Although measured and predicted sound levels are often reported to the TABLE 2 A-weighted sound levels Approximate sound level Noise source or criterion 140 Threshold of pain 122 Supers
Trang 1Noise and sound refer to audible pressure fluctuations in air
Both are characterized by sound level in decibels and
fre-quency content in hertz Although sound is vital for
commu-nication, noise is one of our greatest problems Intentionally
generated acoustic signals including speech and music are
usually referred to as sound Noise is a term used to identify
unwanted sound, including sound generated as a byproduct
of other activities such as transportation and industrial
opera-tions Intrusive sound, including speech and music unwelcome
to the hearer, are also considered noise Thus, the distinction
between noise and sound is subjective, and the two terms are
often used interchangeably
When a body moves through a medium or vibrates, some
energy is transferred to that surrounding medium in the form
of sound waves Sound is also produced by turbulence in air
and other fluids, and by fluids moving past stationary bodies
In general, gases, solids and liquids transmit sound
Well-documented effects of noise include hearing
damage, interference with communication, masking of
warning signals, sleep interruption, and annoyance Noise
detracts from the quality of life and the environment; it
con-tributes to anger and frustration and has been implicated as a
contributor to psychological and physiological problems
The National Institute for Occupational Safety and
Health (NIOSH) named hearing loss as a priority research
area, noting that noise-induced hearing loss is 100%
prevent-able, but once acquired, it is permanent and irreversible The
Occupational Safety and Health Administration (OSHA)
noted that hearing loss can result in a serious disability, and
put employees at risk of being injured on the job The World
Health Organization (WHO) notes that noise-induced hearing
impairment is the most prevalent irreversible occupational
hazard, and estimates that 120 million people worldwide
have disabling hearing difficulties In developing countries,
not only occupational noise but also environmental noise is
an increasing risk factor for hearing impairment
The European Union (EU) identified environmental
noise caused by traffic, industrial and recreational activities
as one of the main local environmental problems in Europe
and the source of an increasing number of complaints It is
estimated that 20% of the EU population suffer from noise
levels that both scientists and health experts consider
unac-ceptable An additional 43% of the population live in ‘gray
areas’ where noise levels cause serious daytime annoyance
Estimates of the cost of noise to society range from 0.2% to
2% of gross domestic product
Noise control involves reduction of noise at the source,
control of noise transmission paths, and protection of the receiver Source control is preferred For example, design of transportation systems and machinery for lower noise output may be the most effective means of noise control But, after trying all feasible noise source reduction, airborne noise and/
or solid-borne noise may still be objectionable Interruption
of noise transmission paths by means of vibration isolation, source enclosures, sound absorbing materials, or noise barri-ers is then considered
In some industrial situations, excessive noise is still pres-ent after all attempts to control noise sources and transmission paths Administrative controls—the assignment of employees
so that noise exposure in reduced—should then be consid-ered As a last resort, employees may be required to use per-sonal hearing protection devices (muff-type and insert-type hearing protectors) Communities often resort to ordinances that limit noise levels and restrict hours of operation of noise-producing equipment and activities Community noise con-trol methods also include zoning designed to separate noise sources from residential and other sensitive land uses
FREQUENCY, WAVELENGTH AND PROPAGATION SPEED
Frequency Audible sound consists of pressure waves with
frequencies ranging from about 20 hertz (Hz) to 20,000 Hz, where 1 Hz 1 cycle per second Sound consisting essen-tially of a single-frequency sinusoidal pressure wave is called
a pure tone In most cases, noise consists of sound waves
arriving simultaneously from a number of sources, and having a wide range of frequencies A sound wave which has
a frequency below the audible range is called infrasound
and sound of frequency above the audible range is called
ultrasound
Propagation speed The propagation speed of airborne
