         Bureau of Standards Applied Mathematics Series 55, June 1964.

B-14.    Sutherland, L.C., "Air-to-Ground Sound Propagation — Some Practical
         Consideration," 82nd Meeting  of the Acoustical Society of America, Denver,
         Colorado,  October 1971.

B-15.    Society of Automotive Engineers, "Method for Calculating the Attenuation
         of Aircraft Ground to Ground Noise Propagation During Takeoff and Landing,"
         AIR 923, August 1966.

B-16.    Sutherland, L.C., "A Review of the Molecular Absorption Anomaly,"
         77th Meeting of The Acoustical  Society of America, Philadelphia, April 1969.

B-17.    Evans, L.B., Bass,  H.E. and Sutherland,  L.C., "Atmospheric Absorption
         of Sound, Theoretical Predictions," 82nd Meeting of The Acoustical Society
         of America, Denver, Colorado, October 1971.

B-18.    Piercy, J.E., "Role of the Vibrational Relaxation of Nitrogen in the
         Absorption of Sound in Air," Journal of the Acoustical Society of America,
         Vol. 46, September 1969.

B-19.    Harris, C.M., "Absorption of Sound in Air Versus Humidity and Temperature,"
         NASA Contractor Report 647, January  1967.

B-20.    Society of Automotive Engineers, "Standard Values of Atmospheric Absorp-
         tion as a Function of Temperature and Humidity for Use in Evaluating
         Aircraft Flyover Noise," ARP 866, August 31, 1964.

B-21.    Wyle Laboratories,  (unpublished data).

B-22.    Stephenson, R.J. and Vulkan,  G.H.,  "Traffic Noise,"  Journal of Sound
         and Vibration, March 1968.

B-23.    Delany, M.E., "Range Prediction for Siren Sources, " Special Report 033,
         Aerodynamics Division, National Physical Laboratory, November,  1969.

B-24.    Dickerson, D.O. (Editor),  "Transportation Noise Pollution: Control and
         Abatement, " NASA Contract NGT 47-003-028, National Aeronautics and
         Space Administration, Lang ley  Research Center, and Old Dominion University,
         Summer,  1970.
                                      B-46

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B-25.    Estep, A.C.,  "1967 Classified Vehicle Study, " Business and Transportation
         Agency, Department of Public Works, Division of Highways, Sacramento,
         California,  December 1970.

B-26.    Bishop, D.E.,. etal,  "Procedures for Developing Noise Exposure Forecast
         Areas for Aircraft Flight Operations, " FAA DS-67-10, Federal Aviation
         Administration, August 1967.

B-27.    Wyle Laboratories,  'Supporting Information for the Adopted Noise Regula-
         tions for California Airports, WCR 70-3(R), Final Report to the California
         Department  of Aeronautics, January 29,  1971.

B-28.    Galloway, W.J. and Bishop, D.E., "Noise Exposure Forecasts:  Evolution,
         Evaluation,  Extensions, and Land Use Interpretations," FAA NO-70-9,
         Federal Aviation Administration, August  1970.

B-29.    Bishop, D.E. and Horonjeff, R.D.,  "Noise Exposure Forecast  Contours for
         Airport Noise  Tradeoff Studies at Three Major Airports, " FAA-NO-70-7,
         Federal Aviation Administration, July 1970.

B-30.   Johnson, D.R. and Sounders,  E.G., "The Evaluation of Noise from Freely
         Flowing Road Traffic, " Journal of Sound and Vibration, Vol. 7,  pp. 287-309,
         March 1968.

B-31.    Gordon, C.G., etal, "Evaluation  of Highway Noise," NCHRP 3-7/1
         Highway Research Board, National Academy of Sciences, Washington, D.C.,
         January 1967.

B-32.    1970 National Highway Needs Report, 91-28, Bureau of Public Roads,
         Federal Highway Adminstration,  U.S. Department of Transportation,
        September 1970.

B-33.    Thiessen,  G.J., "Community Noise — Surface Transportation, " 74th Meeting
         of The Acoustical Society of America, Miami, Florida, November 1967.

B-34.    Passenger Car  Noise .Survey, California Highway Patrol, January 1970.

B-35.    Beaton, J.L. and Bourget,  L.,"Can  Noise Radiation from  Highways be
         Reduced by  Design," Highway Research Record No. 232,  Highway Research
         Board, National Academy of Sciences, Washington, D.C.,  1968.

B-36.    Pegrum, D.F., "Residential Population and Urban Transport Facilities, in the
         Los Angeles Metropolitan Area, " Occasional  Paper No. 3,  Bureau of Business
         and  Economic  Research, University of California,  Los Angeles, California
         1964.
                                     B-47

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B-37.    1968 Traffic Statistics, Department of Traffic, City of Los Angeles,
         California.

B-38.    Highway Statistics/1969, Federal Highway Administration, U.S. Department
         of Transportation.

B-39.    Webster, J.C.,  "SIL-Past, Present and Future, " Sound and Vibration,
         August 1969.

B-40.    Kryter,  K.D., "Methods for the Calculation and  Use of the Articulation
         Index, " Journal of The Acoustical Society of America, Vol.  34, 1962.
                                      B-48

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                                   APPENDIX C
                      NOISE  GENERATOR CHARACTERISTICS

This appendix provides a detailed analysis of the characteristics of the principal noise
generators in the transportation category. The  noise sources to be analyzed are:
            •   jet engines,
            •   propellers and rotors,
            •   internal combustion engines, and
            •   tires.

C.I         Jet  Engine Noise
            There  are three primary sources of noise on a commercial jet aircraft:
engines, boundary layer pressure fluctuations and internal equipment. Engines produce
noise  at inlets and at the exhaust regions of fan exit ducts and the primary nozzle.
Pressure fluctuations in the fuselage boundary layer excite structural components that
in turn radiate acoustic energy into the aircraft interior.  Equipment such as pumps,
blowers and auxiliary power plants installed on an aircraft  create noise problems in air-
craft interiors.   The latter two noise sources are the primary contributors  to the noise
levels in the passenger cabin during cruise.  The major aircraft noise problems, how-
ever,  are associated with the noise levels imposed upon communities adjacent to large
airports. Noise generated by the jet engines constitutes the dominant component  in
producing this noise impact.
            The two principal sources of noise in a jet engine are the jet exhaust and
the fan/compressor. As illustrated in Figure C-l, for the case of a low bypass-ratio
turbofan engine, jet noise radiates mainly toward the rear of the engine.  Fan/com-
pressor noise radiates forward out through the engine inlet and aft through the fan
exhaust duct. Figure C-2 shows the effect of engine power setting on the relative
contributions from  the jet and fan noise sources.  On takeoff, the jet noise contributes
measurably to the overall noisiness.  During landing approaches, however, the fan
                                        C-l

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Inlet
       Fan
                Fan Discharge Duct
                    '     /    \
                    I    / '   *  *
                       /  x  VI   /
                                                  Takeoff
                                           110  120 dB
                                                  Landing Approach
                    Fan Noise from Inlet
                    Fan Noise from Fan Exit
            	Primary-Jet Noise
            	   Overall Sound-Pressure Level
       Figure C-l.  Turbofan-Engine Noise Sources and Distribution
                                    C-2

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              120
              no
Perceived-
Noise Level
  (PNdB)
              100
               90
               80
                                   wtx
                                             Composite
                                                         Fan Whine f om Discharge Duct

                                                Fan Whine from Inlet
  Takeoff
Thrust Range
        Secondary
          Jet
                                               Landing-Approach
                                                 Thrust Range
                                   6          8         10         12

                                      Engine Net Thrust (1,000 Ib)
                             14
                Figure C-2.  Turbofan-Engine Noise at 400-Foot Altitude
                                         C-3

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whine from the inlet and discharge ducts is 10 to 20 PNdB higher than the jet exhaust
noise.
            Engine design is a critical governing factor in determining the balance
between jet and fan noise. In the early turbojet engines, the jet noise component was
dominant throughout the range of  power settings.  Subsequent high bypass-ratio turbo-
fan engines generate significantly reduced jet noise levels.  However, as the fan noise
radiation is reduced through improved fan design technology and fan duct noise attenu-
ation, both sources of noise retain their significance in determining the total jet engine
noise levels.  The following two sections contain brief accounts of the generation and
radiation characteristics of these sources of jet engine noise.
C.I.I      Jet Exhaust Noise
            The noise generation  processes in the exhaust wakes of current and antici-
pated future turbofan engines are  dominated by quadrupole noise radiation.  This
mechanism is caused by the turbulent mixing that occurs along the boundary between
the high-velocity exhaust jet and the quiescent atmosphere. The mixing  process
generates a series of flow fluctuations with small turbulent eddies formed  close to the
                                            j
nozzle orifice.  Increasingly larger eddies are generated within the developing-
mixing layer progressively farther downstream, as illustrated in Figure C-3.  However,
these fluctuations degenerate into smaller scale structures.  They  also interact with
each other and with the mean flow to form both larger and smaller eddies. This inter-
action results in a distribution of turbulence scales at any location within the mixing
layer, with the mean turbulence scale proportional to the local mixing layer width.
            The acoustic pressure fluctuations associated with the turbulence fluctu-
ations are distributed in a corresponding manner, with the peak frequencies generated
varying continuously from high frequencies in the thin mixing layer close to the
nozzle exit to low frequencies in  the wide mixing layer far downstream.  However,
once generated,  the acoustic waves interact with other turbulent  structures (diffraction)
and mean flow gradients (refraction) to emerge from the jet flow with different
directional  and physical characteristics than originally emitted.   These phenomena
are qualitatively illustrated in Figure  C-3.
                                        C-4

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                                                     TURBULENCE NOISE
n
 i
Ul
                                                                                                             u(x,y)
                                      L(P,T)
                                     Ambient
                                                       Layer
                                                (Mixing Flow)
             DM~.»-,I«  roreriTiai v-ore    •	—•	__
             Nozzle	m-.rrr^	••"-	=

                   Small Scale
                  Shorter Lived  Eddies
Velocity Fluctuation   P>   Pressure Fluctuation
                               (Acoustic)
                                     Energy
      (Eddy)

Source Distribution

Eddy Degeneration

Eddy Interactions

Eddy Convection
                                                                   Energy
                                                           V
                               • x/D
                   x For Max Level of f
                                                                            Large Scale
                                                                            Longer Lived Eddies

