550/9-74-001A
CONTROL OF MOTORCYCLE NOISE
VOLUME I
TECHNOLOGY AND COST
INFORMATION
JUNE 1974
U. S. Environmental Protection Agency
Washington, D.C. 20460
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Document is available to the public through the National Technical
Information Service, Springfield, Virginia 7.2151
Document is available in limited quantities through the Environmental
Protection Agency, Office of Noise Abatement and Control, Arlington,
Virginia 20460
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550/9-74-001-A
CONTROL OF MOTORCYCLE NOISE
VOLUME I
TECHNOLOGY AND COST INFORMATION
JDNE1974
Prepared For:
U.S. Environmental Protection Agency
Off ice of Noise Abatement and Control
Under Contract No. 68-01- 1537
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.
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FOREWORD
The Environmental Protection Agency is publishing a series of
reports prepared by contractors describing the technology, cost, and
economic impact of controlling the noise emissions from commercial
products. It is hoped that these reports will provide information
that will be useful to organizations or groups interested in develop-
ing or implementing noise regulations. This report was prepared by
Wyle Laboratories under EPA Contract #68-01-1537.
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TABLE OF CONTENTS
Page
1. INTRODUCTION 1
2. STUDY APPROACH 3
3. THE MOTORCYCLE INDUSTRY . 6
4. MOTORCYCLE CONSTRUCTION AND NOISE CHARACTERISTICS . 8
Introduction 8
Measurement Procedures 11
A-Weighted Noise Levels 13
Noise Sources 22
5. SELECTED NOISE LEVELS 29
Introduction 29
6. NOISE REDUCTION TECHNIQUES AND COSTS 37
Noise Reduction from Subsources 37
Advanced Concepts for Noise Reduction 52
Achievement of the Selected Noise Levels Through Application of
Noise Reduction Techniques 52
7. CONCLUSIONS 59
REFERENCES 61
APPENDIX A - CONTACTS A-l
APPENDIX B - MEASUREMENT STANDARDS B-l
APPENDIX C - CURRENT REGULATIONS C-l
APPENDIX D - NOISE REDUCTION EXAMPLES D-l
APPENDIX E - NOISE REDUCTION OF MOTORCYCLES
CURRENTLY IN USE E-l
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LIST OF TABLES
Number Poge
1 Market Shares of Principal Motorcycle Manufacturers 7
Involved in the United States Market
2 Manufacturer Specification Ranges for Standard Highway 10
Motorcycles and Motor-Driven Cycles
3 Selected Motorcycle Noise Levels 35
4 Required Exhaust System Modifications and Associated Costs 41
to Achieve the Selected Noise Levels
5 Required Intake System Modifications and Associated Costs 44
to Achieve the Selected Noise Levels
6 Required Engine/Mechanical Noise Modifications and 51
Associated Costs to Achieve the Selected Noise Levels
7 Estimated Per-Machine Manufacturing Cost Increases for 53
Noise Reduction of Typical Full-Size Motorcycles >200 cc
8 Estimated Per-Machine Manufacturing Cost Increases for 54
Noise Reduction of Typical Small Motorcycles (Motor-
Driven Cycles) <200 cc
9 Information Explaining Tables 7 and 8 55
10 Estimated General New Motorcycle Noise Reduction Costs 58
vii
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LIST OF FIGURES
Number Page
1 Motorcycle Noise Sources and Configurations 9
2 Noise Levels of 1973 Model Motorcycles 15
3 Noise Levels of 1973 Model Motorcycles 16
4 Noise Levels of 1973 Model Motorcycles 16
5 Difference Between CHP Method Acceleration and Steady 20
Speed Noise Levels for 1973 Model Motorcycles
6 Typical Component Contributions to Total Noise Level When 21
Measured per California Highway Patrol Procedures (dBA at
50 feet) for Typical 1973 Model Motorcycles >200 cc
7 Narrow Band Exhaust Noise Spectrum for > 200 cc Muffled 24
Four-Cycle Twin Cylinder Motorcycle
8 Passby Noise Spectrum for <200 cc Unmuffled Two-Cycle 24
Single Cylinder Motorcycle
9 Estimated Costs for Reduction of Motorcycle Exhaust Noise 40
10 Estimated Costs for Reduction of Motorcycle Intake Noise 43
11 Estimated Costs for Reduction of Motorcycle Engine/Mechanical 50
Noise
12 Estimated Noise Reduction Costs for Motor-Driven Cycles <200 cc 57
13 Estimated Noise Reduction Costs for Motorcycles >200 cc 57
ix
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1. INTRODUCTION
Because of the notoriety of the motorcycle noise problem, several
states and municipalities have enacted noise regulations specifically
limiting the noise levels of both new machines and those already in use
(see Appendix C). These regulations, within the last 5 years, have
caused a significant decrease in the noise levels of new vehicles, and a
great deal of noise reduction activity among the manufacturers. Still,
the products of one manufacturer were denied registration by the State
of California for several months during 1972 until adequate demonstration
of noise control abilities was made.
In support of this activity, this study was commissioned to (1) deter-
mine the noise levels of current (1973) model motorcycles, (2) evaluate
available motorcycle noise reduction technology to determine noise reduc-
tions feasible for future new machines, and finally (3) to estimate the
increases in manufacturing cost required to achieve these noise reductions.
The results are displayed in Chapter 6 on several charts and tables.
Defined noise levels achievable for various motorcycle types (developed in
Chapter 5) are shown along with required manufacturing cost increases.
Noise levels, reductions, and estimated costs associated with specific noise
sources on the machines are also given, along with limited general infor-
mation on expected performance changes.
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These investigations have been carried out through the use of data
supplied principally by the motorcycle manufacturers listed in Appendix A,
without whose cooperation a project of this sort could not have been
completed. Wyle Research sincerely wishes to thank all of the listed
organizations for their participation in this program.
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2. STUDY APPROACH
The prime purpose of this study was to estimate the manufacturing cost increases
necessitated by the reduction of noise from future motorcycle models. As a result of
the noise control work which has been necessary since 1969 due to nonfederal noise
regulations, the motorcycle industry has collected a substantial amount of data con-
cerning both general motorcycle noise characteristics, and the noise produced by
specific model lines. Therefore, the main body of data used in this study was available
from the manufacturers. Supplemental information was obtained from exhaust system and
accessory manufacturers, industry organizations, independent motorcycling journals,
and independent organizations which have performed motorcycle noise measurements.
Upon evaluation of all the available data, an independent physical testing program
was deemed unnecessary for this study.
Initial contacts were established with firms which manufactured 95 percent of the
new machines sold in the United States during 1972. These contacts resulted in per-
sonal questioning of manufacturers supplying 80 percent of the new machines sold during
the first quarter of 1973. The following information was requested, as a minimum, from
each contact:
1. 1971, 1972, and 1973 model brochures and prices.
2. Noise levels of all 1971, 1972, and 1973 models measured according to
standard procedures either SAE J331 or "The California Highway Patrol "
(CHP) method.
3. The listed information regarding the following'subsources" of noise on a
motorcycle:
Subsources:
Exhaust - Outlet, Wall Radiation
Intake
Engine Mechanical, Combustion
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Drive System - Drive Chain, Internal (primary drive, clutch, gearset)
Tires
Miscellaneous vibration of external parts
Wind
Requested Information for Each Subsource:
a. Subsource noise level contribution to overall noise at 50 feet when
measured per SAE J331 or CHP method
b. Typical frequency spectra with specified conditions
c. Near-field or other supplementary or clarifying data
d. Modifications accomplished in the past to achieve present levels:
Reduction in 50 foot overall noise level per modification
Change in manufacturing cost per modification
e. Modifications available for the future:
Reduction in overall 50 foot noise level
Reduction in the particular subsource noise level at 50 feet
Change in manufacturing cost resulting
Performance or styling changes required
Date of availability or stage of development
4. The company noise reduction timetable for implementing the above
modifications.
5. The modifications intended for use to comply with future California
noise level requirements, and the expected manufacturing cost changes.
6. Measurements of minimum noise achievable by unpowered passby.
7. Share of the United States motorcycle market.
8. Opinions on reasonable progressively lower future regulations and test
procedures.
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9. Official policy statements.
10. General corporate financial brochure.
Partial or complete responses to the inquiries were received from manufacturers
which provided 93 percent of the new motorcycles sold in the United States during
the first quarter of 1973. Data resulting from previous Wyle Research contacts with
the motorcycle industry combined to yield a data base representing over 97 percent
of new machine sales in the United States. Similar information was also received
from over 50 percent of after-market exhaust system manufacturers. Many of the
manufacturers considered their data proprietary, and for this reason, company names
will not be identified with specific noise or cost data. The information received was
sufficient to allow reasonable estimates, through the analysis described in Chapters 5
and 6, of the manufacturing cost increases associated with varying degrees of noise
reduction for future new motorcycles.
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3. THE MOTORCYCLE INDUSTRY
Motorcycles are an unusual consumer product on the United States market. Over
90 percent of sales consist of products of foreign origin with 88 percent produced in Japan.
The only sizable U.S. manufacturer, AMF/Harley-Davidson, represents about 5 percent
of U.S. unit sales. The market also exhibits a high degree of concentration, with only
six of over 40 U.S. involved manufacturers obtaining approximately 95 percent of American
sales. These large manufacturers span the product range by offering the consumer
machines of varied size and purpose. Also, these major suppliers manufacture a wide
field of other products, or are subsidiaries of diversified manufacturers. A listing of
principal suppliers of motorcycles to the United States is given in Table 1.
In addition to the principal manufacturers noted above, there are approximately
15 minor American manufacturers producing limited numbers of medium to small size
machines for domestic sale. In general, foreign engine, engine silencing, and gear-
box units are fitted to frames manufactured by the American factories. This sector of
the market provides approximately 1 percent of United States sales, and over half of
these machines are of the "minibike" variety (described in Chapter 4) which is not
intended for regular licensed use. Due to the extremely low portion of machines sup-
plied, and the very limited noise control experience of these small shops, they are
not included in the project's analysis.
To preserve the confidentiality requested by industry, and in view of the homo-
geneous, concentrated foreign nature of nearly the entire industry supply, this study
has not grouped manufacturers according to geographical, technical, or economic
parameters. Rather, the following analysis will attempt to relate the costs of noise
reduction to physical motorcycle characteristics.
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Table 1
Market Shares of Principal Motorcycle Manufacturers
Involved in the United States Market
Manufacturer
Honda Motor Company
Yamaha Motor Company, Ltd.
Suzuki Motor Corporation
Kawasaki Motors Corporation
AMF/Harley-Davidson
Motor Company, Inc.
The Birmingham Small
Arms Co., Ltd.
(BSA, Triumph)1
Bavarian Motor Works
Bultaco Motors
Hodaka Industrial Co., Ltd.
OSSA
Husqvarna
Benelli
Location
Japan
Japan
Japan
Japan
U.S.A.
England
Germany
Spain
Japan
Spain
Czechoslovakia
Italy
Percent of Units
Sold in
United States2
48.6
18.9
12.2
8.2
4.6
3.2
0.6
0.6
0.4
0.4
0.3
0.2
98.2$
Source: 1973 CYCLE Magazine Buyers Study2 conducted by AHF Marketing
Research, Inc.
The BSA Co., Ltd. has recently consolidated with other British motorcycle
firms to form Norton Villiers-Triumph Corporation.
2
Figures from other independent market studies agree closely with those of
this table.
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4. MOTORCYCLE CONSTRUCTION AND NOISE CHARACTERISTICS
Introduction
The contemporary motorcycle is a highly developed, modern, high performance
transportation vehicle, and as such, becomes a notably complex source of noise. The
exposed condition of the vehicle components allows several of them to contribute
significantly to total vehicle noise. Basic motorcycle configurations with noise sources
identified are shown in Figure 1.
With few exceptions, the motorcycle is a two wheeled vehicle powered by a
carbureted spark ignition air cooled reciprocating two or four stroke cycle engine
driving through a manual clutch and multiratio gearset. Motorcycle size is conven-
tionally indicated by total engine displacement, expressed in cubic centimeters (cc).
Single row roller chain conveys engine driving effort to the rear wheel. Both wheels
are of the wire spoked variety, mounted on a damped spring suspension, and contain
independently operated drum or disc brakes. The operation of controls for brakes,
clutch, throttle, and gearset is by small hand or foot movements, and all controls can
be operated simultaneously without removing hand or foot from its particular control/s.
Ranges of dimensions and characteristics represented by available 1973 models are
shown in Table 2. Directional changes are made through a combination of turning the
handlebars front wheel assembly, and shifting of body weight. The constant imme-
diate availability of control mechanisms and use of subtle changes of body position
creates a sensation of motoring involvement for the motorcyclist which is generally
quite pleasing and sporting. This sporting interpretation is also intimately related to
the machine's sound. A motorcycle's exhaust noise is often referred to by the enthu-
siast as a "note, " indicating a kind of aural aesthetic quality. Thus, a saleable motor-
cycle, in addition to possessing traditional unfettered agility and stirring performance,
must present an acceptably impressive sound.
For purposes of this study, four basic styles represented by current models will
be defined. Highway motorcycles, which span the entire size and performance range.
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External Parts Vibration
Intake
Drive Chain
Exhaust
Outlet
Tires
Exhaust
Wall Radiation
Internal
Drive Components
HIGHWAY MOTORCYCLE
Engine Combustion
Aerodynamic Noise
of Complete Machine
and Moving Parts
Engine Mechanical
OFF-ROAD MOTORCYCLE
MINIBIKE
Figure 1. Motorcycle Noise Sources and Configurations
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Table 2
Manufacturer Specification Ranges for Standard Highway
Motorcycles and Motor-Driven Cycles
Displacement, cc
Maximum Power, hp
Maximum Engine Speed, rpm
Specific Power Output, hp/100 cc
Weight, Ib
"Power to Weight Ratio, " Ib/hp
Wheel base, in
Number of Gear Ratios
Top Speed, mph
Fuel Consumption, mpg
50 to 1200
4.9 to 82
5900 to 10,000
4.5 to 12.7
143 to 722
5.9 to 25.5
43.3 to 61.5
3 to 10
50 to 130
~ 20 to 90
are standard transportation models produced for licensing and use on public highways.
They contain all required safety equipment (lights, horn, passenger seat and handhold,
turn signals, etc.,) and have the least critical weight and size requirements. Dual
purpose motorcycles are a design compromise including features which allow reasonable
operation both on the highway and in nonpaved or natural areas. Differences from
pure highway machines include generally smaller components for less weight, increased
ground clearance usually requiring a high mounted and smaller exhaust, changes in
frame geometry, suspension, engine output characteristics, and occasionally different
tire size and tread type. Off road motorcycles are designed for use over natural terrain
only, and contain no features oriented toward highway use. Performance demands for
off road use, which often includes racing and other competitive events, require
extreme light weight, balance and agility. Thus, items such as seat, fuel tank, fenders,
intake, and exhaust systems are of minimal functional dimensions. Unfortunately, this
configuration has in the past produced noise levels of other than minimal dimensions.
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Dual purpose and off road motorcycles are available in sizes of 500 cc or less.
Mini bikes exist in many forms, from accurately scaled down motorcycles to simple
tube frames on small tires powered by lawn mower type engines. Intended for general
off road use by children, some highly developed examples produced by large manu-
facturers contain the equipment necessary for highway licensing.
Sales of all four types are nearly equally divided between machines powered by
two stroke cycle and four stroke cycle engines, with the exception of off road motor-
cycles, for which the lighter weight two-cycle engine is more common.
Average vehicle lifetime varies appreciably with machine type and use. In
general, off road motorcycles are active between 3.5 and 5 years; dual purpose or
highway machines under 350 cc can remain in use up to 6 years; and large motorcycles
exhibit an average lifetime of between 5 and 10 years. At these replacement rates,
somewhat more than 75 percent of the field of smaller machines is renewed every 5
years, and at least a similar portion of large motorcycles are replaced in less than a
decade.
Measurement Procedures
Since the noise level of any acoustic source can be meaningfully measured and
recorded only with reference to a specified measuring technique, it becomes extremely
important to establish a firm procedure when measuring or discussing motorcycle noise.
Five such procedures exist (see Appendix B) which apply, in one way or another, to
new motorcycles sold in the United States, and the noise level values obtained for any
particular machine differ greatly between these procedures.
Only two of these procedures, however, are widely used in establishing vehicle
noise levels for legal compliance, and almost all noise level data and familiarity with
motorcycle noise is based on these methods. In the State of California, the California
Highway Patrol (CHP) has established a vehicle noise measurement procedure applicable
to motorcycles in which the maximum A-weighted sound pressure level is measured as
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the motorcycle accelerates past at a 50 foot distance in one of the lower gears under
wide open throttle. This is the procedure used for new vehicle noise testing by
California authorities. The Society of Automotive Engineers (SAE) Standard J331
Sound Levels for Motorcycles measures the same quantity under similar conditions
except that the acceleration is arranged for individual machines so that maximum
rated engine power will be achieved quite close to the test microphone. This arrange-
ment has caused measured levels to be from zero to 10 dB greater than levels achieved
by the same machine operating under the CHP procedure. Unfortunately, there is no
straightforward relationship between values obtained with the two procedures. Studies
accomplished during 1970-71 show the differences between SAE and CHP values which
existed for various size machines of that period/'^ From this information, a conversion
curve of dB with displacement can be obtained which represents the mean difference
relationship for 1970 model machines. Due to significant changes in motorcycle noise
characteristics since that time which have been forced by state legislation, this rela-
tionship is not strictly valid for 1973 machines.** Thus, any conversion between SAE
and CHP values for current models based on the 3 year old data will contain some
degree of inaccuracy.
Nearly 80 percent of the noise level data obtained for this project were meas-
ured according to CHP procedure, the remainder being measured according to the
SAE procedure. Although SAE results more closely approximate maximum noise, the
interest of accuracy will be served by converting the 20 percent SAE data into its
approximate CHP equivalent and presenting all noise levels as being obtained from
the CHP test method. Based on interpretation of the 1971 data, it will be assumed
that the CHP level is 2 dB lower than the SAE level for motorcycles under 400 cc
displacement, and 4 dB lower for motorcycles of 400 cc and larger. This creates an
uncertainty of approximately ±1.5 dB from true CHP method values.
The CHP and SAE test standards appear to have equivalent technical foundation,
and measurements of motorcycle acceleration noise can be made with equal precision
using either method. Hence, no lack of data quality was incurred by choosing the
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CHP method for use in this project. As mentioned above, the SAE method allows
achievement of maximum rpm consistently close to the microphone, and provides as
accurate a measurement as has been devised for maximum possible noise (see
Appendix B). Because the SAE procedure more closely measures motorcycle noise at
an absolute level of performance (maximum rpm at wide open throttle), it might be
the most objectively useful type of measurement for community noise assessment or
regulation enforcement. Because lower noise level values are usually generated by
the CHP method, it is more widely endorsed by industry. "Same-day" repeatability
of both procedures is usually within 1 dB, but occasional consecutive measurements of
the same machine differ by as much as 2 dB. During both the CHP a:.d SAE procedures,
accelerations of up to 0.3 g are produced. Although this level can be exceeded by some
large displacement machines, it defines the maximum normal duty acceleration. In addi-
tion, as will be seen in the Cruise-By section of this chapter, a CHP method noise level
may accurately indicate the maximum steady speed passby noise to be expected from a
given machine during typical use. One inequity in both these methods is variable
rider weight. Clearly, a machine burdened with an excessively heavy operator will
accelerate more slowly than with a light rider, and will likely produce less noise during
the test. Also, several "treatments" have been discovered which can be applied to any
particular test vehicle to reduce its test noise level below that of a machine normally
prepared for routine operation. Boiling the final drive chain in grease, using unusually
heavy oil, providing abnormally high tire air pressure, and adjusting the fuel mixture
to a "lean" condition will cause the machine to accelerate more slowly against less
resistance, and is reported to reduce noise levels from a mechanically loud vehicle by
as much as 3 dB. In summary, however, the SAE and CHP acceleration test methods
appear equivalently repeatable, meaningful in terms of in-use noise levels, and accept-
able to industry as a useful method for determination pf the noise levels of individual
motorcycles.
A-Weighted Noise Levels
Noise levels have been obtained for most popular 1973 models as measured with
the California Highway Patrol test procedure. Reported noise levels obtained with the
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SAE procedure have been converted using the previously described adjustments. All of
the levels are displayed in Figure 2, with distinctions shown between motorcycles with
two-cycle engines, four-cycle engines, and mini bikes. Off road motorcycles not subject
to registration are omitted. Noise level differences of up to 4.5 dB have been found
between different machines of the same model. This noise level spread is similar to those
of other vehicle types, and the data of Figure 2 represent the louder extremity of this
quality control region. Thus, practically all of the individual vehicles represented by
each point on the figure will be at or below the indicated noise level. The levels are
as measured, with the 2 to 3 dB "tolerance" sometimes found in vehicle noise measure-
ment procedures not applied, and represent vehicles as sold throughout the country.
The noise level spread evident for all motorcycle size ranges results from differences in
the configurations of engines, intake silencers, mufflers, and other noise sources on
the machine which will be discussed in detail further on in this chapter.
It is seen how the high displacement portion of the region in Rgure 2 tapers off
roughly asymptotic to the 86 dBA level. Data from the previous years 1970-712'3/6'7'8
are distributed in a more linear manner, proceeding through the 86 dBA level and con-
tinuing through 95 dBA for the large machines. This difference indicates the high
degree of noise control which has been effected, primarily on the large displacement
machines and loudest small machines, since 1970. The values are not incidental, but
reflect the requirements of the California Vehicle Code which has set the national pace
in regulation of new-vehicle motorcycle noise by reducing permissible levels (for
machines of over 15 horsepower) from 92 dBA for machines of pre-1970 manufacture,
to 86 dBA for those of 1973-74 manufacture (see Appendix C). Almost all new motor-
cycles sold in the U.S. are equipped to meet this regulation. Consideration of
Figures 3 and 4 reveals the same noise level trend whether engine displacement, maxi-
mum rated horsepower, or retail price is used as size discriminator thus illustrating
the close relationship between these quantities and justifying the use of engine displace-
ment as a good size discriminator for noise control analysis.
