905-R-80-117
NOISE LEGISLATION
TRENDS AND IMPLICATIONS
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TABLE OF CONTENTS
PAGE NO.
I NOISE LEGISLATION: TRENDS AND IMPLICATIONS
INTRODUCTION I - 1
LEGISLATION TO REDUCE INDUSTRIAL HEARING LOSS I - 1
LEGISLATION TO REDUCE ANNOYANCE I - 3
II SOME FUNDAMENTALS OF SOUND AND ACOUSTIC TERMINOLOGY
INTRODUCTION II - 1
CHARACTERISTICS OF SOUND II - 1
ACOUSTIC TERMINOLOGY II - 3
DECIBEL II - 3
SOUND PRESSURE LEVEL II - 4
COMBINATION OF SOUNDS II - 6
SOUND POWER LEVEL II - 9
FREQUENCY ANALYSIS 11-11
MASKING II - 14
AMBIENT NOISE II - 14
CLASSES OF SOUNDS 11-15
III CRITERIA FOR RATING SOUNDS
INTRODUCTION III - 1
RESPONSE CHARACTERISTICS OF THE HUMAN EAR III - 2
SINGLE-NUMBER RATINGS FOR NOISE III - 4
CALCULATED LOUDNESS III - 6
PERCEIVED NOISE LEVEL (PNL) III - 7
THE "EFFECTIVE" PERCEIVED NOISE LEVEL (EPNL) II! - 8
NOISE AND NUMBER INDEX (NNI) III - 9
SPEECH INTERFERENCE LEVEL (SIL) III - 9
NOISE RATING NUMBER (N) III - 10
NOISE CRITERION NUMBER (NC) III - 11
SUMMARY III - 13
IV THE CHARACTER OF URBAN NOISE
INTRODUCTION IV - 1
FACTORS AFFECTING NOISE LIMITS IV - 6
PRESENT LEVELS OF AMBIENT NOISE AND DISCRETE NOISE SOURCES IV - 10
PROPOSED LEVELS FOR AMBIENT AND DISCRETE NOISE SOURCES IV - 13
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LIST OF FIGURES
FIGURE
2-2.
2-1.
2-3.
2-4.
2-5.
TYPICAL SOUND SOURCE VIBRATIONS
SOME COMMONLY ENCOUNTERED NOISE LEVELS
TYPICAL POWER LEVELS FOR VARIOUS ACOUSTIC SOURCES
TYPICAL OCTAVE BAND FILTER CHARACTERISTICS
FREQUENCY SPECTRA FOR REPRESENTATIVE SOUNDS
3-1. EQUAL LOUDNESS CONTOURS FOR PURE TONES
3-2. EQUAL LOUDNESS CONTOURS FOR RELATIVELY NARROW BANDS
OF RANDOM NOISE
3-3. INTERNATIONAL STANDARD A, B, AND C WEIGHTING CURVES
FOR SOUND LEVEL METERS
3-4. FREQUENCY SPECTRA FOR IDENTICAL OVERALL SOUND LEVELS
3-5. EQUAL LOUDNESS CONTOURS
3-6. EQUAL NOISINESS CONTOURS
3-7. SPEECH INTERFERENCE EFFECTS OF NOISE
3-8. NOISE RATING NUMBER CURVES AND CRITERIA
3-9. NOISE CRITERION CURVES
4-1. MANUFACTURER'S SALE OF SELECTED PRODUCTS
4-2. MOTOR VEHICLE REGISTRATION TRENDS IN THE UNITED STATES
4-3. TOTAL AIRCRAFT OPERATIONS AT AIRPORTS HAVING FAA
TRAFFIC CONTROL SERVICE
4-4. CALCULATED AMBIENT NOISE LEVELS FOR THREE DIFFERENT
POPULATION DENSITIES
4-5. SUSCEPTIBILITY OF ADULTS TO NOISE
.4-6. COMPARATIVE JUDGEMENTS OF DIFFERENT NOISES
4-7. SUBJECTIVE EVALUATIONS OF TRANSPORTATION NOISE IN
COMMUNITIES
4-8. REPRESENTATIVE AMBIENT NOISE LEVELS
4-9. TYPICAL LEVELS OF OUTDOOR NOISE PRODUCED BY TRANS-
PORTATION VEHICLES
PAGE NO.
II - 2a
II - 8
II - 10
II - 12a
II - 16a
III - 2a
III - 2a
III - 4a
III - 6a
III - 6b
III - 8a
III - lOa
III - lOb
III - lla
IV - 2
IV - 3
IV - 4
IV - 5
IV - 7
IV - 8
IV - 9
IV - 11
IV - 12
H
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•I
TABLE
2-1
2-2
3-1
3-2
LIST OF TABLES
ACOUSTIC ENERGY VS. SPL
CHANGE IN SPL FROM COMBINATION OF TWO SOURCES
PAGE NO.
II - 7
II - 15
REPRESENTATIVE VALUES OF LOUDNESS LEVEL AND LOUDNESS III - 4a
REPRESENTATIVE NOISE CRITERIA (NC) VALUES FOR DIFFERENT
SPACES III - 12
4-2a SOURCES OF RESIDENTIAL NOISE ANNOYANCE SOCIAL SURVEY
RESULTS IV - lOa
4-1 ANNOYANCE LEVEL ORIENTATIONS IV - 11
4-2 NOISE LEVELS OF TYPICAL SOURCES IN URBAN AREAS IV - 12
4-3 RECOMMENDED COMMUNITY NOISE CRITERIA IV - 14
4-4 RECOMMENDED TRANSPORTATION NOISE CRITERIA FOR LOS
ANGELES IV - 14
4-5 RECOMMENDED OUTDOOR NOISE LEVELS - SWITZERLAND IV - 15
4-6 TOLERATED CONSTRUCTION NOISE LEVELS AT NEAREST WINDOW -
ENGLAND IV - 15
4-7 RECOMMENDED INDOOR NOISE LEVELS - ENGLAND LEVELS
SHOWN SHOULD NOT BE EXCEEDED MORE THAN 10% OF THE TIME IV - 15
, 1
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&>.
7
Oa
1
2
4
4
5
NOISE LEGISLATION: TRENDS AND IMPLICATIONS
INTRODUCTION
Noise has recently been labelled the 'fourth pollutant' and defined
by some as the 'unwanted sound' that pervades our work environments and
the privacy of our homes. This concern for noise and its effects has re-
sulted due to our nation's increasing population density, the increasing
use of mechanized conveniences, the influx and growing use of mass trans-
portation systems, and the public's awareness that noise not only 'annoys'
and can increase everyday tensions and anxieties, but at certain levels
can cause permanent hearing loss.
In order to curb the 'noise problem' legislators and public officials
began applying legal controls to noisy activities and machines. Noise
legislation is usually written to accomplish one or both of two
objectives: to minimize loss of hearing, primarily among industrial
workers; and/or to reduce irritating or annoying noises to "acceptable"
levels.
LEGISLATION TO REDUCE INDUSTRIAL HEARING LOSS
The Federal Council for Science and Technology has stated that at
least a million workers now living suffer from some degree of deafness.
Estimates are that another 6 to 16 million are exposed to noise levels
which may cause eventual hearing loss.
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Examples of legislation designed to reduce occupational deafness are
the Walsh-Healey Act Amendments (1969); provisions of the Occupational
Health and Safety Act of 1970*; and a number of state laws, most of them
similar or indentical to federal legislation. Noise exposure limits
specified are based on studies of thousands of workers over the past
twenty years.
All feasible administrative and engineering controls must be utilized
to reduce noise levels to permissible limits; only as a last resort
is ear protection to be substituted for noise reduction.
Audiometic testing is an important part of the hearing conservation
programs anticipated by federal regulations. Testing of new employees
protects the employer from possible compensation for hearing loss
incurred prior to employment. Periodic testing thereafter indicates
the amount and duration of temporary threshold shift in hearing produced
by noise exposure. Even if permissible noise exposures are not exceeded,
some employees may experience eventual hearing loss (for which the
employer is liable) because they are more "noise sensitive" than others.
Although enforcement of the Walsh-Healey regulations has been relatively
minor to date, the future will surely bring increasing application of
noise exposure limits to a wider and wider range of industrial activity.
*This act applies the Walsh-Healey noise exposure limits to all businesses
in interstate commerce.
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I - 3
In turn, equipment manufacturers will experience increasing pressure not
only to design quieter machines but also to include meaningful acoustic
performance data in equipment specifications. This data will serve a-
a basis for predicting noise levels within and around new plants
during initial design stages. As a result, the acoustic environments
will be "designed-in" rather than "added-on" as an afterthought.
LEGISLATION TO REDUCE ANNOYANCE
A second major objective of noise legislation is to reduce irritating
or annoying sounds (primarily in urban areas) to "acceptable" levels.
Restrictions are usually in the form of city, county, or state
ordinances and regulations in several categories:
1. Noise in residential areas, including sources within such areas
(air conditioning systems, automobiles, construction equipment, etc.)
as well as noise produced at residential area boundaries from external
sources.