sound is temperature dependent It is given by:
c 20.04[T 273.16] 1/2 (1.1)
where c propagation speed, i.e the speed of sound, (m/s)
T air temperature (C)
At an air temperature of T 20C (68F), the
propaga-tion speed is c 343 m/s (approx) Sound waves propagate
at a different speed in solids and liquids The propagation speed for axial waves in a steel rod is about 5140 m/s Note that
Trang 2c is a wave a propagation speed; it does not represent particle
velocity within the medium
Wavelength If a pure-tone pressure wave could be
observed at a given instant, the length of one cycle of the
wave in the propagation directly could be identified as the
wavelength Thus,
where λ wavelength (m), c propagation speed (m/s) and
f frequency (Hz) The effectiveness of noise barriers and
sound-absorbing materials is dependent on the sound
wave-length (thus, effectiveness is frequency-dependent)
SOUND PRESSURE AND SOUND PRESSURE LEVEL
One standard atmosphere is defined as a pressure of 1.01325
10 5 Pa (about 14.7 psi) Typical sound pressure waves
rep-resent very small disturbances in ambient pressure Sound
pressure level is defined by
2 ref 2
10 ⎡⎣ ⁄ ⎤⎦20 1 [ ] (2.1)
where L p sound pressure level in decibels (dB), lg
common (base-ten) logarithm, p rms root-mean-square sound
pressure (Pa) and p ref reference pressure 20 10 −6 Pa
Sound pressure represents the difference between
instan-taneous absolute pressure and ambient pressure For a
pure-tone sound wave of amplitude P,
The reference pressure is the nominal threshold of hearing,
corresponding to zero dB Sound pressure may be determined
from sound pressure level by the following relationship:
10 ⁄ 20 2 10[ 100 ] ⁄ 20
(2.2)
A-WEIGHTING
Human hearing is frequency-dependent At low sound levels,
sounds with frequencies in the range from about 1 kHz to
5 kHz are perceived as louder than sounds of the same sound
pressure, but with frequencies outside of that range A-, B-
and C-weighting schemes were developed to compensate for
the frequency-dependence of human hearing at low,
moder-ate and high sound levels Other weightings are also used,
including SI-weighting which relates to speech interference
A-weighting has gained the greatest acceptance; many
stan-dards and codes are based on sound levels in A-weighted
decibels (dBA) When noise is measured in frequency bands,
the weighting adjustment may be added to each measured
value Sound level meters incorporate weighting networks
so that weighted sound level is displayed directly
A-weight-ing adjustments are shown in Table 1
Some representati Most values are approximate; actual noise sources produce a wide range of sound levels
EQUIVALENT SOUND LEVEL Sound energy is proportional to mean-square sound pressure
Equivalent sound level is the energy-average A-weighted sound level over a specified time period Thus,
0
⁄ ( )
⎡
where L eq equivalent sound level (dBA), L instantaneous sound level (dBA) and T averaging time, often 1 hour, 8
TABLE 1 A-weighting Frequency
Hz
Adjustment dB
31.5 39.4
250 8.6
315 6.6
400 4.8
500 3.2
630 1.9
800 0.8
1,000 0 1,250 0.6
1,600 1.0
2,000 1.2
2,500 1.3
3,150 1.2
4,000 1.0
5,000 0.5
6,300 0.1
8,000 1.1
10,000 2.5
12,500 4.3
16,000 6.6
20,000 9.3
ve sound levels are given in Table 2
Trang 3hours, 24 hours, etc The time period may be identified by the
subscript, e.g L eq24 for a 24 hour averaging time
Integrating sound level meters compute and display
equivalent sound level directly If equivalent sound level is
to be determined from a number of representative
instanta-neous measurements or predictions, the above equation may
be rewritten as follows:
i
N
1
⁄ ( )
⎡
⎣
⎦
⎥
⁄
=
If a large number of readings are involved, it is
con-venient to incorporate the above equation into a computer
program If the base-10 logarithm is not available on the
computer it may be obtained from
lg( )x 1n( )x ⁄1n 10( ) (4.3)
where ln is the natural (base-e) logarithm
Example Problem: Equivalent Sound Level
Considering four consecutive 15-minute intervals, during
which representative sound levels are 55, 58, 56 and 70 dBA
respectively Determine equivalent sound level for that hour
Solution:
Leq lg 1 4
dBA
64 5
⁄
It can be seen that higher sound levels tend to dominate when
determining L eq Note that the mean average sound level (55
58 56 70)/4 59.8 has no significance
DAY–NIGHT SOUND LEVEL Day–night sound level takes into account the importance of quiet during nighttime hours by adding a 10 dBA weighting
to noise during the period from 10 pm to 7 am It is given by
t
L
L
pm
pm am
10
10 7
10
10 7
⎣⎢
{
⎤
⎦
⁄
∫
d⎥⎥} (5.1)
where L DN day–night sound level and t time (hours)
COMBINING NOISE FROM SEVERAL SOURCES