Further examination of Figure 2 reveals an apparent noise level difference
between two distinct groupings. Motorcycles of under 100 cc displacement show wide
14
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90
CN
86
Z 1 84
a "S
o -=
in .0)
80
o
1 E
«s 75
-------
90
«
85
CM £
ir
80
i?
P
1973 California New
Vehicle Requirement
O
O
8
o
o
DO
Source: Reference 8
0>200cc
0<200cc
Each Point Represents a Different Make and Model
To 2*03o 40 so~
Maximum Rated Power (H.P.)
60
70
80
Figure 3. Noise Levels of 1973 Model Motorcycles
90
If.
04 o
ir 8°
T 1 1 1 r
o °
T r
OOQO
n oo
J|75
S~o
a o a
o a3
o
J"8
J B
70
T 1 r
o
OOoO 0
o o
Source: Reference 8
0> 200 cc
0< 200 cc
Each Point Represents a Different Make and Model
800 1000 1200 1400 1600 1800 2000 2200
Manufacturers Suggested Retail Price (S)
2400
Rgure 4. Noise Levels of 1973 Model Motorcycles
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scatter in achieved noise levels, from 71 to 83 dBA, while models of 250 cc and above
range from 78 to nominally 86 dBA. The 200 cc size represents the approximate transi-
tion between the "motorcycle" and "motor-driven cycle" as usually denoted in state
vehicle laws and by the Society of Automotive Engineers." Motor-driven cycles,
defined in California as two wheelers of under 15 horsepower, are restricted from cer-
tain high speed roads and, in California, are subject to stricter noise requirements.
Motorcycles, those of 15 horsepower or more, are afforded full vehicle status. The
state of modern engine development is such that the 15 horsepower figure is usually
attained by engines in the 150 cc to 200 cc range, and thus the below 200 cc category
contains principally motor-driven cycles. These small machines are generally suitable
for arterial, neighborhood or lower speed travel, while 250 cc or larger motorcycles
may be operated easily at freeway speeds. Given the differences in noise levels,
classification, and use of these groupings, discussion of noise levels in this report will
consider machines larger and smaller than 200 cc separately, with additional comment
on the exceptionally low noise levels of motor-driven cycles smaller than 100 cc.
Several additional considerations have become apparent from the acceleration
noise level data. Foremost, and a matter of immediate curiosity to most motorcyclists,
is the difference in noise level between vehicles powered by two-cycle and four-cycle
engines. Figure 2 indicates, however, that little difference exists between the two.
Throughout the 100 to 200 cc range, and for the popular 250 cc, 350 cc, 500 cc, and
750 cc sizes, the A-weighted sound pressure levels as determined by CHP procedure
for the two engine types are well integrated, with no distinctive differences apparent.
This fact must not be construed to mean that a listener's perception of the two sounds
of equal noise level will be the same, for the differing frequency content of the noises
will cause dissimilar tonal quality. In the under 100 cc range, all of the low noise level
cycles (with the exception of minibikes) are two-cycle powered. This difference will be
discussed in the following sections and chapters dealing with exhaust and mechanical
noise.
Another prime matter of interest is the comparison of noise levels of dual purpose
motorcycles to those of the highway variety. The question arises due to the traditional
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use of lightweight and noisier components on motorcycles intended for part-time off
road use. Although not pic tori ally shown, 42 percent of the available data represents
dual purpose machines, and again, no significant difference can be noted between
the respective collective noise levels in any size range. Finally, attention is directed
at the effects of the recent trend toward multicylinder engines. Three and four cylinder
engines have become common since 1970, but once again, no detectable general dif-
ference between singles, twins, triples, and fours exists in the data.
Off road motorcycles not subject to registration, licensing, or police surveillance
become a special case. Highly prone to individual post-purchase modifications com-
plimenting owners' tastes, exhaust and intake systems are commonly replaced with
various after-market units. In many cases, these accessory systems provide little
silencing, and for this reason factory noise specifications for off road models do not
truly indicate the noise levels of post-purchase vehicles. Unmuffled two-cycle
powered off road machines can generate over 110 dBA during the CHP test, but areas
where unmuffled operation is within the law are becoming extremely scarce (see
Appendix C). Muffled levels from 80 dBA to 97 dBA, with most in the 90 dBA region,
are typical. Due to the difficulty of assessing noise impact from off road vehicles, the
difficulty in enforcing regulations more complex than the "adequate muffler" variety,
and the performance requirement, off road motorcycles will not be included in the
economic evaluation of noise control potential.
Mini bikes are a final small category including less than 5 percent of recent two-
wheeled vehicle sales. Noise levels range throughout the under 200 cc category noise
level spread. Included in the above percentage figure are the once popular motor
scooters, which represent less than 0.4 percent of total sales. The little noise level
data which exists for motor scooters is within the range of under 200 cc noise levels,
but too little noise or economic data has been obtained to allow their inclusion in
/
the project analysis.
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Cruise-By
Noise levels obtained with the CHP procedure lie somewhere between the maxi-
mum and minimum levels of which the tested machine is capable, the proportion between
the two being a function of the test procedure JO ft has been stated earlier that the
CHP procedure usually yields noise levels below the maximum possible for a given
machine. There also appears to be a relationship between CHP measurements and lower
motorcycle noise levels. Figure 5 shows the difference between CHP method values and
steady speed passby values at 50 feet for all motorcycle sizes. The shaded regions are
uniformly represented by a distribution of noise data, and thus it is seen that 1973 model
motorcycles operated in the lower speed range of 25 to 40 mph can be much quieter
(5 to 25 dBA) than when measured during the CHP test. Also, even at maximum in-use
speeds, constant speed noise levels still do not substantially exceed those determined
by the CHP procedure, suggesting that the CHP standard may provide a good indicator
of near-maximum levels generated by this mode of real life use. It should be mentioned
that the function of steady speed noise level with speed for a particular machine does
not necessarily monotonically rise. Speed increases of as much as 10 mph may have no
effect on noise level, depending on motorcycle construction, and the use of higher
gears can even show reductions in total noise level with speed gains.
Coast-By
Discussion of vehicle noise control often includes allusion to a noise "baseline"
or "noise floor" being the minimum possible noise level of an ideally silenced vehicle.
Such descriptions can be highly misleading, and any mention of lower bounds must
include exact specifications of the vehicle, its operation, measurement techniques,
and all other applicable conditions. Such minimum levels for motorcycles are usually
portrayed by unpowered passbys at 50 foot distance which include noise contributions
from drive chain, tires, roadway excited vibration, freewheeling internal drive systems,
and windage. Maximum total levels between 60 and 68 dBA have been recorded for
19
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Source: References 8, 10
-5
200
300
400
500 600 700 800
Engine Displacement (cc)
900
1000 1100 1200
Figure 5. Difference Between CHP Method Acceleration and Steady
Speed Noise Levels for 1973 Model Motorcycles
moderate speeds of 30 to 40 mph, but no well-founded portioning of this noise between the
contributing sources has been accomplished. Estimates which have been made are included
in Rgure 6. It is likely that the combined level of these coasting noise sources is the same
during powered passby, since all operate in the same mode with the exception of chain
load reversal. Although reductions in coast-by noise could be accomplished through such
devices as full chain cases, shaft drive, or solid wheels, the contributions of these sources
is clearly negligible (see Rgure 6) when compared to noise generated by the engine.
Thus, consideration of "noise floor" levels is currently of little practical use in the reduc-
tion of noise from existing models.
20
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Exhaust Outlet
Noise 81
Intake
Noise
79
Engine Mechanical
Noise 78
84.2-
66.6-
-84.5
Total Noise Level
Drive Choin 61*
Noise
Tire-Roadway
Noise 60*
Internal Drive
Mechanical 60*
Noise
Aerodynamic 58* ^_^_^_
Noise
Combustion Noise
and Exhaust 55*
Radiation
Misc. 55*
Vibration
* Values estimated by motorcycle manufacturers ond Wyle Research .
Figure 6. Typical Component Contributions to Total Noise Level When
Measured per California Highway Patrol Procedures (dBA at 50 feet)
for Typical 1973 Model Motorcycles >200 cc
Operator Noise Levels
Finally, noise levels experienced by motorcycle operators may be considered.
Recent studies have demonstrated the high levels of noise present at the ear during expo-
11 10
sure to airflow past the head. ' For motorcycles/ at-ear noise levels (measured at the
ear with a small microphone) below 40 miles per hour vary with the type and operation
of the motorcycle, and have been reported to be around 100 dBA at 20 mph. Above
40 mph, at-ear total noise levels become a function of speed alone, being completely
determined by aerodynamic noises, although certain narrow frequency ranges of the
machine radiated noise may still be apparent to the rider. Noise levels are reported
21
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at these speeds from 100 dBA at 40 mph to over 110 dBA at 70 mph. Use of protective
safety helmets has been shown to cause moderate reductions of at-ear noise depending
on speed, fit, style, and type of eye protection. Still, the motorcyclist is constantly
exposed to high noise levels by virtue of his unshielded passage through the air.
Noise Sources
As stated at the beginning of this section, the modern motorcycle is a complex
noise generator, several exposed components of which contribute significantly to the
total noise produced. These contributing vehicle elements are commonly called noise
subsources. Typical contributions of various subsources to the total motorcycle noise
level as measured by the CHP procedure have been shown in Figure 6. The values are
not from any particular machine, but do represent typical component levels existing
for 1973 model motorcycles of the over 200 cc category. Immediately apparent is the
significance of exhaust outlet, engine intake, and engine mechanical noises, and the
low importance of the other subsources which were principally included in the coast-by
discussion.
Exhaust
Through an opened exhaust valve or port, an exhaust gas pulse with a temperature
of several thousand degrees and a pressure of several hundred pounds per square inch
enters the exhaust system in a matter of milliseconds. This large pressure near-
discontinuity propagates along the exhaust system piping to exit at an amplitude deter-
mined by the system configuration. A running engine can repeat this process over a
hundred times per second, with the resultant perceived noise appearing as a staccato
or smooth tone depending on engine type and speed. As measured using the "A"
weighting network of a sound level meter, unmuffled exhaust outlet noise alone can
be over 110 dBA at 50 feet during a CHP acceleration test. Some of the very simplest
mufflers consisting of a perforated tube surrounded by sound absorbing material will
attenuate exhaust-only noise to below 95 dBA. Further reductions have required more
22
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extensive reactive muffling, and levels of 82 dBA for large highway machines to
70 dBA for under 100 cc machines are generated by the exhaust outlets of 1973 produc-
tion models during the CHP test. It should be added that exhaust levels as low as 76 dBA
are achieved using unusually large standard type muffling systems on some large displace-
ment highway vehicles. For off road motorcycles, exhaust outlet noise has always been
the predominant subsource, and recent muffler and spark arrestor requirements have
caused a lowering of average exhaust noise levels to below 90 dBA for 1973 production
models.
The great pressure differential across an exhaust pulse traveling along exhaust
piping can excite the exhaust system walls into vibration which allows direct trans-
mission of exhaust noise through the system walls. The exact contribution of exhaust
wall radiation to CHP method total noise levels has not been determined. It is estimated
that, although at present exhaust radiated noise is not a major contributor, its importance
on some machines may increase as total noise levels are reduced.
Immediately apparent to a listener is the difference in tonal quality between two-
cycle and four-cycle engined motorcycles. The origin of this difference must lie among
the vehicle subsources, and of those, only the engine sources vary. Although disparity
will be found between mechanical and intake noises from the two engine types, the pri-
mary difference accountable for the unique tonal interpretations is the exhaust. Figures
7 and 8 illustrate the characteristic difference in exhaust noise spectra. Figure 7 is a
representation of exhaust-only noise as measured a short distance from the exhaust outlet
of a muffled four-cycle motorcycle engine. The shape of the curve clearly corresponds
to combustion exhaust characteristics, with most of the energy below 500 hertz, and
slowly trailing off into the high frequency region. Figure 8 shows total passby noise
as measured for an unmuffled two-cycle machine where exhaust noise is the only signif-
icant subsource. The trend of increased energy content at higher frequencies contrasts
sharply with that of the four-cycle engine, and accounts for the higher pitched noise
associated with two-cycle machines. Due to the differing test natures, the respective
23
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200 cc Muffled Four-Cycle
Twin Cylinder Motorcycle See Text
a>
a>
£
1
T3CM
S E
T» 3.
<=>
u
o
0)
6
no
100
90
80
70
60
50
~ r
T 1 I T
A: Fundamental Firing Frequency at 10,000 rpm
Source: Reference 2
20
50
100
2000
200 500 1000
Frequency (Hz)
Rgure 8. Passby Noise Spectrum for <200 cc Unmuffled Two-Cycle
Single Cylinder Motorcycle See Text
24
5000 10,00
-------
numerical levels indicated on the figures cannot be meaningfully compared. It is
probable that some high frequency noise was already attenuated by the four-cycle muf-
fler, thus causing the two curves to diverge more widely than in equivalent comparison.
These small inaccuracies aside, the pertinent fact is that in each case exhaust noise
was the principal quantity measured, and a clear difference is apparent.
Relating the discreet tonal interpretations of two-cycle and four-cycle motorcycle
engines to irritability is difficult, for annoyance in this case is largely determined by
variable physical and psychological factors. Even scientific measures of subjective
noisiness which allow for frequency content and pure tones do not account for the
sensory difference between the two engine types .^ Thus, two motorcycles, even of
the same engine type, with equivalent A-weighted sound levels can be perceived as
of different loudness and quality, with attendant difference of irritation due to the
dissimilarity of exhaust noise spectral distribution.
Intake
With the reduction of exhaust noise prompted by recent regulations, noise from
the intake system soon assumed important levels, and for current models, the two sub-
sources are of approximately equal noise level for all motorcycle sizes. They both
correspond to throttle opening, engine speed,and load, and are the two predominant
noise sources for most/nodes of operation . Although for over 10 years, some sort of
air cleaner has been fitted to almost every standard machine, improved intake silencer
designs have been required in order to produce current intake noise levels which range
from 77 to 84 dBA for machines larger than 200 cc. Two-cycle engines which, for a
given speed, induct nearly twice the volume of air as four-cycles of equal size, have
traditionally generated high intake levels, but recent improvements in silencing prac-
tice have reduced these levels to those of the exhaust. Also, there is some indication
that, as exhuast muffler 'back pressure" increases, intake noise levels may also
increase. Intake and exhaust mechanisms are the boundary elements of the general
problem of flow through the propulsion assembly, and their close interrelation is the
subject of many current theoretical and empirical investigations.
25
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Engine Noise
As is characteristic of any vehicle propelled by an air cooled engine, a notice-
able mechanical clatter and ringing accompanies the passage of most motorcycles.
Although the contribution of mechanical subsources to the total noise level determined
by the CHP test is difficult to measure, near field measurements have been made which
allow estimates in the 68 to 80 dBA range. Mechanical noises directly transmitted
from within the engine result from the actual striking together of engine parts, such
as piston slap, valve and valve train clatter (present in four-cycle engines only),
gear meshing, and noise from the roller and ball bearings widely used in motorcycle
engines. Secondary mechanical noise is that radiated from the vibrating engine sur-
faces, such as cooling fins and casings, which become excited by the aforementioned
collisions of engine parts and combustion pulses. Industry sources have found this
mechanical sound power to rise approximately with the fourth power of engine speed
(12 dB per doubling of rpm). The common small engine noise source of flywheel
windage and vibration appears to contribute very little. Directly transmitted combus-
tion noise, a final source of engine noise, is considered by the industry to be of an
insignificant level in relation to the major sources for most modes of operation. Thus
it is principally the mechanical sounds which provide engine noise of level and tonal
characteristics sufficient to vitally influence the total level and quality of a motor-
cycle's sound. Reduction of total motorcycle noise levels may require a dispropor-
tionate reduction of mechanical noise in order to produce a resultant sound sufficiently
free from the 'bolts in a can " effect.
Drive Noise
Drive noise is here considered to consist of noise from internal and external drive
system components, and tire noise. Internal sources are of two categories, gearset and
primary drive. Gearset noise originates with the meshing and movements of gears and
bearings within the gear ratio assembly. The primary drive system, comprised of the
clutch and chain or gear linkage between engine crankshaft and gear set, creates
26
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additional contact sounds which are at times complemented by vibration noise from
clutch components. The total of these levels is generally lower, however, than that
produced by the external drive chain, which itself is not an important contributor during
the CHP test. The modem trend toward sporty vehicles has discouraged use of fully
enclosed chains or shaft drive, thus maintaining final drive noise levels at a maximum.
Of course, these drive system subsources assist in the excitation of external gearset
cases, primary cases, and other vehicle parts which radiate additional sound. As stated
earlier, coast-by levels of 60 to 68 dBA have been recorded, and considering the higher
loading and vibration present under power, contributions of between 65 and 70 dBA
might result from current power drive systems. Tire noise, a normally predominant
component of total vehicle noise as speeds increase, is found among the minor motor-
cycle subsources. Due to the extremely small contact surface and relatively well
damped sidewalls, tire noise, even at high speeds, ranges near 60 dBA. Off road
"knobby" tread types, when used on pavement, have been noted to raise tire noise
levels 1.0 to 1.5 dB above those of highway tires, but such increased levels would
still not become important until total levels are reduced below 75 dBA. In any case,
highway use of these louder tread patterns will not become widespread due to extremely
high wear rates and reduced traction.
Aerodynamic and Miscellaneous Noises
Aerodynamic noise, that caused by the turbulent passage of air in and around the
motorcycle components and rider, may become more significant than 58 dBA (indicated
in Rgure 6) as speeds increase. Spoke tip speeds of greater than 100 feet per second
with respect to oncoming airflow are achieved at freeway speeds. Such sources, com-
bined with the dominance for the operator of wind noise at high speeds, indicate that
high speed chainless coast-by tests might show surprisingly high aerodynamic/tire noise
levels. Radiation of noise from remaining motorcycle components such as fenders, fuel
tank and side panels due to the various engine, drive, and road excitations is difficult
to quantify except by process of elimination. In this way, the level entered in Figure 6
27
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has been developed to closely represent the noise originating from these components
on an average 1973 machine.
Noise Source Relationships
The absolute levels and ranking of subsources shown in Figure 6 are representative
contributions to the maximum acceleration noise as measured by the CHP procedure. For
other modes of vehicle operation, the relative prominence of the subsources may change.
During acceleration, intake and exhaust noise are at their peak since they correspond
directly together to throttle opening and load. Partial throttle closure to a steady speed
will cause a de-emphasis. Engine and vibration noises then assume more importance and,
at proper speeds, can effectively mask intake and exhaust. Thus, along with a change
in total noise level, the tonal quality of the machine's sound changes with the operating
mode, and can give rise to further virtual or perceived changes in "noisiness. " Several
instances have occurred where, when comparing the noise of two motorcycles, observers
have judged the machine with the lower A-weighted noise level to be the noisier of the
two. Thus,quieting of a motorcycle does not exclusively imply a lowering of total sound
pressure level, but can in some cases be achieved through tonal modifications, while
retaining a tone which renders the machine desirable to the consumer.
Noise source relationships may also change with vehicle use. Little data exist
which show noise level changes of properly maintained motorcycles with mileage accumu-
lation. One investigation, however, did note a significant increase in the level of a
new 250 cc two-cycle off road machine. Initial acceleration noise levels of 85 to
86 dBA were increased to 96 dBA after a few hundred miles of severe off road use, the
increase apparently divided between exhaust and mechanical noise. This lone example
cannot be considered to represent typical noise level changes with use, but does confirm
that transpositions of noise subsource importance, as well as total noise level increases,
are possible.
28
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5. SELECTED NOISE LEVELS
Introduction
The 1973 models for which noise levels are shown in Figure 2 can be conveniently
grouped into two general classes, representing two distinct engine size ranges. As
explained in Chapter 4, the operating characteristics of these classes separate near an
engine displacement of 200 cc. Furthermore, noise levels of the smaller machines with
engine displacements less than 200 cc again naturally divide into two regions, namely
0 to 100 cc and 100 to 200 cc. Figure 2 illustrates a proven industry ability to achieve
uniquely low levels for motorcycles in the 0 to 100 cc range, and so this size category
will be considered independently in the assessment of noise reduction capability.
Machines of the 100 to 200 cc class, although generating noise levels similar to those
of very large motorcycles, are often similar in construction and operation to the smallest
category. In fact,this 100 to 200 cc size range ss a transition region containing machines
of large, small, and heterogeneous character, and thus noise reduction abilities will also
be determined separately for this range. The discussion of noise control feasibility, then,
will distinguish as far as possible between technology for the following classes:
Class 1 -Oto 100 cc
Class 2-101 to 200 cc
Class 3 - over 200 cc
The discussion of present and future noise levels of these three classes can be
facilitated by concentrating on a few representative levels. It has been decided , in
consultation with the EPA^ that three different noise levels will be examined for each
motorcycle class based on the information and data supplied by the manufacturers. The
three levels may be summarized as fol lows:
Level 1 - Typical level of the quietest 1973 models
Level 2 Level of the most quiet product which could be available in
October 1975, using ail known or shortly available technology
29
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Level 3A level somewhere between the first two, if widely divergent, repre-
senting a practical industry goal for October 1975 using available technology.
In Chapter 4 it was stated that noise levels from different vehicles of the same
make and model can differ by as much as 4.5 dB. Thus, in order to insure that all
machines of a specific model will exhibit noise levels below any given figure, many
factories attempt to achieve an average level for the model approximately 2 dB below
the goal figure. Considering this practice, and the fact that the noise levels of Figure 2
represent loudest production examples, the selected levels herein defined will be achiev-
able for almost all machines in each model line indicated as being able to meet these
levels.
It must be recognized that there exists in the motorcycle industry a diversity of
"character" provided by the varied approaches adopted by different factories to the
basic motorcycle concept. Machines of quite diverse basic style and design are avail-
able, from huge V-twins to small three cylinder two-strokes, and the 'personalities"
of several of these arrangements represent decades old traditions. The experienced
motorcyclist can immediately sense, for example, English, Japanese, or Italian flavor
in a motorcycle's styling, its sound, its ride, or even the form of a single part. Hence,
the noise level values developed in this section must be average interpretations of this
wide range of machinery. The remainder of this section presents the rationale for the
establishment of the selected noise levels for each vehicle class. A discussion of
specific noise reduction techniques is presented in Chapter 6.
