United States
Environmental Protection
Agency
January 1981
OPA 22/1
&EPA
Noise
and its
Measurement
-------
T
he damage done by the pollution of our air and
water is widely recognized. The evidence is right
before our eyes, in contaminated water, oil spills and
dying fish, and in smog that burns the eyes and
sears the lungs.
Noise is a more subtle pollutant. Aside from sonic
booms that can break windows, noise usually leaves
no visible evidence, although it also can pose a
hazard to our health and well-being. An estimated
14.7 million Americans are exposed to noise that
poses a threat to their hearing on the job. Another
13.5 million of us are exposed to dangerous noise
levels without knowing it from trucks, airplanes.
motorcycles, hi-fi's, lawnmowers, and kitchen ap-
pliances.
Recent scientific evidence shows that relatively
continuous exposures to sound exceeding 70
decibels expressway traffic, for instance can be
harmful to hearing. More than that, noise can cause
temporary stress reaction which includes increases
in heart rate, blood pressure, blood cholesterol levels
and effects in the digestive and respiratory systems.
With persistent, unrelenting noise exposure, it is
possible that these reactions become chronic stress
diseases such as high blood pressure or ulcers.
Knowing the damage that noise is doing, what can
we do about reducing it?
First we musl identify the noise source and
measure its output. Accurate analysis and measure-
ment are the first steps in controlling noise.
What Is Sound?
Sound travels in waves through the air like waves
through water. The higher the wave, the greater its
power. The greater the number of waves a sound
has, the greater is its frequency or pitch.
The strength of sound, or sound level, is measured
in decibels (dB). The frequency is measured in Herlz
(Hz) (cycles per second). However, the human ear
does not hear all frequencies. Our normal hearing
ranges from 20 Hz to 20,000 Hz or, roughly, from the
lowest note on a great pipe organ to the highest note
on a violin.
The human ear also does not hear all sounds
equally. Very low and very high notes sound more
faint to our ear than 1000 Hz sounds of equal
strength. This is the way our ears function.
The human voice in conversation covers a
median range of 300 to 4000 Hz. The musical scale
ranges from 30 to 4000 Hz.
Noise in these ranges sounds much louder to us
than very low or very high-pitched noises of equal
strength.
-------
Loudness and Decibels
Because hearing also varies widely between
individuals, what may seem loud to one person may
not to another. Although loudness is a personal
judgment, precise measurement of sound is made
possible by use of the decibel scale. This scale.
shown below, measures sound pressure or energy
according to international standards
Sound Level;
Common Sounds
Carrier deck
|et operation
Air raid siren
Jet takeoff (200 feet)
Thunderclap
Discotheque
Auto horn (3 feet)
Pile drivers
Garbage truck
Heavy truck (50 feet)
City traffic
Alarm clock (2 feet)
Hair dryer
Noisy restaurant
Freeway traffic
Man's voice (3 feet)
Air conditioning unit
(20 feet)
Light auto traffic
(100 feet)
Living room
Bedroom
Quiet office
Library
Soft whisper (15 feet)
Broadcasting studio
» and H
Noise
Level
(dB)
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
luman Response
Effect
Painfully loud
Maximum vocal effort
Very annoying
Hearing damage (8 hours)
Annoying
Telephone use difficult
Intrusive
Quiet
Very quiet
Just audible
Hearing begins
This decibel (dB) table compares some common sounds and
shows how they rank in potential harm to hearing Note that
70 dB is the point at which noise begins to harm hearing. To
the ear. eacti 10 dB increase seems twice as loud
-------
The decibel scale is logarithmic (based on powers
of ten), not linear like a ruler. Therefore, a small
increase in decibels represents a great increase in
intensity. For example, while 10 decibels is 10 times
more intense than one decibel, 20 decibels is 100
times more intense (10x10. rather than 10+ 10), 30
decibels is 1000 times more intense (10 * 10 x 10)
and so on. The sound intensity multiplies by 10 with
every 10-decibel increase. The reason for such a
scale is simply that the human ear is sensitive over
such a wide range of acoustic energy that the
numbers involved had to be compressed for con-
venience.
In some ways, the decibel scale resembles the
Richter scale for earthquakes A small numerical
increase represents a great increase in intensity.
The ear can detect a very slight change in noise
intensity. Even a small reduction in decibels then
can make a difference.
Measuring Noise Scientifically
In response to mounting public concern over
environmental noise, new and better ways of
measuring it have been developed. In the past.
typical sound level meters were the size of TV sets.
Now they are no larger than pocket transistor radios
and measure noise with laboratory accuracy. In
addition, their use requires no special scientific
training.
This means that the average citizen or city
employee can reliably monitor noise, making
possible new opportunities for noise abatement and
control. Prices for good sound level meters start
around S200. a cost within the reach of most
municipal budgets.