Correlated sound waves Sound waves with a precise time
and frequency relationship may be considered correlated
A sound wave arriving directly from a source may have a precise phase relationship with a reflected sound wave from the same source The sound level resulting from combining two correlated sound waves of the same frequency depends
on the phase relationship between the waves Reactive muf-flers and silencers are designed to produce reflections that cancel the progressive sound wave
Active noise control is accomplished by generating
sound waves out-of-phase with the noise which is to be cancelled Active noise control systems employ continuous measurement, signal processing, and sound generation
Uncorrelated noise sources Most noise sources are not
correlated with one another The combined effect of two or more uncorrelated sources is obtained by combining the energy from each at the receiver To do this, we may add mean-square sound pressures In terms of sound levels, the result is
i
N
i
=
∑
1
where L T total sound level due to N contributions L i (dBA
as measured or predicted at the receiver)
For two contributions, the total sound level is
L L
T
DIF 10
lg 10
lg 1 10
10
1
⁄
where L 1 the greater sound level and DIF L 1 L 2 , the difference between the two sound levels
The last term in equation 6.2 may be identified as L (add), the quantity to be added to L 1 to obtain total sound level L T L (add)
Values are given to the nearest one-tenth decibel Although measured and predicted sound levels are often reported to the
TABLE 2 A-weighted sound levels Approximate
sound level Noise source or criterion
140 Threshold of pain
122 Supersonic aircraft A
120 Threshold of discomfort
112 Stage I aircraft A
110 Leaf blower at operator
105 OSHA 1 hr/da limit B
99 EEC 1 hr/da limit B
90 OSHA and EEC 8 hr/da limit B
70 EPA criterion for hearing conservation C
67 DOT worst hour limit D
65 Daytime limit, typical community ordinance
45 Noise limit for virtually 100% indoor speech intelligibility
35 Acceptable for sleep
0 Threshold of hearing
Notes:
A: Aircraft measurements 500 ft beyond end of runway, 250 ft to side.
Stage 3 aircraft in current use are quieter.
B: Criteria for worker exposure (US Occupational Safety and Health
Administration and European Economic Community).
C: Environmental Protection Agency identified 24-hr equivalent sound level.
D: Department of Transportation design noise level for residential use.
is tabulated against DIF, the difference in levels, in Table 3
Trang 4nearest whole decibel, fractional values are often retained for
comparison purposes, and to insure accuracy of intermediate
calculations
Note that addition of the contributions of two equal but
uncorrelated sources produces a total sound level 3 decibels
higher than the contribution of one source alone
If the difference between contributions is 10 or more
decibels, then the smaller contribution increases total sound
level by less than one-half decibel If the difference is 20
or more decibels, the smaller contribution has no significant
effect; for DIF 20, L (add) 1/20 This is an important
consideration when evaluating noise control efforts If
sev-eral individual contributions to ovsev-erall sound level can be
identified, the sources producing the highest sound levels
effect of combining noise levels
Example Problem: Combining Noise Contributions
The individual contributions of five machines are as follows
when measured at a given location: 85, 88, 80, 70 and 95 dBA
Find the sound level when all five are operating together
Solution:
Using equation 6.1, the result is L T 10 lg[10 85/10
use Table 3 instead Combining the levels in ascending order,
the result is
80.4 85 86.3 and
86.3 88 90.3 and
90.3 95 96.3 dBA
Fractional parts of one dBA are only retained for purposes
or illustration
For several sources which contribute equally to sound
level at the receiver, total sound level is given by
where L 1 sound level contribution at the receiver due to
a single source and n the number of sources Table 3 and
related) contributions
SOUND FIELDS
The region within one or two wavelengths of a noise source
or within one or two typical source dimensions is called the
near field The region where reflected sound waves have a
significant effect on total sound level is called the
reverber-ant field Consider an ideal nondirectional noise source which
generates a spherical wave For regions between the near field
and the reverberant field, sound intensity is given by
IW⁄ ⎡⎣4p r2⎤⎦ (7.1)
TABLE 3 Combining noise from two uncorrelated sources
L1 greater sound level, L2 lower sound level DIF L1 L2, Combined sound level LT L1 L(add).