Level 1
The first level is representative of the best well established noise control tech-
nology existing for the 1973 model year, and indicates where the industry stood in
terms of noise control at the start of this project.
For Class 1 vehicles (0 to 100 cc), noise levels which extend below 75 dBA are
principally for mint-cycle vehicles which constitute less than 25 percent of the Class 1
sales market and offer characteristically lower performance than standard Class 1 motor-
cycles. The groupings of noise levels above 80 dBA represents approximately 50 percent
30
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of the Class 1 vehicles sold; these being mainly powered by four-cycle engines. The
distribution of the remaining machines with noise levels between 75 and 80 dBA,
powered mainly by two-cycle engines, is fairly even. Thus, Level 1 is established at
79 dBA as representative of the best well demonstrated level of noise control for existing
vehicles taking into consideration the higher noise levels evident for four-cycle machines.
An abrupt difference is seen for Class 2 vehicles (101 to 200 cc) where no noise
levels are below 76 dBA. In fact, very few are below 80 dBA, and 81 dBA represents
Level 1 for this class, the lower limit for well-established levels.
For Class 3 vehicles (greater than 200 cc), a quite distinct lower level is apparent
and separate from the main data body, representing advanced and special machines
atypical of the class. A level 1 of 82 dBA is the lower bound representative of the
majority of the large machine field.
Level 2
The second level, that of the quietest possible product which could be available
in 1975, is based upon liberal application of the available noise control technology
to the quietest of existing machines without eliminating the basic performance
characteristics.
Noise levels of quiet Class 1 vehicles presently lie between 71 and 75 dBA. Since
the principal difficulties which manufacturers encounter in reducing noise lie with
the larger machines, most previous subsource analyses and noise control activities
have not been directed toward vehicles in Classes 1 and 2. Furthermore, given the
extremely low minimum noise levels already achieved, which approach coast-by levels,
the indication is that saleable, production motor-driven cycles with noise levels less
than 70 dBA could not be manufactured by the date of interest. In one case a noise
level of 68 dBA has been achieved with intake and exhaust silencers of disproportionate
size together with fully enclosed drive chain and mechanical treatments, but only with
excessive degradation of operating characteristics, which industry believes would
seriously limit marketability. Thus Level 2 for Class 1 vehicles is established at 70 dBA.
31
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This represents an absolute minimum for the class, is a full 10 dBA below present levels
of the class1 main body, and would not be achieved by more than 25 percent of Class 1
machines by the date of interest.
In Class 2, one minibike already exists with a noise level near 76 dBA, and
several other standard machines are at or below 80 dBA. Thus, it is reasonable to
expect that, given the noise reduction discussions of Chapter 6, the capability exists
to produce standard machines with a Level 2 of 76 dBA by the date of interest. For
Class 3 vehicles, two manufacturers currently produce models (representing about 2 per-
cent of the market) with noise levels of 78 dBA. The remaining manufacturers have yet
to develop or prove the reliability of prototypes with noise levels of 80 dBA. The noise
level reductions required from the various subsources to achieve a total noise level of
80 dBA have been established, but specific design modifications are still experimental
in most cases. It is also unlikely that further significant reductions could be available
by October 1975 for the 78 dBA machines through improvement of the treatments which
are to be described in Chapter 6. Rather, extension of these available techniques to
the principal field of noisier machines for compliance with impending state regulations
will consume manufacturer activities. Thus, the lack of available technology to achieve
levels below 78 dBA, together with the belief expressed by several principal manufacturers
that this level represents the minimum possible for Class 3 machines establishes Level 2
at 78 dBA.
Level 3
Level 3 indicates the noise levels which could be attained by the principal body
of machines by October 1975.
Although the ability to produce Class 1 machines with noise levels in the 72 to
73 dBA region has been demonstrated, Level 3 is selected as 76 dBA, since demonstra-
tion of the lower levels has been achieved only for motorcycles powered by two-cycle
engines. Approximately half of the Class 1 range of machines are so powered, and
32
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design similarities render it reasonable to expect that all such vehicles could meet the
76 dBA level by October 1975. The other half of Class 1 vehicles, propelled by four-
cycle engines, appear to suffer a lack of available technology to reduce mechanical
and exhaust noises characteristic of this engine type. Thus not all of these vehicles
can be expected to achieve the 76 dBA level by the date of interest. One 90 cc four-
cycle model currently exists with a noise level of 77 dBA, and other four-cycle powered
mini-cycles have noise levels below 75 dBA. From this indication, and the specific
considerations of noise control in Chapters 4 and 6, it is reasonable to expect that
roughly half of the existing four-cycle machines with noise levels greater than 80 dBA
can be reduced to 76 dBA by the target date. These vehicles, when combined with the
two-cycle powered machines which should virtually all be capable of achieving 76 dBA
constitute an estimated achievement potential of 75 percent of all Class 1 machines
which could attain Level 3 of 76 dBA by October 1975. Selected noise levels have
been developed for Class 1 as a whole since insufficient specific subsource noise level
and cost data has been accumulated for Class 1 vehicles to allow separate noise level
analyses for two- and four-cycle powered machines.
For Class 2 vehicles, the level of 80 dBA has been attained by both two- and
four-cycle machines. Moreover, noise level data from the two engine types is more
homogeneously distributed, indicating an equivalence of available noise reduction
technology. As described in the introduction to this chapter, Class 2 represents a
transition region in which individual vehicles have construction, operation, and noise
characteristics which can be similar to those of either Class 1 or Class 3 machines.
Thus, Level 3 should represent a goal attainable by both types of Class 2 vehicles.
From Figure 2 it is seen that the minimum noise level already attained by both large
and small Class 2 machines is 79 dBA, and therefore Level 3 is selected at 79 dBA.
Approximately 90 percent of the 1973 Class 2 vehicles currently have noise levels
above 79 dBA, and it is reasonable to expect that, of these, at least those with prin-
cipally Class 1 characteristics could be reduced to 79 dBA by the target date. This
33
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would result in approximately 55 percent of all Class 2 vehicles meeting Level 3. It is
also expected that nearly half of the larger style Class 2 vehicles could be reduced to
79 dBA, yielding a total estimated potential compliance to Level 3 of approximately
75 percent of all Class 2 vehicles.
Considering Class 3 motorcycles, a noise level of 82 dBA as measured by the CHP
procedure would constitute a conservative goal, with over 50 percent of the industry
possessing good achievement potential by October 1975. However, manufacturers
involved in about 20 percent of U.S. sales claim a demonstrated ability to achieve the
1975 California regulation of 80 dBA with prototype or experimental Class 3 machines,
and the remaining manufacturers are in the midst of intensive test and development pro-
grams oriented toward this goal. The machines currently produced with noise levels
below 80 dBA constitute only 2 percent of current sales and contain unique design
qualities to reduce mechanical noise levels which normally become significant at or
about a total noise level of 80 dBA. Thus, on the basis of prototype achievements,
industry orientation, and available technology, 80 dBA is selected for Level 3. This
level should be within reach for almost half of the 1976 model Class 3 machines with
concentrated development.
The three selected noise levels for each of the motorcycle size classes are listed
in Table 3 on the following page.
The target date of October 1975 has been chosen to facilitate quantification of
industry noise reduction potential and to conform to requirements set forth in the "Noise
Control Act of 1972. " Considering instead a date of October 1976, selected Levels 2
and 3 could be attained by higher percentages of the market. Level 2, which constitutes
the lowest levels possible in 1975, would not be significantly lowered, but could be more
widely achieved by all size classes. Level 3 would also be more feasible. It has been
estimated that about 75 percent of the Class 1 machines could achieve Level 3 by
October 1975, and that this would require application of improved mechanical and
exhaust noise reduction methods for four-cycle powered vehicles. Assuming a continued
34
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Table 3
Selected Motorcycle Noise Levels1
Selected Noise
Level2
Level 1
Level 2
Level 3
Size Class
Class 1
(0 to 100 cc)
79dBA
70dBA
76dBA
Class 2
(101 to 200 cc)
81 dBA
76dBA
79 dBA
Class 3
(>200cc)
82 dBA
78 dBA
80 dBA
Noise levels measured according to the California Highway Patrol motor-
cycle noise measurement procedure (see Appendix B and text).
2
See definitions of Selected Noise Levels, Page 29.
ability to apply these new techniques to more four-cycle models, it is likely that over
80 percent of the Class 1 machines could attain Level 3 by October of 1976. It has
also been estimated that 75 percent of Class 2 vehicles could be produced with noise
levels at or below Level 3 by October 1975, and that this would require improved
techniques of reducing noise from those Class 2 vehicles which have physical and
noise characteristics similar to those of the larger Class 3 vehicles. Assuming continu-
ing ability to apply these new techniques to large style Class 2 motorcycles, it can be
expected that over 80 percent of these machines could meet Level 3 by October of
1976. For the large displacement Class 3 motorcycles, it has been estimated that
approximately 50 percent of the vehicles available in October 1975 could, through
concentrated effort, meet Level 3 without extreme performance degradation. Even
including an extra year, it cannot be predicted at this time that the percentage achieve-
ment would be much greater in 1976. However, approximately half of the industry is now
able to achieve Level 3 with modifications which also result in serious decreases in maneu-
verability and performance. In view of this, it is reasonable to expect that greater
than half of the machines available in 1976 could attain Level 3 with some significant
35
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reductions in all phases of performance. The consumer desirability of such machines
is estimated by the industry to be quite low. Thus It is seen that, especially for motor-
cycles with engines smaller than 200 cc (constituting about 40 percent of all motorcyles
sold in the United States), Levels 2 and 3 would be attainable by somewhat higher
percentages of the market by October 1976.
36
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6. NOISE REDUCTION TECHNIQUES AND COSTS
In the preceding chapter, three selected noise levels were developed for each
motorcycle size class. This chapter will first present methods for achieving reductions
from individual motorcycle noise sources. The cost of applying this technology to
achieve the three selected noise levels for each vehicle class will then be developed
through examples of average 1973 machines.
Noise Reduction from Subsources
The following motorcycle noise subsources will be discussed in this section:
Exhaust
Intake
Engine and Mechanical
Aerodynamic and Tires
For each of these subsources a brief description will be given of applicable noise
control techniques, followed by a numbered listing of these techniques and a chart
giving the associated increase in manufacturing costs. These costs have their basis
in engineering consideration of general industry data which relate absolute or per-
centage costs to degrees of total noise reduction. The allotment of these group costs
among the various individual subsource modifications was accomplished by evaluation
of the difficulty, of physically effecting the different modifications using:
Past and present industry predictions of noise reduction costs for certain
modifications to specific models
Recent industry estimates of general costs for noise reduction of specific
motorcycle types
Prototype examples of noise reduction costs which could be checked directly
using parts and labor estimates for existing machines-
Established noise reduction costs which have accompanied previous quieting of pro-
duction machines were checked with the new information and found to roughly define
a lower bound for the predicted future costs.
37
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The industry data comprising the foundation of this analysis has been supplied
principally by the five main motorcycle manufacturers who produce nearly 95 percent
of all motorcycles sold in the United States. It is our opinion that the cost information
provided by these manufacturers substantially represents industry expectations. Other
data from smaller suppliers or accessory manufacturers has been incorporated whenever
appearing reasonable and somewhat consistent.
Exhaust
Most of the early successes in noise reduction that were achieved after the
introduction of local vehicle noise regulations involved improvements in exhaust
silencing. Techniques using larger volume, more restrictive sound baffles in the
mufflers, multiple mufflers, and the interconnection of header pipes on multicylinder
engines have reduced exhaust outlet noise to current levels. For large highway
machines of both the two- and four-cycle variety, further reductions of 2 to 5 dB in
exhaust outlet noise, as generated during the CHP procedure, will involve a 30 to
100 percent increase in the volume of the exhaust system, requiring up to 30 pounds
additional weight, and more effective baffling. Radiation of noise from exhaust
system walls will also need to be considered. In one manufacturer test, covering the
exhaust walls with thermal-shrinlc tubing caused near-field reductions in wall radiation
noise level of from 6 to 8 dB. Thermal-shrink tubing is not practical for use on
production machines, but many manufacturers are planning exhaust systems with double
construction damped walls filled with acoustically absorptive material to reduce
exhaust system wall noise radiation.
Although initial improvements in muffler technology in some cases increased engine
power output, while at the same time providing additional silencing, such benefits with
noise reduction can no longer be expected. The use of internal absorbing materials,
double walled header pipes, and additional baffling in the above mentioned larger
systems may provide reductions in exhaust noise of up to 8 dB from present levels, but
consistent demonstration of this has not been achieved. New muffling concepts have
38
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recently been demonstrated in the after-market motorcycle muffler industry, involving
the use of silicone elastic components and radial outlets. Manufacturers have demon-
strated reductions of exhaust-only noise on highly sensitive two-cycle racing machines
from over 100 dBA to the range of 76 to 82 dBA (depending on engine size) by merely
fitting such silencers to the vehicles' open tuned exhaust systems. Net changes
in engine power output are less than 5 percent positive or negative depending on the
operating range. This type of silencer is currently being specified as original equip-
ment on several dual purpose and off road machines, and further development may
permit a more effective and cosmetic application to highway vehicles.
As described in Chapters 4 and 5, for Class 1 machines (< TOO cc), a clear
difference in achieved noise levels between two-cycle and four-cycle powered vehicles
is apparent. This may be due in part to the difference in exhaust noise spectrum
noted in Chapter 4. The higher frequency nature of two-cycle engine exhaust noise
renders it more easily attenuated by motorcycle-size reactive mufflers.
In summary, the most promising techniques for future reduction of exhaust noise,
considering available technology, reliability, and industry familiarity, are as follows":
T. Muffler volume increase of 50 to 100 percent
2. Simply modified muffler baffles
3. Use of elastic components and radial outlets
4. Double wall construction of headers and mufflers
5. Increased and more constrictive muffler baffling.
The progressive application of these techniques to machines with typical 1973
noise characteristics is necessary in order to achieve the three selected total noise
levels. The estimated costs of applying the techniques, together with the corres-
ponding approximate noise reductions/ are shown generally in Figure 9, and speci-
fically in Table 4 for reduction to the three selected noise levels.
39
-------
10
9 -
8 -
7 -
o
I 6
0)
w>
I s
D
O
c
o
1 to 5
1 to 5
1 to 5
1, 3,4
- 1 to 4
- 1 to 3
1, 2, 3, 5
^T * ]' 2
Class 3 Motorcycles
(>200 cc)
* Class 2 Motorcycles
(101 to200cc)
0 2 4 6 8 10 12 14 16 18 20 22 24 26
Estimated Per-Machine Manufacturing Cost Increase ($)
Figure 9. Estimated Costs for Reduction of Motorcycle Exhaust Noise
Insufficient noise level/cost data exist for inclusion of Class 1 (< 100 cc)
motorcycles.
These estimated cost ranges are for typical example modifications to
various machines of average 1973 noise characteristics as summarized
in Tables 7, 8 and 9.
Numbers represent noise control techniques listed in text.
40
-------
Table 4
Required Exhaust System Modifications and Associated Costs to
Achieve the Selected Noise Levels
Selected
Nofse
Level
Typical
1973
Level
1
Level
3
Level
2
Machine
Class
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Average Exhaust
Noise Contribution
(CHP Test Method)1
_4
~78 dBA
77 to 82 dBA
_4
~ 75 dBA
75 to 77 dBA
_4
~74 dBA
74 to 77 dBA
_4
~ 70 dBA
~72 dBA
Maximum
Modifications
Required2
_5
_5
_5
_4
1, 2
1, 2, 3
_4
1, 2, 3, 5
1, 2, 3
1, 2, 3, 4, 5
1, 2, 3, 4, 5
Per-Machine
Estimated
Manufacturing
Cost Increase3
.J5
_5
$0 to $26
$5 to $8
$4 to $.15
$0to $36
$6 to $12
$4 to $15
$1 to $5*
$8 to $18
$8 to $24
These exhaust noise level ranges are those required to achieve the Selected Levels
with typical 1973 machines when combined with the necessary intake and mechan-
ical subsource noise levels developed elsewhere in this section.
A
Numbers represent noise control techniques listed in text.
All costs are increases from mid-1973 manufacturing costs including direct and
indirect labor and materials, and engineering and development.
Insufficient data exist to accurately determine average subsource noise levels for
machines smaller than 100 cc.
r»lot applicable.
Costs for under 100 cc machines are estimated from cost projections for total noise
reduction provided by industry.
41
-------
Intake
The reduction of intake noise is effected in a manner similar to that employed
for the exhaust, and has played a fundamental part in the recent lowering of total
noise levels. Techniques such as the reduction of the inlet cross-sectional areas to
the minimum required for adequate intake supply, the use of noise baffles along the
intake tract, large rubber enclosed plenum volumes along the intake tract, and posi-
tioning of inlet apertures behind filtration elements in acoustically shielded portions
of the machine have been used to achieve current intake noise levels. Reductions to
levels below 79 dBA can be obtained by providing more complete inlet aperture
enclosures, more extensive internal baffle systems, double walled container structures,
a greater increase in system volume and additional acoustically absorptive material.
One manufacturer expects that in order to achieve a total Class 3 vehicle noise level of
75 dBA, intake filter/silencer volume will need to be increased fourfold from 1973
sizes,' which will require entirely new spatial configurations and changes in the
vehicle frame. No new concepts or techniques are anticipated which will ease these
basic intake silencing requirements. Thus, it is expected that these methods for
reduction of intake noise will be more extensively applied to coming models. The
methods of intake noise reduction are summarized below:
6. Minimize inlet aperture cross-section
7. Add plenum chamber to intake tract
8. Add internal baffles to intake tract/silencer
9. Shield inlet aperture behind special barriers or other motorcycle parts
10. Increase intake tract volume (including plenum volume) 50 to 100 percent
11. Double construction of intake system walls
12. Apply acoustically absorptive materials in addition to air filtration elements.
The estimated costs of applying these techniques, together with the corresponding
approximate reductions in intake noise are shown generally in Figure 10 and specifically
in Table 5 for reduction to the three selected noise levels.
42
-------
10
8
CO
I
-o
SJ
d>
o
"c
c
0
T
-
6 to 12
6 to 12
-6,10,12
A-
6 to 12
- 6 to 12
6 to 10, 12
-6 to 10, 12
-« 6 to 10
6 to 9
- 6 to 10
6 to 9
- Class 3 Motorcycles
(>200 cc)
* Class 2 Motorcycles
(101 to200cc)
02 46 8 10 12 14 16 18 20 22 24
Estimated Per-Machine Manufacturing Cost Increase ($)
Figure 10. Estimated Costs for Reduction of Motorcycle Intake Noise
Insufficient noise level/cost data exist to include Class 1 (0 to 100 cc)
machines.
These estimated cost ranges are for typical example modifications to
various machines of average 1973 noise characteristics as summarized
in Tables 7, 8 and 9.
Numbers represent noise control techniques as listed in text.
43
-------
Table 5
Required Intake System Modifications and Associated Costs to
Achieve the Selected Noise Levels
Selected
Noise
Level
Typical
1973
Level
1
Level
3
Level
2
Machine
Class
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Average Intake
Noise Contribution
(CHP Test Method)1
_4
~80 dBA
77 to 82 dBA
_4
~78dBA
77 to 79 dBA
_4
~ 74 dBA
74 to 78 dBA
_$
-72 dBA
~72dBA
Maximum
Modifications
Required2
_5
_5
_?
_4
6, 7, 8, 9
6, 1, 8, 9, 10
_4
6,7,8,9, 10, 12
6,7,8,9, 10, 12
_4
6,7,8,9,10, 12
6,7,8,9,10,11,12
Per-Machine
Estimated
Manufacturing
Cost Increase3
._5..._
_5
J
$0 to $2*
~$3
$4 to $9
$0to$36
~$5
$5 to $1 1
$1 to $66
$5 to $7
$6 to $15
These intake noise level ranges are those required to achieve the Selected Levels
with typical 1973 machines when combined with the necessary exhaust and
mechanical subsource noise levels developed elsewhere in this section.
Numbers represent noise control techniques listed in text.
o
All costs are increases from mid-1973 manufacturing costs including direct and
indirect labor and materials, and engineering and development.
Insufficient data exist to accurately determine average subsource noise levels for
machines smaller than 100 cc.
Not applicable.
Costs for under 100 cc machines are estimated from cost projections for total noise
reduction provided by industry.
44
-------
Intake and exhaust flows are of similar and related character, and thus the two
noise sources are generally treated similarly and simultaneously. The paths for move-
ment of gasses into and out of the engine also become paths for the escape of sound.
The difficulty, then, is constructing a system which will not pass the sound, but
which will pass the required gasses with little flow restriction. Appropriate balance
between the acoustical and flow performance of the two systems is required for opti-
mum engine performance with minimum noise. It has been suggested, for example,
that intake noise increases with increasing exhaust "backpressure. " The intake/
exhaust modifications which have been effected since 1969 are reported to have reduced
maximum power outputs for some large and small machines as much as 5 percent while
providing the bulk of noise reduction achieved. Experimental vehicles have
demonstrated further noise reduction capability through additional intake/exhaust
changes (see Appendix D). One powerful 750 cc machine was lowered from 84 to
78 dBA, as measured per CHP procedure, by the addition of a large truck type intake
silencer and extensive muffling. Similar reductions invojving unusually large compo-
nents are obtainable for Class 1 and 2 machines. Power and performance losses are
almost exclusively due to intake and exhaust changes which increase intake and
exhaust flow resistance and disrupt system acoustic tuning. Total noise levels in
the range 78 to 80 dBA are widely believed to be the limit for noise reduction of
large machines through intake and exhaust treatment alone. At lower noise levels
than this, the contribution from the engine is, in most cases, equal to or greater
than that from the exhaust and inlet combined.