2. Noise in commercial-industrial areas, primarily at property lines
between adjoining businesses and at boundaries between areas zoned for
different uses.
3. Noise from aircrafts and airports, including landing, takeoff, and
taxiing. The Federal Aviation Administration has specified permissible
noise levels at or near airport facilities for individual aircraft,
while local regulations attempt to control number of flights and use
of runways.
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4. Noise from motor vehicles, including certification of new models.
California and Connecticut are examples of two states with legislation
specifically designed to control freeway noise.
5. Noise in buildings, especially between adjoining units in multi-
family dwellings. Materials or performance levels are specified for
party walls, floor-ceiling constructions, and other noise paths.
Drafting and enforcing fair, effective legislation to control irritating
or annoying noises is a difficult task. The provisions have generally
taken the form of nuisance ordinances which restrict or prohibit certain
activities or the use of equipment such that they do not create a
'noise nuisance1 to the surrounding area. The nuisance ordinance has
been effective in many instances, but the subjective analsis inherent
in its application has resulted in a questioning of what is unnecessary,
unreasonable, or acceptable.
A relative newcomer to noise control legislation has been the performance
code. This type of ordinance incorporates maximum noise levels in
decibels that are permissible at a given location. The objective
criteria of performance codes have given relief from the subjective con-
notations of the noise nuisance ordinance. However, determining noise leve'
that are realistic, equitable, acceptable, and enforceable for a
given community needs special and careful consideration. In some
instances, noise levels that were specified did not relate to the
environment or location to which they applied. The noise levels pre-
scribed were, in effect, unrealistic and in some cases physically im-
possible to achieve in an urban community.
1
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In summary, the control of urban noise is complicated by two factors:
1. What are "acceptable" noise levels? Susceptibility to annoyances
varies between individuals and their activities. If the permissible
levels are too liberal, the legislation fails to accomplish its in-
tended purpose. If the permissible levels are too restrictive, the
legislation is unenforceable and is usually employed as a threat only
in extreme cases.
2. What criteria should be employed to evaluate given noises, and how
should measurements be obtained? The A-weighted sound pressure level is
easiest to measure, but is not a uniformly good indicator of annoyance
for all classes of noise. Octave band criteria may be more accurate
for assessing annoyance, but are more time-consuming, costly, and
difficult to employ.
Within the next two decades, effective regulation and control of
urban noise will become commonplace in the United States. Action is
now proceeding in several areas to accomplish this objective:
1. Trade associations and professional societies are developing stand-
ardized methods and criteria for product noise certification.
2. Land-use planning, the key to containment of objectionable noise
within specified boundaries, is growing rapidly.
3. Experience with noise regulation throughout the world is being
compiled, analyzed, and disseminated through conferences, reports, and
technical journals.
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I -6
A primary purpose of the text which follows is to provide public
officials responsible for drafting, enacting, and enforcing noise
legislation with information about the characteristics of noise,
methods of measurement and evaluation, and current trends in noise
legislation. However, urban noise control goes beyond implementing
engineering noise control knowledge into the legal format of a code.
Enforcement procedures, land use and urban planning concepts and
public attitudes are all part of the total abatement scheme.
These areas are investigated in some detail.
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II - 1
II SOME FUNDAMENTALS OF SOUND AND ACOUSTIC TERMINOLOGY
INTRODUCTION
In order to have a better understanding of the characteristics of sound
and the meaning of acoustical terms, a foundation of basic principles,
definitions, and techniques is essential. However, when one" enters in-
to a discussion of the characteristics and properties of sound, it is
possible for the discussion to quickly become comprehensive and techni-
cal. Such an approach in this manual would be incontrast to its pur-
pose. Therefore, only the basic fundamentals will be presented, some-
times without elaboration but with appropriate references listed, in
the interests of simplicity and ease of understanding.
CHARACTERISTICS OF SOUND
Basically, the sound we experience in our everyday lives is a result of !
objects or bodies being set into vibration. More specifically, a vibrat- i
ing surface imparts its motion to the medium that surrounds it, in our
case air, and a minute variation in atmospheric pressure called 'sound
pressure1 results. The word "minute" is obviously a relative term and ;
it is of interest to investigate just how small the sound pressure quanti-
ty really is. '
!
i
In order to adequately describe the magnitude of the sound pressure, a '
measuring unit is needed. Our intuition might suggest the familiar pounds
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II - 2
per square inch (psi); however, the terms microbar (ubar) and Newtons
f\
per square meter (N/m ) have become accepted. One microbar is approxi-
mately one-millionth of normal atmospheric pressure, and one Newton per
square meter equals ten microbars. Using the microbar as our unit, a
barely audible whisper and a jet engine at close range would correspond
to .0002 and 200 microbars respectively. Clearly, the sound pressures
we encounter are extremely small, yet span a very wide range of valves
Figure 2-1).
Vibrations of the sound source may be "harmonic", "periodic", or "ran-
dom" (Figure 2-2). The medium surrounding the source moves in a similar
fashion, and the resulting disturbance propagates outward from the source.
If the distrubance is harmonic in nature, the number of pressure fluctua-
tions occurring each second is termed the "frequency" of the disturbance.
The units applied to frequency are cycles per second (cps), or hertz
(Hz); both are equivalent.
Since air can be compressed and rarefied, a "wave motion" occurs and a
"sound wave" tends to propagate outward and away from its source. How-
ever, as the wave propagates its front spreads out (often in a spherical
manner). Thus the sound energy passing through each unit of area be-
comes less and less, and the sound pressure decreases with distance.
The decrease in volume of a sound source with increasing distance is a
common occurence we have all experienced.
Perhaps a more easily pictured example of these characteristics is the
following 'pond analogy'. Imagine if you will a pebble thrown into a
quiet pond. The resulting ripple propagates outward from its point
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II - 2a
2
in
93
s_
§
to
time
harmonic (single frequency)
in
in
§
to
(A
I/I
0)
s.
a.
•o
.time
periodic (non-harmonic)
time
\i
random
Figure 2-2. lypical Sound Source Vibrations
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II - 3
of origin, and continues outward in the absence of reflecting surfaces
(such as the shore). As the ripple continues outward, it is dissipated
and eventually fades away.
Thus, the minute pressure disturbances we call sound waves have four
characteristics:
1) The magnitude of the sound pressure (normal range: 0.01 - 100
Microbars)
2) The frequency of the sound wave (normal range: 50 - 10000 Hz)
3) The sound wave propagates away from its point of origin
4) The sound pressure of the wave almost always decreases with
increasing distance from its source.
ACOUSTIC TERMINOLOGY
DECIBEL
j One of the more difficult quantities to define is the decibel. What ex-
I actly is it? How is it used and applied?
The decibel (dB) is used universally to describe the level of sound. It
is a dimensionless unit which expresses the ratio between two values
(i.e. a measured quantity and a reference quantity) logarithmically. The
decfbel has been applied to the acoustics field for several reasons:
1) If one used the almost unbearable roar of a jet engine at close
range and the barely audible whisper as-the dynamic range of the
human ear, the corresponding sound pressures have a ratio of
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II - 4
1,000,000 to 1. With this tremendous span, it is Impossible to
manipulate or to have any feeling for the physical quantities
involved. Likewise, it would be almost impossible to manu-
facture an instrument with one million linear scale divisions.
By employing the logarithmic feature inherent in the decibel's
definition, this tremendous pressure response is resolved into
a condensed and more meaningful scale that ranges from 0 dB
(by definition) to approximately 120 dB (Figure 2-1).
2) The ear tends to respond in a logarithmic manner. The human audi-
tory response to a given increase in sound pressure is approximate-
ly proportional to the ratio of the increase in sound pressure to
the sound pressure already present. To give an example: the ear
is capable of detecting a very small increase in sound pressure when
the ambient level is low; with high ambient level, a much larger
increase is necessary to give the ear the same sensation.
( 1 )
3) Under ideal laboratory conditions, the average ear can detect a
minimum sound pressure level change of IdB. In everyday encoun-
ters, a 3 dB change in sound pressure level is just perceptable,
whereas a 5 dB change is clearly noticeable. ( 2 )
SOUND PRESSURE LEVEL
When sound pressure is expressed in decibel form (Sound Pressure Level, SPL)
we are measuring it with respect to a reference. The reference that has
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been agreed upon is the minimum audible sound pressure for humans, or
.0002 microbar. The sound pressure level (measured in decibels) is de-
fined mathematically as follows:
Sound Pressure Level (dB) : 20
pref
Where: P - Sound pressure, microbars
= The minimum audible sound pressure
for humans, .0002 microbar.
As will be shown later, instruments which measure sound pressure level
are currently available and in wide use.
An important point to illustrate is that the sound pressure level of a
source will, in general, vary with a change of the local surroundings.
A typical example would be parking a car in a garage. The sound level
we hear inside the garage is different from that which we hear while
parked on the driveway. Another example is the household vacuum clean-
er. From experience we know that this appliance appears to produce dif-
ferent levels of sound when used in a carpeted living room and in the
tiled recreation room.