Difference in levels
3.5 3 2.5 2 1.5 1 0.5 0
FIGURE 1 Combining noise levels.
should be considered first Figure 1 is a graph showing the
Figure 2 show the effect of combining n equal (but
Trang 5where I sound intensity (W/m 2 ), where sound pressure
and particle velocity are in-phase, W sound power of the
source (W) and r distance from the source (m) The above
equation is called the inverse square law
Scalar sound intensity level is given by
where L I scalar sound intensity level and I ref 1012 W/m 2
For airborne sound under typical conditions, sound
pres-sure level and scalar sound intensity level are approximately
equal, from which
Lp艐 LI 10lgW20lgr109 (7.3)
for the spherical wave where L p and L I are expressed in dB If
sound power has been A-weighted, L p and L I are in dBA
When the inverse-square law applies, then sound levels
decrease with distance at the rate: 20 lg r Thus, if sound
level is known at one location, it may be estimated at another
location Table 4 and Figure 3 show the distance adjustment
to be added to sound level at distance r 1 from the source to
obtain the sound level at distance r 2
MEASUREMENT AND INSTRUMENTATION
Sound level meters The sound level meter is the basic tool
for making noise surveys A typical sound level meter is a hand-held battery-powered instrument consisting of a micro-phone, amplifiers, weighting networks, a rootmean-square rectifier, and a digital or analog sound level display The A-weighting network is most commonly used This network
so that sound level is displayed in dBA When measuring out-of-doors, a windscreen is used to reduce measurement error due to wind impinging on the microphone Integrating sound level meters automatically calculate equivalent sound level If
a standard sound level meter is used, equivalent sound level may be calculated from representative measurements, using the procedure described later
Frequency analysis The cause of a noise problem may
sometimes be detected by analyzing noise in frequency bands An octave band is a frequency range for which the upper frequency limit is (approximately) twice the lower
TABLE 4 Spherical wave attenuation
Distance adjustment based
on the inverse-square law
L(r2) L(r1) ADJ.
Distance ratio r2/r1
10
5
0
–5
–10
FIGURE 3 Distance adjustment based on the inverse-square law
Number of equal contributions
ce 10
8
6
4
2
0
FIGURE 2 Combining n equal contributions.