Engine and Mechanical
To reduce total noise levels below about 82 dBA for the majority of larger
machines requires curtailment of mechanical noise from both engine and drive system
components. For conventional engine designs, little success has generally been
achieved by limiting engine part working clearances, and for the high specific output
45
-------
motorcycle engine, reliability is jeopardized. Attempts to date at limiting mechanical
noise have reduced total noise levels less than 2 dB, and have included items such as
cast-in or rubber damping webs between cooling fins, staggered casting of fin surfaces,
addition of stiffening ribs in engine covers, polishing and running-in of gear contact
surfaces, and elastic isolation of engine and drive units. One prototype machine in
Class 3 complements advanced intake and exhaust silencing with such mechanical
modification, and yet reaches a total noise level of only 80 to 82 dBA measured
according to the CHP test procedure with performance decreased about 10 percent.
Furthermore, experimentation is proceeding on such advanced techniques as the use
of nonresonating materials for lightly loaded components, use of quieter plain bearings
instead of the common roller or ball variety, increased forced lubrication, more effec-
tive decoupling of components from the engine or frame, water cooling (already used
on large displacement multicylinder two-cycle machines), drive chain enclosures,
shaft drive, and double construction or increased damping of engine and transmission
cases. Mechanical levels between 78 and 74 dBA constitute the horizon of industry's
engineering predictions incorporating combinations of the above treatments for Class 3
machines. Extensive machine redesign is indicated by several of these treatments;
hence, mechanical levels will not be reduced at the source without a great deal of effort.
For the small Class 1 motorcycles, the mechanical noise levels from four-cycle
engines may be significantly more difficult to reduce than two-cycle mechanical noise.
This is suggested by Figure 2, which shows 1973 model two-cycle Class 1 machines to
be quieter than four-cycle models. Such a situation might be expected, since two-
cycle engines do not contain the kind of valve systems which are responsible for much
four-cycle engine mechanical clatter. Thus, reduction of mechanical noise from four-
cycle engines smaller than 100 cc may require a more extensive and complicated
application of noise reduction techniques than necessary for two-cycle counterparts.
46
-------
A standard approach to reduction of mechanical and engine noise in transpor-
tation vehicles involves acoustic encapsulation or shielding of the noise sources.
Barriers and engine compartments provide a considerably less costly and complex
solution to the problem than extensive mechanical rework, and could conceivably
provide a noise reduction of up to 5 dB, as with larger automotive vehicles.
Effective encapsulation is difficult to provide for air cooled engines due to necessary
provisions for the cooling airflow (inlet and outlet apertures, ducting, blower). When
the weight, spatial, and extreme cooling requirements of a motorcycle are considered,
applicability of encapsulation appears more uncertain. Motorcycle manufacturers
claim that encapsulation or shielding of mechanical noises is completely inapplicable
to their products due principally to cooling requirements, but less importantly because
of other standard performance reasons, such as increased weight. Still, certain large
size English models with semi-enclosed engines have infrequently appeared as recently
as the mid-1960s with no apparent mechanical difficulties. Also, the Italian style
motor scooters and well known "Honda 50" type machines^have been quite popular in
recent years and acceptably reliable with partially enclosed engines. Thus, although
no noise data has become available for these examples, shielding of mechanical noises
to some extent may be feasible for today's vehicles. It may be noted that the manu-
facturers of the above-mentioned English machines were since forced to retire from
the motorcycle business. Although engine enclosures were not likely to blame, they
do represent an old style design philosophy quite different from the current U.S. fashion.
The conceivable changes in appearance, weight, bulk, simplicity, power, and ease
of maintenance could perhaps create serious marketing difficulties. Alternatively,
the streamlined fairings now popular in Europe may significantly shield mechanical
noise while improving high speed performance (See Aerodynamic Section, Page 49). The
lack of industry experimentation leaves the actual aesthetic and noise reduction potential
undetermined.
47
-------
Exceptions to the rule of high engine noise levels do exist. One manufacturer,
whose product has been characterized for many years by smooth running and high
reliability, deals very effectively with primary noise sources through an elaborate
enclosed intake system and large mufflers. Also, an impressive lack of engine mechan-
ical noise is evident, due largely to use of solid bearings and small clearances. The
enclosed shaft drive, whose ring and pinion gears are preassembly run in, eliminates
final drive noise. Vibration is greatly limited by the "opposed" engine design which
almost completely balances primary reciprocating engine forces. In this way, a
reasonably performing large displacement 1973 production motorcycle attains noise
levels below 80 dBA. However, the machines have only recently begun to escape
long standing characteristics of low performance and slow response. While maintain-
ing low noise levels and high reliability, the rated power is from 5 to 39 percent below,
and retail price from 5 to 75 percent above values from machines of equal engine dis-
placement exhibiting higher noise levels. Thus, penalties have been incurred in this
classic example of smooth machinery and noise control.
The in-use and prospective techniques for reducing mechanical noise levels
may be summarized as fol lows:
13. Stiffening of cooling fins with rubber or cast-in webs, and stiffening
of engine/drive cases with cast-in webs
14. Staggered shape casting of cooling fins
15. Rnely finished and run-in gears; use of helical primary drive gears
16. Simple engine/drive unit vibration isolation
17. Enclosed final drive chain
18. Heavy final drive chain case
19. Double construction and damping of engine/drive cases
20. Advanced engine/drive isolation system
21. Use of plain bearings
22. Increased lubricant flow and pressure
48
-------
23. Encapsulation of engine/drive units
24. Liquid cooling
25. Shaft final drive
26. Decreased working clearances.
The costs of applying these techniques together with the corresponding approxi-
mate reductions in engine associated noise are shown generally in Figure 11, and
specifically in Table 6 for reduction to the three selected noise levels.
Aerodynamic and Tires
Typical noise levels produced by the combination of aerodynamic sources and
tire/roadway interactions are in the range of 60 to 65 dBA at 50 feet from the motor-
cycle. Although these levels are negligible contributions to present day total motor-
cycle noise levels, existing future requirements for 75 and 70 dBA motorcycles may
require serious investigation of these sources. Turbulence caused by the motion of
machine parts through the air may be reduced with detail part changes. Solid or
thick spoked cast alloy wheels instead of wire spoke wheels are appearing on custom and
s
racing machines, and may provide substantially less air disturbance. It has also been
suggested that the now common disc brake produces more air flow turbulence, and thus
more flow noise, than the conventional drum type. The maze of cables, levers, and
wires undoubtedly contributes to aerodynamic noise which streamlining or routing
through vehicle components might reduce. The question of overall vehicle streamlining
to eliminate the various protuberances has long been posed by various safety advocates,
and reduced windage noise could be a result. Fairings, fiberglass streamlinings
covering the entire front of the machine, are commonly found in Europe and may
represent a first step. Their aerodynamic qualities are known to yield 5 to 10 percent
increases in maximum speed. Little research has been conducted regarding motor-
cycle tire noise due to the low magnitude of the problem, common investigations
being oriented toward higher traction and longer wear for the powerful machines
appearing on the market. Tubeless tires exist for road racing purposes, but it is unknown
whether these or various highway tread patterns have differing noise characteristics.
49
-------
8
CQ
S 6
»
*
U
-o
&
8 5
*j
o
Z
~o
u
4
o
CD O
13 to 19, 21, 23
13, 15 to 19, 20, 22, 23
U3,15 to 18, -
20, 23
- 13 to 20,
22
to 17, 20, 22
13 to 16 13 to 17
13 to 17, 20, 22
-13 to 17, 20, 22
13, 15 to 18,
20, 23
_ 13,15,16
13,15,16
13 to 16
0 Class 3 Motorcycles
(>200 cc)
A A Class 2 Motorcycles
(101 to200cc)
02 4 6 8 10 12 14 16 18 20 22 24 26
Estimated Per-Machine Manufacturing Cost Increase ($)
Figure 11. Estimated Costs for Reduction of Motorcycle Engine/Mechanical Noise
Insufficient noise level/cost data exist for inclusion of Class 1 (0 to 100 cc) machine!
These estimated cost ranges are for typical example modifications to various machine)
of average 1973 noise characteristics as summarized in Tables-7, 8 and 9.
Numbers represent noise control techniques as listed in text.
50
-------
Table 6
Required Engine/Mechanical Noise Modifications and Associated Costs to
Achieve the Selected Noise Levels
Selected
Noise
Level
Typical
1973
Level
1
Level
3
Level
2
Machine
Class
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Average Mechanical
Noise Contribution
(CHP Test Method)1
_4
~ 77 dBA
78 to 80 dBA
_4
~ 75 dBA
75 to 78 dBA
_4
~ 74 dBA
74 to 78 dBA
_4
~72dBA
74 to 75 dBA
Maximum
Modifications
A
Required
_5
_5
J
_4
13, 15, 16
13, 15, 16, 17
_4
13,15,16,17,20,23
13 to 17, 20, 22
_4
13,15,16,17,20,23
13 to 19, 21, 23
Per-Machine
Estimated
Manufacturing
Cost Increase3
_5
J
J
$0 to $26
$1 to $5
$5 to $8
$0 to $46
$2 to $7
$6 to $16
$1 to $6*
$2 to $9
$7 to $21
These mechanical noise level ranges are those required to achieve the Selected
Levels with typical 1973 machines when combined with the necessary exhaust
and intake subsource noise levels developed elsewhere in this section.
2
Numbers represent noise control techniques listed in text.
A
All costs are increases from mid-1973 manufacturing costs including direct and
indirect labor and materials, and engineering and development.
Insufficient data exist to accurately determine average subsource noise levels for
machines smaller than 100 cc.
Not applicable.
Costs for under 100 cc machines are estimated from cost projections for total noise
reduction provided by industry.
51
-------
Advanced Concepts for Noise Reduction
The noise control techniques included above are conventional methods applicable
to most types of machinery and approachable through standard engineering procedures.
For many of them, much experimentation and development remains to establish effects
or feasibility, but they do not involve radical departure from existing configurations.
Exceptions to such modifications include repowering with new engine types. Electrically
powered two-wheeled vehicles are now being produced in limited numbers in the United
States, but most performance characteristics are below average for current model gaso-
line motorcycles of comparable price. Production rotary Wankel powered models are
expected to be available in late 1974 with CHP procedure noise levels approaching
80 dBA. However, performance comparability to reciprocating engine machines and
in-service reliability have not yet been established. Reciprocating steam and gas
turbine motorcycles have been constructed for various experimental purposes, and
although they might be workable with development, none show exceptional promise
for noise control in the near future.
Achievement of the Selected Noise Levels Through Application of Noise Reduction
Techniques ~ ~~~ ~~~
The previous discussion of techniques to reduce noise emitted from various
individual sources on the motorcycle has focused on reducing exhaust, intake, and
mechanical noise. The noise control cost information developed for these subsources
can be combined to determine the total costs of noise reduction to the three selected
noise levels. These costs, together with the required modifications and individual
subsource levels are shown in Tables 7and 8 for typical 1973 motorcycles.
For motorcycles in Class 3, cases in which total vehicle noise is dominated by
exhaust, intake, and mechanical sources, and in which all subsources are about equal,
are analyzed. The subsource noise levels used are average levels for 1973 model machines,
and the modifications accomplished to reduce these levels, indicated in the vertical
columns of Table 7 by estimated costs, represent typical approaches to total
52
-------
Table 7
Estimated Per-Machine Manufacturing Cost Increases, for Noise Reduction of Typical FullSize Motorcycles 5-2OO cc.
1
g1"
o
y
u:
1
01
u
D
0
J3
3
Selected Achieved Total
Vehicle Modified*
EXHAUST
Increase Volume
50 to 100*
Modify Baffles
Elastic Components
Double Walls
Increase Baffling
INTAKE
Minimize Inlet
X-Section
Plenum Chamber
Internal Baffles
Inlet Shielding
Increase Enclosure
Volume 50 to 100£
Double Walls
Apply Absorptive
Linings
MECHANICAL
Stiffening Fin and
Cose Webs
Change Fin Shape
Finish and Run-in
Helical Geors
Simple Isolation
Enclose Chain
Heavy Chain Case
Double Coses
Improve Isolation
Plain Bearings
Increase Lubrication
Encapsulation
Liquid Cooling
Shaft Drive
Decrease Clearances
Total Manufacturing
Cost Increase
82dBA
E(50*)
82-»77dBA
$3 to $12
SI
SI to S2
_
-
77dBA
-
_
-
_
-
_
-
78dBA
-
_
-
_
_
_
-
-
.
-
-
_
-
-
54 to $15
Leve
82dBA
1(40*)
77* 75 dBA
S3 to S8
$1
_
.
82- 78 dBA
$1
51 to S2
$1 to S2
$1
SI to $3
.
-
78dBA '
-
_
-
_
.
-
-
_
-
-
_
-
-
$9 to S18
1*1
82dBA
M(5#)
79- 77 dBA
S3 to S8
$1
.
..
.
79- 78 dBA
SI
51 to S2
51 to $2
SI
-
_
-
80-»78dBA
51 to S2
_
S2
$2
.
.
-
..
-
-
..
-
- .
513 to $21
82dBA
A**(5<)
80-75 dBA
S3 to $12
$1
_
..
-
80-»79 dBA
$1
SI to S2
$1 to S2
$1
-
.
-
78-75 dBA
$1
$1
$2
S2
52
.
-
.
_
-
-
_
-
-
$16 to S27
80 dBA
I (50* )
82- 77 dBA
$3 to $12
$1
$1 to S2
_
.
77-75 dBA
51
SI to $2
SI to S2
SI
$1 to S3
.
-
78-75 dBA
SI
SI
S2
S2
S2
-
-
$1 to S3
_
$1 to $3
-
_
-
-
$20 to $38
Level "3
80 dBA
I (40*)
77-* 74 dBA
$3 to $10
SI
.
»
.
82-* 78 dBA
SI
SI to S2
$1 to S2
SI
SI to S3
-
-
78* 74 dBA
$1 to $2
$2
$2
$2
$2
-
-
$1 to $3
_
SI to $3
-
_
-
-
$20 to $36
80 dBA
M(5«)
79-»74 dBA
$3 to $12
$1
S2
_
-
79-74 dBA
SI
$1 to S2
SI to S2
$1
$1 to S3
.
SI to $2
80-»78 dBA
$1
$1
$2
$2
_
-
-
-
-
-
-
_
-
-
$13 to $32
78 dBA
E (50*)
82-*72 dBA
$3 to $12
$1
$2
$4 to 56
$2 to S3
77-72 dBA
$1
$1 to $2
$1 to $2
$1
$1 to S3
-
$1 to $2
78-»75dBA
$1
$2
$2
$2
_
-
-
-
.
-
-
-
-
-
$26 to $45
Level *2
78 dBA
I(40<)
77-72 dBA
$3 to $10
$1
-
$4 to 56
-
S2-.72 dBA
$1
$1 to 52
SI to S2
SI
$1 to $3
$2 to 54
SI to $2
78-. 74 dBA
$1 to $2
$2
$2
$2
$2
-
-
$1 to $3
-
$1 to $3
-
-
-
-
$28 to $48
78 dBA
M(5*)
79-72 dBA
$3 to $12
$1
$2
$4 to 56
.
79-72 dBA
SI
$1 to $2
$1 to 52
$1
$1 to $3
$2 to 54
$1 to S2
80-75 dBA
$1 to $2
$2
$2
$2
$2
$1
$4
$1 to 53
-
$1 to $3
-
.
-
-
$34 to $57
. 7A rJAA
A**(5*j
80-* 72 dBA
$3 to 512
-
52
S4 to 56
-
80*72 dBA
' $1
. SI to S2
$1 to S2
SI
$1 to $3
$2 to S4
$1 to S2
78-70 dBA
$2
S2
52
. 52
SI
54
SI to S3
-
51 to $3
-
$2 to $10
-
-
-
$34 to $64
'Vehicle Modified" indicates typical vehicle with dominant exhaust (E), Intake (I), mechanical (M), or even (A) noise sources followed by percent of new vehicles in each category.
Interpretation of specific manufacturer data.
-See Table 9 for noise description of 'Vehicle Modified, "time required, and additional information.
-------
Table 8
Estimated Per-Machine Manufacturing Cost Increases for Noise Reduction of
Typical Small Motorcycles (Motor-Driven Cycles) <200 cc
t
5
6
'6
ti=
T*
1
s
l/l
\
Selected Achieved Total
Noise Level
Vehicle Size Modified
EXHAUST
Increo»e Volume 50 to 100< Modify BofFlei
Extra Baffles, Elastic Components
Double Walls
Appropriate Combination
^_ INTAKE
Minimize Inlet X-Section, Interior Baffles,
Plenum, Shielding
Increase Inlet Enclosure Volume 50 to 100?,
Apply Absorptive Linings
Double Waited Enclosure
Appropriate Combination
MECHANICAL
Fin and Case Stiffening Webs, Finish and Run-in
Helical Gears, Engine Isolation
Enclose Chain, Improve Isolation,
Encapsulation
Double Construction Cases,
Increase Lubrication
Appropriate Combination
Total Manufacturing Cost Increase
Leve
79dBA
0 to 100 cc
_
_
_
$0ro$2
-
-
-
$0ta$2
-
-
-
SO to 52
SO to $4
I'l
81 dBA
1 00 to 200 cc*
78-»75 dBA
S5 to S8
.
80-*78 dBA
S3
IB
-
-
77-»75 dBA
SI to $5
-
-
e>
$9 to 516
Leve
76 dBA
_
^
SO to S3
-
-
.
SO to S3
-
-
-
SO to 54
SO to $10
l'3
79 dBA
78-*74 dBA
55 to S8
51 to 54
.
-
80-74 dBA
S3
S2
-
.
77-»74 dBA
$1 to $5
$1 to S2
-
_
$13 to $24
Leve
70 dBA
0 .to 100 cc
_
$1 to $5
-
-
-
SI to 56
-
- '
-
$1 to $6
S3 to $17
l»2
76 dBA
100 to 200 cc
7870 dBA
55 to 58
51 to 54
52 to $6
-
80-*72 dBA
53
S2toS4
-
_
7772 dBA
51 to 55
SI to 54
-
_
$15 to $34
7A /4RA
100 to 200 cc*
78-69 dBA
S5 to S8
51 to 54
52 to S6
-
80-70 dBA
S3
S2to S4
S3 to 56
_
7770 dBA
51 to 55
$1 to $2
51 to $4
_
S19 to 542
Based on interpretation of specific manufacturer data.
See Table 9 for noise description of 'Vehicle Size Modified, " time required, and additional informaHon.
-------
Table 9
Information Explaining Tables 7 and 8
Tables 7 and 8 itemize the estimated increases in the "cost of goods manufactured"
including engineering costs required per unit for application of various noise
reduction techniques to motorcycles with specific typical 1973 model noise char-
acteristics in order to achieve selected reduced noise levels. The cost ranges
developed represent all normal production machines in each model line capable
of meeting the selected levels with the modifications indicated.
These estimated cost increases are for achievement of the Selected Noise Levels
by October 1975 and, therefore, essentially represent the differences between
the 1973 model and 1976 model manufacturing costs which would be anticipated
due to modifications for noise reduction only.
Total noise levels are those which would be measured by the California Highway
Patrol motorcycle measurement procedure (see Appendix B),
Noise Levels given for exhaust, intake, and mechanical subsources are the
approximate contributed levels from these subsources to the total level measured
during the California Highway Patrol acceleration noise test.
The reduction in the noise level contributions of the various noise subsources
(which are accomplished by the costed modificiations) are shown in the horizontal
rows labeled Exhaust, Intake, and Mechanical.
The cost ranges given include machines powered by both two-cycle and four-
cycle engines.
Noise characteristics of the "typical 1973 vehicles" modified in Tables 7 and 8
are:
Motorcycles>200cc
Noise Character
Exhaust Dominated
Intake Dominated
Mechanical Dominated
All Sources ~ =
Total
Noise Level
84dBA
84dBA
84dBA
84dBA
Exhaust
Contribution
82dBA
77dBA
79dBA
SOdBA
Intake
Contribution
77 dBA
82dBA
79 dBA
SOdBA
Mechanical
Contribution
78 dBA
78 dBA
80 dBA
78 dBA
Motor-Driven Cycles <200cc
Engine Size Range
100 - 200cc
<100cc
Total
Noise Level
83 dBA
~80 dBA
Exhaust
Contribution
78 dBA
Intake
Contribution
SOdBA
Insufficient Detailed Data
Mechanical
Contribution
77 dBA
Available
55
-------
noise reduction. Values for typical 1973 subsource levels are given in Table 9.
At the bottom of each column in Table 7, the total estimated increase in manu-
facturing cost is given for the vehicle described in that column to achieve the
selected noise level. The specific reductions of subsource levels are shown in the
appropriately labeled horizontal row.
This information for machines in Classes 1 and 2 is shown in Table 8, which is
similar to Table 7. Because there is less available data for small machines, costs are
given for groups of modifications rather than individual cases. For Class 1 motor-
driven cycles, little information is available on the effectiveness of subsource modi-
fication and so subsource noise reduction costs have been extracted from manufacturers'
estimates of the total percentage retail cost which will be required to attain the
selected noise levels.
A summary of the developed manufacturing cost increases for achieving the
selected noise levels is given in Table 10 and Figures 12 and 13. This information
includes average costs, cost ranges as developed for the specific models of Tables 7
and 8, and the range of general industry cost estimates. Specific estimates are shown
to fit well within the general manufacturer predictions in Figures 12 and 13.
Table 10 and Figures 12 and 13 also include costs which have been incurred by
manufacturers in reducing the noise levels of their machines from 92 dBA the
regulation in California prior to 1970 down to 84 and 86 dBA, the existing California
regulations for motor-driven cycles and full size motorcycles respectively. The new
costs developed in Tables 7 and 8 are substantially higher than the costs for past noise
reductions because, as noise levels become lower, new techniques have to be
developed and applied to an increasing number of subsources. It must be emphasized
that the cost figures have been determined for average motorcycle noise characteristics
using little precise information on specific modifications. Thus, they serve only as a
guide to increased manufacturing costs, due to noise reduction alone, and may vary
appreciably for individual models with specific problem subsources.