                                                            Sound Path Effects
                                                            Diffraction Refraction
                                                            Velocity and Temperature Gradients

                                                          f =  frequency
                                                          D =  nozzle.diameter
                                                          x =  distance downstream from nozzle
                                                     -L(P,t) =  length of potential core
                                                            =  jet spreading angle
                                               Figure C-3.  Jet Noise Generation

-------
            The basic mathematical model of this noise generation process was first
                      1  2
formulated by Lighthill  '  who combined the equation of continuity and momentum
into the inhomogeneous Lighthill wave equation:

                        2               2         ^  T
                        ^         r\     ^         o  i • -
                      -H  -  %   -H   -
                           ax.-       3xi 3xj

T..  =  Lighthi 11's turbulence stress tensor
 'J                       2
    -  nu.u.  +  P..  - a   ofi.-
       p  i  J      ij      o M uij
u.   =  velocity in the  i  direction
a   =  speed of sound in the uniform medium
 o      r
p   =  density  of the flow
P..  =  tensor incorporating pressure and viscous terms
6..  =  Kronecker delta
The well-known solution of this  differential equation may be written:
Numerous theoretical investigations of jet noise generation have arrived at analytical
                                                     3—6
results by means of careful manipulation of this solution.      The approach has been
developed to a high degree of sophistication and permits qualitative estimates of the
noise radiation as a function of the flow velocity and Mach number.  However, the
Lighthill theory has its basic limitations.  It is not well suited to describe flows in
which the speed of sound and the mean density vary. Therefore, the effects of temper-
ature and temperature gradients, although implicit  in the formal solution,  are usually
neglected.  In addition, the connected path of sound through the mean shear layer is
not readily accounted for.  These restrictions on the application of the Lighthill theory
                                                                                    7-9
have resulted in the formulation of new mathematical approaches by various investigators.
                                        C-6

-------
These will not be discussed here,  since they have not brought on improved techniques
for the quantitative evaluation of jet noise radiation.
            The application of dimensional analysis to Lighthill's solution yields the
dimensional law for the intensity of the acoustic radiation from a jet flow to:
                      I
    / £\
5   V /                5
                           pa     V      (1 - M cos 6)
                           'o  o
where
            I    =  acoustic intensity
            U   =  flow velocity
            p   =  atmospheric density
            D   =  flow dimension (jet diameter)
            M-  =  flow Mach number
            r    =  source-observer distance
            0   =  angle subtended by source-observer with respect to
                   flow direction
                                                                              o
            This result has  been well  substantiated by experiment, although the U
law somewhat overestimates the intensity at high jet velocities., Furthermore, the
empirical dependence of intensity on  the jet density p is a function of the jet velocity.
        2
Thus,  p   appears to correlate the experimental data at jet velocities greater than
1800 feet/second, whereas at lower speeds,  Q provides the better correlation parameter.
With certain similarity assumptions concerning the variation of the peak frequency  f,
the mean velocity U,  and the wake  diameter  D  with distance along the jet axis, the
above equation leads to expression for the power spectral density of the sound power
emitted by the jet flow.  At high frequencies well above the typical frequency
f  =  0.2 U /D  defining the peak of the power spectrum, the  asymptotic expression
becomes:
                                        C-7

-------
where
            W  =  acoustic power
            f   =  frequency
  subscript  e   =  nozzle exit
At the low frequency limit, the corresponding variation is:
                                   dW     ,2
                                  ~sr  ~ f
Figure C-4 shows a normalized sound power spectrum obtained from measurements on a
wide  range of jet engines and scale model air jets.    The spectrum shows the theoreti-
cally predicted trends at the low  and high frequency limits.
            Figure C-5 presents a generalized correlation of the peak polar sound
pressure levels generated  by jet engine exhausts and scale model air jets.    The
correlation'on the basis of p  yields acceptable data scatter, although the increasing
spread of the data at the low velocity end is of particular note.  The, cause of this
anomaly is additional noise generated upstream of the nozzle exit and propagating out
through the jet wake into the  far  field. This noise is generally dipole (U ) in character,
hence its dominance at  low velocities. Referring to Figure C-5,  line B-B shows the
peak  polar sound pressure levels measured with a.noiser-generating obstruction installed
in the upstream pipe; line C-C shows the same measurements with the obstruction
removed.   Line D-C is obtained if the upstream pipe is carefully treated to eliminate
all possible upstream sources of noise. The  immediate conclusion from this is that the
line A-B, which represents data from a wide range of jet engines and model rigs, is
influenced by sources other than the jet mixing noise.  In the case of scale model air
jets,  these sources may  be simple upstream obstructions.  For the full-scale jet engines,
                                                      i          •' . .
however,  there are numerous additional and as yet incompletely defined sources.  These
additional sources are often termed engine core noise and are of significance for new
technology engines which have subsonic primary exhaust velocities.
            Current and advanced technology turbofan engines are characterized by
having a lower velocity fan exhaust stream surrounding the primary jet exhaust.  The
generation of the noise  field by these multiflow jets is even more complicated than  for a
                                        C-8

-------

-10
-20
-30
   .01
            I    '   '  I  • i
                      f
                     W(f)
                     wt
                     Ue
   •  ( =
     I =
frequency
acoustic power/cps
total acoustic power
exit velocity
effective exit diameter  :    '
de for subsonic jets
sonic velocity at nozzle throat
ambient velocity of sound '
                                                I I I
                                 1
                                                  r2    -i
.05     .1     .2
                 ;5      1.0    2.0
                                                                        I I  I I
5.0
10
                 Modified Strouhal Number
                                          fda.
                                           Jea0
     Figure C-4. Normalized Power Spectrum for Axisymmetric
               Jets Issuing from Convergent Nozzles
                 (Data from Eldred,  Reference 10)
                                C-9

-------
         180

—T	"  170
 -N
_o|cs_2  160

  ^      150
     <
     in
     ~   140
   O
  dT
  .3
  o
   I
  _l
  Q_
  I/)
  <
  o
130
120
110
         100
                -0.6
                                 500
                                         1000
   R  = djstqnce From jet exit
  a   = ambient speed of sound
   o
  T   = ambient temperature
  p   = ambient density
  A.  = nozzle exit area
   J
  p.   = jet density

,. Subscript ISA% refers to standard
    day ambient condition
   	,   Standard Day Jet Velocity
    1500          ft/sec
                    -0.4
-0.2
   Lo
         0;2
0.4
                          Figure C-5.  Jet Noise Correlation Peak Polar OASPL
                                   (Data from Bushel I,  Reference  11)
                                             C-10

-------
single jet.  One significant aspect of jet noise generation is that the sound results
from an extended source volume over the length of the mixing flow.  Variations to
this mixing flow caused by the interaction of the two  jets will  result in different noise
                                           12
characteristics.  A recent experimental study   included a detailed examination of
the effects of the bypass flow on the total noise radiation, resulting  in the following
conclusions:
           •    The reduction  in jet noise due to  shrouding of primary flow by
                secondary flow is maximum for a secondary to primary velocity
                ratio near 0.57 on a constant thrust basis.
           •   "The reduction  in jet noise increases with increasing area ratio.
           •    The noise reduction is independent of the pressure ratio of the
                priiTiory r.czzlc end the tcto! t6r™r>6rc!t|Jr(? of the nrimarv flow.
           These concepts are illustrated in Figure C-6. A noise reduction of
10 PNdB at a 1500-foot sideline is achieved at an area ratio of  10 as compared with
a single nozzle jet (area ratio zero)  having  the same thrust.
C.I.2     Fan/Compressor Noise
           Compressors generate two distinct types of sound,  broadband and harmonic.
The random broadband sound extends over a very wide range of frequencies.  The har-
monic sound has one or more fundamentals corresponding to the blade passage fre-
quencies of the compressor stages, together  with associated harmonics.  A third type
of compressor noise,  combination tones, is important in high bypass ratio turbofan
engines operating at takeoff power.  A typical compressor noise spectrum is shown in
Figure C-7.
Broadband  Noise
           Broadband noise is  attributable  to the  action of turbulence and other
                                                              13
irregular flow disturbances upon the  compressor blades.  Sharland   studied compressor
broadband  noise radiation both  theoretically and experimentally, and his work  forms
much of the basis for present knowledge.  Basically, there are two primary mechanisms
for broadband noise generation. The first is associated with the passage of a blade into
                                        C-11

-------
            Ratio of Secondary Velocity to Primary Velocity
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i 	 0

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                                                                         Area Ratio
   Figure C-6.  Effect of Velocity Ratio on Maximum Perceived Noise Level

 on a 1500 ft Sideline Using Secondary Velocity as Reference at Constant Thrust

                       (Data from Eldred, Reference 12)
                                      C-12

-------
Sound-
Pressure
 Level
                                    Fundamental
                                    Blade-Passing
                                       Tones

                                     Third Stage •

                                    Second Stage -

                                      First Stage -
                  60
200        600      2000

    Frequency (Hz)
                                Second Harmonic
                                of Blade-Passing
                                     Tones

                               	First Stage
                               	Second Stage
                               I— Third Stage
                         Combination Tones
6000      20,000
                  Figure C^-7.  Typical Compressor-Noise Spectrum
                                        C-13

-------
an existing region of turbulent flow caused by upstream disturbances, which in
practice may be various compressor stages of rotor, stators, inlet guide vanes, struts,
et cetera. The velocity fluctuations in the oncoming flow generate lift fluctuations
at the blade surface, which in turn radiate noise.  The second mechanism is essentially
self-generated and arises even for  a blade operating  in undisturbed air.  At sufficiently
high Reynolds numbers, typical of  compressor blading, the boundary layer becomes
unstable.  In addition to generating direct pressure fluctuations on the blade surface,
it gives rise to an unsteady wake which in turn induces pressure fluctuations at the
blade trailing edge.
            .For an infinite rigid surface, the monopole and dipole terms in the
                                         14
equation for sound radiation  by turbulence    disappear,  while the quadrupole term
must be integrated over all space including an image turbulence behind the surface.
That is, the quadrupole radiation,  which is doubled due to reflection,  is the only
source of noise in this case.   However, for a finite surface (e.g.  a compressor blade),
the reflection is not complete and  a magnification of the  quadrupole field results.
In this case,  it is  convenient for analysis purposes to regard the surface pressure fluctu-
ations as the source of noise, which is therefore of a dipole nature. These observations
                                          g                                  X
suggest that large surfaces will  radiate as U   while small ones will radiate as  U .
Whether the surface is "large" or "small" depends upon its size relative to both acoustic
(\)  and turbulence  (&)  wavelengths.
            Since the latter quantities are related by the flow Mach number
N =  i/\r one can state that for a surface of dimension  d,  the  radiation is quad-
rupole if  M  »  jj/d,  and dipole  if M << A/d.  Since  f,  is also proportional  to
frequency, higher frequencies are  more likely to radiate as quadrupoles.
            The two  sources of random sound discussed above can be related to two
basic situations.   The first is  the production of noise on a blade due to the boundary
layer actually  set up on that  blade.  This is termed  "self-generated" noise;  it is small-
scale (i.e., high  frequency), and  it quadrupole in nature. The second is the noise
produced by passage  pf the blade through turbulence generated upstream of  the blade.
                                         C-14