electronically adjusts the signal in accordance with Table 1,
Trang 6limit An octave band is identified by its center frequency
defined as follows:
(8.1)
where f c the center frequency, f L the lower band limit,
and f u the upper band limit, all in Hz The center
frequen-cies of the preferred octave bands in the audible range are
31.5, 63, 125, 250 and 500 Hz and 1, 2, 4, 8 and 16 kHz The
center frequencies of the preferred one-third-octave bands are
Real-time analyzers and Fast-Fourier-Transform (FFT)
analyzers examine a signal in all of the selected frequency
bands simultaneously The signal is then displayed as a
bar-graph, showing the sound level contribution of each selected
frequency band
Sound intensity measurement Vector sound intensity
is the net rate or flow of sound energy Vector sound
inten-sity measurements are useful in determining noise source
power in the presence of background noise and for location
of noise sources Sound intensity measurement systems
uti-lize a two-microphone probe to measure sound pressure at
two locations simultaneously
The signals are processed to determine the particle
veloc-ity and its phase relationship to sound pressure
Calibration Acoustic calibrators produce a sound level
of known strength Before a series of measurements, sound
measurement instrumentation should be adjusted to the
cali-brator level Calibration should be checked at the end of each
measurement session If a significant change has occurred,
the measured data should be discarded Calibration data
should be recorded on a data sheet, along with
instrumenta-tion settings and all relevant informainstrumenta-tion about the
measure-ment site and environmeasure-mental conditions
Background noise When measuring the noise
contribu-tion of a given source, all other contribucontribu-tions to total noise
are identified as background noise Let the sound level be
measured with the given source operating, and then let
ground noise alone be measured The correction for
back-ground noise is given by
COR10 lg 1 10 DIF 10⁄
where DIF Total noise level – background noise level,
and the noise level contribution of the source in question is
given by:
Background noise corrections are tab
plotted in Figure 4 Whenever possible measurements should
be made under conditions where background noise is
negli-gible When total noise level exceeds background noise by at
least 20 dB, then the correction is less than 1/20 dB Such ideal
conditions are not always possible Truck noise, for example,
must sometimes be measured on a highway with other moving
vehicles nearby If the difference between total noise level and
background noise is less than 5 dB, then the contribution of the source in question cannot be accurately determined
HEARING DAMAGE RISK The frequency range of human hearing extends from about
20 Hz to 20 kHz Under ideal conditions, a sound pressure level of 0 dB at 1 kHz can be detected Human hearing is less sensitive to low frequencies and very high frequencies
Hearing threshold A standard for human hearing has
been established on the basis of audiometric measurements
at a series of frequencies An individual’s hearing threshold represents the deviation from the standard or audiometric-zero levels A hearing threshold of 25 dB at 4 kHz, for example, indicates that an individual has “lost” 25 dB in ability to hear sounds at a frequency of 4 kHz (assuming the individual had
“normal” hearing at one time)
A temporary threshold shift (TTS) is a hearing thresh-old change determined from audiometric evaluation before, and immediately after exposure to loud noise A measurable permanent threshold shift (PTS) usually occurs as a result
of long-term noise exposure The post-exposure audiometric measurements to establish PTS are made after the subject has been free of loud noise exposure for several hours A com-pound threshold shift (CTS) combines a PTS and TTS There
is substantial evidence that repeated TTS’s translate into a measurable PTS Miller (1974) assembled data relating TTS, CTS and PTS resulting from exposure to high noise levels
Occupational Safety and Health Administration (OSHA criteria OSHA (1981, 1983) and the Noise Control
Act (1972) set standards for industrial noise exposure and guidelines for hearing protection OSHA criteria have resulted
in reduced noise levels in many industries and reduced the incidence of hearing loss to workers However, retrospective studies have shown that some hearing loss will occur with long-term exposure a OSHA-permitted sound levels
The basic OSHA criterion level (CL) is a 90 dBA sound exposure level for an 8 hour day An exchange rate (ER)
of 5 dBA is specified, indicating that the permissible daily
Total - background level
0
–0.5
–1
–1.5
–2
–2.5
FIGURE 4 Background noise correction.