56
-------
0,
WJ
I/I
a
CO
C
'iZ
_D
"o
"D
c
C
ID
60
50
40
30
20
10
0
Costs re 1973
84 dBA Requirement
100 to 200 cc
<100cc
Costs re Pre-1970
Noise Levels
90 85 80 75
Noise Level per CHP Procedure (dBA at 50 feet)
Figure 12. Estimated Noise Reduction Costs for Motor-Driven Cycles <200 cc
Si
s
u
^c
1
u
CO
u
£
D
C
C
D
240
220
200
180
160
140
120
TOO
80
60
40
20
0
Costs re 1973
86 HBA Requirement
Industry general estimates
Industry specific estimates
Wyl e estimates from
Tables 7 and 8
Costs re Pre-1970
Noise Levels-,
92
90 85 80 75
Noise Level per CHP Procedure (dBA at 50 feet)
Figure 13. Estimated Noise Reduction Costs for Motorcycles >200 cc
70
57
-------
Table 10
Estimated General New Motorcycle Noise Reduction Costs
Cost
Characteristic
Manufacturing
Cost Increase
Class 1
Manufacturing
Cost Increase
Class 2
Manufacturing
Cost Increase
Class 3
Average3
Specific Range4
General Range5
Average
Specific Range
General Range
Average
Specific Range
General Range
Loss of Maximum Performance7
Fuel Consumption Increase
1 973 Calif.
Require-
ments'
1 to 3<
$1.50h>$10
1 to 2. 5*
$3 to $15
I#to5#
$12 to $68
I#to5#8
_9
Sele<
Level #12
$3
$0to $6
$4 to $25
$13
$9 to $16
$8 to $20
$13
$4 to $27
$10 to $90
_9
_9
:ted Noise L<
Level #2*
$10
$3 to $17
"Large"
$24
$15 to $32
$18 to $40
$37
$26 to $57
$20 to $150
-9
_9
svels6
Level #32
$5
$0 to $10
$20 to $40
$19
$13 to $24
$10 to $35
$28
$20 to $38
$15 to $110
5#to20#8
*io*'°
1 Costs to achieve this level are for the reductions from typical noise levels which
existed under the pre-1970 92 dBA California requirement.
M
Costs to achieve this level are for reductions from typical 1973 noise levels, and
include all normal production machines in the model lines which are capable of
achieving the selected noise levels.
3Average values have been determined from specific examples of Tables 7 and 8 based
on percentage of 1973 models with various dominant noise sources.
Specific ranges are the extremes from the specific examples of Tables 7 and 8.
General ranges are manufacturer estimates based on general percent of retail cost
or production cost.
Selected noise levels, as measured per California Highway Patrol motorcycle noise
measurement procedures, are given in Table 3.
Includes maximum speed, acceleration, cornering speed, etc.
g
Range of general industry estimates for production machines.
a
Insufficient data.
10,
Estimate from one major manufacturer.
58
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7. CONCLUSIONS
This study has shown that, although significant reductions in noise from production
motorcycles sold in the U.S. have been effected since 1969, further substantial reduc-
tions are possible. Treatment principally of intake and exhaust noise has brought large
motorcycles within the 1973 California requirement of 86 dBA as measured with the
California Highway Patrol procedure, and has been responsible for certain performance
decreases and production cost increases of up to 5 percent of preregulation levels. All
small machines have been brought into compliance with their lower current regulation
of 84 dBA. The principal manufacturers are now working hard toward meeting the dif-
ficult 1975 California requirement of 80 dBA with large machines through addition of
mechanical noise treatments and further improvements in intake and exhaust silencing.
Although some models have already achieved 80 dBA, the main body of available
models will suffer further performance and cost changes to meet this level.
In the opinion of Wyle Research, based on the current available data developed
during this project, it is within industry capability to reduce the noise levels of approxi-
mately half of the field of motorcycles over 200 cc displacement (herein defined as
Class 3) to 80 dBA as measured by the CHP standard by October of 1975. This will
involve substantial manufacturer development effort and will necessitate production
cost increases averaging $28 per machine. Performance could further diminish more
than 5 percent, and general industry predictions of fuel consumption increases range
as high as 10 percent. The 80 dBA level is within reach for nearly all of the
under 200 cc machines by the date of interest. For machines with engine displace-
ments between 100 and 200 cc (Class 2), about three-quarters of the vehicles available
in October 1975 could be produced with noise levels at or below 79 dBA for an
average per-machine manufacturing cost increase of $19. It is finally estimated that
the industry is capable of manufacturing about 75 percent of the under 100 cc machines
(Class 1) available in October 1975 with noise levels of 76 dBA or less, with per-
machine manufacturing cost increases averaging $5 over 1973 manufacturing costs.
59
-------
Methods for achieving noise levels below 80 dBA for large motorcycles and
76 dBA for small machines have not been widely developed. The following aspects
of noise reduction will require extensive research before widespread lower levels can
be expected.
Mechanical Noise Shielding The use of barrier or encapsulation techniques
to attenuate engine and drive system mechanical noise in its path as an alter-
native to involved mechanical redesign. Related problems such as engine
cooling effects should be addressed. The noise masking effects of existing
motorcycle fairings should be determined.
Use Cycle Although most of the industry appears content with existing
maximum acceleration noise test standards, typical use cycle data would
provide information allowing correlation of current noise measurement
procedures to real traffic noise levels or development of a new procedure
directly related to in-use noise.
New Power Sources Further investigation into applicability of unconven-
tional engine types, particularly rotary combustion, should be undertaken
to help determine future noise reduction potential.
Minor Sources Specific investigation into the presently less important
noise subsources: windage, tires, final drive chain, component vibration,
etc., should be undertaken to (1) provide data useful in further noise
reduction, and (2) define lower bounds for obtainable motorcycle noise
reduction.
60
-------
REFERENCES
1. "Cost Effectiveness Study of Major Sources of Noise, Phase I - Ranking of Major
Noise Sources," Wyle Research, for U.S. Environmental Protection Agency,
April 20, 1973.
2. "Noise Measurements of Motorcycles and Trucks," Bolt Beranek and Newman,
Inc., Report 2079, for Automobile Manufacturers Association, Inc., Vehicle
Noise Study Subcommittee, June 1971
3. "Motorcycle Noise Test Procedure Evaluation," California Highway Patrol,
January 1971.
4. Wyle Research (unpublished analysis), September 1973.
5. Wyle Research (unpublished data), 1971.
6. Transportation Noise and Noise from Equipment Powered by Internal Combustion
Engines" Wyle Laboratories, for Environmental Protection Agency, Report No.
NTID300.13, p 171, December 31, 1971.
.7. "CHP Data on 1970 Model Motorcycles," cited in "Hearings Before the Sub-
committee on Public Health and Environment of the Committee on Interstate
and Foreign Commerce," House of Representatives Serial No. 92-30, June
16-24, 1971.
8. Manufacturers' Noise Level Data Submitted to Wyle Research.
9. SAE Recommended Practice J213a - Definitions - Motorcycles, March 1972.
10. "Sound Pressure Levels Observed During Motorcycle Tests: Street Vehicles,
1973 Stock Model," Bolt Beranek and Newman, Inc., for Motorcycle Industry
Council, December 12, 1972.
11. Harrison, R., "The Effectiveness of Motorcycle Helmets as Hearing Protectors,"
USDA Forest Service Equipment Development Center, San Dimas, California,
September 1973.
12. Howell, A.R., "A Study of Wind Induced Noise in the Human Ear," The
Industrial Research Institute of the University of Windsor, IRI Project 6-28,
for Outboard Marine Corporation, July 1973.
13. Irving, PoEo, Motorcycle Engineering, Floyd Clymer Publications.
14. Memorandum from Dr. Ben Sharp, Wyle Research, to Mr. Hugh Kaufman, U.S.
Environmental Protection Agency, July 19, 1973.
61
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APPENDIX A
CONTACTS
Motorcycle Manufacturei/Distributors Providing Quantitative Data
American Honda Motor Company, Incorporated
Gardena, California
Butler & Smith Corporation
Norwood, New Jersey
(Distributor: BMW Motorcycles)
The Birmingham Small Arms Company Incorporated
Duarte, California
(Distributor: Triumph, BSA, Rickman Motorcycles)
AMF/Harley-Davidson Motor Company, Incorporated
Milwaukee, Wisconsin
Kawasaki Motors Corporation, U.S.A.
Santa Ana, California
Pacific Basin Trading Company
Athena, Oregon
(Distributor: Hodaka Motorcycles)
U.S. Suzuki Motor Corporation
Santa Fe Springs, California
Yamaha International Corporation
Buena Park, California
A-l
-------
Accessory Manufacturers Providing Quantitative Data
Manufacturer
Bassani Manufacturing
Anaheim, California
Discojet Corporation
Davis, California
Hooker Headers
Ontario, California
J&R Manufacturing Company
Bell Gardens, California
Murphy Muffler
Long Beach, California
Skyway Cycle Products
San Fernando, California
Torque Engineering Company
Northridge, California
Products
Bassani competition exhausts,
silencers
Xdusor mufflers
Hooker mufflers, competition
silencers
J&R spark arrestors, silencers
Strato-Flex mufflers
Skyway silencers and spark
arrestors
Silencers, spark arrestors, competition
exhausts
Other Information Sources
American Motorcycle Association
Westerville, Ohio
City of Chicago
Department of Environmental Control
Chicago, Illinois
CYCLE Magazine
New York, New York
DIRT BIKE Magazine
Encino, California
Motorcycle Industry Council
Washington, D.C.
United States Department of
Agriculture
Forest Service Equipment Develop-
ment Center
San Dimas, California
A-2
-------
APPENDIX B
MEASUREMENT STANDARDS
B-l
-------
CALIFORNIA HIGHWAY PATROL NOISE MEASUREMENT PROCEDURE
EDITED FOR NEW VEHICLES
ORDER ADOPTING, AMENDING, OR REPEALING
REGULATIONS OF THE DEPARTMENT OF THE
CALIFORNIA HIGHWAY PATROL
After proceedings had in accordance with the provisions of
the Administrative Procedure Act (Gov. Code, Title 2, Div. 3,
Part I, Chapter 4.5) and pursuant to the authority vested by Sec-
tion 2402 of the Vehicle Code, and to implement, interpret, or
make specific Sections 23130 and 27160 of the Vehicle Code, the
Department of the California Highway Patrol hereby adopts, amends,
or repeals regulations in Chapter 2, Title 13, California Adminis-
trative Code, as follows:
(1) Amends Article 10, Subchapter 4 to read:
Article 10. Vehicle Noise Measurement
1040. Scope of Regulations. This article contains procedures
implementing Section 23130 of the Vehicle Code which applies to the
measurement of noise from motor vehicles and combinations of vehi-
cles subject to registration when operated on a highway, and Sec-
tion 27160 of the Vehicle Code which applies to the measurement of
noise from new motor vehicles offered for sale.
1041. Definitions. The following definitions shall apply
wherever the terms are used in this article:
(a) First Gear. The "first gear" is the highest numerical
gear ratio of the transmission which is commonly referred to as
low gear.
(b) Maximum RPM. The "maximum rpm" is the maximum governed
engine speed, or if ungoverned, the rpm at maximum engine horse-
power as determined by the engine manufacturer in accordance with
the procedures in SAE J245, April 1971.
(c) Vehicle Reference Point. The "vehicle reference point"
is the location on the vehicle used to determine when the vehicle
is at any of the points on the vehicle path. The vehicle reference
point shall be the front of the vehicle unless such position is
more than 16 ft from the exhaust outlet, in which case both the
front of the vehicle and the exhaust outlet shall be used as ref-
erence points.
B-2
-------
1042. Personnel. Persons selected to conduct noise measure-
ment testing or to measure noise level of vehicles operated on a
highway shall have been trained and qualified in the techniques of
sound measurement and the operation of sound measuring instruments.
1043. Instrumentation. Equipment used in making vehicle
noise measurements shall be selected by technically trained person-
nel and shall meet the following requirements:
(a) Sound Level Meter. The sound level meter shall meet
the requirements of ANSI Standard SI.4-1971 for Types 1, 2, or S2A.
(b) Sound Level Calibrator. The sound level calibrator
shall calibrate the entire sound level meter with an acoustic cali-
brator of the coupler-type.
(c) Tachometer. A calibrated engine speed tachometer shall
be used to determine when maximum rated rpm is attained in con-
ducting the tests specified in Section 1046 of this code.
(d) Anemometer. An anemometer shall be used to measure
the wind speed at the test site when conducting tests specified in
Section 1046 of this code.
1044. Noise Measurement Sites. Noise measurement sites shall
be selected to meet location,ground condition, and roadway surface
requirements in the following subsections (a) and (b):
(a) Measurement Sites for Vehicles on the Highway.
(b) Measurement Sites for New Motor Vehicles. Sites for
measuring noise from new motor vehicles to determine compliance
with Section 27160 of the Vehicle Code shall meet the following
conditions:
(1) Location. The location shall be a flat open
space free of large vertical sound-reflecting surfaces
such as signboards, buildings, hillsides, or trees
within 100 ft of the microphone and within 100 ft of
the centerline of the path of the vehicle from the
point where the throttle is opened to the point where
the throttle is closed.
(2) Ground Condition. The ground surface between
the microphone and the path of the vehicle shall be
asphalt or concrete free of powdery snow, loose soil,
or ashes.
(3) Roadway Surface. The surface over which the
vehicle travels shall be dry and relatively smooth con-
crete or asphalt pavement free of extraneous material.
B-3
-------
1045. Microphone and Personnel Positions. The microphone
for the sound level meter and the personnel involved in all types
of vehicle noise measurements shall be positioned as follows:
(a) Microphone Location. The microphone shall be located
50 ± 1 ft from the centerline of the lane of travel of the vehicle
at a height of 4 ± 1/2 ft above the plane of the roadway surface.
(b) Microphone Orientation. The microphone shall be ori-
ented in relation to the source of the sound in accordance with
the instrument manufacturer's instructions. Where the instruction
manual is vague or does not include adequate information, a specific
recommendation shall be obtained from the manufacturer.
(c) Technician Location. The technician making direct
readings of the meter shall be positioned in relation to the micro-
phone in accordance with the instrument manufacturer's instructions.
Where the instruction manual is vague or does not include adequate
information, a specific recommendation shall be obtained from the
manufacturer.
(d) Bystander Location. During noise measurements, by-
standers shall remain at least 50 ft from the microphone and the
vehicle being measured, except for a witness or .trainee, who may
be positioned beyond the technician on a line with the technician
and the microphone.
1046. Operation of New Motor Vehicles. New motor vehicles
tested to determine compliance with Section 27160 of the Vehicle
Code shall be operated in conjunction with any auxiliary equipment
that would be in use while the vehicle is operated on the highway,
including but not limited to cement mixers, refrigerator units,
and garbage compactors.
(a) Heavy Trucks, Truck Tractors, and Buses.
(b) Light Trucks, Truck Tractors, Buses, and Passenger Cars.
(c) Motorcycles. The test procedure for motorcycles shall
be as follows:
(1) Test Area Layout. The test area layout for
motorcycles shall be the same as specified in subsec-
tion (b) (1) and Figure 3 for light trucks, truck trac-
tors, buses, and passenger cars. (See next page.)
(2) Gear Selection. Motorcycles shall be oper-
ated in second gear.Vehicles which reach maximum rpm
at less than 30 mph or before a point 25 ft beyond the
microphone point shall be operated in the next higher
gear.
B-4
-------
U-25M
*-25'-«j
\
Microphone
Location
100' Radius
A Microphone point
B ~ Acceleration point
C * End point
D - End zone
Test Area Layout. The test area shall include
a vehicle path of sufficient length for safe accelera-
tion, deceleration, and stopping of the vehicle. The
vehicle path (shown with only one directional approach
in Figure 3 for purposes of clarification) shall be
marked with the following zone and points:
(A) Microphone point - the location on
the centerline of the vehicle path that is
closest to the microphone.
(B) Acceleration point - a location
25 ft before the microphone point.
(C) End point - a location 100 ft be-
yond the microphone point.
(D) End zone - the last 75-ft distance
between the microphone point and the end
point.
Figure 3. Test Area Layout for Light Trucks, Truck Tractors,
Buses, Passenger Cars, and Motorcycles
B-5
-------
(3) Acceleration. The vehicle shall proceed along
the test path at a constant approach speed which corre-
sponds either to an engine speed of 60% of maximum rpm
or to 30 mph, whichever is lower. When the vehicle
reference point reaches the acceleration point, the
throttle shall be fully opened. The throttle shall be
held open until the rear of the vehicle is approximately
100 ft beyond the microphone or until the maximum rpm is
obtained, at which point the throttle shall be gradually
closed. Wheel slip shall be avoided during this test.
(4) Engine Temperature. The engine temperature
shall be within normal operating range before each test
run.
(d) Deceleration. Tests during deceleration shall be con-
ducted when deceleration noise appears excessive. The vehicle shall
approach the end point from the reverse direction at maximum rpm in
the same gear selected for the tests during acceleration. At the
end point, the throttle shall be closed and the vehicle shall be
allowed to decelerate to 1/2 of maximum rpm.
1047. Meter Operation. The sound level meter shall be oper-
ated in accordance with the instrument manufacturer's instructions
and as follows:
(a) Meter Setting. The A-weighting network and the fast
meter response shall be used.
(b) Calibration Check. An external calibration check shall
be made before and after each period of use and at intervals not
.exceeding 2 hr when the instrument is used longer than a 2-hr period.
(c) Meter Reading. The reading recorded shall be the highest
sound level obtained as the vehicle passes by, disregarding unrelated
peaks due to extraneous ambient noises.
(d) Ambient Sound. Measurements shall be made only when the
A-weighted ambient sound level, including wind effects, due to all
sources other than the vehicle being measured, is at least 10 dB(A)
lower than the sound level of the vehicle.
(e) Wind. Measurements shall be made only when the wind
velocity is less than 12 mph.
B-6
-------
1048. Vehicle Noise Level. The measured noise level of a
vehicle shall be reported as follows:
(a) Vehicles on the Highway
(b) New Motor Vehicles. The sound level readings for deter-
mining compliance o± new motor vehicles .with Section 27160 of the
Vehicle Code shall be obtained after sufficient preliminary runs to
enable the test driver to become familiar with the operation of the
vehicle and to stabilize engine operating conditions.
(1) At least four measurements shall be made from
each side of the vehicle. When the exhaust outlet is
more than 16 ft from the driver's position, at least
two runs in each direction shall be performed with each
of the reference points described in Section 1041 (c)
of this code.
(2) The A-weighted sound level for each side of
the vehicle shall be the average of the two highest
readings on that side which are within 2 dB(A) of each
other. The noise level reported for the vehicle shall
be the sound level of the loudest side.
B-7
-------
January 18, 1971
Draft #4
61.A1245.A1430
SOUND LEVELS FOR MOTORCYCLES - SAE J331 SAE standard
1. INTRODUCTION
This SAE Standard established test procedure, environment, and
instrumentation for determining maximum sound levels for all
classes of motorcycles.
2. SOUND LEVEL LIMITS
3. INSTRUMENTATION
The following instrumentation shall be used for the measure-
ment required:
3.1 A sound level meter which meets the requirements of
International Electroacoustic Commission Publication 179, Precision
Sound Level Meters (IEC) and American National Standards 1.4-1961
'^General Purpose Sound Level Meters" (ANSI).
B-8
-------
3.1.1 As an alternative to making direct measurements using
a sound level meter, a microphone or sound level meter may be used
with a magnetic tape recorder and/or a graphic level recorder or
indicating meter providing the system meets the requirements of
SAE Recommended Practice J184, Qualifying a Sound Data Acquisition
System.
3.2 A sound level calibrator (see Section 6.3.4).
3.3 A calibrated engine speed tachometer.
3.4 An anemometer.
4. TEST SITE
4.1 A suitable test site is a flat open space free of
large reflecting surfaces, such as parked vehicles, signboards,
buildings, or hillsides, located within 100 ft of either the vehi-
cle or the microphone.
4.1.1 The ambient sound level at the test site (including
wind effects) due to sources other than the vehicle being measured
shall be at least 10 dB(A) lower than the level of the tested
vehicle.
4.1.2 The surface of the ground within the measurement area
between the vehicle being measured and the microphone shall be dry
concrete or asphalt, free from powdery snow, loose soil, or ashes.
4.2 The test area layout shall include a vehicle path that
is of relatively smooth, dry concrete or asphalt, free of extra-
neous materials such as gravel and of sufficient length for safe
acceleration, deceleration, and stopping of the vehicle. The
following points and zones shall be established on the vehicle paths
B=9
-------
4.2.1 The microphone shall be located 50 ft ± 1 ft from the
centerline of the vehicle path and 4 ft ± J ft above the ground
plane. The microphone point is that location on the centerline of
the vehicle path which is closest to the microphone.
4.2.2 The end point shall be established on the vehicle path
25 ft from the microphone point.
4.2.3 The end zone is the lat 10 ft of vehicle path prior to
the end point.
4.2.4 The acceleration point shall be established so that
the vehicle will be in the end zone as near as practical to the
end point when the engine speed at maximum rated horsepower is attained,
*
To establish the acceleration point, approach the end
point in low gear from the reverse direction at a constant speed
obtained from 2/3 of the engine speed at maximum rated horsepower.
At the end point fully open the throttle and accelerate past the
microphone point under full acceleration. By trial select the
lowest transmission gear that will result in the vehicle traveling
the shortest distance from the end point to the place where the
engine speed at maximum rated horsepower is reached, but not less
than 50 ft. The location on the vehicle path with respect to the
operator's position when the engine speed at maximum rated horse-
power is attained is the acceleration point.
5. PROCEDURE
5.1 For the test under acceleration, the vehicle shall
proceed along the vehicle path at a constant approach speed in the
gear selected in paragraph 4.1.4 and at 2/3 of the engine speed at
maximum rated horsepower.
B-10
-------
When the driver's position is at the acceleration
point, the throttle shall be rapidly and fully opened. Full
throttle shall continue until the engine speed at maximum rated
horsepower is reached, which shall be within the end zone as near
as practical to the end point. When the engine speed at maximum
rated horsepower is reached, the throttle shall be closed. Wheel
slip which affects the maximum sound level shall be avoided and
the manufacturer's safe maximum rpm shall not be exceeded.
5.2 For the test under deceleration, approach the end
point from the reverse direction at an engine speed of maximum
rated horsepower in the gear selected for the acceleration test.
At the end point, close the throttle and allow the vehicle to
decelerate to an engine speed of at least one-half of the rpm at
maximum rated horsepower.
5.3 The engine temperature shall be within the normal
operating range prior to each run.