To obtain a better appreciation for the sound pressure levels of typical
noise sources, refer to Figure 2-1. These noise levels can be considered
to be'representative', although it must be remembered that sound pressure
level readings are dependent upon local surroundings and distance from
the noise source. The sound pressure level readings given are those that
would be typically present in the environments specified.
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COMBINATION OF SOUNDS [
\
i
The total sound at a given location is usually a combination of sounds
from many different sources. For example, the listener may be exposed
simultaneously to the sounds from a barking dog, a power mower, a garbag
disposal, and a ringing telephone. What is the total sound that the lis
tener hears? For most types of sounds, the total is obtained by summing
the acoustic energie's, produced by each source, that arrive at the lis-
i
tener's ear in a given time interval. This combination yields an "effec- '
tive sound pressure" that can be easily converted to decibels SPL. In !
I
fact a "sound level meter" is an instrument that performs this operation
automatically and displays the result (in SPL) on a meter.
Let us now consider what happens when two sources produce identical sour
^
pressure levels at the location of a sound level meter. This means that
i
the same amount of acoustic energy is arriving per unit time from each
source. If the SPL from either one of the sources is, say, 80 dB, what I
does the meter read when both sources are operating? Because SPL value:'
i
are logarithmic, the answer is not 160 dB. Combining the two sounds on
an energy basis shows that the total SPL is 83 dB.
We have just seen that, for most types of sounds, a 3 dB change is bare
1
noticeable; yet this change represents a halving or doubling of the acc^
!
energy. Table2-l shows the reduction in acoustic energy radiated from •
i
source that is required to obtain a specified decrease in sound pressu:1
level.
L-
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Table 2-1
Acoustic Energy vs. SPL
Change in SPL Percent decrease in
(dB) acoustic energy
0 0
-1 20
-2 37
-3 50
-4 60
. -5 68
-6 75
-7 80
-8 84
-9 87
-10 90
Note that significant reductions in acoustic energy are needed to obtain
even modest decreases in SPL.
For comparison consider a sound source that radiates into an area that is
C ;
, relatively free from buildings or other large obstructions. Under these
circumstances, the SPL decreases about 6 dB for each doubling of distance
from the source.
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Sound pressure
In bar
1
mbar
100
(tbar
10
pbar
1
pbar
0.1
^bar
0.01
/ibar
0.001
jubar
0.0002
Sound level In dB
140
. 134
130
120
• 114
110 „
100 .
" 94
90 .
60 .
• 74
70 .
60 .
54
50 .
40 .
34
30 .
20 .
14
10 T
Environmental conditions
Threshold of pain
Pneumatic chipper
Loud automobile horn (dlst. 1
m)
Inside subway train (New York)
Inside motor bus
Average traffic on street comer
Conversational speech
Typical business office
Living room, suburban area
Library
Bedroom at night
Broadcasting studio
I Threshold of hearing
^bar J 0 -j-
Figure 2-1. Some Commonly Encountered
Noise Levels (3)
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SOUND POWER LEVEL <
i
Since the sound pressure level is a function of environment, a character-
istic of a sound source that is absolute and independent of its surround-
ings would be useful. One such characteristic is the "sound power" of a :
source. The sound power of a source (at specified operating conditions)
is a measure of the acoustic energy it produces per unit time, a fixed I
valve which is usually independent of source location. The measuring
1
unit that is applied is the acoustin watt. Like sound pressure, sound \
•*.
power has an overwhelming range of values. Typical values for the very
soft whisper and jet engine are .000,000,0001 and 100,000 watts, |
respectively. Again, the logarithmic character of thedecibel is advantageous.
When sound power is measured in decibels (Sound Power Level), a reference '
quantity is mandatory, as was the case with sound pressure. The universal ',
-12 - i
sound power reference level is 10 watts. The formal definition of
sound power level (measured in decibels) is as follows:
Sound Power Level (PWL) = 10 log-,,, W
' u Q , n
"ref do
Where: W = Sound power of the source in Watts
•I O
Wref: 10 Watts, reference level.
The sound power and corresponding sound power level of some typical noise
sources are shown in Figure 2-3.
If sound power is a non-variant with respect to source location, one might
ask: "Why do we measure the sound pressure level of a source instead of
the sound power level? There are at least two reasons for doing so:
1) Sound power level measurements require special test
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ii - ic
ACOUSTIC POWER
I»O*CR TOWER LEVEL
(W4TTSI (fttHC 10-'3 WATT)
>5 TOM MILLION
•.•00,000,01
195
SATUftM ROCKf T
70
60
50
40
30
20
10
00
JO
10
'0
0
0
0
•AM JET
TUISO-JET ENGINE WTM AFTERSURNE*
TunO-JET ENGINE, JOJJ.LB THRUST
4-PROPELLER AIP.LINER
TS^IECE 0»CHEST»A \ PEA« DMS LEVELS P
PIPE OOCAN J I/VSECONO MTEtV
SMALL AWCRAFT ENGINE
LAOGE CHIPPING HAMMER
PIANO -)
WPEAK RMS LEVELS IN
•tP TIIPA J 1/t.SECONO INTERVALS
•LMWC HAOIO
CENTRIFUGAL VENTHATMC FAN (11,000 CFMI
«' LOOM
AUTOONHKMW»»
VAHEAXIAL VENTILATING FAN (1900 CFM)
VOCC - SHOUTING (AVERAGE LONG-TIME ««)
VOICE - COHVEHATIONAL LEVEL
(AVCKAGE LONO-TIMC RMS)
30
VOCE . VERT (OPT IMISPCR
Figure 2-3 Typical Power Levels for
Various Acoustic Sources £4)
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II - 71
conditions and environments that often are not available
on location.
2) Sound power levels, at the current state of the art, can
not be obtained directly, but must be calculated from
sound pressure measurements.
The primary purpose of determining the sound power of a source is that
once this value is known, the sound pressure level can be estimated,
knowing the sound qualities of the proposed or actual surroundings. An
example might be wanting to know how much the sound pressure level will
increase if an air-conditioner is added to an already noisy office.
In summary, then, two quantities have been described that are measured
in decibels: sound pressure level (SPL), and sound power level (PWL).
When either of these quantities is used, the reference value is understood.
In all other cases, the reference value must be stated if the decibel value
is to have meaning.
FREQUENCY ANALYSIS
As was shown earlier, one of the important chanacteristics of sound is
its "frequency" or "frequency content". The spectrum (or range) of fre-
quencies of interest to us is the human auditory range. This spectrum
typically extends from approximately 20 to 20,000 Hz but for ""ise per-
sons the range is 40 - 13,000 Hz, and decreases with age. This spec-
trum can be thought of as a contiguous band of frequencies each 1 cycle
wide.
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The simplest of all sounds are those composed of a single frequency.
These sounds are called 'pure tones'. However, the sounds to which
we are usually exposed are much more complex than pure tones. These
sounds are composed of many frequencies, each occurring simultaneously
at its own sound pressure level. The striking of a chord on the piano
or guitar are examples. Often, the sound does not appear to have any
'tonal quality1. Examples of this category would be ventilating duct
noise or the sound produced by escaping steam. The important point
to remember is that our world of sound is composed of many frequencies,
each at a given sound pressure level, occurring simultaneously and
generally changing with time. In order to investigate the frequency
content of a sound, a procedure known as a 'frequency analysis' can be
performed. This procedure enables us to obtain a sound pressure level
versus frequency "picture" or "spectrum" of a sound source.
When a frequency analysis is performed, the auditory spectrum is
electronically divided into adjoining frequency bands and an average
SPL is computed for each band, called "band level". The basic scheme
employs "octave bands" to divide the spectrum into ten continuous
and adjoining frequency bands (Figur 2-4), The upper frequency of
each band is twice the lower frequency, and the middle (or "center")
frequency of each band is twice and one-half, respectively, of the
adjoining frequency bands. The precision instrument which divides
the spectrum and measures the SPL for each octave band is known
as an "octave band analyzer".
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ft
10 M 100 >00 900 1000 200O MOO IO.OOO tO.OOO
Figure 2-4. Typical Octave Band
Filter Characteristics (4)
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Instead of naming the upper and lower frequencies of each band,
4 it has become standard practice to specify a 'center frequency'
within each band. The standardized octave band center frequencies
in use today (the "Preferred Octave Bands") are as follows:
31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000, 16,000 Hz. An
older series of octave bands is sometimes encountered in noise
standards and codes. This older series is comprised of the
following frequency bands: 37.5-75, 75-150, 150-300, 300-600,
600-1200, 1200-2400, 2400-4800, and 4800-9600 Hz. It is
importanct to note that the band levels for these two series
of octave bands cannot be interchanged. In other words, the
75-150 Hz band level can not be substituted for the preferred
63 Hz band level. For detailed procedures concerning manipul-
ation and conversion of the older series, see Appendix A.
In summary then, a frequency analysis defines two characteristics
of a sound source:
1) The frequency distribution of the sound
2) The amount of sound energy concentrated in the various
frequency bands.
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II -]<
MASKING
Masking is the "covering up" of one sound by another. Speci-
fically, masking also makes comprehension of speech difficult
and obsecures waring signals. The masking process is most
effective when the frequency composition of the sound source
is similar to that of the masking sound.