-------
This is "externally generated," has a much larger scale (lower frequency), and is dipole
in character.
            A dimensional  analysis of the various sources yielded the following relation-
ships for the total power (W) radiated from an area (S):
                                External Turbulence
                                           4   2
                           ...     1       IT MS                ,,.  ,  ,
                           W  =  -7- p   	                (dipole)
                                             o

                  Self-Induced Boundary Layer Pressure Fluctuations

                                      -7     PC0'3                              3
                              W  =  10      —	           (dipole)          a 3

                     Reflection of Boundary Layer "Self-Noise"

                                        -8     Pb^5                             5
                            W =  6x10     	          (quadrupole)     a
                                                  o
            It turns out that for turbulence levels in excess of 0.001, the first
equation dominates and suggests that "external  turbulence" is a very significant noise
source.
            The prediction of broadband noise  radiation, although analytically
straightforward, is critically dependent upon the nature of the spatial correlation of
the surface pressure fluctuations. The problem  reduces to that of estimating the
variation of spanwise and chordwise correlation lengths with  the compressor operating
configuration.
Harmonic Tones
            The main difference between harmonic and broadband noise generation is
that the former is associated with periodic rather than random flow disturbances in the
compressor duct.  Otherwise, the mechanisms are very similar.  The word "periodic"
                                        C-15

-------
here essentially includes the fundamental or steady velocity terms which are associated
with the steady thrust and torque forces acting upon the blades.  Since this is the basic
mechanism of propeller noise radiation, this source of compressor sound is sometimes
referred to as the propeller mode.  Its origin was first analyzed by Gutin,    whose
theory is still widely used for propeller noise prediction.
            Of much more importance is the noise radiated by the action of fluctuating
forces upon the blades due to the presence of "higher harmonic" flow fluctuations.
These flow fluctuations are due to the presence of obstructions such as struts, guide
vanes, or stators, which produce velocity defects and potential flow interactions.
Figure C-8 shows the basic geometry for stator-rotor interaction.  Several  alternative
theories are available for the prediction of  harmonic noise generation. Lowson's
theory   will be used to describe the problem.
            Like Curie's theory  of sound radiation by surfaces, Lowson's analysis
starts with Lighthill's basic equation for aerodynamic sound generation:
      2        9     2
     o  p  _a2   5  P   =
               °
                                            st
The left-hand side is the acoustic-wave equation, and on the right-hand side are the
three source terms corresponding to monopole, dipole and quadrupole radiation,
respectively.  The only term of significance for most applications is the  second,  which
corresponds to noise radiation by surface forces. Retaining only this term, the solution
may be written:
                      -^rff
                        4ira   J J
(x,
                 '   "   "      ~            i* ~ii
where the integration must be performed over the entire source region.
                                        C-16

-------
Stator
Stator
         R = rotor radius .
         fi = rotational frequency in radians/sec
         d = stator-rotor spacing
         a =  stator exit swirl angle
         p =  rotor turning angle
         w =  flow velocity
         Figure C-8.  Basic Wake Geometry
          (Data from Lowson, Reference 16)
                         C-17

-------
If one of the aerodynamic force components acting on the blade,  namely the thrust,
is written in its Fourier form,  the nth harmonic can be written:
                                T  = T  cos
                                      n
Upon substitution, the integral solution can be integrated for one revolution to yield:
  c   -
where

            m
            B

=  sound pressure ampli-
   tude of the nth sound
   harmonic
=  order of the harmonic
=  number of blades
=  rotational speed
=  Bessel  function of
                                              M
                                              g
                                               6

                                               X
                                                    =  blade Mach number
                                                    =  speed of sound
                                                    = , distance from  blade
                                                    =  angle from fan axis to
                                                       field point
                                                    =  multiple of load harmonic
                             II.IIUII Ul
                     order mB
When n = 0, this reduces to the Gutin equation.  The important thing to note about this
equation for any value of m is that any thrust harmonic can generate any sound harmonic.

            Outside  a certain range of frequencies, however, the acoustic efficiencies
of these harmonics are low; for practical purposes, only values of the load harmonic
number (k)  need be considered lie in the range:
                         -Msine) 
-------
            Such equations, although based upon a number of simplifying assumptions,
give convenient solutions for the sound radiated by rotors and stators, which have been
demonstrated by Ollerhead and Munch    to be remarkably accurate for the first  har-
monic radiation  by typical fan configurations.  However, these computations, like  all
solutions to  compressor noise generation, are only as accurate as the force-input  terms.
These correlations were obtained with use of airfoil-wake data to estimate the harmonic
content pf velocity profiles behind compressor stages.  The scatter in the data shown in
Figure C-9 reflects this uncertainty in the force-input terms.  Typical  velocity profiles
were assumed for the theoretically determined line in the figure.   Improved knowledge
of these profiles should close the discrepancy between the theoretical and experimental
noise levels.
Combinarion Tones
            Combination tone noise is radiated from the inlet of turbofan  engines
having fan blades rotating with supersonic tip speeds; hence, it is a prominent type of
noise from the current high bypass ratio turbofan engines at takeoff power. This effect
                           18
is illustrated in Figure C-10.    Unlike  the sound field produced by fans  at subsonic
operation, where discrete tones  are produced at harmonics of blade passage frequency,
fans at supersonic tip speeds generate a multiplicity of tones  at essentially all integral
multiples of engine rotation frequency.
            The essential features of combination  tone generation are well established. '
Shock waves are produced at the leading edge of each blade and spiral forward of the
fan, conveying sound energy out of the inlet to the far field. The waveforms are fairly
uniform close to the fan, both in shock amplitude  and  in spacing between shocks.
Farther forward of the fan, however, much of the  blade-to-blade periodicity is lost and
variations in shock amplitude and spacing become prominent. Since the shocks form a
fairly steady but irregular pattern  rotating with the fan,  the corresponding noise spectrum
is composed of a series of tones at harmonics of the shaft rotation frequency.
            This loss of blade-to-blade periodicity can be explained on the basis of
finite amplitude wave theory. Close to the fan, the intervals between shocks are quite
                                        C-19

-------
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                   300           500               1000

                         Vf — Mechanical Tip Speed, ft/sec
                                                                1500    2000
 Figure C-9.  Comparison of "Theory" and Experiment.  Maximum Fan Discharge Noise
           in Octave Band Containing Fundamental Blade Passage Frequency

                         (Data from Lowson,  Reference 16)
                                        C-2C

-------
CO
0)

-------
uniform due to the regular spacing of the blades.  Some variation in shock amplitude,
however, is inevitable because of small  manufacturing variations in the incidence
angles and other geometric properties of the blades.  As the waves  spiral forward of the
fan, this amplitude variation creates significant interval variation because of the
influence of shock strength on the rate of propagation.  Strong shocks travel  faster
than relatively weak shocks; thus an initial small variation in shock strengths of two
consecutive shocks will cause the spacing between these shocks to vary with  distance
away from the fan.  At the same time, both shocks are decaying and they eventually
reach a stable situation where the spacing is unchanged with further propagation.
            A feature of the combination tone noise spectra in the  engine far field is
that two fans, although identical in design, produce  different spectral signatures.  The
fact is that each blade is slightly different within well defined manufacturing tolerance
bands.  When the blades are assembled to produce fans,  the small deviations of each
fan from design will  be different from fan-to-fan.  A deterministic  prediction procedure
for a given design would thus require knowledge of the variation in manufacture of all
blades on each fan.  Since this is impractical both in advance of and during  production,
an estimate of the average spectrum for a given fan design represents the practical
limits in combination tone prediction.  This average will not only depend on relevant
geometric  blade parameters, but also on their standard deviations from design.
C.2        Propeller and  Rotor Noise
            The mechanisms by which rotors,  propellers and fans produce intense sound
pressures have been  the subject of much work, especially in recent years.  Traditionally,
noise generated by propellers has been separated into two parts called  the rotational and
vortex components.  Rotational or periodic noise here describes all  sound which is identi-
fied with discrete frequencies occurring at harmonics of the blade passage frequency.
            Vortex or broadband noise  describes the modulated sound produced by the
unsteady pressure field associated with  vortices shed from the trailing edge and tips of
the blades, as well as some of the noise sources associated with turbulence effects in
the air stream.  The helicopter rotor deserves separate consideration.  Although much
                                        C-22

-------
of its noise can be explained in terms of propeller noise sources, there are a number of
other sources exclusive to that device which make significant contributions to the over-
all levels.
Rotational Noise '
            All  real rotating airfoils, i.e., those having thickness, have a pressure
distribution when moving relative to the surrounding medium.  This pressure distribution
can be resolved  into a thrust component normal to the plane of rotation and a torque
component in the plane of  rotation. This pressure field on the air is steady relative to
the blade and rotates with  it if operating under conditions of uniform inflow. For non-
uniform inflow,  such as a helicopter rotor in steady forward flight, the difference in
relative blade speed during forward and backward motion of the blade relative to the
flight path require? a cy.lie incidence variation to provide a reasonably uniform lift
over the disc. To a first approximation, the forces on the air next to the disc would be
constant under these conditions; the effects of incidence changes would appear only as
variation of chordwise loading over the blade. From a fixed point on the disc,  the
rotating field appears as an oscillating pressure.  The frequency of the oscillation is the
frequency with which a blade passes that point (blade passage frequency) and the wave-
form of the oscillating pressure is determined by the chordwise distribution of pressure
on the blades.
            In addition to  experiencing a fluctuating force, an element of air in the
disc will be physically moved aside by the finite thickness of the blade.  In a fixed
frame of reference, this displacement is equivalent to a periodic introduction and
removal of mass  at each element of air near the disc.  The rate of mass introduction at
a point,  which is determined by the blade profile,  incidence and speed, can then be
expressed as the strength of a simple source.  Up to values of resultant tip speed
approaching sonic, thickness noise  is generally found to be small compared with ttie
noise arising from torque and thrust. At higher tip speeds,  however, it may assume
equal importance.
                                        C-23