those listed in the first column of Table 1 (Section 3)
ulated in Table 5 and
Trang 7exposure time is halved with each 5 dBA sound level increase
The threshold level, the sound level below which no
contribu-tion is made to daily noise dose, is 80 dBA (threshold level is not to be confused with hearing threshold) When noise
expo-sure exceeds the action level (85 dBA) a hearing conservation
program is to be implemented A hearing conservation program should include noise exposure monitoring audiometric testing, employee training, hearing protection and record-keeping
According to OSHA standards continuous noise expo-sure (measurable on the slow-response scale of a sound level meter) is not to exceed 1151 dBA For sound levels L where
80
8⁄ ⎡⎣2( CL) ER ⁄ ⎤⎦ 8⁄ ⎡⎣2( L 90 ) ⁄5⎤⎦
(9.1)
where T allowable exposure time (hours/day) The result
is shown in Table 6
Noise dose When sound levels vary during the day, noise
dose is used as an exposure criterion Noise dose is given by
i
N
100∑ i⁄ i
1
where C actual exposure of an individual at a given sound
level (hr), T allowable exposure time at that level and N
the number of different exposure levels during one day Noise
dose D % should not exceed 100% As an alternative to moni-toring and calculations, workers may wear dosimeters which automatically measure and calculate daily dose
An exchange rate of 3 dB is used in occupational noise exposure criteria by some European countries This exchange rate is equivalent to basing noise exposure on L eq
Environmental Protection Agency (EPA) identified levels Using a 4 kHz threshold shift criterion, protective
noise levels are substantially lower than the OSHA criteria
EPA (1974, 1978) in its “Levels” document identified the equivalent sound level of intermittent noise:
Leq24 70dBA
as the “(at ear) exposure level that would produce no more than 5 dB noise-induced hearing damage over a 40 year period” This value is based on a predicted hearing loss smaller than 5 dB at 4 kHz for 96% of the people exposed
to 73 dBA noise for 8 hr/da 250 da/yr 40 yr With the
following corrections, the 73 dBA level is adjusted to L eq24
70 dBA the protective noise level:
1.6 dBA to account for 365 da/yr exposure,
4.8 dBA to correct for 24 hr/day averaging,
5 dBA assuming intermittent exposure and
1.6 dBA for a margin of safety
NON-AUDITORY EFFECTS OF NOISE The relationship between long-term exposure to industrial noise and the probability of noise-induced hearing loss is
TABLE 5 Background noise correction
0.8 7.7 6.5 1.1
1.0 6.9 7.0 1.0
1.2 6.2 7.5 0.9
1.4 5.6 8.0 0.7
1.6 5.1 8.5 0.7
1.8 4.7 9.0 0.6
2.0 4.3 9.5 0.5
2.2 4.0 10.0 0.5
2.4 3.7 10.5 0.4
2.6 3.5 11.0 0.4
2.8 3.2 11.5 0.3
3.0 3.0 12.0 0.3
3.2 2.8 12.5 0.3
3.4 2.7 13.0 0.2
3.6 2.5 13.5 0.2
3.8 2.3 14.0 0.2
4.0 2.2 14.5 0.2
4.2 2.1 15.0 0.1
4.4 2.0 15.5 0.1
4.6 1.8 16.0 0.1
4.8 1.7 16.5 0.1
5.0 1.7 17.0 0.1
5.2 1.6 17.5 0.1
5.4 1.5 18.0 0.1
5.6 1.4 18.5 0.1
5.8 1.3 19.0 0.1
6.0 1.3 19.5 0.0 DIF total noise level–background noise level Sound level due to source total noise level COR.
TABLE 6 Allowable exposure times
Time T
hr/da
Sound level L
dBA
1/4 or less 115
* The 32 hr exposure time is used
in evaluating noise dose when sound levels vary.
Trang 8well-documented And, we can estimate the effect of
intru-sive noise on speech intelligibility and masking of
warn-ing signals Equivalent sound levels and day-night sound
levels based on hearing protection, activity interference, and
Bureau identified noise as the top complaint about
neighbor-hoods, and the major reason for wanting to move In a
typi-cal city, about 70% of citizen complaints relate to noise The
most common complaints are aircraft noise, highway noise,
machinery and equipment, and amplified music
Noise tolerance varies widely among individuals It is
difficult to relate noise levels to psychological and
auditory physiological problems But there is anecdotal
evi-dence that violent behavior can be triggered by noise In a
New York case, one man cut off another man’s hand in a
dispute over noise In another noise-related incident, a New
Jersey man operated his motorcycle engine inside his
apart-ment, leading a neighbor to shoot him
Chronic noise exposure has been related to children’s
health and cognitive performance In a study of British
schools, Stansfield and Haines (2000) compared reading
skills of students at four schools with 16-hour equivalent
sound levels less than 57 dBA and four schools with levels
greater than 66 dBA After adjustment for socioeconomic
factors, lower average reading scores were found at the