AMBIENT NOISE
Ambient noise is defined as 'the all encompassing noise associated
with a given environment, being usually a composite of sounds,
from many sources far and near'. (12) When noise emitted by a
source is measured, we may justifiably question wheteher the
resulting decibel value is truly due to the source alone or is
possibly the source plus ambient noise. A simple rule-of-thumb
has become accepted and is quite accurate: "If the sound pressure
level in all octave bands is 10 dB SPL or greater than the am-
bient level with the source operating, the contribution- due to
the ambient noise is negligible." The decibel values thus obtained
are essentially those due to the source. This same rule applies
to weighted sound level readings as well. Table 2-2 shows the
effect on overall SPL when two sources are combined.
-------
~ 11-15
Table 2-2
Change in SPL from Combination of Two Sources
Difference in source Increase in SPL due to
levels. SPL addition of weaker source
0 \3
1 + 2.5
2 + 2.2
3 + 1.8
4 + 1.4
5 ' +1.2
6 +1.0
7 + 0.8
8 + 0.6
9 + 0.5
10 , + 0.4
CLASSES OF SOUNDS
The types of sounds that people are exposed to in an average
working day are indeed many and varied. Thus, in an attempt to
differentiate or classify these sounds, similar sounds have
been 'typed' and are generally grouped together under the following
categories which describe their character. Typical octave band
frequency analyses for the first three categories are shown in
Figure 2-5.
-------
II - 16
Broad Band - Continuous Noises
As the name inplies, Broad Band noises have a frequency
spectrum which encompasses a large portion of the auditory
range. The added condition of being continous implies that
the noise is not intermittent or transient, but occurs
over a long period of time. Some common examples of these
noises are:
1} community background noise
2) ventilating duct noise
3) air-conditioned noise
Narrow Band - Continuous Noises |
Narrow Band noise sources generally have a frequency spectrum
of only a few hundred cycles in width. This spectrum of
frequencies can be located anywhere in the auditory range;
the important fact being that the width of the spectrum is
considerably smaller than Broad Band sources. Examples are:
1) transformer noise
2) circular saw noise
Pure Tones
Pure tones are sounds that consist of a single frequency.
Examples are the striking of a single piano notl, or the
*Providing that only the fundamental (lowest ) frequency of the
note is considered.
-------
II - 16a
O.
C/1
•O
c
IO
2
u
o
•a
c
£
$
<0
+J
u
O
31.5 63 125 250 500 1000 2000 4000 8000
frequency, Hz
31.5 63 125 250 500 1000 2000 4000 8000
frequency Hz
31.5 63 125 250 500 1000 2000 4000 8000
frequency Hz
Figure 2-5. Frequency Spectra for Representative Sounds
-------
II - 17
, . ?
sound produced by a tuning fork. Pure tones often do not I
I
occur by themselves, but can be thought of as being 'super- 1
*
imposed1 upon broad or narrow band noise. When this occurs, •
i
:
the noise is said to have a 'pure tone component'. Noises
with pure tone components are particularly annoying. Often- {
I times these noises are below acceptable levels for broad band
• noise, but are still considered disturbing or unacceptable .
Examples of this last category are:
1) noise from an unbalanced fan or pump impeller. ,
I 2) turbine or gear noise.
i
i Impulsive (Impact) Noises
I
i
i Impulsive noises are those which occur over a very short time
period (i.e. 5 to 200 microseconds). These noises are often
1 thought to be loud and startling; however, this need not always
be the case. Examples are:
1) a sonic boom
2) a gun shot
3) a barking dog
4) a single bounce of a golf ball on the floor
5) the dropping of a pencil
!
1
Repeated Impulsive (Impact) Noises
These noises exhibit the same characteristics as impulsive
-------
II -1?
noises but are repeated (often rapidly) in time. Examples
are:
1) typewriter noise
2) pneumatic hammer or pavement breaker noise
3) machine-gun noise
Transient or Intermittent Noises
Transient noises occupy the realm between the continuous
and impulsive classifications. Transient noises are usually
of short duration but not as short as the impulsive category.
Transient noises may be broad or narrow band and may or may
not have pure components. Examples are:
1) aircraft flyovers
2) the passing of a train or ambulance
-------
Ill - 1
III CRITERIA FOR RATING SOUNDS
INTRODUCTION
As was mentioned earlier, the only objective characteristics
of sound that our present day equipment can measure are the
sound pressure level and the frequency content. Thus the sub-
jective response of the public to various sounds and noise
sources must be correlated in some manner to these two quanti-
ities, in addition to the number of occurences within a given
period, and whether these sounds occur during the day or night.
Much work has been done in this area and although the optimum
method has yet to be contrived, numerous methods of approach have
become accepted and widely used. As will become evident in the
discussion which follows, it seems that there is no single mea~
suring method which accurately describes or has been found to
correlate well with the public's reaction to all sounds and noise
sources. Thus, several methods have been devised, each with its
own refinements and proposed area(s) of application. To the unin-
itiated it might appear that acousticians have devised noise
measuring methods that are too limited in application and have
lost sight of the ultimate goal. In reality, all of their efforts
have a common purpose: to produce reaiable measuring or rating
methods which correlate well with the subjective response of the
public to the various classes of urban noise.
-------
Ill - 2
All of the rating methods are based upon the level and frequency
content of the noise. Some also include effects from pure tones,
duration of the noise, number of occurrences, and time of day.
RESPONSExflJARACTERISTICS OF THE HUMAN EAR
Before delving into the various measuring methods it would be best
to investiage the response characteristics of the human ear.
The perception of the loudness of pure tones of different frequencies
was first investigated by Fletcher and Munson almost 40 years ago.
Basically, their procedure was to place an observer in a very quiet
room and subject him to a 1000 Hz reference pure tone. The sound
pressure level of another pure tone of a different frequency was then
adjusted until it was judged 'equally loud' by the observer. The
results of their research were a set of curves similar to those in
Figure 3-1. These contours have been verified and internationally
standardized and are called 'equal loudness level contours for pure
tones.'
Each contour is given a value in 'phons' which corresponds to the
sound pressure level in decibels of the 1000 Hz reference tone. These
contours illustrate that the response of the human ear is dependent
upon not only the frequency of a tone, but also the sound pressure
level. Two examples of the use of the contours are shown below.
-------
Ill - 2a
120
LOUDNESS
120 LEVEL (PHQNt
100
FREQUENCY IN CYCLES
IOOO 5OOO IQ,OOO
PER SECOND (Hi)
Figure 3-1. Equal Loudness Contours for Pure Tones (4)
140
100
SCO IOOO
FREQUENCY IN Hz
sooo
Figure 3-2, Equal Loudness Contours for Relatively
Narrow Bands of Random Noise (4)
-------
Ill - 3
1. An observer would nominally judge a 30 dB SPL, 125 Hz, pure tone
to be equally loud as a 20 dB SPL, 1000 Hz, pure tone. Thus the 30
dB tone has a 'loudness level1 of 20 ohons.
2. An observer would nominally judge an 80 dB SPL, 31.5 Hz pure tone
to be equally loud as a 50 dB SPL, 1000 Hz pure tone. The 80 dB tone
has a 'loudness level' of 50 phons.
It can be seen that the response of the human ear is complex and non-
linear. At lower sound pressure levels, the ear is not as responsive
to low frequencies as at higher frequencies. However, as the sound
pressure level increases, the response of the ear become flatter.
As was mentioned earlier, the sounds we experience rarely consist
solely of pure tones. To take this into account, equal loudness
level contours for narrow bands of noise have been developed and are
similar in appearance to those for pure tones. (Figure 3-2 ).
If the sounds we are exposed to are composed of pure tones or narrow
bands of noise, a phon value for these sounds can be obtained directly
from either Figures 3-1 or 3-2 . If the sounds are complex,(i.e.
broadband with or without pure tone components) an equivalent phon
value can be calculated from an octave band analysis of the noise.
Although the phon scale covers the large dynamic range of the ear, it
does not fit a subjective loudness scale. Doubling th« number of phons.
does not correspong to a subjective loudness increase of two. For loudness levels
-------
Ill - 4
of 40 phons and greater, an increase of 10 phons corresponds to a sub-
jective doubling of loudness. To obtain a quantity proportional to
"loudness", a scale has been defined in which the unit is called a 'sone'.
• This loudness scale (in sones) corresponds fairly closely to our subjec-
1 tive sensation of loudness. Using this scale we can say that a jet air-
craft at takeoff is approximately 50 times as loud as loud as normal
' conversation. Stating that jet aircraft generated 120 phons in contrast
| to 60 phons for ordinary conversation probably conveys less meaning. Table
3; 3-1 gives some typical loudness levels in phons and loudness in sones.
i
!
| SINGLE-NUMBER RATINGS FOR NOISE
I
The simplest noise measuring technique would be to measure the noise level
using a 'sound lever meter', SLM. This instrument includes a microphone,
an amplifier, an output meter, and frequency weighting networks. The
frequency weighting networks are referred to as the 'A1, 'B', or 'C1
scales.* The frequency characteristics of these scales have become
internationally standardized and are show in Figure 3-3.