-------
Interaction and Distortion Effects
            Certain periodic effects are usually identified with helicopter rotors, but
may occur to a lesser degree in propellers.  Impulsive noise, blade bang or blade slap
may consist of high-amplitude periodic noise plus highly modulated vortex noise caused
by impulsive fluctuating forces on the  blades.  The mechanisms by which these forces
may arise are:  (1) blade-vortex interaction, (2) periodic stalling and unstalling of a
blade, and (3) shockwave formation and collapse due to unsteady periods of local
supersonic flow.  The first and second  conditions (and possibly the third) may occur  .
(1) when a blade passes through or near a  tip vortex, or (2) when an unsteady  wake is
generated by a preceding blade.  Operation in this unsteady flow condition leads to
strong fluctuating forces. Here,  aeroelastic properties  may become significant
parameters.   The third mechanism may also result directly from operation of a  blade at
high tip speed (such as an advancing helicopter blade during high speed flight). When
high tip speed occurs, blade slap is by far the dominant source of aerodynamic noise.
Vortex Noise
            The dominant source of broadband  noise is called vortex noise, which has
been defined as that sound which is generated by the formation and shedding of vortices
in the flow past a blade. For an infinite  circular cylinder, normal to the flow and in
                                    2      5
the range of  Reynolds numbers from 10  to 10 , it is well known that the vortices are
shed in an orderly vortex street which  is a function of cylinder diameter and flow
velocity. The process in the case of a rotating airfoil is similar and since there is a
different velocity associated with each chordwise station along the span,  a broadband
of shedding frequencies results.   This produces  a dipole form of acoustic radiation in
which the strength of the source is proportional to the sixth power of the section velocity.
Hence the frequencies associated with the area near the tip tend to be of greatest
amplitude.  Also, since a blade develops  lift (thrust), tip and spanwise vorticity of
strength proportional to the thrust gradients  are generated and shed. Their dipole
acoustic  radiation combines with that from the  trailing edge vortices to make up the
so-called vortex  noise.
                                        C-24

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C.2.1       Propeller Noise
            As discussed above, the noise produced by an operating propeller has been
an object of scientific interest for many years.  All of the early work in the aeronautical
noise field,  both analytical and experimental, was concerned with the propeller noise
                                                                         20
problem or with allied configurations such as Yudin's  work with rotating rods.
            Although closely related to the noise produced by  rotors and fans,  the
problem of propeller noise is simpler in some respects  because of the configuration and
operating conditions of the propeller.  The small number of blades in a normal  pro-
peller, together with the flow velocity through the propeller disc, minimizes the inter-
ference effects due to operation in the wake of preceding blades.  The structure and
location  of the propeller is such that noise due to blade flutter and asymmetrical  induced
flow are  not normally encountered.  At moderate tip speeds,  i.e., slightly below the
onset of compressibility effects, both vortex noise  and rotational noise due to thickness
are lower than the rotational noise due to thrust and torque.  Consequently, most of
the noise work on propellers, of both a theoretical and experimental nature, has con-
centrated on the effects of thrust and torque.  In studies  dealing with the  reduction of
overall propeller noise, however, vortex noise has been  shown to be an important
contributor and in  the case of high-speed flight, the  level of thickness noise may
exceed that of thrust and torque noise.
Rotational Noise
            The theoretical work of Gutin   provides the equation for the sound
pressure of the'mth harmonic tone;                                   ,
                     169.3rr.BRM,
                p  -
                 m ~      SA
where
- T cos 6

         2
            P   =  rms sound pressure level (SPL) in dynes/cm
            m   =  order of the harmonic
            S   =  distance from propeller hub to observer, ft
                                        C-25

-------
            R   =  propeller radius, ft
                                       2
            A   =  propeller disc area, ft
            P,   =  absorbed power, horsepower
            T   =  thrust, Ibs
            B   =  number of blades
            M   =  tip Mach number
           Jmg =  Bessel function of order mB
            x   =  argument of Bessel function 0.8 M mB sin Q
            Q   =  angle from forward propeller axis  to observer
            The expression gives reasonable agreement with experimental results for the
first few harmonics  of conventional  propellers operating at moderate tip speeds and for-
ward velocities.  In these circumstances, summation of the square root of the sum of
the squares of the solutions to the above expression for  m = 1, 2, 3, 4  will yield an
adequate approximation of the overall sound  pressure  of the thrust and torque com-
ponents.  Under such conditions,  it is a suitable estimate of the total noise as well.
            As tip Mach number is reduced to the range between  0.5 and 0.3,  experi-
mental results begin to diverge from the predicted values in the direction of higher
levels.   In this region, vortex noise,  which originates in the variable forces acting on
the medium during flow past the blade,  makes itself known.
Vortex Noise
	                                2j
            An equation developed by Hubbard,   which was based on Yudin's original
                                            22
work, additional work by Stowell and Deming,    and others, is frequently used to
calculate vortex noise in  terms of SPL:

                                    kA  (V    )6
                     SPL =  10 log  	    U./	  (dB at 300  ft)
                                       io16
v/here
            k   =  constant of proportionality
                                        C-26

-------
                                         2
            A,  =  propeller blade area, ft
           V-. 7 =  velocity at 0.7 radius
            The expression indicates that vortex noise is a strong function of blade
velocity; doubling the blade velocity increases the SPL by 18 dB.  The effect of
doubling blade area is less severe; the SPL is increased by 3 dB.  This suggests that the
way to reduce vortex noise is to minimize the tip velocity and to make up the  required
thrust by increasing blade area as far as possible within the constraints of efficiency
and structure.  It should be remembered, however, that the vortex noise of propellers
does not become significant until the blade velocity is  already below normal operational
values.
C.2.2      Rotor Noise
Rotational  Noise
            The study of rotor noise has had the advantage of drawing on the  knowledge
gained from earlier interest in the propeller.  It was found, however,  that although
propeller noise theory was fairly  accurate in describing the sound level of the  first
harmonic of rotors,  it was grossly in error for the higher harmonics.  This is not alto-
gether surprising when one considers the relative complexities of the two systems.  The
propeller that Gutin described was a rigid device  rotating in steady, uniform  flow.
The modern rotor is quite a different system.  The  main feature of the rotor aerodynamics
is the lack of symmetry. In transitional and forward flight, the rotor disc encounters
highly nonuniform inflow, and the mechanism by which forward thrust is obtained gives
rise to cyclic pitch  and fluctuating airloads.  Under these operating conditions, velocity
fluctuations are induced which give rise to a multitude of blade-loading harmonics.
The calculation or experimental determination of these higher harmonic blade  loads is
                                                                    23-25
extremely complex and has met with only limited success. Many authors      are of the
opinion that all the significant higher harmonic sound effects (except possibly  at
transonic or supersonic  speeds) can be attributed to these unsteady higher harmonic
loadings and, further, that any sound harmonic receives contributions from  all loading
harmonics.
                                        C-27

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                                 23
            Lowson and Ollerhead  have undertaken to avoid the problem of theoreti-
cally determining the blade-loading harmonics by deriving empirical harmonic decay
laws.  A study of the available full-scale blade-loading  data revealed that the amplitude
of the airload harmonics decayed approximately  as some inverse power of harmonic
number,  at least in the range which covered the first 10 harmonics.  For steady flight
out of ground effect,  the optimum value for the exponent was found to be -2.07 so
                                                                   -2.0
that the amplitude of the  mth  loading harmonic was proportional to m .     This law
was then extrapolated indefinitely to higher frequencies in order to provide some esti-
mate of the higher harmonic airload levels.  However, before  this could be used as a
basis for noise calculation, account had to be taken for phase  variations around the
rotor azimuth and along the rotor span.  It was assumed that  the phases could be ran-
domized. In the case of the spanwise loading variations, this  was accomplished by the
introduction of a "correlation  length" concept such as commonly used in turbulence
theory.  By assuming that the correlation length  was inversely  proportional to frequency,
this resulted in an  approximate net effect of adding a further -0.5 to the exponent of
the loading power law. Also, an  effective rotational Mach  number concept is introduced
which enables the.effects of forward speed to be calculated directly from results for the
hover case.
            Using these approximations, the rotational noise spectrum for the Bell UH-1
helicopter was  calculated for comparison with available measurements.  The comparison
is shown in Figure C-l 1.  Because of uncertainties regarding the overall levels, they
were normalized on the basis of power in the third and higher harmonics. Although for
this reason,  nothing can  be said about overall levels, the agreement, insofar as spectral
shape is concerned,  is good up to  the thirtieth harmonic.
Broadband (Vortex) Noise
            The fundamental generation mechanism of broadband  and, more  particularly,
vortex noise  from rotors is not yet  fully understood. In Yudin's early work with rotating
rods, vortex  noise was considered  to be a  viscous wake-excited phenomenon and indeed
it must be in that case.  However, in the  case of a lifting airfoil  such as a rotor,  the
                                        C-28

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    -30
    -40
    -50
— — — Theory, M = 0.5,
O Elevation - 10 deg
High Collective
A Elevation = 5 deg,
V Elevation - 10 deg
— — -^
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Elevation = 5 deg
, r = 100 ft, Ground Running at
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r = 600 ft, Hover over Grass
, r = 200 ft, Tiedown over Grass

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                                 Harmonic Number
           Figure C-ll.  Noise Spectrum; Comparison of Theory and Experiment

                      For a Two-Blade Rotor (UH-1A and UH-lB)

                     (Data from Lowson/Ollerhead, Reference 23)
                                         C-29