5.4 Measurement's.
5.4.1 While making sound level measurements, not more than
one person other than the observer reading the meter shall be
within 50 ft of the vehicle or microphone, and that person shall
be directly behind the observer reading the meter, on a line
through the microphone and the observer.
5.4.2 The meter shall be set for "fast" response and for the
A-weighting network.
B-H
-------
5.4.3 The meter shall .be observed while the vehicle is ac-
celerating. The applicable reading shall be the highest sound
*
level obtained for the run ignoring unrelated peaks due to ex-
traneous ambient noises.. At least four measurements shall be made
for each side of the vehicle. All values shall be recorded. Suf-
ficlent"preliminary runs to familiarize the driver and to establish
the engine operating conditions shall be made before measurements
begin.
5.4.4 The sound level for each side of the vehicle should be
the average of the two highest readings which are within 2 dB(A)
of each other. The sound level reported shall be that of the
loudest side of the vehicle.
6. GENERAL COMMENTS
6.1 Technically trained personnel should select equipment
and tests should be conducted only by qualified persons trained in
the current techniques of sound measurement.
6.2 An additional 2 dB tolerance over the sound level
limit is recommended when rechecking a vehicle at a different time
and location should be allowed to provide for variations in test
site, vehicle operation, temperature gradients, wind velocity
gradients, test equipment, and inherent differences in nominally
identical vehicles.
6.3 Proper usage of all test instrumentation is essential
to obtain valid measurements. Operating manuals or other litera-
ture furnished by the instrument manufacturer should be referred
to for both recommended operation of the instrument and precautions
to be observed. Specific items to be considered are:
B-12
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6.3.1 The type of microphone, its directional response
characteristics, and its orientation relative to the ground plane
and source of noise;
6.3.2 The effects of ambient weather conditions on the per-
formance of all instruments (e.g.. temperature, humidity, and
barometric pressure);
6.3.3 Proper signal levels, terminating impedances, and
cable lengths on multi-instrument measurement systems;
6.3.4 Proper acoustical calibration procedure, to include
the influence of extension cables, etc. Field calibration shall
be made immediately before and after each test sequence. Internal
calibration means is acceptable for field use, provided that ex-
ternal calibration is accomplished immediately before or after
field use.
6.5 Vehicles used for tests must not be operated in a
Banner such that the break-in procedure specified by the manu-
facturer is violated.
7. REFERENCES
Suggested reference material is as follows:
1. ANS Sl.l - 1960 Acoustical Terminology
2. ANS SI.4 - 1961 General Purpose Sound Level Meters
3. ANS SI.2 - 1962 Physical Measurement of Sound
4. I. E. C. Publication 179, Precision Sound Level Meters
(available from ANSI).
Applications for copies of these documents should be addressed
to the American National Standards Institute, Inc., 1430 Broadway,
New York, New York 10018.
B-13
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UDC 534 Ref. No.: ISO/ R 362 - 1964 (E)
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ISO RECOMMENDATION
R362
MEASUREMENT OF NOISE EMITTED BY VEHICLES
1st EDITION
February 1964
COPYRIGHT RESERVED
The copyright of ISO Recommendations and ISO. Standards
belongs to ISO Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
B-14
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
-------
BRIEF HISTORY
The ISO Recommendation R 362, Measurement of Noise Emitted by Vehicles, was
drawn up by Technical Committee ISO/TC 43, Acoustics, the Secretariat of which is held
by the British Standards Institution (B.S.I.).
Work on this question by the Technical Committee began in 1958 and led, in 1960, to
the adoption of a Draft ISO Recommendation.
This first Draft ISO Recommendation (No. 419) was circulated to all the ISO Member
Bodies for enquiry, in November 1960. Taking into account the observations put forward
by the Technical Committee ISO/TC 22, Automobiles, regarding mechanical specifications,
Technical Committee ISO/TC 43 presented a Second Draft ISO Recommendation, which
was circulated to all the ISO Member Bodies in May 1962, and which was approved,
subject to a few modifications of an editorial nature, by the following Member Bodies:
Australia France Poland
Austria Germany . Portugal
Belgium Greece Spain
Brazil Hungary Sweden
Canada India Switzerland
Chile Ireland United Kingdom
Czechoslovakia Israel U.S.A.
Denmark Netherlands U.S.S.R.
Finland New Zealand Yugoslavia
One Member Body opposed the approval of the Draft: Japan.
The second Draft ISO Recommendation was then submitted by correspondence to the
ISO Council, which decided, in February 1964, to accept it as an ISO RECOMMEN-
DATION.
B-15
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ISO/R 362-1964 (E)
ISO Recommendation R 362 February 1964
MEASUREMENT OF NOISE EMITTED BY VEHICLES
1. SCOPE
This ISO Recommendation describes methods of determining the noise emitted by motor vehicles,
these being intended to meet the requirements of simplicity as far as is consistent with repro-
ducibility of results and realism in the operating conditions of the vehicle.
2. GENERAL REQUIREMENTS
2.1 Test conditions
This ISO Recommendation is based primarily on a test with vehicles in motion, the ISO
reference test. It is generally recognized to be of primary importance that the measurements
should relate to nor.nal town driving conditions, thus including transmission noise etc.
Measurements should also relate to vehicle conditions which give the highest noise level
consistent with normal driving and which lead to reproducible noise emission. Therefore,
an acceleration test at full throttle from a stated running condition is specified.
Recognizing, however, that different practices already exist, specifications of two other
methods used are also given in the Appendix. These relate to:
(a) a test with stationary vehicles (see Appendix Al) and
(b) a test with vehicles in motion, under vehicle conditions which (in the case of certain
vehicles) are different from those in the ISO reference test (see Appendix A2).
When either of these tests is used, the relation between the results and those obtained by
the ISO reference test should be established for typical examples of the model concerned.
2.2 Test site
The test methods prescribed call for an acoustical environment which can only be obtained
in an extensive open space. Such conditions can usually be provided
for type-approval measurements of vehicles,
for measurements at the manufacturing stage, and
for measurements at official testing stations.
It is desirable that spot checking of vehicles on the road should be made in a similar
acoustical environment. If measurements have to be carried out on the road in an acoustical
environment which does not fulfil the requirements stated in this ISO Recommendation,
it should be recognized that the results obtained may deviate appreciably from the results
obtained using the specified conditions.
2.3 Interpretation of results
The results obtained by the methods specified give an objective measure of the noise emitted
under the prescribed conditions of test. Owing, however, to the fact that the subjective
appraisal of the annoyance or noisiness of different classes of motor vehicles is not simply
related to the indications of a sound level meter, it is recognized that the correct interpre-
tation of results of the measurements in this ISO Recommendation may require different
limits to be set for the corresponding annoyance of different classes of vehicles.
B-16
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ISO/R 362-1964 (E)
3. MEASUREMENT EQUIPMENT
A high quality sound level meter should be used. The weighting network and meter time constant
employed should be curve " A " and " fast response " respectively, as specified in Recommen-
dation No. 123 of the International Electrotechnical Commission for Sound Level Meters. A
detailed technical description of the instrument used should be supplied.
NOTES
1. The sound level measured using sound level meters having the microphone close to the instrument
case may depend on the orientation of the instrument with respect to the sound source, as well as on
the position of the observer making the measurement. The instructions given by the manufacturer
concerning the orientation of the sound level meter with respect to the sound source and the observer
should therefore be carefully followed.
2. If a wind shield is used for the microphone, it should be remembered that this may have an influence
on the sensitivity of the sound level meter.
3. To ensure accurate measurements, it is recommended that before each series of measurements the
amplification of the sound level meter be checked, using a standard noise source and adjusting as
necessary.
4. It is recommended that the sound level meter and the standard noise source be calibrated periodically
at a laboratory equipped with the necessary facilities for free-field calibration.
Any peak which is obviously out o; character with the general sound level being read should be
ignored.
4. ACOUSTICAL ENVIRONMENT
The test site should be such that hemispherical divergence exists to within ± 1 dB.
NOTE.A suitable test site, which could be considered ideal for the purpose of the measurements, would
consist of an open space of some 50 m radius, of which the central 20 m, for example, would consist of
concrete, asphalt or similar hard material.
In practice, departure from the so-called " ideal" conditions arises from four main causes:
(a) sound absorption by the surface of the ground;
s
(b) reflections from objects, such as buildings, and trees, or from persons;
(c) ground which is not level or of uniform slope over a sufficient area;
(d) wind.
It is impracticable to specify in detail the effect produced by each of these influences. It is con-
sidered important, however, that the surface of the ground within the measurement area be free
from powdery snow, long grass, loose soil or ashes.
To minimise the effect of reflections, it is further* recommended that the sum of the angles sub-
tended at the position of the test vehicle by surrounding buildings within 50 m radius should not
exceed 90° and that there be no substantial obstructions within a radius of 25 m from the vehicle.
Acoustical focussing effects and sites between parallel walls should be avoided.
Wherever possible, the level of ambient noise (including wind noise andfor stationary tests
roller stand and tyre noise) should be such that the reading produced on the meter is at least
10 dB below that produced by the test vehicle. In other cases, the prevailing noise level should be
stated in terms of the reading of the meter.
NOTE.Care should be taken that gusts of wind do not distort the results of the measurements.
The presence of bystanders may have an appreciable influence on the meter reading, if such
persons are in the vicinity of the vehicle or the microphone. No person other than the observer
reading the meter should therefore remain in the neighbourhood of the vehicle or the microphone.
NOTE.Suitable conditions exist, if bystanders are at a distance from the vehicle which is at least twice
the distance from vehicle to microphone.
B-17
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5. MEASUREMENTS WITH VEHICLES IN MOTION
5.1 Testing ground
The testing ground should be substantially level, and its surface texture such that it does
not cause excessive tyre noise.
5.2 Measuring positions
The distance from the measuring positions to the reference line CC (Fig. 1) on the road
should be 7.5 m. The path of the centre line of the vehicle should follow as closely as
possible the line CC.
The microphone should be located 1.2 m above the ground level.
5.3 Number of measurements
At least two measurements should be made on each side of the vehicle as it passes the
measuring positions.
NOTE.It is recommended that preliminary measurements be made for the purpose of adjustment.
Such preliminary measurements need not be included in the final result.
Microphone e../J "i-l1 ' " Microphone
Fig. 1. Measuring positions for measurement with vehicles in motion
5.4 Test procedure
5.4.1 General conditions
The vehicle approaches the line A A in the appropriate conditions specified below:
When the front of the vehicle reaches the position, in relation to the microphone,
shown as A A in Figure 1, the throttle is fully opened as rapidly as practicable and held
there until the rear of the vehicle reaches position BB in Figure 1, when the throttle is
closed as rapidly as possible.
Trailers, including the trailer portion of articulated vehicles, are ignored when con-
sidering the crossing of line BB.
NOTE.If the vehicle is specially constructed with equipment (such as concrete mixers, com-
pressors, pumps, etc.), which is used Whilst the vehicle is in normal service on the road, this
equipment should also be operating during the test.
B-18
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ISO/R3BZ-1981 (t)
5.4.2 Particular conditions
5.4.2.1 VEHICLE WITH NO GEAR-BOX. The vehicle should approach the line AA at a steady
speed corresponding
either to an engine speed of three quarters of the speed at which the engine
develops its maximum power,
«
or to three quarters of the maximum engine speed permitted by the governor,
or to 50 km/h,
whichever is the lowest.
5.4.2.2 VEHICLE WITH A MANUALLY OPERATED GEAR-BOX. If the vehicle is fitted with a two-,
three-, or four-speed gear box, the second gear should be used. If the vehicle has
more than four speeds, the third gear should be used. Auxiliary step-up ratios
(" overdrive ") should not be engaged. If the vehicle is fitted with an auxiliary
reduction gear box, this should be used with the drive allowing the highest vehicle
speed.
The vehicle should approach the line AA at a steady speed corresponding
either to an engine speed of three quarters of the speed at which the engine
develops its maximum power,
or to three quarters of the engine speed permitted by the governor,
or to 50 km/h,
whichever is the lowest.
5.4.2.3 VEHICLE WITH AN AUTOMATIC GEAR-BOX. The vehicle should approach the line AA
at a steady speed of 50 km/h or at three quarters of its maximum speed, whichever
is the lower. Where alternative forward drive positions are available, that position
which results in the highest mean acceleration of the vehicle between lines AA
and BB should be selected.
The selector position which is used only for engine braking, parking or similar
slow manoeuvres of the vehicle should be excluded.
5.4.2.4 AGRICULTURAL TRACTORS, SELF-PROPELLED AGRICULTURAL MACHINES AND MOTOR CUL-
TIVATORS. The vehicle should approach the line AA at a steady speed of three
quarters of the maximum speed which can be achieved, using the gear-box ratio
which gives the highest road speed.
5.5 Statement of results
All readings taken on the sound level meter should be stated in the report.
The basis of horsepower rating, if appropriate, should be stated in the report.
The state of loading of the vehicle should also be specified in the report.
B-19
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ISO/R 362-1964 (E)
APPENDICES
Al. MEASUREMENTS WITH STATIONARY VEHICLES
A1.1 Measuring positions
Measurements are made in each of the four main directions at a distance of 7.0 m from
the nearest surface of the vehicle. The actual positions used for the measurements are
shown in Figure 2. If measurements arc required in more than the four measuring
positions shown in Figure 2, they should be taken from chosen positions on the circles
shown i.e. the circles with radius 7.0 m.
The microphone should be located 1.2 m above the ground level.
MOTORCYCLE WITH OR
WITHOUT SIDE-CAR
CAR WITH OR WITHOUT
TRAILER
Test area
perimeter
Fig. 2. Measuring positions for measurement with stationary vehicles
A 1.2 Number of measurements
At least two measurements should be made in each measuring position.
A 1.3 Vehicle conditions
The engine of the vehicle without a speed governor should be run at three quarters of
the number of revolutions per minute at which, according to the manufacturer, it
develops its maximum power. The engine speed, expressed in revolutions per minute,
is measured by means of an independent instrument, e.g. by the use of free-running
rollers and a tachometer. A governed engine should be run at maximum speed.
The engine should be brought to its usual working temperature before measurements
are carried out.
A 1.4 Statement of results
All the sound level readings observed in each measuring position should be stated in
the report. B-20
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A2. MEASUREMENTS WITH VEHICLES IN MOTION (MODIFIED METHOD)
A2.1 Testing ground
The testing ground should be substantially level, and its surface texture such that it
does not cause excessive tyre noise.
A2£ Measuring positions
The distance from the measuring positions to the reference line CC (Fig. 1) on the
road should be 7.5 m. The path of the centre line of the vehicle should follow as closely
as possible the line CC.
The microphone should be located 1.2 m above the ground level.
A 2.3 Number of measurements
At least two measurements should be made on each side of the vehicle as it passes the
measuring positions.
NOTE.It is recommended that preliminary measurements be made for the purpose of adjust-
ment. Such preliminary measurements need not be included in the final result.
A 2.4 Test procedure
A2.4.1 General conditions
The vehicle approaches the line A A in the appropriate conditions specified below:
When the front of the vehicle reaches the position, in relation to the microphone,
shown as A A in Figure 1, the throttle is fully opened as rapidly as practicable and
held there until the rear of the vehicle reaches position BB in Figure 1, when the
throttle is closed as rapidly as possible.
Trailers, including the trailer portion of articulated vehicles, are ignored when
considering the crossing of line BB.
NOTE.If the vehicle is specially constructed with equipment (such as concrete mixers,
compressors, pumps, etc.), which is used whilst the vehicle is in normal service on the
road, this equipment should also be operating during the test.
A2.4.2 Particular conditions
Vehicles should be driven in such a manner as to comply with either of the following
conditions:
A2.4.2.1 VEHICLE WTTH A MANUALLY OPERATED GEAR BOX, WITH OR WITHOUT AUTOMATIC
CLUTCH. The vehicle should approach the line AA (Fig. 1) at a steady speed
corresponding to three quarters of the revolutions per minute at which the
engine (according to the manufacturer) develops its maximum power. The
gear ratio should be chosen such that the road speed most closely approaches
50 km/h at this engine speed. However, if the vehicle has more than three
forward gears, the first gear should not be used.
A2.4.2.2 VEHICLE WITH AN AUTOMATIC GEAR BOX. The vehicle should approach the line AA
at a steady speed of 50 km/h or at three quarters of its maximum speed, whichever
is the lower. Where alternative forward drive positions are available, the position
which results in the highest sound level of the vehicle should be selected.
The selector position which is used only for engine braking, parking or similar
slow manoeuvres of the vehicle should be excluded.
A2.5 Statement of results
All readings taken on the sound level meter should be stated in the report.
The basis of horsepower rating, if appropriate, should be stated in the report.
The state of loading of the vehicle should also be specified in the report.
B-21
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MOTORCYCLE INDUSTRY COUNCIL SUPPORTED NOISE TEST PROCEDURE
FOR NEW VEHICLES
1. INTRODUCTION
This Standard establishes maximum sound levels for motorcycles and
motor driven cycles and describes the test procedure, environment,
and instrumentation for determining these sound levels.
2. INSTRUMENTATION
The following instrumentation shall be used for the measurement
required:
2.1 A sound level meter which meets the requirements of Inter-
national Electroacoustic Commission Publication 179, Precision
Sound Level Meters.
2.1.1 Alternatively, a microphone/magnetic tape recorder/indicating
meter system whose overall response is equivalent to the above
may be used.
2.2 A sound level calibrator (see paragraph 4.5)
2.3 A calibrated windscreen or nose conejsee paragraph 4.4)
3. PROCEDURE
3.1 A test site suitable for the purpose of measurements shall
consist of a flat open space free of large reflecting surfaces
such as signboards, buildings, or hillsides located within
100 ft. of either the vehicle or the microphone.
3.1.1 The surface of the ground within the measurement area shall
be dry concrete or asphalt, free from powdery snow, loose
soil or ashes.
3.1.2 Because bystanders may have an appreciable influence on
meter response when they are in the vicinity of the vehicle
or the microphone, not more than one person other than the
observer reading the meter shall be within 50 ft. of the vehi-
cle or microphone, and that person shall be directly behind
the observer reading the meter, on a line through the micro-
phone and the observer.
.3.1.3 The ambient sound level (including wind effects) due to sources
other than the vehicle being measured shall be at least lOdbA
lower than the level of the tested vehicle.
3.1.4 The path of vehicles shall be of relatively smooth, dry concrete
or asphalt, free of extraneous matter such as gravel.
B-22
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3.1.5 The microphone shall be located 50 ft. from the centerline of
the vehicle path at a height of 4 ft. above the ground plane.
3.1.6 An acceleration point shall be established on the vehicle path
25 ft. before the line through the microphone and normal vehi-
cle path.
3.2 VEHICLE OPERATIONS
3.2.1 The vehicle shall use second gear. Vehicles which reach maxi-
mum rated engine speeds before reaching a point 25 ft. beyond
the microphone shall be tested in third gear.
3.2.2 The vehicle shall proceed along the test path at a constant
approach speed which shall correspond to either the engine
speed of 60% of the speed at which the engine develops
maximum horsepower or at 30 mph whichever is lower. When
the front of the vehicle reaches the acceleration point, the
throttle shall be opened wide, and maintained until the front
of the vehicle is 100 ft. beyond the microphone, or until the
maximum rated engine speed is reached, at which point the
throttle shall be closed.
3.2.3 Wheel slip which affects the maximum sound level must be
avoided.
3.3 MEASUREMENTS
3.3.1 The meter shall be set for "fast" response and for the A-weighted
network.
3.3.2 The meter shall be observed while the vehicle is accelerating.
The applicable reading shall be the highest sound level obtained
for the run, ignoring unrelated peaks due to extraneous ambient
noises. Sufficient preliminary runs to familiarize the driver
and to stabilize the engine operating conditions shall be made
before measurements begin. Immediately after the preliminary
runs, at least two measurements shall be made for each side
of the vehicle. All of the values shall be recorded.
3.3.3 The sound level for each side of the vehicle shall be the average
of the two highest readings which are within 2db of each other.
The sound level reported shall be that of the louder side of the
vehicle.
4. GENERAL COMMENTS
4.1 It is strongly recommended that technically trained personnel
select equipment and'that tests be conducted only by qualified
persons trained in the current techniques of sound measurement.
B-23
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4.2 An additional 2db allowance over the sound level limit is
recommended to provide for variations in test site, vehicle
operation temperature .gradients, wind velocity gradients,
test equipment/ and inherent differences in nominally iden-
tical vehicles.
4.3 Instrument manufacturers' specification for orientation of the
microphone relative to the meter should be adhered to.
4.4 When a windscreen is required, a previously calibrated wind-
screen should be used. It is recommended that measurements
be made only when wind velocity is below 12 mph.
4.5 Instrument manufacturers' recommended calibration practice
should be followed. Field calibration should be made imme-
diately before and after each test sequence. Either an external
calibrator or internal calibrator means is acceptable for field
use, providing that external calibration is accomplished imme-
diately before and after field use.
5. REFERENCE MATERIAL
Suggested reference material is as follows;
USASI SI. 1-1960 Acoustical Terminology
USASI SI. 2-1962 Physical Measurement of Sound.
International Electroacoustic Commission
Publication 179, Precision Sound Level
Meters (available from USASI).
(Application for copies of these documents should be addressed
to ANSI, 10 East 40th Street, New York, New York 10016).
B-24
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c
Proposed M.I.C. 4-Mode Motorcycle Noise Measurement Test Data Sheet
Manufacturer:
Model:
Displacement:
I I Motorcycle
I | Motor-Driven Cycle
California Law defines a motor-driven cycle on the basis
of the engine producing less than 15 gross brake horsepower.
Motorcycle Data
Mode
Number
1.
2.
3.
4.
Description
CHP Maximum Noise Procedure
Steady 65 mph driveby (top gear)
Steady 40 mph driveby (top gear)
2000 rpm (neutral)
Vehicle stationary with front at end
point (refer to CHP Procedure)
dB(A)
Test Result
Multiply By
Weighting Factor
0.5
0.2
0.2
0.1
Weighted
Result
Total -
V. ' (Add Weighted Results) J
Motor-Driven Cycle Data
Mode
Number
1.
3.
4.