As shown in the figure, the 'A1 scale attenuates those frequencies below
approximately 500 Hz. in other words, frequencies above 500 Hz are
weighed more heavily in an attempt to parallel the response characteristics
of the human ear. Careful comparison of the A weighing network and the
equal loudness level curves will reveal that the A weighting approximates
*0n some sound and level meters, a 'D' weighting network has been added
to provide an indication of "perceived noise decibels" (PNdB). See p.lli-7.
-------
Ill - 4a
Loudness
Ltvtl (phons)
140
120
100
80
60
40
90
3
Threshold of pain
Jet aircraft
Truck
Orator
Low conversation
Quiet room
Rustling of leaves
Hearing threshold
Loudness
(sones)
1024
256
64
16
4
1
Table 3-1. Representative Values of Loudness Level
and Loudness (6)
(RELATIVE SOUND PRESSURE LEVEL (dB)
S 6 8 ii 5 o S S
/
/A
/
^
y\
' B
/
/
/
f
/
^x
^
/_
— — —
\
^
V
S
20 50 100 200 500 1000 2000 5000 10.000 20.000
FREQUENCY
-------
" III - 5
an'lnverted' 40 phon contour. Likewise, the B weighting network ap-
proximates an inverted 70 phon contour. The C network is essentially
flat and approximates the response of the ear to intense sound
pressure levels.
When a sound is measured with a sound level meter, the weighting
network must always be stated. For example, if a measurement was
performed using the 'A1 scale, the results should be specified as
i
dB (A) or dBA. Noises can also be measured without using a weighting }
network. When this is done all frequencies are admitted unat- f*
tenuated to the sound level meter and what is termed an 'overall
SPL' results. When an overall reading is taken it can correctly
be described as follows: The noise was 50 dB SPL (overall); or
50 dB overall SPL; or 50 dB OSPL.
A similar situation occurs when we obtain octave band data. The
decibel values we obtain from each band are SPL's, since all
frequencies within each band are admitted unattenuated. Thus we
can conclude by saying that when a weighting network is employed,
the resulting decibel values are "sound levels' and the appropriate
weighting must be specified. When no weighting is employed, the
decibel values are either 'Overall SPL1 for sound level meters
or just sound pressure levels for octave band data.
Before we continue to other noise measuring methods, two important
points concerning 'Overall SPL1 and A, B, or C weighted sound
levels must be presented.
-------
Ill -6
!. His possible for two
identical
frequency
-
significantly
content of the sound
to
are
prov«e
«e additional
. order to be eva
luated.
noise sources to produce
^ dlfferent
overall sound
QSPL or
efre,Wcy
to the frequency
sound
°SPL
not'
• octave band data in
^^
The cauuuted 10udness -** " " „ steady, «ide band noise
for cmpl, sounds and Pr«r-^ ^ „ use;
wo ^d. of P""-« " CU^ ker procedur,
tte Steven, procedure and tne «* P
the curves for obtainin, the ,n -
the
„,
- sone v,ue for
The equivalent sone value
-------
III - 6a
Sound - prtuurt Iml U koxJ.
d6 n 0.0002 micrebw
5 8 S 3 8 I
4
U)
a
X
/]
"^~""
/
s
k,
^
\
X
"^^
OnriH 145 75 150 100 600 1,200 2,400 4,600
75 150 300 600 1,200 2,400 4,600 9,600
Frt0.ucncj bond, (Dl
63 125 250 500 IK 2K 4K 8K
FREQUENCY IN CYCLES PER SECOND
Figure 3-4. Frequency Spectra for Identical
Overall Sound Levels
-------
Ill - 6b
Sencs - Phons
S00_p130
400-
300-E
200-!
150-f
-100
100-:
80-T
70-:
60-
50-:
40- r
30-E-9"
,5JrW
io^r
---w
s- r
4 -MO
3- L
2-1-50
1 -i-40
0.5-»-30
woo •
FREQUENCY
* 10000 V,
Figure 3-5. Equal Loudness Contours (3)
-------
III - 7
Seq = (Z0.3Sn ) + 0.7
Where S
eq
max
= equivalent sone value
= octave band sone value
= maximum octave band sone value
The equivalent phon value can be obtained from the conversion
chart supplied with Figure 3-5.
One advantage of the calculated loudness method is that some people
tend to indentify more readily with the sone unit rather than the
decibel. They grasp the concept of one sound being twice or three
times as loud as another more easily than the decibel scale.
PERCEIVED NOISE LEVEL (PNL)
"Kryter has followed a procedure similar to that used for loudness,
but he asked the observer to compare noises on the basis of thetr
acceptability or their 'noisiness.' The judgements were found to be
similar to those for loudness, but enough difference was observed
to give a somewhat different rating for various sounds. On the basis
of these results, Kryter has set up a calculation procedure for
'perceived noise level.1 (11) In essence, then, the PNL concept accounts
for the "noisiness" or "intrusiveness" rather than the loudness.
The perceived noise level is registered in perceived noise decibels,
PNdB; it has found particular use in gaging response to aircraft noise.
-------
Ill - 8
The calculation procedure for PNdB is identical to that used for
calculating loudness, except that curves of constant 'noy1 values
are used (Figure 3-6), The effective noy value is given by
Nt = (£0.3Nn) + 0.7 N,
max
where N. = effective noy value
N = noy value corresponding to each octave band SPL
N_'- *:'* maximum octave band noy value
max -i
Ah equivalent PNdB value is obtained by using the conversion chart
provided in Figure 3-6. On some sound level meters, the 40
noy curve has been incorporated into an additional weighting
network (D weighting) to provide a direct approximation to PNL.
The proposed D weighting curve is shown in Figure 3-3.
THE"EFFECTIVE" PERCEIVED NOISE LEVEL (EPNL)
The "effective" perceived noise level (EPNL) is similar to the PNL
concept and is again applicable mainly to measurement of aircraft
noise. This method, however, adjusts the PNL to account for two
additional factors which affect subjective evaluations:
1) the effects of pure tone components or narrow bands of high
frequency noise generated by today's commercial jet aircraft.
2) the time history of the event (such as a flyover, takeoff,
or landing).
-------
Ill - 8a
WOO
FREQUENCY IN Hi
10,000 20000
Figure 3-6. Equal Noisiness Contours (3)
-------
NOISE AND NUMBER INDEX (NNI)
Several single-number ratings include corrections for number of
events and in some cases, time of occurence. One example of these
is the Noise and Number Index (NNI), which is based upon surveys
and sociological investigations made near London's Heathrow Airport
and is used for measuring aircraft noise. Conceivably it could also
be used to gage the response to other transient noise sources such
as trains. Essentially, the NNI takes an average peak PNL and adjusts
it in relation to the number of events that occur, day or night; i.e.
number of aircraft flyovers. Since this method was conceived for
use in a particular geographical area with possibly unique air
traffic densities and flight patterns, it may not be universally
applicable to other airport situations.
SPEECH INTERFERENCE LEVEL (SIL)
The Speech Interference Level (SIL) predicts the masking effect of
noisy environments. The inability to converse or to hear adequately
at normal distances is a common occurence at cocktail parties or
conventions. Also the inability to hear telephone conversations is
characteristic of many office and/or industrial work areas.
"The region of intelligibility for the human voice is roughly from 300
to 3000 Hz." (13) Thus the SIL is defined as the arithmetic average
of the 500, 1000, and 2000 Hz octave band levels, since noise in these bands
r
-------
Ill - 10
interferes with (masks) effective speech communication more than
the rest of the spectrum. When this averaged number (in decibels,
SPL) exceeds a certain value, speech comprehension becomes difficult
or impossible (Figure 3-7). For example, an SIL of 66dB would require
a very loud voice level for reliable conversation at a distance of 6
ft. An SIL of 65 to 80 dB makes telephone use difficult.
NOISE RATING NUMBER (N)
The Noise Rating method is based on a set of curves as shown in
Figure 3-8. This family of curves is similar to the 'equal loudness >
contours', and attempts to approximate the subjective characteristics
of the ear to various types of sounds. These curves are used to judge
the acceptability of noises for different environments with primary
emphasis on the annoyance character of the noise. The method of
approach is to plot the octave band sound pressure levels on the
family of curves. The noise rating number of the noise is the number
of the curve that lies just above the plotted spectrum. Specific noise
rating criteria for various environments have been established and
are shown in Figure 3-8. A sample spectrum also has been plotted
in Figure 3-8; its N value is 45.
The "corrected noise rating " is an N number that has been cor-
rected for specific environments or circumstances. Corrections
for dwellings are indicated in Figure 3-8.