-------
experimental evidence could support equally well the contention that it is caused by a
random movement of the lifting vortex in the tip region.  Quite likely, both the tip
vortex and the vortex sheet shed  from the upper surface of the airfoil contribute in
varying degrees, depending on the configuration and operating conditions.  There is
evidence,  however, that a portion of what was originally identified as  broadband
vortex noise may, in fact, be higher harmonic rotational  noise.  Lowson and Ollerhead
report that the rotational noise of rotors may dominate the noise spectrum up to 400 Hz
and higher. At any rate,  broadband noise is generated and can be dominant under
some  rotor operations, e.g., at very low rotational velocities with two-bladed or
three-bladed rotors, where even  higher harmonics of  the blade passage  frequency may
                                 26
be inaudible.   Hubbard and Regier    extended the work  of Yudin and postulated that
for propellers with airfoil sections, as for rotating circular rods, the vortex noise energy
was proportional to the first power of blade area and  to the sixth power of the section
velocity.  Experimental  measurements, where they are available and reliable, should
be used to evaluate the constant  for a particular set of conditions.
Modulation (Blade Slap) Noise
            Rotors suffer more from distortion noise than any other aerodynamic noise
generator.  Blade slap is the colloquialism that has been applied to the sharp cracking
sound associated with helicopter  rotor noise sources.    To date, the only attempt at a
quantitative study of the problem seems to be the papers published by Leverton and
       27 28
Taylor.  '     In the latest, Leverton lists the three main mechanisms generally
postulated for blade slap in the literature:
            •    Fluctuating forces caused by blade-vortex interaction.
            •    Fluctuating forces resulting from stalling and unstalling of the
                 blade.
            •    Shock wove formation due to local supersonic flow;  it  is suggested
                 that this is either (a) a direct result  of operating a blade at a high
                 tip speed, or (b) caused by a blade-vurtex interaction.
                                        C-30

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            At the present time, detailed information on these mechanisms is still
limited; therefore, it is almost impossible to state which is the most likely mechanism.
However, a blade intersecting the tip vortex shed by a  preceding blade could itself
cause the other two mechanisms to occur.  Leverton assumes that blade slap is the
direct result of the fluctuating lift caused by the interaction of a blade and a vortex
filament.  .This can  be either an actual intersection when  a blade cuts a vortex fila-
ment or the effect of a blade passing very close to a vortex filament.
            Although it is easy to  imagine a blade and  a tip vortex intersecting, it is
extremely difficult to visualize the details of such an encounter and practically
impossible to describe it mathematically. As a blade intersects or comes near a
vortex filament, the blade circulation and hence the lift profile will become severely
distorted.  On a single rotor lift system,  a blade will most likely pass near, or cut
through, a tip vortex shed by a preceding blade (Figure C-12 (a) ).   On a tandem
rotor lift system,  it  is more likely that one rotor will cut the vortex filament generated
by the other disc  (Figure C-12 (b)  ).  The fact that large fluctuations in lift occur
when  a blade passes close to a vortex filament  is obvious.
C.3        Internal Combustion Engine  Noise
            The externally-radiated noise from internal combustion engines results from
a multitude of noise-generating mechanisms. Unlike the jet engine, for which one or
two sources of noise dominate the noise-radiation  characteristics,  several noise sources
contribute measurably to the noise signatures of internal combustion  engines.  The
following major source categories are commonly recognized:
            •   exhaust noise
            •   intake noise
            •   engine-radiated noise due to cylinder  pressure development
                (combustion noise)
            •   engine-radiated noise due to mechanical  components
                (mechanical noise)
            •   cooling fan noise
                                        C-31

-------
(a) Single Rotor System
(b) Tandem Rotor System
                                 Aircraft
    Figure C-12.  Typical Blade-Vortex Intersections for a Single
           Rotor System (a), and a Tandem  Rotor System (b)
                 (Data from Leverton,  Reference 28)

                                 C-32

-------
            Several specific subsources are distinguished in the engine-radiated noise
category.  These will be discussed below in the detailed evaluation of the separate
noise categories.
C.3.1      Exhaust and Intake Noise
            Exhaust noise is potentially the greatest noise source of the automotive
engine.  It is produced by the sudden release of gas into the exhaust system by the
opening of the exhaust valve.  The closing of the valve produces only minor effects.
The fundamentals and harmonics of the firing frequency are  the principal components
which have to be dealt with in the exhaust-muffler system.  At high speeds,  the
individual frequency components are masked by a more continuous spectrum attributed
to turbulence noise associated with the high velocity of the exhaust gases over the
valve seat.
            Intake noise is produced by both the opening and the closing of the inlet
valve.  At opening,  the pressure in the cylinder is  usually above atmospheric and a
sharp positive pressure pulse sets the air in the inlet passage into  oscillation at the
natural  frequency  of the air column.  The oscillation is rapidly damped by the changing
volume  caused by  piston motion downward.  Closing of the  inlet valve produces similar
oscillations, which are relatively undamped.  In practical  installations, measurements
indicate that intake noise is not fully silenced and  in some  vehicles it is the pre-
                        29
dominant source of noise.
            Figure C-13 shows spectra of the noise radiation from a diesel engine
running at  1500  rpm with (a) open exhaust' and inlet, (b) silenced exhaust, and (c)
silenced exhaust and inlet.    Comparison of spectra (a) and (b) shows that exhaust
noise predominates by  about 10 dB over the whole frequency range. Comparison of
spectrum (b) with the spectrum with the air inlet silenced (c) shows that the next
greatest noise source i: the air  inlet.  The remaining noise, spectrum  (c), is emitted
by the engine structure itself from vibration of the external  surfaces and by the cooling
fan.  In the diesel engine, air  inlet noise generally predominates only in the  low  and
middle frequencies, up to 1000 Hz.  In the gasoline engine, this inlet noise may also
                                        C-33

-------
          T  I  I I
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                    (a)
                                            Open Exhaust and Inlet
90
     80
70
Open Inlet
Silenced Exhaust
     Silenced Exhaust and Inlet
60
           I   I  I I I
                              J	I
                  100
                                                 000
                                                     10,000
                                      Frequency (Hz)
              Figure C-13,  Octave-Band Spectra of Inlet and'Exhaust Noise of
                        2-Litre Diesel Engine at 1500 rpm Full Load
                             (Data from Priede, Reference 30)
                                            C-34

-------
predominate in the high frequency range owing to the "hissing" noise produced in the
carburetor.
            Both exhaust and intake noise show the same dependence on engine
speed:
                       Sound Level dB(A)  =  45 Log]()N + k
where
            N   = engine speed - rpm
            k   = undetermined parameter
The noise levels increase with increasing engine load; from no-load to full-load,  the
intake noise increases between 10 and 15 dB for diesel engines and between 20 and
25 dB for gasoline engines.  Intake  noise is also affected by the construction of the
exhaust system; restrictions in  the exhaust markedly increase the intake noise.  Both
exhaust and intake noise are greatly influenced by design variables such as the size
of the valves, their timing and the construction of the parts.
            Automotive engines are normally equipped with exhaust mufflers and  intake
silencers.  In some cases these are inadequate because of space and cost I imitations,
even though techniques for silencing to  any desired degree are well known.
            Large mufflers must be used to obtain adequate silencing with  low back
pressures.  Two mufflers in series are sometimes used (for example, on bus engines).
The ratios of net muffler volume to engine displacement volume of a group of typical
older passenger cars indicate values between  1.5 to 4.2.  For some quieter mufflers,
the volume ratio is double these values.
            The location of the muffler  along the exhaust pipe is  important, especially
with the simpler mufflers, because of pipe resonances. The most advantageous muffler
location for single-muffler systems is indicated at the center of the exhaust pipe,  which
                                        32
allows for cancellation of pipe resonances.
                               32
            According to Martin,    it has been demonstrated by  experiment and  theory
that the direct gas flow through a muffler can considerably affect the silencing effect.
Considering, first, a reactive  muffler with resonant chambers and flow interruptions
                                        C-35

-------
(staggered tubes in successive bulkheads), let D  be the attenuation in decibels
through the muffler without gas flow and  D  the practical silencing of the various
frequencies with superimposed gas flow through the muffler, as measured on the actual
engine.  Then, as a first approximation, the following relation between  D  and D
is given:
                                       D
                               D  = T-^TI    dB
                                r    1 - a M
where
            M  = Mach number of the mean gas flow in the muffler
            a   = nondimensional coefficient whose value falls between 1.0  to
                   1.2, depending on the muffler design
            Thus,  muffling  improves with Mach  number within the engine operating
range and full-throttle operation is better silenced than idling operation.  On the
other hand,  absorption type mufflers with a  straight-through passage in a perforated
pipe surrounded by a concentric container filled with fibrous sound-absorbing material
show  better silencing,   D ,  at idling than at full-throttle, according to the relation:
                              t
                              D  = D  (1 - pM1//3) dB
                                a     o

Again,  P is a nondimensional constant, dependent on muffler design, and falling
between 1.0 and 1.2 in magnitude.
            Intake silencers are usually of the straight-through design,  using resonant
side chambers to control both low frequency and high frequency noise, and a "hiss
felt"  for control of the high frequency noise spectrum.  Figure C-14 shows octave band
intake noise spectra at 3 feet for two diesel engines at full power, 2000 rpm operation,
with normal  inlet silencers  and with completely silenced inletsp^  The upper set of
curves, (a), is for a 2-liter engine and includes no-load intake noise spectra.  The
lower set of curves, (b), is  for a  larger 4.2-liter engine.  Intake noise on both engines
reaches a substantial 95 to 97 dB peak in the low frequency octave bands at about
120 to 250 Hz at full load.   The  no-load intake noise octave band peak for the smaller
                                        C-36

-------
    TOO
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     90
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      70
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      70
                             i  i
                                                   Full Load
                                                  Normal Inlet
                                                    Silencer
             (a)
                                  y ^— No Load
                                 y      Normal Inlet
                                /        Silencer
                                               Full Load
                                              Completely
                                            Silenced Inlet
                                                          Full Load
                                                         Normal Inlet
             (b)
                                                    Full Load
                                                   Completely
                                                  Silenced Inlet
                                                                                                00
                                          Frequency (Hz)
                Figure C-14.  Octave Band Spectra (5) of Noise of Two Diesel Engines
                   With Normal and With Fully Balanced Air Inlets; (a) 122 cu in
                          Engine, 2000 rpm; (b) 256 cu in Engine, 200 rpm
                              (Data from Soroka/Chien, Reference 33)
                                                C-37