nois-ier schools The difference was equivalent to six months of
learning over four years
A study by Zimmer et al (2001) examined aircraft noise
exposure and student proficiency test results at three grade
levels Communities with comparable socioeconomic status
were selected for the study Noise-impacted communities
with a day-night sound level greater than 60 dBA and
com-munities with a level of less than 45 dBA were compared
If proficiency test results are extrapolated to educational
attain-ment and salary level, one could predict a 3% salary level
dis-advantage for students from the impacted communities
COMMUNITY NOISE
Contributors to community noise include aircraft, highway
vehicles, off-road vehicles, powered garden equipment,
construction activities, commercial and industrial activities,
public address systems and loud radios and television sets
The major effects of community noise include sleep
interfer-ence, speech interferinterfer-ence, and annoyance
Highway noise Noise levels due to highway vehicles
may be estimated from the Federal Highway Administration
(FHWA) model summarized by the sound level vs speed
relationships in Table 7 These values make it possible to
pre-dict the impact of a proposed highway or highway
improve-ment on a community
The contribution that a given class of vehicles makes to
hourly equivalent sound level is given by
A S
10 25
(10.1)
where D o 15 m, V volume (vehicles/hr), S speed
(km/hr) A B, D, F, G and S are adjustments for barriers, distance, finite highway segments, grade and shielding due to buildings, respectively Each term is applied to a given class of vehicles and traffic lane For acoustically absorptive sites, the distance adjustment is
where D distance from the traffic lane (m) Hourly equiva-lent sound level at any location is predicted by combining the contributions from all vehicle classes and traffic lanes The result is
L
i
eqH COMBINED
N
1
lg L Hieq
(10.3)
Design noise levels for highways Design noise levels specified by the Federal Highway Administration (1976) are traffic on proposed highways are compared with the design levels These data aid in selecting a highway design and routing alternative including the “no-build” alternative
Aircraft noise Noise contour maps are available for
most major airports These enable one to make rough predic-tions of the impact of aircraft noise on nearby communities
Federal Aviation Administration publications (1985a and b) outline aircraft noise certification procedures and aircraft noise compatibility planning Many of the existing airport
noise contour maps are based on the descriptor Noise
expo-sure forecast (NEF) An approximate conversion from NEF
to L DN is given by
where L DN day-night sound level ( about 3 dBA)
Community noise criteria There are thousands of
dif-ferent community noise ordinances, with a wide range of permitted sound levels Their effectiveness depends largely
on the degree of enforcement in a particular community The Environmental Protection Agency has identified the noise
TABLE 7 Energy mean emission levels for vehicles Vehicle
class
Sound level
L0dBA
Speed S km/hr
Autos 31.8 lg S 2.4 50
Med trucks 33.9 lg S 16.4 50
Heavy trucks 24.6 lg S 38.5 50
Heavy trucks 87 50 Sound levels at 15 meters Source: Barry and Reagan (1978).
annoyance are given in Table 9 The United States Census
summarized in Table 8 Noise predictions based on projected
Trang 9levels in Table 9 as protective of public health and welfare
All are based on an average 24 hour day
Control of community noise Environmental noise
problems are particularly difficult to solve due to problems
of shared responsibility and jurisdiction In many cases,
Federal laws preempt community regulations Highway
noise and aircraft noise, often the most significant
contribu-tors to community noise levels, are largely exempt from local
control In spite of the difficulties encountered, however, the
importance of protecting the quality of life makes
environ-mental noise control efforts worthwhile Depending on the
circumstances, some of the following courses of action may
be considered
a) Review the applicable noise ordinance Compare
it with a model noise ordinance Check to see if specific limits are set in terms dBA Determine whether or not sound level meters are available and whether or not the ordinance is actually enforced
b) Meet with representatives of the local governing
body or environmental commission Make them aware of noise related problems in the community
c) Initiate a campaign for public awareness with