-------
HI - 10a
Loss Of Intelligibility
At Normal Voice Level
Normal
Speech Receptions
w
30
246
Distance Between Speaker and Listener in Feet
Figure 3-7. Speech Interference Effects of Noise (9)
-------
Ill - lOb
a
a
tu
140
130 -
20
10
-10
2
3
Z
1C
O
Z
Cri-
terion
15
20
25
a
broadcasting studio
concert hall, legitimate theatre
500 sects
class room, music room, TV studio,
conference room, 50 seats
steeping room (see corrections
below)
conference room 20 seals or with
public adress system, cinema, 30
hospital, church, courtroom, library
living room (see corrections below) 30
private office 40
restaurant 45
gymnasium so
office (type writer*) 55
workshop 65
Correction* lor dwellings c
•) Pure tone easily perceptible
b) impulsive .net/or intermittent — 5
c) Noise only during working hours + 5
d) Notae during 25 % of time + 5
- " +10
+ 15
+20
+25
+30
e) Very quiet suburban
suburban
residential urban
urban near aome industry
aree of heavy Industry
Estimated Community Reaction
— s
0
+ s
+10
+15
Corrected
Noise RQHHK
No Observed Reaction Less than 40
Sporadic Complaints 40-50
Widespread Complaints 45-55
Threats of Community Action 50-60
Vigorous Community Action Above 65
62.5 12S 250 500 1000 2000 4000 8000 Hz
e» MIDFREQUENCIES OF OCTAVE BANDS
Figure 3-8. Noise Rating Number Curves (6) and Criteria (3)
-------
Ill - 11
An illustration of this procedure follows:
Suppose, for example, that a municipal maintenance crew was removing
a diseased or dying tree from your immediate neighborhood. The
maximum Corrected Noise Rating that should be allowed in your living
room under this criterion would be:
N = 30 for living rooms
+ 5 correction for assuming removal work
occurred during the daytime
+ 5 correction for assuming removal work occurred
25% of the time (of each hour)
+ 5 correction for assuming a residential
urban neighborhood
Corrected Noise Rating Number = 45
NOISE CRITERION NUMBER (NC)
The Noise Criterion method is almost indentical to the Noise Rating
Procedure but applies mainly to "...the steady, continual ambient
levels within a space or neighborhood, as opposed to specific noises
or intermittent activities occurring there." { 2) The family of curves,
however, are slightly different. The NC contours are more lenient
from the 500 Hz octave band up through the 8000 Hz octave band. The
process of plotting the local noise spectrum on the family of curves
is identical for both NR and NC ratings. Representative NC values '
for different spaces are shown in Table 3-2.The NC number for the
spectrum plotted in Figure3-9 is: NC = 49
-------
Ill - Ha
I
i
uJ
s
10
jj* ^.^n'. im~ i m i
tOO 200 MO 10OO 2000
FREQUENCY IN CYCLES PER SECOND
Figure 3-9. Noise Criterion Curves (8)
-------
Ill - 12
Table 3-2 Representative Noise Criteria (NC) Values For Different Spaces (2)
Subjective
Clarification
Quiet
Critical Hearing
And Listening
Normal
Noisy
Very Noisy
Function
Sleeping
Music
Di cuss ion
Mental And
Creative Tasks
Dining
Clerical
Sports
Transportation
Computing And
Calculating
Production
Space
Bedrooms
Hospital Rooms
Concert And
Recital Halls
Classrooms
Conference Rooms
Executive Offices
Study Rooms
Restaurants
Kitchens
Stenography And
Duplicating
Stadiums
Railroad Stations
Computer Rooms
Factories And
Shops
NC Level
30
30
25-30
30
25-30
30
35
45
55
50
55
55-65
70
50-75
-------
Ill - 13
SUMMARY
Perhaps the best explanation for the use of the various noise rating
methods and their associated acronyms was given by Preston Smith,
a respected acoustician:
"Because of the complexity of that all-too-human experience which is
assault by noise, the process of organizing raw information to achieve
a scientific description of noises and their effects on man has taken
many paths.
"A large number of methods have been invented for rank-ordering
sounds, to the point where the choice between them might be called
the game of Criteria.
"And it is a game —a curious but serious one. It is a game where
we know the rules by which to score, but must invent the implements
to play with. The score is simply the success with which the test
by criterion yields a correct judgment respecting the noise.
"We have the misfortune to be playing the game while designing the
implements. For some time to come, we will have to live with a
variety of rating schemes, distinctions between which will not
always be clear. The process of re-evaluation, modification, and
refinement of existing schemes will continue. This will be an awkward
period.
, ?
-------
Ill - 14
" The engineer interested in applications must study these changes
and adapt his procedures to the new methods. Old conclusions based
on earlier methods may be upset; that will be the price of progress
and a reflection of inaccuracies in the old methods." ( 22 )
-------
IV - 1
IV THE CHARACTER OF URBAN NOISE
INTRODUCTION
Now that the physical nature of noise and some of the criteria
for its evaluation have been described,some general trends
in urban noise will be examined.
"Urban noise" is a variable mixture of transportation, con-
struction, manufacturing, industrial, and residential noises.
Its primary impact occurs in residential areas and is felt in
two ways:
1) as a gradual increase in the ambient level
2) as a-disturbance or intrustion that is superimposed upon,
and distinguishable from, the ambient level.
In most urban areas, the ambient noise is predominantly steady-
state ground transportation noise.* However, growing sales of
aircraft, air conditioning units, and power lawnmowers have also
contributed to increasing ambient levels (Figures 4-1 -4-3).
According to one study, average ambient levels in urban areas
have been increasing at about 0.5 dB per octave band per year
(Figure 4-4), with increases in some critical areas reaching 1
dB (A) per year.
*A1though heavier trucks presently comprise less than 5 percent of '
the total vehicle population, their noise output almost equals ,
t
that of all other vehicles combined. !
-------
IV - 2
5000
en
o
CO
o
o
CO
CO
2
fc
cr
4000
3000
2000
1000
POWER LAWN
MOWERS
ROOM
AIR-CONDITIONING
UNITS
I960
I960
YEAR
CENTRAL
AIR-CONDITIONIN:
UNITS
1970
Figure 4-1. Manufacturer's Sales of Selected Products (19)
-------
IV - 3
I80r
2 ISO!
i
z
^ 120
90i
6
o:
g 30
o
TRUCKS
AND
BUSES
1980
Figure 4-2. Motor Vehicle Registration Trends
In The United States (19)
-------
CO
_
i
z
CO
cr
ui
a.
o
o:
1
60
50
40
20
10
1955
IV -4
TOTAL,
GENERAL
AVIATION
AIR CARRIER
MILITARY
i960
1965
1970
YEAR
Figure 4-3. Total Aircraft Operations At Airports
Having FAA Traffic Control Service (19)
-------
IV - 5
fteasured value for community with
population densit
of 5000 \,
1980
1985
Figure 4-4. Calculated Ambient Noise Levels For Three
Different Population Densities (9)
1
P
-------
IV - 6
FACTORS AFFECTING NOISE LIMITS
Before reasonable and effective limits for urban noise can be
established in a given area, several factors must be considered:
1) The level of ambient noise in the area. Requiring that
the source be submerged in the ambient noise, so that it
contributes nothing to the overall level, is difficult to
ascertain and may be impossible to achieve. On the other
hand, allowing the source to exceed the ambient level by
a specified margin may create an ambient level that con-
tinually creeps upward as more sources are added.
2) The sensitivity of persons in the area to noise (Figure
4-5). This is a highly subjective matter that is determined
by social, economic, and personal factors, among others.
However, it has been shown that deviations of the noise
level above the ambient level, including duration, number
of occurrences, and character of the distrubance, have a
strong influence on general public reaction. Deviations of
5 dB (A) or less have little significance, while a 15 dB (A)
increase can produce strong complaints. However, the levels
at which various degrees of annoyance occur depend to some
extent on the noise source (Figure 4-6). Figure 4-7 suggests
probable community response to the peak levels (primarly
from traffic) indicated.
-------
IV - 7
12345
SUSCEPTIBILITY RATING OF ADULT PEOPLE TO NOISE
Figure 4-5. Susceptibility of Adults to Noise
This bar graph shows the percentage of 1377 residents interviewed
in depth in a 1961 Central London survey for each of five cat-
egories of noise susceptibility rating. The susceptibility
rating was derived from the answers to six questions on a 40-
item questionnaire that evoked statements from the interviewees
about their sensitivity to noise (23).
-------
IV - 8
120
110
100
•a
. 80
5 70
a>
-1 60
-o
§ 50
o
"» 40
AIRCRAFT
\
MOTOR VEHICLES !
STREET NOISES
quiet moderate noisy very noisy
(acceptable)
Figure 4-6. Comparative Judgements of Different Noises (23)
-------
Disturbance Effect of Transportation Noise
IV - 9
Potential damage , d|{,A|
to hearing with >
sustained exposure
Physiological
Reactions
Recommended
Noise Level
(Exterior Urban'
Environment)
75
dB(A)
Average Peak
Loudness }
dB(A) I
91-96 «
85-90
79-84
72-78
10%
20%
30%
40%
50%
60%
70%
80%
Community Response
(Percentage of those, at each level.
who report each type of disturbance)
dB(A)
90 T
80-
60-1
Community Activity
and Legal Action
Petition of Protest
Letters of Protest
Complaints Likely
Possible Complaints
Rare Complaints
Acceptance Figure 4-7. Subjective Evaluations of
Transportation Noise in Communities
(24, 9)
-------
IV - 10
3) The type of rating scale to be specified. For monitoring
purposes, peak dB (A) and PNdB* criteria generally show
good correlation with community response, although octave
band levels may be more useful for identifying sources and
establishing proof of violation. Other criteria, such as
the Traffic Noise Index (TNI) and Composite Noise Rating
(CNR), include the influence of noise duration and/or
number of occurrences, as well as peak level.
r
PRESENT LEVELS OF AMBIENT NOISE AND DISCRETE NOISE SOURCES
j Table 4-1 and Figure 4-8 indicate source and ambient noise levels
I
• {in PNdB) for a typical urban area. A recent survey in resident-
I
• ial areas of Detroit, Boston, and Los Angeles (selected to include
] a variety of traffic situations) showed a 41-65 dB (A) range
I
in daytime levels and a 30-60 dB(A) range in nighttime levels.