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engine is about 10 dB lower (88 dB) than the full-load peak (97 dB), with a slight up-
ward shift in frequency.  With  complete silencing of the intake noise under full load,
the predominant noise is  in the upper frequency range from 1000 Hz and up.
C.3.2      Combustion and Mechanical Noise
            The noise from the structure of an internal  combustion engine is produced
by forces of mechanical origin  and by gas forces acting on the pistons resulting from
compression and subsequent combustion. Both produce vibrations of the external sur-
faces which emit the noise.  Noises of mechanical origin are those due to operation of
the piston-crank system,  valve-gear mechanism,  various auxiliaries and their drives.
In practice, mechanical  noise is defined as  that of the motored engine.  This definition,
however,  includes the effect of gas forces developed during compression; but the con-
tribution from the compression pressure is rather small.   The noise of the running engine
(addition of the gas forces due  to combustion)  is invariably greater than that of the
motored engine.  Thus, combustion is the major noise source in an internal combustion
engine.
            The effect of combustion on engine noise is illustrated in Figure C-15
which shows spectra for diesel and gasoline  engines, both  motored and running, with
                                             33
different forms of cylinder pressure development.    In both types of engines, the noise
can be varied some 10 dB by changing the form of the cylinder pressure.  Hence,  worth-
while reductions of engine noise may be attainable if the effect on noise of the form of
cylinder pressure development is known. Figure C-16  shows some examples of cylinder
                                                                   33
pressure spectra from a gasoline and  a diesel engine at full and no load.
            Both diesel and gasoline  engine cylinder pressure spectra show a high level
for the first few harmonics, followed  by a steady  decrease of the level of higher order
harmonics by some 30 to  50 dB  per decade.
            The low frequency parts of  the spectra, up to  about 300 Hz or 20th har-
monic, are  hardly influenced by the form of pressure diagram, but are largely determined
by the peak pressure.  A large  reduction of  the level of this part of the spectrum is
observed only with a considerable reduction of peak pressure such as occurs with a
                                        C-38

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CM






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-------
Gasoline Engine
   Full Load
                                                 Diesel Engine
                                          \(      Ful1 Load
                     Gasoline Engine
                         No Load
                                                ///////// it/// / / / / / / r// ///////
                      100
1000
10,000
                          Frequency (Hz)
   Figure C-16.  Cylinder Pressure Spectra for Diesel  Engine C and
         Gasoline Engine at 2000 rprp Full ,Load and No, Load •
             (Data from So rok a/Chi en, Reference 33)
                                C-40

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gasoline engine on no-load.  The level's of the harmonics above 20th order are
affected more and more by the actual form of the pressure diagram; thus, at higher
frequencies,  the spectra of diesel engines diverge from those of gasoline engines and
have higher levels, particularly in the range from 800 Hz to 3000 Hz.
            This difference is ascribed to  the different mechanism of ignition.  In the
gasoline engine,  the flame is initiated from a spark (that is, a point source) from which
the flame gradually propagates until the whole charge contained in the chamber is
burned.  Thus, a  very smooth blending with the compression is obtained.  In the diesel
engine, on the other hand, ignition is spontaneous and an appreciable volume of pre-
mixed fuel and air burns extremely rapidly.  This rapid combustion results in the
marked  discontinuity (that is, rapid initial pressure rise), invariably observed on the
cylinder-pressure diagrams of diesel  engines.
            Noise measurements on a large  number of automotive diesel engines (with
inlet and exhaust silenced) have shown a striking simi.larity  in shape of noise spectrum.
All spectra show a bro'dd.peak in the frequency range from 800 to 2000 Hz, similar to
that of the octave band spectrum (c) of Figure C-13.  From  oscillographic investigation,
it has been shown that the noise is emitted in impulses coinciding with the rapid increase
of cylinder pressure.  It is the objectionable hard "knock" characteristic of diesel
engines.
                                                    !          ,
            the spectrum  of'the gasoline engine  is different.  The components in the
frequency range 800 to 2000  Hz are of lower intensity and the largest peaks in the
spectrum are in the frequency range 400 to 600 Hz.  These differences correspond
exactly to the differences previously noted in cylinder pressure spectra. The different
noise characteristics of diesel and gasoline engines therefore are due not to any
differences of the structure but to differences in excitation due to cylinder pressure.
            The effect of  load on the cylinder pressure spectra (Figure C-16) is very
marked  in the gasoline engine, but is very slight in the diesel engine.  This is due to
throttling the gasoline engine intake at no-load.  These  observations again are found
to be in agreement with noise measurements as shown  in  Figure C-17, where the overall
                                        C-41

-------
                                                         i   r
   100
           2 Liter Diesel
    90
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                                   30           50               100

                           Cylinder Pressure Diagram Loading — psi
                   200
            Figure C-17,  Effect- of Load on Overall Calculated Sound Pressure Level
                          Fora Diesel Engine and a Gasoline Engine

                          (Data from Soroka/Chien, Reference 33)
                                             C-42

-------
sound pressure levels are plotted against  load for a diesel engine and a gasoline engine
at 2000 rpm?3 In the diesel engine, the sound pressure level at no-load differs only
slightly from that at full-load; whereas in the gasoline engine, the sound pressure level
at no-load is less than that at full-lead by some 10 dB.
            The relationship between the cylinder pressure spectrum and the engine noise
radiation depends on the relative levels of the combustion and mechanical noise com-
ponents.  Smoothing or reducing the cylinder pressure belowa certain "critical" value
will have only a negligible  effect on the engine noise because of the constant level of
the mechanical noise.
            If the cylinder pressure level is above the "critical level," the level  of the
emitted noise is proportional to that of cylinder pressure. This makes it possible to define
the vibrational and radiating properties or the "noisiness" of an engine structure by a
quantity:
        attenuation in decibels =  cylinder pressure  level - sound pressure level
The attenuation is represented by a single curve covering the audio frequency range
which  is independent of engine operating conditions — speed, timing  and load.
            Figure C-18 shows the attenuation curves of four diesel engines and a
                                               33
gasoline engine of similar size  (2-liter capacity).    As can be seen, variation of
attenuation among the diesel engines of  current design is not very large and the curves
are found to lie within a range of some 6 dB.  Also, the attenuation curve of the
gasoline engine lies mainly  within the group of curves for the diesel engines, which
indicates that its structure is not dissimilar, as regards noise,  from that of the diesel
engines.
            The attenuation is  high at low frequencies and declines at a steady rate by
about 50 dB/decade up to about 1000 Hz.  Above 1000  Hz, attenuation declines  at a
considerably lower rate, by about some 10 dB/decade.   Investigations have shows that
the high attenuation at low  frequencies is partly due  to higher attenuation of vibration
by the stiffness of the structure and partly due to higher radiation attenuation, since
the wavelength of the sound exceeds that of the linear dimensions of the engine.  At
                                        C-43

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CO
.2
"o

0)
     120
     no
     100
      90
      80
      70
      60
                                               Gasoline
            I  I  I  I
I     I    I   I  I  I I
I     I   I    I  I  I  I
                 100
                   1000
                10,000
                                          Frequency (Hz)
                Figure C-18.  Attenuation Curves for Gasoline Engine and Diesel Engines
                              (Data from Soroka/Chien, Reference 33)
                                                C-44

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'high frequencies, from 800 Hz upwards, the noise is due to vibration of resonating
 sections of engine surfaces, generally of the crankcase, resulting from transmission of
 forces due to cylinder pressure both directly from and via the crankshaft.
             The pressure diagram in an engine tends to remain of simil.ar form with
 change of speed; therefore, to a first approximation the cylinder pressure spectra will
 be geometrically similar at different speeds but with a shift parallel to the frequency
 axis corresponding to the change of speed. Thus, the increase of engine noise will
 depend on the general slope of the cylinder pressure spectrum.  For example, with
 cylinder pressure spectra having  a slope of 30 dB/decade (corresponding to the slope
 of cylinder pressure spectra in most  diesel  engines), one can expect an increase of
 engine noise by 30 dB for the tenfold increase of engine speed.
                                                                   33
             This is confirmed by the test results shown in Figure C-19.    The
 straight lines give a good fit in the  case of aM four diesei  engines.  The noise of the
 gasoline engine increases in speed at a higher rate; this corresponds to the greater slope
 of the cylinder pressure spectrum of this engine (Figure C-16).  Thus, the engine noise
                                                 31
 levels may be expressed by the simple relationships:
          .   Sound Level dB(A) =  30  Logir.N + k for diesel engines,  and
             Sound Level dB(A) =  50  Loglf.N + k for gasoline engines.
             The effect of the engine size  is also clearly seen from Figure C-19.  If the
 amplitude of vibration of engine surfaces does not vary with engine size, the increase
 in intensity of sound radiated should be due only to the  increase in the radiating sur-
 face area and the noise would increase by 13.3 dB for a tenfold increase of engine
 capacity.  This can be seen from the data on the few diesel engines; an increase of
 about  14 to  16 dB is obtained, which is very close to the above value.  In general
 this gives the result that, power  for power, a large engine running slowly is quieter
 than a smaller one running  faster.
 C.3.3      Cooling Fan Noise
             Cooling fan noise is a nuisance noise in the automobile.  Aerodynamic noise
 is generated directly through  vortex formation by the fan blades. The most common type
                                         C-45

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    100
4
*   90
CN
 0)
 5
co
-o
 c
     Diesel Engines
 0)
 I
 2
 a
 £
 O
-to
80
     70
                                    Liter
                             t    Gasoline Engine
                                     I
                                                 I
                         I	I
           I   I   I  I
                   500
                               1000
       2000
Engine rpm
4000
             Figure C-19. Calculated Overall Sound Pressure Level versus Speed
                        for Four Diesel Engines and Gasoline Engine
                         (Data from Soroka/Chien, Reference 33)
                                             C-46