regard to the environment including the noise environment Make use of the local papers
d) Consider a ban or limitation on all-terrain- vehicles
(ATV’s) Determine whether muffler requirements are actually enforced
e) Encourage planning and zoning boards to require
an environmental impact statement (EIS), including
a noise report, before major projects are approved
f) Support noise labeling for lawn mowers and other
power equipment
g) Attend and participate in hearings involving plans
for airports, heliports, and highways Consider noise impact when evaluating the cost/benefit ratio for proposed facilities
h) Evaluate the feasibility of noise barriers on
exist-ing and proposed highways in sensitive areas
i) Support legislation to reduce truck noise emission limits
j) Support legislation enabling airport curfews
REFERENCES
Barry, T.M and Reagan, J.A FHW A highway traffic noise prediction
model FHWA-RD-77-108, 1978
Environmental Protection Agency, Information on levels of environmental
noise requisite to protect public health and welfare with an adequate margin of safety, EPA 550/9-74-004, 1974
Environmental Protection Agency, Model community noise control ordinance,
EPA 550/9-76-003, 1975
Environmental Protection Agency, Protective noise levels, EPA 559/979-100,
1978
Federal Aviation Administration, Noise standards: aircraft type and
air-worthiness certification, FAR part 36, 1985(a)
Federation Aviation Administration, Airport noise compatibility planning,
FAR part 150, 1985(b)
Federal Highway Administration, Procedures for abatement of highway
traffic noise and construction noise, FHPM 7-7-3, 1976
Federal Register, Code of federal regulations, 29, parts 1900 to 1910, 1985
Miller, J.D., “Effects of noise on people,” J Acoust Soc Am 56, no 3,
pp 729–764, 1974
Noise control act of 1972, PL 92-574, HR 11021, Oct 27, 1972
Occupational Safety and Health Administration, “Occupational noise
exposure hearing conservation amendment” Federal Register, 46 (11),
4078–4181 and 46 (162), 42622–42639, 1981
Occupational Safety and Health Administration, “Guidelines for noise
enforce-ment”, OSHA Instruction, CPL2-2.35,29 CFR1910.95(6) (1), 1983
Peterson, A.P.G., Handbook of noise measurement, GenRad, Concord, MA,
9th ed., 1980
Stansfield, S and M Haines, “Chronic aircraft noise exposure and chil-dren’s cognitive performance and health: the Heathrow studies”, FICA symposium, San Diego CA, 2000
Wilson, C., Noise Control, Krieger, Malabar FL, 1994
Zimmer, I.B., R Dresnack, and C Wilson, Modeling the impact of aircraft noise on student proficiency”, NOISE-CON Portland ME, 2001 The following Internet resources may contain current information of interest:
www.faa.gov Federal Aviation Administration
www.icao.int International Civil Aviation Administration
www.fhwa.dot.gov Federal Highway Administration
environment/noise www.osha.gov Occ upational Safety and Health
Administration
TABLE 8 Design noise levels Sound level
LeqHdBA
Measurement location Land use category
57 Exterior Tracts of land in which
serenity and quiet are of extraordinary
significance.
67 Exterior Residences, schools,
churches, libraries, hospitals, etc.
72 Exterior Commercial and other
activities.
52 Interior Residences, schools,
churches, libraries, hospitals, etc.
TABLE 9 Protective noise levels
Hearing protection Leq24 All areas See Section 9.
Outdoor activity LDN Outdoors in residential
areas.
Interference and annoyance Leq24 Outdoor areas where
people spent limited amounts of time.
Indoor activity LDN Indoor residential areas.
Interference and annoyance Leq24 Other indoor areas with
human activities such as schools, etc.
Source: EPA (1974, 1979).
Trang 10www.cdc.gov/niosh Nat ional Institute for Occupational Safety and
Health
europe.osha.eu.int Eur opean Agency for Safety and Health
at Work
europa.eu.int European Union
en/record/green
www.epa.gov Environmental Protection Agency
www.who.int/ World Health Organization
environmental_
information/noise
CHARLES E WILSON
New Jersey Institute of Technology
... levels of environmentalnoise requisite to protect public health and welfare with an adequate margin of safety, EPA 550/ 9-7 4-0 04, 1974
Environmental. .. Dresnack, and C Wilson, Modeling the impact of aircraft noise on student proficiency”, NOISE- CON Portland ME, 2001 The following Internet resources may contain current information of interest:... A.P.G., Handbook of noise measurement, GenRad, Concord, MA,
9th ed., 1980
Stansfield, S and M Haines, “Chronic aircraft noise exposure and chil-dren’s