Differences in day-night noise patterns and sources of discrete
noise were noted.
Typical levels in residential areas of common noise sources are
presented in Figure 4-9 and Table 4-2. Many of the levels shown
cause underlying dissatisfaction and annoyance among significant
numbers of residents. Table 4-2a.
* For community noise, it has been shown that PNdB = 1.02 dB(A)
+ 11.5, approximately.
-------
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Table 4-1. Annoyance Level Orientations (9)
IV - 11
PNdB
132
128
118
115
1)3
109
105
100
96
94
92
87
Sounds
Ear damage 30 mm. ex-
posure
Subsonic jet at 700 ft.
Blast furnace
Truck at 50 feet
City Center back-
ground
Ringing phone at 8-10 feet
Acoeptability
Unacceptable
Barely accept-
able
Acceptable
Of no concern
Annoyance
Very annoying
Annoying
Moderately annoying
Intrusive
A little annoying
Noticeable
Not at all annoying
Daytime
Major Commercial Airport
Freeway at
500 Ft.
Commercial
Noisy Daytime Residential
or Light Industrial
Quiet Daytime
Residential
Quiet Nightime
Residential
50
60
70
PNdB
Figure 4-8. Representative Ambient Noise Levels (9)
100
-------
IV - 12
Orinntntion
Noise in a car thai is
passing a truck at 60 mph
Noise from a Boeing 727
taxiing toward the lis-
tener and approximately
350 feet away
Briggs and Stratton 3 hp
lawn mower at the operator's
position
Phone ringing 10 feet awav
Electric alarm clock (3 feet)
Exhaust from an 8000 BTU air-
conditioner at 7 feet away
Residential area at 7 p m.
Inside a house at night, win-
dows closed, no appliances
running.
dB(A)
95
95
90
78
64
59
48
.33
d£
110
107
%
79
66
68
63
56
120
CD
•o
LU
UJ
3
en
UJ
o.
40,
IK)
100
90
80
70
60
50H PASSENGER CAR-
50 TO 60 MPH
TURBOFAN JET
AT TAKEOFF
J
DIESEL TRAIN
.30 TO 50 MPH
TRUCK OR
MOTORCYCLE
MAXIMUM
HIGHWAY
SPEED OR
ACCELERATING
'50 100 ZOO 400 800
DISTANCE FROM VEHICLE, FEET
Table .4-2. Noise Levels
of Typical Sources in
Urban Areas (9)
Figure 4-9. Typical levels
of outdoor noise produced
by transportation vehicle.
Squares represent the es-
timated levels at houses
typically nearest the nor
sources.
1600
-------
IV - 13
PROPOSED LEVELS FOR AMBIENT AND DISCRETE NOISE SOURCES
Many investigators have proposed maximum ambient levels for
urban noise as well as permissible levels for common sources of
discrete noise. Representative examples are shown in Tables
4-3 - 4-7. In addition, noise levels specified in existing
performance -codes are summarized in Section VII. While most or
all of these requirements may be highly desirable, it must be
remembered that:
1) Some of the levels specified are not technologically or
economically feasible at the present time,
2) Other unregulated or unidentifiable sources may essentially
determine the ambient level, even when specifically reg-
ulated sources are operating at levels greater than those
recommended .
However, the data in Tables 4-3 - 4-7 are indicative of an
international trend to impose increasingly severe restrictions-
on permissible noise levels in urban areas. Although not all
limits are reasonable, realistic, or effective, their collective
impact should produce a noticeable reduction in urban noise
within the next decade.
-------
Table 4-3. Reconmended Coimunity Noise Criteria (25)
IV - 14
Outdoor
Indoor
Airports
at property
line)
Day
80*
Night
80*
Industrial
Day
6^3
80**
light
55O
80**
Commercial
Day
60
50
Night
50
50
Urban
Residential
Day
50
45
Night
45
35
Suburban
Residential
Day
45
45
Night
40
35
Rural
Residen-
tial
3ay
40
40
Jight
30
30
:ntic,il 1:0;"..
Arms
Hospitals
Day
40
40
Nlyht
35
35
L,
•ho*
D.ly
40
50
* With current technology this limit can probably be met only by expanding airport
land areas greatly.
9 Levels specified to protect residents in and near this area.
** Maximum for unprotected ear.
Table 4-4. Reconmended Transportation Noise Criteria for Los Angeles (24)
, MAXIMUM PERMISSIBLE NOISE LEVEL
' it. f
*< Ir
*!
ntnsv eTuurwB i 505
_. _>
AIRPORTS
ALL TYPES
URBAN OVERFLIGHT
(FEDERAL)
PASSENGER CARS
(STATE AND LOCAL)
TRUCKS AND BUSES
(STATE AND LOCAL)
MOTORCYCLES
(STATE AND LOCAL)
CONSTRUCTION
EQUIPMENT
d8(A)
dB(A) '
dBW
d8(A)
dB(A)
dB(A)
OTHER VEHICLES.
EQUIPMENT. TOOLS. dB(A)
ETC.
-• »»"* j*
3,2
(500)
(low :
(SO)
t For explanation and justification of (his noise level cri-
terion, see p 75 Appendix A. Rationale (or Overhead
Aircraft Noise Limit
2 Approximate' (a) distance from automobile In the* moving
traffic lane nearest the sidewalk to the front of buddings
set back 15 feet from the property line, (b) distance ol
pedestrian on sidewalk from truck In tha nearest lane
beyond a parking lane Sound reading taken at power
output and tira noise equal to 65 mph on level ground
in still air
3 Sound reading taken at maximum operating power output
4 Fines collected from owner or user of aircraft, automotive
vehicle, or powered equipment, tools, and toys as In-
dicated In Recommendation 3 above,
-------
IV - 15
Table 4-5. Recommended Outdoor Noise Levels -
Switzerland (18)
Background \oisr Frrqueiil Peak s
Kan Peaks
Arta
Health resort
Quiet residential
Mixed
Commercial
Industrial
Traffic arteries
NiKhl
dB(A)
.15
45
45
50
55
60
Day
dH( A)
45
55
60
60
65
70
Ni*ht
dB(A)
45
55
55
60
60
70
Day
dB(A)
50
65
70
70
75
80
Niltht
dB(A)
55
65
65
65
70
80
Day
dB(A)
55
70
75
75
80
90
Measurement with microphone at open window recommended.
Desirable values 10 dB less, but not more than 30 dB less.
Background noise: mean value (average noise value without peaks).
Frequent peaks: 7-60 peaks per hr.
Rare peaks: 1-6 peaks per hr.
Table 4-6. Tolerated Construction Noise Levels at
Nearest Window - England (18)
Situation
Level
Rural, Suburban, Urban Areas, Away
from Main Road Traffic and Industry 70 dB(A)
Urban Areas, Near Main Roads and
Heavy Industrial Areas 7} dB(A)
Table 4-7. Recommended Indoor Noise Levels - England (18).
Levels shown should not be exceeded more than 102 of the
time.
Lntl
Situation
Day
Night
Country Areas 40 dB(A) 30 dB(A)
Suburban Areas, Away from
Mam Traffic Routes 45 dB(A) 35 dB(A)
Busy Urban Areas 50 dB(A) 35 dB(A)
-------
LIST OF REFERENCES
1. Randall, AJI Introduction to Acoustics, Addison - Wesley, 1951.
2. Verges, Sound ,Noise and Vibration Control, Van Nostrand, 1969.
3. Brock, Acoustic Noise Measurements . B & K Instruments (Cleveland),
1969.
4. Peterson and Gross, Handbook of Noi se Measurement , General
Radio Company, 1967.
5. Donley, "Equipment and Techniques for Noise Measurements,"
Sound and Vibration, January, 1967.
6. Acoustics Handbook, Hewlett - Packard Co., Palo Alto, Calif,
7. "Aircraft Noise Measurement, Evaluation, and Control," B & K
Technical Review, no. 4, 1965
8. Acous ti cs i n Ai r Condi t i oni ng , The Fane Company (La Crosse,
Wisconsin), 1967.
9. Transportat i on Noi se Poll uti on : Control and Abatement, Langley
Research Center, 1970.
10.. Blazier, "Criteria for Control of Community Noise", Sound
and Vibration, May 1968.
11. Architectural Acoustics, B & K Instruments (Cleveland), 1968.
12. American National Standards Institute, Acoustical Terminology,
1960.