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of engine cooling fan is the axial flow type. This is used invariably to draw air through
the radiators of water-cooled engines.  Centrifugal fans are sometimes used with air-
cooled engines. The mechanisms of noise generation by axial flow fans have been dis-r
                 34
cussed by Sharland    and others. These mechanisms are identical  to those described
in Section C.I .2 for jet  engine fans and compressors and in Section C.2 for aircraft
propellers and helicopter rotors, and will  not be discussed separately in this section.
A general empirical  expression for the noise levels generated by cooling fans may be
written in the form:
                     Sound Level dB(A)  = 60 log^N + k
where
            N   =  fan rotational speed
            k   =  undetermined parameter
            At present, the method of testing fan acoustic performance consists of
installing various designs of fans which will give the required cooling, then road-
                                                                           33
testing the car  at different speeds and  selecting by ear the most satisfactory fan.
Design constraints on the fan covering space occupied,  rotational  speed,  amount of
airflow,  position in car,  and other factors cause difficulty in making a quiet fan.
            Blade spacing  can be used successfully to distribute the level of harmonics
over the  operating range.  Four blade  fans with 76 degree blade spacing have been
found to  be a good choice. On the average, slow running fans are the quietest. For
automotive fans, noise is increased by 60 dB per tenfold increase of tip speed. Inten-
sity is proportional to about the 6th power of rpm and therefore a special coupling to
reduce fan speed at high engine speeds is one of the most effective ways of con-
trolling the noise.  Fan noise has the peculiar quality that sometimes it is difficult to
mask below other car noises, particularly when the other engine noises are suppressed.
C.4         Tire Noise
            Noise generated by tire-roadway interaction is one of the prime sources of
annoyance for several classes of road vehicles.  For example, at vehicle speeds above
                                        C-47

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30 to 35 mph, tire noise may be the principal  component of the overall automobile
and small truck noise spectrum.  Figure C-20 shows how the engine noise levels compare
                                                                           35
with the noise levels produced by various classes of tires for a single-axle truck.
Although the "quiet" tires fall below  the engine noise levels over the entire range of
vehicle speeds, the difference in levels is sufficiently small that a moderate reduction
in engine noise would leave tire noise as the principal  component even for these tires,
especially at the higher velocities.                                        /
            The important source mechanisms in the tire/roadway interaction are:
            •   "Air pumping" from tread and roadway activities — the sudden out-
                flow of air trapped in the treads or roadway cavities when the tire
                contacts the road surface, and the sudden inflow of air when the
                tire lifts away from the contact area.
            •   Casing vibration — excitation of the casing and tread by roadway
                roughness or by the tire itself.
            •   Aerodynamic— (a) "spinning  disc" noise,  (b) impingement of
                turbulence upon all or parts of the tire, (c) impingement of dis-
                placed air on the roadway surface.
                   oz
            Hayden   has made a detailed analytical investigation of these noise
sources and  concludes that the third mechanism is negligible except at very high
vehicle speed.  Thus, aerodynamic  noise mechanisms may be considered to represent
a lower bound for the tire-roadway  noise.
            The first  two  noise source mechanisms are discussed below, on the basis
                    36                                       - \                   •
of Hoyden's analysis.
Air Pumping from Tire and Roadway Cavities
            When a section of the tire tread contacts the road surface, some of the
air in the spaces between the treads is displaced, thus creating  a locally-unsteady
volumetric flow.  Similarly, when the tire rolls over and partially fills cavities in the
roadway, some of the air  is squeezed out of these cavities.  Finally, when tire seg-
ments leave the contact area, spaces  enclosed by the tire and roadway expand rapidly
                                        C-48

-------
    90
    80* _
CD

T3
"»   70  -
-a
 c
     60  -
  Retread







  1/2 Worn Crossbars







  New Crossbars


  Uneven Wear Rib



  New Rib
                              30             40


                                 Speed - mph
        Figure C-20.  The Significance of Tire Noise Relative

             to Engine Noise for a Typical Single Axle Truck

                   (Data from Tetlow,  Reference 35)
50
                                     C-49

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and a volumetric flow transient is created by the air rushing to fill the expanding
cavity.  Such fluctuations in volumetric flow rate characterize the driving mechanisms
of the acoustic monopole (or "simple source").   The narrow-band mean-square acoustic
pressure due to the "point" monopole source may be written:
o M =
P \r;
2 2 T
Oo Q 0 In5
22 	 C IU
16 IT r
u Q
2
r
where
            p   =  the acoustic pressure
            p   =  the ambient density of the medium
            r   =  the radial distance from the source
            Q   =  the volumetric flow rate from the source
            o   =  the circular frequency
            Thus,  to estimate the overall sound pressure, one needs only to estimate
Q and u.   Such a procedure will now be demonstrated for a tire whose geometry is
shown  in an exaggerated fashion in Figure C-21.
            The mean-flow rate from a single cavity is estimated to be:
              rT  -  Volume change   _  (f.c.)gwS  _  ,f
                                __        ^_.         (tmt
for the geometry shown (where f.c. is the fractional change in the cavity volume).
            The characteristic frequency of occurrence of the flow pulse is:
                                 u  =  2irV/S     .
By substituting these relationships into the first equation and taking the logarithm with
respect to the reference pressure 0.0002 jjbar, the following "engineering equation" is
derived (for  n cavities per tire width):
  SPL(r) = 68.5 + 20 log (gw/S) + 10 log n + 20 log (f.c.) + 40 log V - 20 log(r)
                                        C-50

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Direction
of Travel
                                     Observation
                                        Point
CD
CU
cm
EH)
                                                                                 tz
                      U-l
                  V =  forward velocity
                  W =  width of a single cavity or groove in tread
                  g  =  depth of groove = tread depth
                  S  =  circumferential distance between tread grooves
                  s  =  circumferential dimension of tread grooves
                  R  =  tire radius
                  r  =  distance to observation point
      (Note:  The respective values of W, g, S, and s on a given tire may be different
             for individual cavities.)
                            Figure C-21, Tire Terminology
                          (Data from Hayden, Reference 36)
                                         C-51

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This equation is valid for the case of a non-directional sound source and hemispherical '
spreading.                                                                      •'
            A similar equation may be derived for the sound due to a smooth tire
rolling over cavities in the.roadway.  If there are m  cavities in the roadway per
width of the tire (m = W /S )  and the  cavities are d  deep, w  wide and have a
spacing of S ,   then the sound pressure level is:
  SPL(r) = 68.5 + 20 log (d^/SJ +  10 log n + 20 log (f.c.) + 40 log V - 20 log r
Tire Vibration
            The excitation of tires by road roughness and resultant tire vibration is
complex, making the prediction of associated sound radiation somewhat difficult.
Reasonable analytical  formulations of tire vibration and the resultant sound radiation
would require much presently unavailable knowledge about tire dynamics and dynamic
behavior of the tire/roadway interface. With so much of the needed information
lacking, an experimental approach may be taken to determine the  roadside noise due
to tire casing vibrations.  The empirical curve for predicting sound radiation from the
acceleration input spectrum shown in  Figure C-22 was obtained by placing a tire in  a
reverberant chamber and measuring the sound power level spectra for various vertical
                                    36
input acceleration levels and spectra.    It may be noted that the tire responds strongly
within a range of frequencies from 125 to  1000 Hz. The cut-on at 125 Hz corresponds
roughly to the fundamental resonances of the tire.  Above 1000 Hz, the input acceler-
ation levels are strongly damped.
            Vibrational sound from a passenger car tire operating on a granite chip
road surface has been predicted with the use of Figure C-22 from indirectly-measured
                    36
acceleration spectra.    The resultant sound power spectra are shown in Figure  C-23
and the overall levels  at various speeds in Figure C-24.
            The relative importance of each of the previously discussed source
mechanisms to the overall noise radiated by a rolling tire may be estimated from the
relationships developed above.  For several different tires and road surfaces, the
                                       C-52

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      70

 O
  0)

 3   60
  £
  i
 £
2     50
 o
  ID
CO
TJ
Q_
     40
     30
                         I
                                   I
I
                                                                      Highly
                                                                      Damped
                                                                      Regime
_L
I
I
I
       16      31.5     63  .     125     250      500    1000     1600    4000

                          One-Third Octave Band Center Frequencies (Hz)
A.
                                                                                     8000    16,000
     Figure C-220 Empirical Curve for Predicting Sound Radiation from Acceleration Input Spectrum
                                (Data from Hayden, Reference 36)
                                               C-53  .

-------
   100
               I  '   '   I   '   '   I  '   '   I   '  '   I
90
                       Estimated Contribution of Tire Vibration to Tire Noise Spectra
                                   (Tire Rolling on Granite Chip Surface)
    80
o
 £
 0)
 0>
    70
    60
    50
    40
                                                                        30 mph
                    I
I
I
I
I  i  i   I   i
_L
         31.5      63       125     250     500     1000    2000    4000   8000

                       One-Third Octave Band Center Frequencies, Hz


           Figure C-23.  Estimated Contribution of Tire Vibration to Tire Noise Spectra
                            (Tire Rolling on Granite Chip Surface) •
                              (Data  from Hayden, Reference'36)
                                                                                        16,000
                                                  C-54

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    90
    80
                                                                                         I   I
o
 2
CO
    70
    60
o
IO
4-
D

£  50
 "Air
Pump- 4
 ing"
    40
    30
      15
           20
                                       I
                                          1  Truck Crossbar or Auto Snow
                                          2  Motorcycle Crossbar
                                          3  Passenger Rib
                                          4  Roadway Noise - Concrete
                                          5  Roadway Noise - Asphalt
                                          6  Aerodynamic Sources
                                          7  Vibration - Passenger Tire on Concrete
       30           40        50
V = Vehicle Speed (Miles/Hour)
60
70    80    90   100
                     Figure C-24.  Predicted Contribution of Various Source
                                Mechanisms to Roadside Noise
                               (Data from Hayden, Reference 36)
                                              C-55