Description
CHP Maximum Noise Procedure
Steady 40 mph driveby (top gear)
200 rpm (neutral)
Vehicle stationary with front at end
point (refer to CHP Procedure)
dB(A)
Test Result
Multiply By
Weighting Factor
0.5
0.4
0.1
Weighted
Result
Total -
^ (Add Weighted Results) ^
NOTE: THIS METHOD DIFFERS FROM THE PRECEDING M.I.C.
SUPPORTED PROCEDURE.
B-25
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NOISE MEASUREMENT PROCEDURE USED FOR QUALIFICATION IN
AMERICAN MOTORCYCLE ASSOCIATION
SANCTIONED OFF-ROAD COMPETITION
N 50 feet
TIM* fM'vi^1
ESILlG
feprinMd from AMA NEWS
During the FIM spring:, 1972, congress
held in Geneva, Switzerland, the world
governing body for the sport of motor-
cycling adopted noise standards and
testing methods based on proposals made
by the delegates of the American fed-
eration. After experiencing difficulties
with various methods designed for tech-
nical accuracy and sophistication, the
FIM turned to the American Motorcycle
Association for suggestions with the
hope that a world-wide noise abatement
program could be established, based on
a practical, easily-administered method
of noise testing.
The FIM method provides that all ma-
chines under examination be measured
at a distance of 50 feet (15.2m). They
should be running in neutral with the
noise level reading taken at a pre-de-
termined motor speed, depending upon
the size of the motorcycle.
A hand-held meter, such as that avail-
able from the AMA, should be held
about 4 feet (1.2m) from the ground (a
comfortable posture with the elbows
bent) with the microphone pointing at
a right angle to the motorcycle. The in-
dividual holding the meter, preferably
the referee in charge or someone ap-
pointed by him, takes the reading of each
motorcycle and reports it to a clerk who
should record it beside the contestant's
number on an entry list.
With the motorcycle started and run-
ning in neutral, the motor is accelerated
to a certain rpm and held there just
long enough for the reading to be taken.
Care should be taken not to over-rev the
motor or to hold it at speed too long.
Below are the reading speeds estab-
lished by the FIM:
SOcc to 75cc , GOOOrpm
lOOce to 125cc SSOOrpm
175cc to 250cc SOOOrpm
350cc to SOOcc 4SOOrpm
over SOOcc 4000rpm
Note that these recommendations are
based on traditional FIM class designa-
tions. If a motor size falls between cate-
gories, it should be moved to the next
larger class. For example, a ISOce ma-
chine should be measured at 5000 rpm,
falling into the class of motorcycles up
to 250cc.
If the motorcycle has no tachometer,
the testing crew may want to use a
counter which attaches to-the electrical
system, a method suggested by the FIM.
If no such device is available, the motor
speed should be estimated at 2/3 maxi-
mum safe revolutions.
No motorcycle, tested at the motor
speed designated for its motor class, may
exceed 92 decibels (92dB(a)) and be
legal for AMA amateur competition or
professional moto-cross.
Common sense should be followed in
administering this test. For example,
only the motorcycle being tested should
be running. An open area should be
chosen so that the contestant will not
be jeopardized by noise echoing from
walls or other large objects.
This method is designed for Ita sim-
plicity. More sophisticated and accurate
methods are available, but they are more
complicated, difficult and expensive to
administer. Furthermore, with the more
complicated methods, the individual be-
ing: tested can usually find more ways
to manipulate the noise level of his ma-
chine and control the results to his bene-
fit
For those interested in improving the
sport of motorcycling by reducing of-
fensive noise, this simple method, ad-
ministered .in a spirit of cooperation by
official and contestant alike, is a most
convenient and effective techniqoc.
This level is now set at 90 dBA.
B-26
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NOTE - NEW INFORMATION
The two remaining motorcycle noise test procedures are new Society of Automotive
Engineers recommendations received after writing of the report text. Some of the short-
comings discussed in the Measurement Procedures section of Chapter 4, such as variable
rider weight, have been addressed in the new standards. The new SAE Recommended
Practice J331a Sound Levels for Motorcycles is a revised version of J331 similar to
the California Highway Patrol measurement standard. Recommended Practice XJ47
Maximum Sound Level Potential for Motorcycles is essentially the old J331 referred
to in the text.
B-27
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September 10, 1973
SOUND LEVELS FOR SAE RECOMMENDED
MOTORCYCLES - SAE XJ 331a PRACTICE
1. SCOPE
This SAE Recommended Practice establishes the test procedure, environment, and
instrumentation for determining sound levels typical of normal motorcycle operation.
2. INSTRUMENTATION
2.1 The following instrumentation shall be used, where applicable:
2.1.1 A sound level meter which meets the Type 1 requirements of the American
National Standard Specification for Sound Level Meters SI .4-1971. As an alternative
to making direct measurements using a sound level meter, a microphone or sound level
meter may be used with a magnetic tape recorder and/or a graphic level recorder or
indicating meter providing the system meets the requirements of SAE Recommended
Practice J184, Qualifying a Sound Data Acquisition System.
2.1.2 An Acoustic Calibrator (see Section 6.4.4).
2.1.3 A calibrated engine speed tachometer having the following characteristics:
(a) Steady state accuracy of better than 1 percent.
(b) Transient response: Response to a step input will be such that
within 10 engine revolutions the indicated rpm will be within
2 percent of the actual rpm.
B-28
Note: This is a retyped copy of the pending SAE Standard.
-------
2.1.4 A speedometer with steady state accuracy of at least ±10 percent.
2.1.5 An anemometer with steady state accuracy of at least ±10 percent.
2.1.6 An acceptable wind screen may be used with the microphone. To be
acceptable the screen must not affect the microphone response more than ± 1 dB for
frequencies of 20-4000 Hz or ± 1-1/2 dB for frequencies of 4000 - 10,000 Hz.
3. TEST SITE
3.1 The test site for measuring sound levels of motorcycles shall be a flat open
space free of large sound reflecting surfaces (other than the ground), such as parked
vehicles, signboards, buildings, or hillsides, located within 100 ft (30.4 m) radius of
the microphone location and the following points on the vehicle path:
(a) The microphone point.
(b) A point 50 ft (15.2 m) before the microphone point.
(c) A point 50 ft (15.2 m) beyond the microphone point.
3.2 The measurement area within the test site shall meet the following require-
ments and be layed out as described:
3.2.1 The surface of the ground within at least the triangular area formed by the
microphone location and the points 50 ft (15.2 m) prior to and 50 ft (15.2 m) beyond the
microphone point shall be dry concrete or asphalt, free from snow, soil, or other
extraneous material.
3.2.2 The vehicle path shall be of relatively smooth, dry concrete or asphalt,
free of extraneous materials such as gravel, and of sufficient length for safe acceleration,
deceleration, and stopping of the vehicle.
B-29
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3.2.3 The microphone shall be located 50 ft (15.2 m) from the centerline of the
vehicle path and 4 ft (1.2 m) above the ground plane.
3.2.4 The following points shall be established on the vehicle path:
(a) Microphone point a point on the centerline of the vehicle
path where a normal through the microphone location
intersects the vehicle path.
(b) End point a point on the vehicle path 100 ft (30.4 m) beyond
the microphone point.
(c) Acceleration point a point on the vehicle path 25 ft (7.6 m)
prior to the microphone point.
3.2.5 The test area layout in Figure 1 shows a directional approach from left
to right with one microphone location, for purposes of clarity. Sound level measurements
are to-be made on both sides of the vehicle; therefore, it will be necessary to establish
either a corresponding clear area or end points and acceleration points for approaches
from both directions.
B-30
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^_ so- ,|« 100' J
- Microphone point
B - Acceleration point
C - End point
D - End zone
FIGURE 1
25' - 7.6 Metres
50' - 15.2 Metres
100' - 30.4 Metres
4. TEST WEIGHT
4.1 At the start of the test series, the vehicle shall be filled with fuel
/>
and lubricant to not less than 75 percent of capacity.
4.2 The combined weight of the test rider and test equipment used on the
vehicle shall be not more than 175 Ibs (79.4 kg) nor less than 165 (74.8 kg). Weights
shall be placed on the vehicle saddle behind the driver to compensate for any difference
between the actual driver/equipment load and the required 165 Ib (74.8 kg) minimum.
5. PROCEDURE
5.1 The vehicle shall use second gear unless during the test under accelera-
tion the engine speed at maximum rated net horsepower is reached before the vehicle
reaches a point 25 ft (7.6 m) beyond the microphone point in which case the vehicle
shall be tested in third gear.
B-31
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5.2 For the test under acceleration the vehicle shall proceed along the
vehicle path at a constant approach speed which shall correspond to either an engine
speed of 60 percent of the engine speed at maximum rated net horsepower or a vehicle
speed of 30 mph (48 km/h), whichever is slower. When the front of the vehicle reaches
the acceleration point, rapidly and fully open the throttle and accelerate until the front
of the vehicle is 100 ft (30.4 m) beyond the microphone point, or until the engine speed
at maximum rated horsepower is reached, at which point the throttle shall be closed.
Wheel slip which effects the maximum sound level shall be avoided.
5.3 When excessive or unusual noise is noted during deceleration, the
following test shall be performed with sufficient runs to establish maximum sound level
under deceleration.
5.3.1 For the test under deceleration, the vehicle shall proceed along the
vehicle path at an engine speed at maximum rated net horsepower in the gear selected
for the test under acceleration. At the end point, the throttle shall be rapidly and
fully closed, and the vehicle allowed to decelerate to an engine speed of one-half
of the rpm at maximum rated net horsepower.
5.4 Sufficient preliminary runs to familiarize the driver and to establish
the engine operating conditions shall be made before measurements begin. The engine
temperature shall be within the normal operating range prior to each run.
6. MEASUREMENTS
6.1 The sound level meter shall be set for "fast" response and for the
A-weighting network.
B-32
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6.2 The meter shall be observed while the vehicle is accelerating or decelerating.
Record the highest sound level obtained for the run, ignoring unrelated peaks due to
extraneous ambient noises. All values shall be recorded.
6.3 At least six measurements shall be made for each side of the vehicle. The
highest and the lowest reading shall be discarded; the sound level for each side shall be
the average of the remaining four, which shall be within 2 dB of each other. The sound
level reported shall be for that side of the vehicle having the highest sound level.
6.4 The ambient sound level (including wind effects) at the test site due to
sources other than the vehicle being measured shall be at least 10 dB lower than the
sound level produced by the vehicle under test.
6.5 Wind speed at the test site during tests shall be less than 12 mph (19 km/h).
7. GENERAL COMMENTS
7.1 Technically competent personnel should select equipment and the tests
should be conducted only by trained and experienced persons familiar with the current
techniques of sound measurement.
7.2 While making sound level measurements, not more than one person other
than the rider and the observer reading the meter shall be within 50 ft (15.2 m) of the
vehicle or microphone, and that person shall be directly behind the observer reading the
meter, on a line through the microphone and the observer.
7.3 The test rider should be fully conversant with and qualified to ride the
machine under test and be familiar with the test procedure.
B-33
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7.4 Proper use of all test instrumentation is essential to obtain valid measurements.
Operating manuals or other literature furnished by the instrument manufacturer should be referred
to for both recommended operation of the instrument and precautions to be observed. Specific
items to be considered are:
7.4.1 The type of microphone, its directional response characteristics, and its
orientation relative to the ground plane and source of noise.
7.4.2 The effects of ambient weather conditions on the performance of all
instruments (e.g., temperature, humidity, and barometric pressure).
7.4.3 Proper signal levels, terminating impedances, and cable lengths on multi-
instrument measurement systems.
7.4.4 Proper acoustical calibration procedure, to include the influence of
extension cables, etc. Reid calibration shall be made immediately before and after
each test sequence. Internal calibration means is acceptable for field use, provided
that external calibration is accomplished immediately before or after field use.
B-34
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8. REFERENCES
Suggested reference material is as follows:
8.1 ANSI Sl.l - 1960, Acoustical Terminology
8.2 ANSI SI.2 - 1962, Physical Measurement of Sound
8.3 ANSI SI.4 - 1971, Specification for Sound Level Meters
8.4 ANSI SI. 13 - 1971, Method of Measurement of Sound Pressure Levels
8.5 SAE J184, Qualifying a Sound Data Acquisition System
8.6 SAE J47, Maximum Sound Level Potential for Motorcycles. This
procedure is recommended for determining the vehicle's maximum potential sound level.
The procedure does not represent normal motorcycle safe operating practice.
APPENDIX
The SAE recommends that the following sound levels, when measured in accordance
with the test procedure described above, be used as a reference in the design and
development of motorcycles. A 2 dB (A) allowance is recommended to provide for
variations in test site, temperature and wind gradients, test equipment and inherent
differences in nominally identical vehicles.
Engine Displacement A-Weighted Sound Level
169 cc and less 82 dB(A)
170 cc thru 500 cc 84 dB(A)
more than 500 cc 86 dB(A)
B-35
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September 10, 1973
MAXIMUM SOUND LEVEL, POTENTIAL SAE RECOMMENDED
FOR MOTORCYCLES - SAE XJ 47 PRACTICE
1. SCOPE
This SAE Recommended Practice establishes the test procedure, environment and
instrumentation for determining maximum sound level potential for motorcycles.
2. INSTRUMENTATION
2.1 The following instrumentation shall be used, where applicable:
2.1.1 A sound level meter which meets the Type 1 requirements of the
American National Standard Specification for Sound Level Meters (SI.4-1971). As
an alternative to making direct measurements using a sound level meter, a microphone
or sound level meter may be used with a magnetic tape recorder and/or a graphic level
recorder or indicating meter providing the system meets the requirements of SAE
Recommended Practice J184, Qualifying a Sound Data Acquisition System.
2.1.2 An acoustic calibrator (see Section 6.4.4).
2.1.3 A calibrated engine speed tachometer having the following characteristics.
(a) Steady state accuracy of better than 1 percent.
(b) Transient response: Response to a step input will be such that
within 10 engine revolutions the indicated rpm will be within
2 percent of the actual rpm.
B-36
Note: This is a retyped copy of the pending SAE Standard.
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2.1.4 An anemometer with steady state accuracy within ± 10 percent.
2.1.5 An acceptable wind screen may be used with the microphone. To be
acceptable, the screen must not affect the microphone response more than ±1 dB for
frequencies of 20 to 4000 Hz or ± 1-1/2 dB for frequencies of 4000 to 10,000 Hz.
3. TEST SITE
3.1 The test site for measuring sound levels of motorcycles shall be a flat
open space free of large sound reflecting surfaces (other than the ground) such as parked
vehicles, signboards, buildings, or hillsides, located within 100 ft (30.4 m) radius of
the microphone location and the following points on the vehicle path:
(a) The microphone point.
(b) A point 50 ft (15.2 m) before the microphone point.
(c) A point 50 ft (15.2 m) beyond the microphone point.
3.2 The measurement area within the test site shall meet the following
requirements and be layed out as described:
3.2.1 The surface of the ground within at least the triangular area formed by
the microphone location and the points 50 ft (15.2 m) prior to and 50 ft (15.2 m) beyond
the microphone point shall be dry concrete or asphalt, free from snow, soil, or other
extraneous material.
3.2.2 The vehicle path shall be of relatively smooth, dry concrete or asphalt,
free of extraneous materials such as gravel, and of sufficient length for safe acceleration
deceleration, and stopping of the vehicle.
B-37
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3.2.3 The microphone shall be located 50 ft (15.2 m) from the centerline of
the vehicle path and 4 ft (1.2 m) above the ground plane.
3.2.4 The following points shall be established on the vehicle path:
(a) Microphone point - a point on the centerline of the vehicle
path where a normal through the microphone location inter-
sects the vehicle path.
(b) End point - a point on the vehicle path 25 ft (7.6 m) beyond the
microphone point.
(c) Acceleration point - a point on the vehicle path at least 25 ft
(7.6 m) prior to the microphone point established by the method
described in paragraph 4.1.
3.2.5 The test area layout in Figure 1 shows a directional approach from left
to right with one microphone location for purposes of clarity. Sound level measurements
are to be made on both sides of the vehicle; therefore, it will be necessary to establish
either a second microphone location on the opposite side of the vehicle path with a
corresponding clear area or end points, and acceleration points for approaches from
both directions.
B-38
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- Microphone point
B - End point
C - Acceleration
point
D - Center of clear
area radius
FIGURE 1 \ / / 25' - 7.6 Metres
50' - 15.2 Metres
100' - 30.4 Metres
4. PROCEDURE
4.1 To establish the acceleration point, the end point shall be approached
in low gear from the reverse direction at a constant road speed obtained from 60 percent
of the engine speed at maximum rated net horsepower. When the front of the vehicle
reaches the end point, the throttle shall be rapidly and fully opened to accelerate past
the microphone point under wide open throttle. By trial, the lowest transmission gear
shall be selected that will result in the vehicle traveling the shortest distance from the
end point to the place where the engine speed at maximum rated net horsepower is
reached, but which is not less than 25 ft (7.6 m) past the microphone point. The
location of the front of the vehicle on the vehicle path when the engine speed at
maximum rated net horsepower is attained shall be the acceleration point for test runs
to be made in the opposite direction.
B-39
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4.1.1 When the procedure described in paragraph 4.1 results in a dangerous
or unusual operating condition such as wheel spin, front wheel lifting or other unsafe
conditions, the next higher gear shall be selected for the test and the procedure rerun to
establish the acceleration point. In any.event the procedure shall result in the vehicle
being at the end point when the engine speed at maximum rated net horsepower is attained.
4.2 For the test under acceleration, the vehicle shall proceed along the
vehicle path at a constant approach speed in the gear selected in paragraph 4.1 and at
60 percent of the engine speed at maximum rated net horsepower. When the front of
the vehicle reaches the acceleration point, the throttle shall be rapidly and fully opened.
Full acceleration shall continue until the engine speed at maximum rated net horsepower
is reached, which shall be at the end point, at which time the throttle shall be closed.
Wheel slip which affects the maximum sound level shall be avoided, and the manufacturer's
safe maximum engine speed shall not be exceeded.
4.3 When excessive or unusual noise is noted during deceleration, the
following test shall be performed with sufficient runs to establish maximum sound level
under deceleration.
4.3.1 For the test under deceleration, the vehicle shall approach the end
point from the reverse direction at the engine speed at maximum rated horsepower
in the gear selected for the test under acceleration. At the end point, the throttle
shall be rapidly and fully closed and the vehicle shall be allowed to decelerate to
an engine speed of one-half of the rpm at maximum rated net horsepower.
B-40
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4.4 Sufficient preliminary runs to familiarize the driver and to establish the
engine operating conditions shall be made before measurements begin. The engine temperature
shall be within the normal operating range prior to each run.
5. MEASUREMENTS
5.1 The sound level meter shall be set for "fast" response and for the A-weighting
network.
5.2 The meter shall be observed while the vehicle is accelerating or decelerating.
The highest sound level obtained for each run shall be recorded ignoring unrelated peaks
due to extraneous ambient noises.
5.3 At least six measurements shall be made for each side of the vehicle. The
highest and the lowest reading shall be discarded; the sound level for each side shall be
the average of the remaining four, which shall be within 2 dB of each other. The sound
level reported shall be for that side of the vehicle having the highest sound level.
5.4 The ambient sound level (including wind effects) at the test site due to
sources other than the vehicle being measured shall be at least 10 dB lower than the sound
level produced by the vehicle under test.
5.5 Wind speed at the test site during tests shall be less than 12 mph (19 kmA).
6. GENERAL COMMENTS
6.1 Technically competent personnel should select equipment, and the tests
should be conducted only by trained and experienced persons familiar with the current
techniques of sound measurement.
B-41
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6.2 While making sound level measurements, not more than one person other
than the rider and the observer reading the meter shall be within 50 ft (15.2 m) of the
vehicle or microphone, and that person shall be directly behind the observer reading the
meter, on a line through the microphone and the observer.
6.3 The test rider should be fully conversant with and qualified to ride the
machine under test and be familiar with the test procedure.
6.4 Proper use of all test instrumentation is essential to obtain valid measure-
ments. Operating manuals or other literature furnished by the instrument manufacturer
should be referred to for both recommended operation of the instrument and precautions
to be observed. Specific items to be considered are:
6.4.1 The type of microphone, its directional response characteristics, and its
orientation relative to the ground plane and source of noise.
6.4.2 The effects of ambient weather conditions on the performance of all instru-
ments (e.g., temperature, humidity, and barometric pressure).
6.4.3 Proper signal.levels, terminating impedances, and cable lengths on multi-
instrument measurement systems.
6.4.4 Proper acoustical calibration procedure, to include the influence of
extension cables, etc. Field calibration shall be made immediately before and after
each test sequence. Internal calibration is acceptable for field use, provided that
external calibration is accomplished immediately before or after field use.
B-42
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6.5 Vehicles used for tests must not be operated in a manner such that the break-in
procedure specified by the manufacturer is violated.
7. REFERENCES
Suggested reference material is as follows:
7.1 ANSI S1.1 - I960, Acoustical Terminology
7.2 ANSI SI .2 - 1962, Physical Measurement of Sound
7.3 ANSI SI .4 - 1971, Specification for Sound Level Meters
7.4 ANSI SI. 13 - 1971, Method of Measurement of Sound Pressure Levels
7.5 SAE J184, Qualifying a Sound Data Acquisition System
7.6 SAE J331, Sound Levels for Motorcycles. This procedure is recommended
for use in obtaining motorcycle sound levels typical of normal road operation.
B-43
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APPENDIX
The SAE recommends that the following sound levels, when measured in accordance
with the test procedure described above, be used as a reference in the design and develop-
ment of motorcycles. A 2 dB(A) allowance is recommended to provide for variations
in test site, temperature and wind gradients, test equipment, and inherent differences
in nominally identical vehicles.
Engine Displacement A-Weighted Sound Level
169 cc and less 86 dB(A)
170cc thru 500 cc 88 dB(A)
more than 500 cc 90 dB(A)
B-44
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SAE XJ47
2.1.5 Paragraph 2.1.5 has been rewritten to agree with SAE J34 with the
requirements for the windscreen.
3. Paragraphs 3.1 and 3.1.1 have been combined. Paragraph 3.1.2 and
3.1 .3 have been removed from the Site requirements and placed under
paragraph 5, Measurements, and are now paragraphs 5.4 and 5.5 with
no wording change.