13. Newby, Audiology (2nd ed.), Meredith, 1964.
14. Baron, "The Noise Receiver: The Citizen," Sound and Vibration,
May 1968.
15. Congressional Record. 91st Congress, Volume 115, Rumber 176,
Page E 9036 ff, October 29, 1969.
16. Donley, "Community Noise Regulation", Sound and Vibration,
February 1969.
17. Noise in Urban and Suburban Areas. FT/TS-26, Dept. of HUD, March
_
-------
18. Noise As a Public Health Hazard, American Speech and Hearing
Association, June 1968.
19. The Noise Around Us, U.S. Dept. of Commerce, COM 71-OQ147,
Sept. 1970.
20. American Refrigeration Institute, New York, 1967.
21. Botsford, paper presented at Acoustical Society Meeting,
Nov. 1967.
22. Lynch ,"Noise Control," International Science and Technology,
April 1966.
23. Morse, "Community Noise - The State of the Art," presented
Acoustical Society Meeting, Nov. 1967.
24. Outdoor Noise and the Metropolitan Environment, Los Angeles,
-------
A-l
CONVERSION OF OCTAVE BAND DATA FROM OLD SERIES TO
PREFERRED SERIES
APPENDIX A
For broad band noises, the corrections are
To Convert From
Old Octave Band
With Cutoff
Frequencies
18,75 -
37.5 -
75
150
300
600
1,200
2,400
4,800
37.5
75
- 150
- 300
- 600
- 1,200
- 2,400
- 4,800
- 9,600
9,600 -19,200
To Preferred
Octave Bands
With Center
Frequencies
31.5
63
125
250
500
1,000
2,000
4,000
8,000
16,000
Add
1 dB
1 dB
1 dB
1 dB
1 dB
1 dB
1 dB
1 dB
1 dB
1 dB
-------
B-l
APPENDIX B DRAFT OF A MUNICIPAL ORDINANCE TO REGULATE SOUND
PRODUCED BY AIR CONDITIONING AND AIR HANDLING
EQUIPMENT
(AREAS ZONED RESIDENTIAL)
Air Conditioning and Refrigeration Institute
1815 North Fort Myer Drive
Arlington, Virginia 22209
1. This ordinance is designed to control loud and objectionable sounds
which may be produced by air conditioning and air handling equipment
installed in or adjacent to a dwelling unit located in an area zoned
residential. Sound levels of 60 dBA or less, measured in accordance
with Par. 3, with the equipment in operation and regardless of
source(s) are not considered loud and objectionable within the scope
or this ordinance.
2. However^ should the sound level exceed 60 dBA, as measured per 1'ar. 3
with the equipment in operation, additional measurements shall be
made with the equipment not operating in order to determine its con-
tribution to the sound level above 6O dBA. Then, if the difference
in levels exceeds 5 dBA with the equipment operatinrj and not opera tinci
the equipment shall be considered as contributing to loud and objec-
tionable sounds and shall be modified or controlled so that the dif-
ference docs not exceed 5 dBA.
5. Measurements of sound levels required by this ordinance shall bo as
follows:
-------
B-2
a. Sound levels whall be measured on the A weighting network
of a sound level meter meeting the requirements of USA
Standard SI.4-1961 for General-Purpose Sound Level Motors,
or latest revision, (published by the United States of
America Standards Institute, New York, New York), using
the slow meter response. The meter shall be calibrated
and used according to the manufacturer's instructions.
b. Measurements shall be taken with the microphone located
at any point on the property line, but no closer than
three (31) feet from any wall and not less than three
(31 ) feet above the ground.
c. A minimum of 3 readings .shall be taken at 2 minute
intervals. The sound level shall be the average of
these readings.
This ordinance shall become effective immediately upon approval by
the Mayor (or City Manager) and shall apply to equipment installed
on or after the effective date.
Note: United States of America Standards Institute (USASI)
is the former name of:
American National Standards Institute, Inc. (ANSI)
I'i30 Broadway
New York, New York 10018
-------
B-3
DRAFT OF A MUNICIPAL ORDINANCE TO REGULATE SOUND
PRODUCED BY AIR CONDITIONING AND AIR HANDLING EQUIPMENT
(AREAS ZONED FOR APARTMENTS)
Air Conditioning and Refrigeration Institute
1815 North Fort Myer Drive
Arlington, Virginia 222O9
1. This ordinance is designed to control loud and objectionable sounds
i
which may be produced by air conditioning and air handling equipment
installed in or adjacent to a dwelling unit located in an area ?,oned
for multiple dwellings or apartments. Sound levels of 55 dBA or j
less, measured in accordance with Par. 3» with the equipment in !
operation and regardless of source(s) are not considered loud and
objectionable within the scope of this ordinance.
t
I
2. However, should the sound level exceed 55 dBA, as measured per Par. 3
;|
with the equipment in operation, additional measurements shall be made *
with the equipment not operating in order to determine its contribu- :
' 5
tion to the sound level above 55 dBA. Then, if the difference in »
•i
levels exceeds 5 dBA with the equipment operating and not operating,
i
the equipment shall be considered as contributing to loud and objoc- -
j*
tionable sounds and shall be modified or controlled so that the dif-
ference does not exceed 5 dBA.
3. Measurements of sound levels required by this ordinance shall be as
follows:
-------
B-4
a. Sound levels shall be measured on the A weighting network
of a sound level meter meeting the requirements of USA
Standard SI.4-1961 for General-Purpose Sound Level lictcrs,
or latest revision, (published by the United States of
America Standards Institute, New York, New York), using
the slow meter response. The meter shall be calibrated
and used according to the manufacturer's instructions.
b. Measurements shall be taken with the microphone located
outside the window of a room within the dwelling unit
where the sound is alleged to be -loud and objectionable.
The microphone shall be positioned not more than 3 ft.
from the window opening but at least 3 ft. from any other
surface. '...•' V
c. A minimum of 3 readings shall be taken at 2 minute intci—
vals. The sound level shall be the average of these readings.
b. This ordinance shall become effective immediately upon approval
by the Mayor (or City Manager) and shall apply to equipment in-
stalled on or after the effective date.
Note: United States of America Standards Institute (US.vSI)
is the former name of:
American National Standards Institute, Inc. (ANSI)
1430 Broadway
New York, New York 10O18
-------
-------
C-l
-\
APPENDIX C CITIES SURVEYED IN THE CONTROL OF NOISE IN URBAN
AREAS PROJECT
The survey relied heavily upon the noise legislation compilation
in the CONGRESSIONAL RECORD - SENATE, October 29, 1969, pages
E9031 through E9112.
The total listing of cities upon which the compilation was based is
shown below:
Action, Massachusetts
Akron, Ohio
Albany, New York
Albuquerque, New Mexico
Anaheim, California
Anchorage, Alaska
Atlanta, Georgia
Batavia, Illinois 2 _ 3
Bayport, Texas 2-3
Beverly Hills, California t
Birmingham, Alabama
Boulder, Colorado
Boston, Massachusetts
Buffalo, New York
Chicago, Illinois 1 - 2
Cincinnati, Ohio
Columbus, Ohio 2-3
Concord, New Hampshire
Coral Gables, Florida 4
Dallas, Texas 1 .2 - 3 - 4
Dayton, Ohio 1-3
Denver, Colorado
Detroit, Michigan
Downer's Grove, Ilttiois 2
Englewood, New Jersey
Fair Lawn, New Jersey 4
Farnington, Connecticut 4
Fort Lauderdale, Florida
Geneva, Illinois 2-3
Hartford, Connecticut
Heraet, California
Hinsdale, Illinois
Honolulu, Hawaii 1 ~ 3
Houston, Texas
Indianapolis, Indiana
Inglewood, California 4
Irving, Texas
Kansas City, Missouri
Little Rock, Arkansas
Las Vegas, Nevada
1. Cities surveyed in Figure 6-5.
2. Cities surveyed in Figure 6-6.
Los Angeles, California
Maderia Beach, Florida
Maywood, Illinois 2 - 3
Memphis, Tennessee
Miami, Florida 4
Milwaukee, Wisconsin
Minneapolis, Minnesota 2-3
Newark, New Jersey
New Haven, Connecticut
New Orleans, Louisiana
New York, New York
Norfolk, Virginia
Oakland, California
Oklahoma City, Oklahoma
Orlando, Florida 2-3 .4
Park Ridge, Illinois
Peoria, Illinois 2 ~ *
Philadelphia, Pennsylvania
Pittsburgh, Pennsylvania
Portland, Oregon
Raleigh, North Carolina
River Forest, Illinois
Rochester, New York
Sacramento, California
St. Louis, Missouri 4
St. Petersburg, Florida
Salt Lake City, Utah
San Antonio, Texas
San Diego, California
San Francisco, California
San Jose, California
Santa Barbara, California
Seattle, Washington
Syracuse, New York
Trenton, Michigan
Tucson, Arizona
Warwick, Rhode Island 1
Washington, D.C. 2-3
3. Cities Surveyed in Figure 6-7.
4. Cities surveyed in Figure 6-8.
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