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appropriate geometries have been determined for predicting roadside noise from the
                        f\f
"air pumping" mechanism.    The results are shown in Figure C-24. Curves 1 to  5 all
exhibit the 40 log V speed dependence.  In each of these cases, it was assumed that
the fractional volume change (f.c.) is 0.1  and that the dynamics of the air pumping
process'are similar in all instances. The latter assumption is undoubtedly too general,
as one intuitively expects air to be squeezed from rib tires in a different manner than
from crossbar treads or road cavities.  Crossbar type treads are predicted to.be  noisier
than ribs; the concrete road surface examined was rougher than asphalt and thus pre-
dicted to be noisier.                                             .  ;   '
            Comparison of the vibrational sound levels estimated by'the empirical
method with those estimated for the "air pumping" mechanism-tends to indicate that
tire vibration is not a dominant sound-generating mechanism in tires.  However, in -
view of the uncertainties involved in  the input acceleration calculations, this  pre-
diction must be regarded as tentative  and somewhat inconclusive.  It may be noted
that measurements of tire noise on  rough roads suggest that tire vibration noise  can be
           31
significant.   The noise spectra measured on rough roads showed a nearly constant
spectrum level up to 800 Hz, followed by a strong decrease at higher frequencies.
Changes in vehicle speed were found  to result in no significant change in the spectrum
shape.  This behavior agrees with the tire vibration mechanism, whereas the air
pumping mechanism predicts a linear dependence of frequency on the vehicle speed.
            The data obtained on relatively smooth road surfaces, however, appear to
agree with the predictions  of the air pumping model in several respects.   Evaluation
                35
of Tetlow's data>    shown in Figure C-20, confirm the following trends:
            •   Speed dependence of the measured sound approached 40 log V,
                especially at the  higher speeds.
            •   Crossbar treads were found to be noisier than rib-type treads.
            •   Cup-type treads which completely seal upon contacting the road
                were the noisiest; this  suggests that  the  u Q  term is the greatest
                for treads which completely seal, thus the higher acoustic intensities
                from the monopole or "air pumping" sound.
                                      • C-56

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                                                                           35
            These conclusions are further supported by the data of Figure C-25,
which'show  that a 15 dB drop in noise level resulted when a single-axle truck was un-
loaded; load per tire was decreased from 4550 to 1240 pounds.  This effect is simply
explained:  with the truck unloaded, the sides of the tire tread do not touch the
ground an'd hence the cups in the tread cannot seal against the road surface.   Recent
                       36
data obtained  by Hciyden   for the tire noise generated by a coasting automobile show
both the 40  log V shift in'overall level and the linear shift in frequency with vehicle
                                                        o
speed predicted by the air pumping model.
            Hence, it appears that this mechanism of noise generation may be adequate
to explain the tire noise radiation measured in tests over relatively smooth road sur-
faces for a considerable range of vehicle speeds and tire configurations.  The importance
of tire vibration noise has not been satisfactorily resolved.
                                        C-57

-------
    90
    80
co
t>
J.  70
 3
 O
to
    60
                                               	-0
        A  Retread
        O  1/2 Worn Crossbars
           New Crossbars
              20
30             40
     Speed (mph)
50
          Figure C-250  The Effect of Load on Tire Noise.  Solid line
              represents maximum tire load (4500 Ibs); dashed line
              represents minimum tire load (1240 Ibs).  (Data from
              Tetlow, Reference 35)
                                C-58

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                                REFERENCES
C-l.     Light-hill, M.J., "On Sound Generated Aerodynamically; I-General Theory,"
         Proceedings of the Royal Society, Series A, Vol. 211, No.  1107, United
         Kingdom, March 20, 1952.

C-2.     Lighthill, M.J.  "On Sound Generated Aerodynamically; II-Turbulence as a
         Source of Sound, " Proceedings of the Royal Society, Series A, Vol. 222,
         United Kingdom, 1954.

C-3.     Proudman, I., "The Generation of Noise By Isotropic Turbulence, "  Proceed-
         ings of the Royal Society,  Series A., Vol. 214, United  Kingdom, 1952.

C-4.     Ribner, H.S., "On the Strength  Distribution of Noise Sources Along a Jet, "
         UTIA Report 51, Institute for Aerospace Studies, University of Toronto,
         April 1958.

C-5.     Lilley, G.M.,  "On the Noise from Air Jets, "ARC 20,  376-N40-FM 2724,
         Aeronautical Research Council, United Kingdom, 1958.

C-6.     Ffowcs Williams, J.E.,  "The Noise from Turbulence Convected at High
         Speed, " Philosophical Transactions of the Royal Society of London,  Series A,
         Vol. 255,  London,  England, 1963.

C-7.     Ribner, H.S., "Aerodynamic Sound from Fluid  Dilations —A Theory of the
         Sound from Jets and Other Flows, " UTIA Report 86,  Institute for Aerospace
         Studies,  University  of Toronto, 1962.

C-8.     Phillips, D.M., "On the Generation of Sound  by Supersonic Turbulent Shear
         Layers, "Journal of Fluid Mechanics, Vol. 9,  1960.

C-9.     Pao, S.P.,  "A Generalized Theory on Noise Radiated by Supersonic Turbulent
         Shear Layers, " Wyle Laboratories Research Report WR 70-1,  1970.

C-10.    Eldred, K.M., et al,  'Suppression of Jet Noise with Emphasis on the Near
         Field, " ASD-TDR-62-578, Wright Patterson Air Force Base,  Dayton, Ohio,
         1962.

C-ll.    Bushel I,  K.W.,  "A Survey of Low Velocity and Coaxial Jet Noise with
         Application to Prediction, " Journal of Sound and Vibration, Vol. 17,  No. 2,
         1971.
                                     C-59

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 C-12.   Eldred,  K.M., etal,  "Far Field Noise Generation by Coaxial Flow Jet
         Exhausts, " WyIe  Laboratories Research Report WR 70-16, 1970.

 C-13.   Sharland, I.J.,  "Sources of Noise in Axial Flow Fans, " Journal of Sound
         and Vibration, Vol. 1, No. 3, 1964.                           '

 C-14.   Curie, M.,  "The Influence of Solid Boundaries on Aerodynamic Sound,"
         Proceedings of the Royal Society, Series A, Vol. 231, United Kingdom,
         1955.

 .C-15.   Gutin, L.Y., "On the Sound  Field of a Rotating Propeller, " Translated as
         NACA TM-1195, National Advisory Committee on Aeronautics, 1948.

C-16.    Lowson, M.V.,  "Theoretical Analysis of Compressor Noise, "Journal of the
         Acoustical Society of America, Vol.  47, No. 1, January 1970.

 C-17.   Ollerhead, J.B.  and Munch,  C.L.,  "An Application of Theory to Com-
         pressor Noise, " NASA CR-1519, National Aeronautics and Space Admin-
         istration, 1970.                                      t

 C-18.   Kester,  J.D., "Generation and Suppression of Combination Tone Noise
         from Turbofan Engines," Paper No. 19,  Proceedings AGARD Fluid Dynamics
         Panel, Sant-Louis, France, May 1969.
                                                            U"     , .
 C-19.   Sofrin, T.G. and Pickett, G.F.,  "Multiple Pure Tone Noise Generated by
         ; Fans at Supersonic Tip Speed,  " International Symposium  on the Fluid
         Mechanics and, Design of Turbomachinery, Pennsylvania  State University,
         September 1970.

 C-20.   Yudin, E.T.,  "On the Vortex Sound from Rotating Rods, " NACA TM 1136,
         National Advisory Committee  on Aeronautics, March 1947.

 C-21.   Hubbard, H.H., "Propeller Charts for Transport Airplanes, " NACA TN 2918,
         National Advisory Committee  on Aeronautics, June 1953.

 C-22.   Stowell, E.A. and Deming, A.F., 'Vortex Noise from Rotating Cylindrical
         Rods, " NACA TN 619, National Advisory Committee on Aeronautics,
         February 1935.

 C-23.   Lowson, M.V. and Ollerhead, J.B.,  "Studies of Helicopter Rotor Noise, "
         USAAVLABS TR 68-60, U.S. Army Air Mobility Research and Development
         Laboratories, Fort Eustis, Virginia, January  1969.
                                     C-60

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C-24.   Schlegel, R., King, R. and Mull,  H., "Helicopter Rotor Noise Generation
        and  Propagation, " USAAVLABS TR  66-4,  U.S. Army Air Mobility Research
        and  Development Laboratories,  Fort Eustis, Virginia, October 1966.

C-25.   Loewy, G.R. and Sutton, L.R., "A Theory for Predicting the Rotational
        Noise of Lifting Rotors in Forward Flight, Including a Comparison with
        Experiment, " Journal of Sound and Vibration, Vol. 4, No. 3, November
        1966.

C-26.   Hubbard, H.H. and Regier, A.A.,  "Propeller Loudness Charts for Light
        Airplanes, " NACA  TN 1358, National Advisory Committee for Aeronautics,
        July 1947.

C-27.   Leverton, J.W. and Taylor, F.W., "Helicopter Slap Study, " Journal of
        Sound and Vibration, Vol.  4, No. 3, 1966.

C-28.   Leverton, J.W., "Helicopter Noise - Blade Slap, Part I - Review and
        Theoretical Study, " NASA  CR 1221, National Aeronautics and Space
        Administration, October  1968.

C-29.   Austin, A.E.W. and Priede, T., "Origins of Diesel Engine Noise,"
        Proceedings of the Symposium on Engine Noise and Noise Suppression,
        London, England, October  24,  1958,  The Institute of Mechanical Engineers,
        London, England.

C-30    Priede, T., "Noise of Internal Combustion Engines, " Paper C-2, National
        Physical Laboratory Symposium No. 12, England, July 1961.

C-31.   Millard, R.S. (Editor), "A  Review  of Road Traffic Noise - The Working
        Group on Research into Road Traffic Noise, " LR 357, Road Research
        Laboratory, Crowthorne,  England,  1970.

C-32.   Martin, H.,  "Measurement of the Noise of Motor Vehicles, " Proceedings of
        the Symposium on Engine  Noise and Noise Suppression,  London,  England,
        October 24,  1958, The Institute of Mechanical Engineers, London, England.

C-33.   Soroka, W.W. and  Chien,  C.F,, "Automotive Piston-Engine  Noise and Its
        Reduction —A Literature Survey, " SAE No. 690452, Society of Automotive
        Engineers Midyear Meeting, Chicago, Illinois, May 19-23, 1969.

C-34.   Sharland, I.J., 'Sources of Noise  in Axial Flow Fans, " Journal of Sound
        and  Vibration,  Vol.  1, No. 3, 1964.
                                    C-61

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C-35.   Tetlow, D.,  "Truck Tire Noise/ " Sound and Vibration,. August 1971.

C-36.   Hayden, R.E., "Roadside Noise  from the Interaction of a Rolling Tire with
         the Road Surface, " Purdue Noise Control Conference,  Purdue University,
         July 14-16, 1971.
                                       C—62              *U.S. GOVERNMENT PRINTING OFFICE:1973 5M-153/ZZ3 1-3

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