APPENDIX
The recommended A-weighted sound levels have been retyped as they
were under the proposals prior to the June draft. The numbers typed
in the June 8 draft were incorrect.
B-45
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APPENDIX C
CURRENT REGULATIONS
State and municipal vehicle noise regulations display a variety of nature and
intent. Limits are usually presented regarding in-use vehicle operation, and some
authorities such as California and Chicago require noise certifications of new models
before sale is permitted. Noise measurement techniques are predominantly non-
standardized between jurisdictions, with sundry procedures and distances being
prescribed. Most regulations do not specifically identify motor-driven cycles,
but include them in an "other vehicles" category not applying to motorcycles and
heavy trucks. The regulations included here, representing the country's most
sophisticated and restrictive, have been edited to motorcycle application, and sections
which deal generally with horns or equipment installation pertaining to motorcycles
have been omitted.
C-l
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FROM CALIFORNIA STATE VEHICLE CODE
Section 23130. (a) No person shall operate either a motor vehicle
or cento ination of vehicles of a type subject to registration at
any time or under any condition of grade, load, acceleration or
deceleration in such a manner as to excaed the following noise
limit for the category of motor vehicle within the speed limits
specified in this section:
Speed Limit Speed Limit
of 35 mph of more than
or less 35 mph
(1) Any motor vehicle with a
manufacturer's gross vehi-
cle weight rating of 6,000
pounds or more....
(2) Any motorcycle other than a
motor-driven cycle 82 dB(A) 86 dB(A)
(3) Any other motor vehicle and any
combination of vehicles towed by
such motor vehicle 76 dB(A) 82 dB(A)
(b) The noise limits established by this section shall be
based on a distance of 50 feet from the center of the lane of
travel within the speed limit specified in this section. The
Department of the California Highway Patrol may provide for
measuring a distance closer than 50 feet from the center of the
lane of travel. In such a case, the measuring devices shall be
so calibrated as to provide for measurements equivalent to the
noise limit established by this section measured at 50 feet.
(d) This section applies to the total noise from a vehicle
or combination of vehicles and shall not be construed as limiting
or precluding the enforcement of any other provisions of this
code relating to motor vehicle exhaust noise.
C-2
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Section 23130.5. (a) Notwithstanding the provisions of subdivision
(a) of Section 23130, the noise limits, within a speed zone of
35 miles per hour or less on level streets, or streets with a
grade not exceeding plus or minus 1 percent, for the following
categories of motor vehicles, or combinations of vehicles, which
are subject to registration, shall be:
(1) Any motor vehicle with a manufacturer's gross vehicle
Weight rating of 6,000 pounds or more....
(2) Any motorcycle other than a motor-driven
cycle 77 dB (A)
(3) Any other motor vehicle and any combination
of vehicles towed by such motor vehicle .74 dB(A)
No- person shall operate such a motor vehicle or combination
of vehicles in such a manner as to exceed the noise limits specified
in this section.
The provisions of subdivisions (c), (d), (e), and (f) of
Section 23130 shall apply to this section.
(d) The noise limits established by this section shall be
based on a distance of 50 feet from the'center of the lane of
travel within the speed limit specified in this section. The
Department of the California Highway Patrol may provide for
measuring at distances closer than 50 feet from the center of
the lane of travel. In such a case, the measuring devices shall
be so calibrated as to provide for measurements equivalent to the
noise limit established by this section measured at 50 feet.
Section 27150. (a) Every motor vehicle subject to registration
shall at all times be equipped with an adequate muffler in constant
operation and properly maintained to prexrent any excessive or
unusual noise, and no muffler or exhaust system shall be equipped
with a cutout, bypass, or similar device.
(b) Subdivision (a) shall also apply to motorcycles oper-
ated off the highways, except motorcycles being operated in an
organized racing or competitive event conducted on a closed course.
For the purposes of this subdivision, ."closed course" means a
permanent motor racing facility which has one or more of the
following:
(1) Safety crash walls.
(2) Grandstands which seat 500 persons or more.
(3) Sanitation facilities for persons attending events.
(4) A business license or permit from a local authority to
conduct motor racing or--competition events.
C-3
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Section 27151. No person shall modify the exhaust system of a motor vehicle
in a manner which will amplify or increase the noise emitted by the motor of such
vehicle, above that emitted by the muffler originally installed on the vehicle
and the original muffler shall comply with all of the requirements of this chapter.
No person shall operate a motor vehicle with an exhaust system so modified.
Section 27160. (a) No person shall sell or offer for sale a new motor vehicle
which produces a maximum noise exceeding the following noise limit at a
distance of 50 feet from the centerlme of travel under test procedures established
by the department:
(1) Any motorcycle manufactured before 1970 92 dbA
(2) Any motorcycle, other than a motor-driven
cycle, manufactured after 1969, and before
I f /«3 "^^^«»*"»"«^»^»««"«««w»«i" "»«»«««»« OO OO^^
(3) Any motorcycle, other than a motor-driven
cycle, manufactured after 1972, and before
1975 86 dbA
(4) Any motorcycle, other than a motor-driven
cycle, manufactured after 1974, and before
1978 80 dbA
(5) Any motorcycle, other than a motor-driven
cycle, manufactured after 1977, and before
1988 75 dbA
(6) Any motorcycle, other than a motor-driven
cycle, manufactured after 1987 - 70 dbA
(13) Any other motor vehicle manufactured after
1967, and before 1973 86 dbA
(14) Any other motor vehicle manufactured after
1972, and before 1975 84 dbA
(15) Any other motor vehicle manufactured after
1974, and before 1978 - 80 dbA
(16) Any other motor vehicle manufactured after
1977, and before 1988 75 dbA
(17) Any other motor vehicle manufactured after
1987 70 dbA
(b) Test procedures for compliance with this section shall be established
by the department, taking into consideration the test procedures of the Society of
Automotive Engineers.
C-4
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CHAPTER 5. EQUIPMENT OF OFF-HIGHWAY VEHICLES
Section 38275. (a) Every off-highway motor vehicle subject to
identification shall at all times be equipped with an adequate
muffler in constant operation and properly maintained so as to
meet the requirements of Section 38280, and no muffler or exhaust
system shall be equipped with a cutout, bypass, or similar device,
(b) The provisions of subdivision (a) shall not be applicable
to vehicles being operated off the highways in an organized racing
or competitive event upon a closed course and which is conducted
under the auspices of a recognized sanctioning body or by permit
issued by the local governmental authority having jurisdiction.
Section 38280. (a) Notwithstanding the provisions of Section 27160,
no person shall sell or offer for sale a new off-highway motor
vehicle subject to identification which produces a maximum noise
exceeding the following noise limit at a distance of 50 feet from
the centerline of travel under test procedures established by the
Department of the California Highway Patrol:
(1) Any such vehicle manufactured on or after
January 1, 1972, and before January 1, 1973 92 dbA
(2) Any such vehicle manufactured on or after
January 1, 1973, and before January 1, 1975 88 dbA
(3) Any such vehicle manufactured on or after
January 1, 1975 ? 86 dbA
(d) Test procedures for compliance with this section shall
be established by the Department of the California Highway Patrol,
taking into consideration the test procedures of the Society of
Automotive Engineers.
C-5
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CHICAGO NOISE ORDINANCE
From Chapter 17', Chicago Municipal Code
17-4.7 (a) It shr.ll be unlawful for any person
ta operate any motor of a motor vehicle of a
\yeight in excess of four tons (S.OOO Ibs.).!.."
(b) No parson shall sell, or offer for sale, a
new motor vehicle that produces a maximum noise
exceeding the following noise limit at a distance
of 50 feet from the center line of travel under test
procedures established by Section 17-4.24 of this
chapter:
Date of
Manufacture
before 1 Jan. 1970
after 1 Jan. 1970
after 1 Jan. 1973
after 1 Jan. 1975
after 1 Jan. 18SO
after 1 Jan. 19GS
Noise
Limit
92dB(A)
8SdB(A)
SGdB(A)
SltiB(A)
75 dE(A)
SS dB(A)
Type of
Vehicle
(1) Motorcycle
Same
Same
Same
Same
(2) Any motor
vehicle with
a gross
vehicle
weight of
8,000 pounds
or more *
(3) Passenger
cars, motor-
driven cycle
and any
other motor
vehicle
Same after 1 Jan. 1973 S4dB(A)
Same after 1 Jan. 1975 80dB(A)
Same after 1 Jan. 1930 75cB(A)
The manufacturer, distributor, importer, or desin-
natcd ajrent shall certify in writing to the Commis-
sioner that his vehislss sold within the City com-
ply with the provisions of this section.
before 1 Jan. 1973 86 dE(A)
_ (c) No person shall operate within the speed
limits specified in this section either a motor ve-
hicle or combination of vehicles of a type subject
to registration at any time or under any* condition
of grade, load, acceleration or deceleration in such
manner as to exceed the following noise limit for
the category of motor vehicle, based on a distance
of not less than 50 feet from the center line of
travel under test procedures established by Section
17-4.25 of this chapter:
Type of Vehicle
(1) Any motor vehicle
with a mantifac-.
turor's GVW rating
of 8,000 Ibs: or
more, ....
Noise Limit in Relation
To Posted Speed Limit
55 MPll Over
or Less 35 MPH
(2) Any motorcycle
other than a motor-
driven cycle
before 1 Jan. 1978
after 1 Jan. 1978
(3) Any other motor
vehicle and any .com-
bination of motor
vehicles towed by
such motor vehicle
after 1 Jan. 1970
after 1 Jan. 1978
S2dB(A)
78dB(A)
86dB(A)
82dB(A)
76dB(A)
70dB(A)
82dB(A)
79dB(A)
This section applies to the total noise from a
vehicle or combination of vehicles and shall not be
construed as limiting or precluding the enforcement
of any other provisions of this code relating to
motor vehicle mulilers for noise control.
(d) No person shall modify or change the
exhaust muffler, intake mulllcr or any other noise
abatement device of a motor vehicle in a manner
such that the noise emitted by the motor vehicle
is increased above that emitted by the vehicle as
originally manufactured. Procedures used to estab-
lish compliance with this paragraph shall be those
used to establish compliance of a new motor ve-
hicle with the requirements of this article.
C-6
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17-4.22(a) No person shall sell or offer for sale
a new motor-driven recreational or off-highway
vehicle, including dunebuggies, sno\vniobiles, all-
terrain vehicles, go-carls, and mini-bikes, that pro-
duces a maximum noise' exceeding the follov.-ing
noise limit at a distance of 50 feet from the center
line of travel under test procedures established by
Section 17-4.28 of this chapter:
Type of Date of
Vehicle Manufacture Noise Limit
Snowmobile
Any other
vehicle
including
Dune buggy,
all-terrain
vehicle,
go-cart,
mini-bike
after 1 January 1971 80 dB(A)
after 1 January 1973 82 dB(A)
after 1 January 1975 73 dB(A)
(b) It shall be unlawful for any person to oper-
ate a motor-driven vehicle of a type not subject to
registration for road use, at any time or under any
condition of load, acceleration, cr decoloration, in
such a manner as to exceed the following noise limit
at any point on property zoned for business or resi-
dential use at a distance of not less than 50 feet
from the path of travel:
Noise Limit
before 1 January 1973 86 dB(A)
after 1 January 1973 " 82 dB(A)
17-4.23 The operational performance standards
established by this ordinance shall not apply to any
public performance being conducted in. accordance
with the provisions of a special pwmit granted by
the city for the conduct of a public performance.
17-4.24 Test procedures to determine whether
maximum noise emitted by new motor vehicles .sold
or offered for s.nio meet the noise limits slated in
Section 17-4.7(b) of this chapter shall be in sub-
stantial conformity with Standards and Recom-
mended Practice established by the Society of Auto-
motive Engineers, Inc., including SAE Standard
J331; SAE Recommended Practice J1S4; SAE Rec-
ommended Practice J3GG; SAE Standard J9S3 and
such other and further standards as may bo pro-
pounded in the Code of Recommended Practices
of the Department of Environmental Control.
17-1.25 Test procedures to determine whether
maximum noise emitted by motor vehicles in use
meet the noise limits stated in Section 17-1.7(c) of
this chapter shall be in substantial conformity with
Standards and Recommended Practice established-
by the Society of Automotive Engineers, Inc., in-
cluding, SAE Standard JDS6; SAE Standard J331;
Recommended Practice J3G6; Recommended Prac-
tice J18-1; and such other and further standards as
may be propounded in the Code of Recommended
Practices of the Department of Environment:'.! Con-
trol.
C-7
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From Article 5
COLORADO SPRINGS CITY ORDINANCE
Section
8-39. Classification, Measurement of Noise - For purposes of determin-
ing and classifying any noise as excessive or unusually loud as declared
to be unlawful and prohibited by this Article, the following test
measurements and requirements may be applied; provided, however, a
violation of Section 8-38 may occur without the following measurements
being made:
A. Noise occurring within the jurisdiction .of the City shall
be measured at a distance of at least twenty-five (25) feet
from a noise-source located within the public right-of-way,
and if the noise source is located on private property or
property other than the public right-of-way, at least
twenty-five (25) feet from the property line of the prop-
erty on which the noise source is located.
B. 1. The noise shall be measured on the "A" weighing scale-
on sound level meter of standard design and quality
and having characteristics established by the American
National Standards Institute.
2. For purposes of this Article, measurements with sound
level meters shall be made when the wind velocity at
the time and place of such measurement is not more
than five miles per hour, or twenty-five (25) miles
per hour with a wind screen.
3. In all sound level measurements consideration shall be
given to the effect of the ambient noise level created
by the encompassing noise of the environment from all
sources at the time and place of such sound level
measurement.
C-8
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Section
8-46. Vehicles Weighing Less than 10,000 Lbs. - A noise measured or
registered as provided above from any vehicles weighing less than 10,000
Ibs. in excess of 80 decibels in the "A" weighing scale in intensity
shall be and is hereby declared to be excessive and unusually loud and
unlawful.
C-9
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FROM LAKEWOOD, COLORADO MUNICIPAL CODE
Section 10.57.080 MUFFLERS-PREVENTION OF NOISE. (1) It shall be un-
1awful for any person to operate^ or for the owner to cause or knowingly
permit the operation of any vehicle or combination of vehicles, within
this municipality, which is not equipped with an adequate muffler in
constant operation and properly maintained to prevent any unnecessary
noise, and no such muffler or exhaust system shall be modified or used
with a cutoff, bypass or similar device. No person shall modify the ex-
haust system of a motor vehicle in a manner which will amplify or increase
the noise emitted by the motor of such vehicle above that emitted by a
muffler of the type originally installed on the vehicle.
(2) For the purposes of this section, the definitions contained in
Section 9.52.030 of the Lakewood Municipal Code shall be applicable.
Section 10.60.160 MOTOR VEHICLE NOISE. (1) It shall be unlawful for any
peTson to drive or move or for the owner to cause or knowingly permit
to be driven or moved, within this municipality, any motor vehicle
which emits a noise sound pressure level in excess of the dB(A) esta-
blished by subparagraphs (2) and (3) of this section. Noise from a
motor vehicle within the public right-of-way shall be measured at a
distance at least twenty-five feet from the near side of the nearest
traffic lane being monitored and at a height of at least four feet
above the immediate surrounding surface on a sound level .meter of
standard design and operated on the "A" weighting scale. Noise from
a motor vehicle which is located other than within the public
right-of-way shall be measured at a distance at least twenty-five
feet from said motor vehicle and at a height of at least four.feet .
above the immediate surrounding surface on a sound level meter of
type 2 or better, as specified in the American National Standards
Institute Publication SI.4-1971, or successor publications, and
operated on the "A" weighting network.
(2) Motor vehicles weighing less than 10,000 pounds, manufac-
turer's gross vehicle weight (GVW). Any motor vehicle with a weight
of less than 10,000 pounds, manufacturer's gross vehicle weight (GVW),
or any combination of motor vehicles towed by such motor vehicle shall
not emit a noise sound pressure level in excess of 80 decibels in the
"A" weighting network dB(A).
(3) Motor vehicles weighing 10,000 pounds or more,
(4) Subparagraphs (2) and (3) of this section shall apply only
to vehicles traveling on streets with a posted speed limit of forty-
five (45) miles per hour or less.
C-10
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APPENDIX D
MOTORCYCLE NOISE REDUCTION COSTS -
SPECIFIC EXAMPLES
Motorcycle
Category
CHP-Type
Noise Level
Change
Modifications
Production
Cost
Increase
> 200cc
Highway (A)
From 86 to 84 dBA
Smaller intake silencer
apertures
4 mufflers instead of 2
$15.00
+ 15lb
>200cc
Highway (B)
From 84 to 80 dBA
Increase intake baffling
and absorption
Increase exhaust baffling
Interior mechanical
changes
$40.00
>200cc
Highway (A)
From 84 to 78 dBA
Installation of large truck
intake silencer on
passenger seat
Wrap engine and exhaust
in heavy asbestos
Supplemental exhaust
mufflers
Severe
Engine
Cooling
Problems
>200cc
Highway (B)
From 85 to 80 dBA
Increase intake silencer size
Frame change
Water cooling
Large double wall mufflers
Damped double engine case
covers
$87.00
"Very
Difficult"
D-l
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Motorcycle
Category
CHP-Type
Noise Level
Change
Modifications
Production
Cost
Increase
> 200cc
Highway (B)
From 85 to 80 dBA
Increase intake silencer size
Larger double walled
mufflers
Frame change
Improved gear tooth finish
Damped double engine
case covers
$51.00
"Very
Difficult"
>200cc
Highway (B)
From 85.5 to 80 dBA
Increase intake silencer size
Larger double walled
mufflers
Damped double engine
case covers
Improved gear tooth finish
$31.00
"Difficult"
>200cc
Dual
Purpose (B)
From 84 to 80 dBA
Increase intake silencer size
Larger double walled
muffler
Frame change
Damped double engine
case covers
Improved gear tooth finish
$38.00
"Very
Difficult"
>200cc
Highway (A)
From 85 to 80 dBA
Increase intake silencer size
Increase exhaust system size
Interior mechanical
treatments
Reliability
Unproven
Performance
Reduced
5% - 15%
NOTES: See following page.
D-2
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NOTES:
A. Prototype existing machines.
B. Projected ability and costs for a specific model. Duplicated values for
several models are not repeated. These modifications may not be possible
by 1975.
C. This table does not present complete performance or quality degradation
descriptions.
D. It is unlikely that a practical prototype has been constructed yet which
emits a noise level during the CHP test of 75 dBA or less. Manufacturers
claim that lead time of up to 5 years after complete 80 dBA levels are
achieved will be required to produce 75 dBA machines.
D-3
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APPENDIX E
NOISE REDUCTION OF MOTORCYCLES CURRENTLY IN USE
The prospect of quieting vehicles already produced and in use is an essential
consideration in the reduction of transportation vehicle noise impact. In the case of
motorcycles/ requirement of such activity appears highly impractical. Development
of retrofit packages consisting of intake and exhaust system replacements or modifi-
cations for many of the over 4 million motorcycles registered in the United States
would be quite difficult forthe multitude of existing models. In California/ for
example, it is reported that one motorcycle in 12 exceeds state noise regulations.*
Beyond this/ mechanical noises in these old machines may have increased beyond
intake and exhaust levels obtained through retrofit parts, constituting a limit for
potential improvement (excluding possibility of the still unproven shielding concept).
Cost of parts and installation labor would average near $40 a significant percentage
of a used machine's value. More important, the requirement for retrofitting in no way
assures such modifications will be properly effected and maintained by the vehicle
owners. Many motorcycles become to their owners unique expressions of individuality,
and thus the machines tend to become modified to personal taste. Unfortunately, a
common constituent of such taste is loud noise. Hence, over 80 percent of ail excessive
noise violations issued by the California Highway Patrol to motorcyclists are due to
exhaust system modifications made by the owner which cause the machine to exceed
legal noise requirements. It becomes apparent that regulations specifying additional
retrofit parts would find less compliance than existing noise regulations. Considering
these facts, and the short turnover period of the motorcycle population (6 to 10 years
see Chapter 4), the most practical and effective approach to reduction of noise impact
Letter from California State Attorney General's office to "Motorcycle Owners,
Riders and Enthusiasts"(M.O.R.E.)/ October 19, 1973.
E-l
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from motorcycles is vigilant enforcement of existing laws while new vehicle improve-
ments take effect through attrition and replacement. The requirement of solid unit
or all welded exhaust systems, especially for four-cycle machines which typically have
low internal exhaust cleaning requirements, would assist in limiting future modifications,
E-2
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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
550/9-74-001-A
I. Title and Subtitle.-
Control of Motorcycle Noise, Volume 1
Technology and Cost Information
'. Author(s)
Steven R. Skale, Ben H. Sharp
Performing Organization Name ami Address
Wyle Laboratories
'). Sponsoring Organisation Name and Address
Environmental Protection Agency
Office of.Noise Abatement and Control
Crystal Mall #2, 1921 Jefferson Davis Highway
.Arlington, Virginia 2O46O nxgnway
'. Supplementary Notes
3. Recipient's Accession No.
5. Report Date
June 1974
6.
8. Performing Organization Rept.
No.
10. Project/Task/Work Unit No.
11. Contract/Grant No.
68-01-1537
13. Type of Report & Period
Covered
Final (Vol. 1)
14.
16. Abstracts
This document contains information useful for the development of
noise emission standards for motorcycles. Topics covered include
information on motorcycle construction, noise characteristics of
models currently on the market, and noise reduction techniques and
costs necessary to achieve specified noise levels.
17. Key Words and Document Analysis. 17o. Descriptors
Motorcycle noise
Motorcycle noise control
Motor vehicle noise
Motor vehicle noise control
Cost of Noise reduction
17b. Identifiers/Open-Ended Terms
17c. COSATI Fie Id/Group
8. Availability Statcmi-nt
Limited supply available at ONAC, Arlington
Virginia 20460
Available at NTIS
19.. Security Class (This
, Report) ]{
UNCLASSIFIED
20. Security Class (This
Page X
UNCLASSIFIED
21. No. oi riic-.-
22. Price
FORM NTIS-35 (10-70)
USCOMM-DC *.::;"
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