-------
How Meters Work
Sound level meters have three or four scales for
measuring noise The A scale is used most often to
measure neighborhood noise. It electronically filters
the low and high frequencies and responds to
sounds much the same as the human ear The graph
below shows that the ear is most sensitive to sounds
in the 1000-4000 Hz range.
20 50 100
Frequency Hz
200 500 1000 2K
5K 10K 20K
Human response to pure tones of equal
Sound Pressure Level.
The B. C and D scales on noise meters are used
for more specialized noise readings. The D scale, for
instance, is the one being considered for use in
measuring the noise of jet engines at airports.
-70
102
10'
104
10 2 5
Frequency Hz
The Weighting Curves A, B, C and D
While jet engines generate a great concentration
of high frequency noise, diesel locomotives generate
noise that is heavily weighted in the lower frequen-
cies, so a different scale may be used to measure
their noise, usually the C scale.
-------
Breaking Noise Into Parts
The noise abatement engineer may need to
analyze the noise from a particular source so that he
can identify its origin and eliminate the cause.
Using the example of a jet engine, the engineer
may determine that the high-pitched whine comes
from one part of the engine while learning that other.
less bothersome frequencies come from another
part. He will then concentrate his work on the par! of
the engine that makes the most trouble.
To solve the problem, the engineer may use a
sophisticated noise analyzer together with a graphic
sound level recorder to break the noise down into its
individual ingredients.
Summary
With new methods like these, we are coming to
grips with the problem of noise and how to reduce it.
Accurate noise measuring instruments have made it
possible to replace arguments over what is too loud
with statements of scientific fact.
These new instruments are proving invaluable to
manufacturers who want to make quieter equipment.
and to State and local officials who want to reduce
noise.
The Environmental Protection Agency, through its
ten Regional Offices, offers equipment and technical
assistance to State and local governments with
noise problems. EPA technicians also consult with
manufacturers.
By using noise monitoring equipment of simple
design and moderate cost, we can now go a long
way toward reducing noise pollution and benefit the
health and well-being of all Americans.
The tools are there. It is up to us to use them
effectively.
-------
Hearing Protectors
In today's mechanized world it is virtually impossi-
ble for an active person to avoid exposure to poten-
!'aHv harmful sound levels.
For this reason, hearing specialists now recom-
mend that we get into the habit of wearing
protectors, not only to guard against hearing loss but
to reduce the annoying effects of noise.
There are two basic types of hearing protectors:
muffs worn over the ears and inserts worn in the ear.
Well-fitting protective muffs are more effective, but
inserts also do a good job if properly fitted. Since ear
canals are rarely the same size, inserts should be
separately fitted for each ear. Cotton plugs are
virtually useless.
Protective muffs should be adjustable to provide a
good seal around the ear, proper tension of the cups
against the head, and comfort.
Both types of protectors are available at many
sports stores and drugstores. They are well worth
the small inconvenience they cause for the wearer.
Hearing protectors are- recommended for the
following:
At work: Construction. Lumber, Mining. Steel.
Textiles.
During recreational and home activities: Target
shooting and hunting, Power tool use, Lawn mowing.
Snowmobile riding.
Note: These are only some of the jobs and activities
where hearing protectors are beneficial. Protectors
are also helpful when concentration is necessary in
the home or office.
-------
If you have suggestions, questions
or requests for further information, they
may be directed to your nearest
EPA Regional office.
EPA Region 1 JFK
Federal Bldg. Boston
MA 02203 Connec-
ticut. Maine. Massachu-
setts. New Hampshire.
Rhode Island. Vermont
617-223-7223
EPA Region 2 26
Federal Plaza New
York NY 10007. New
Jersey. New York. Puer-
to Rico. Virgin Islands
212-264-2515
EPA Region 3* 6th
and Walnut Streets
Philadelphia PA 19106
Delaware. Maryland.
Pennsylvania. Virginia.
West Virginia. District of
Columbia
215-597-4081
EPA Region 4 345
Courtland Street NE
Atlanta GA 30308.
Alabama. Georgia.
Florida. Mississippi.
North Carolina. South
Carolina. Tennessee.
Kentucky
404-881-3004
EPA Region 5 « 230 S.
Dearborn Chicago IL
60604* Illinois. Indiana,
Ohio. Michigan. Wiscon-
sin. Minnesota
312-353-2072
EPA Region 6 1201
Elm Street* Dallas TX
75270 « Arkansas. Loui-
siana. Oklahoma. Texas.
New Mexico
214-767-2630
EPA Region 7 324
East 11th Street *
Kansas City MO
64106 Iowa. Kansas.
Missouri. Nebraska
816-374-6201
EPA Region 8 1860
Lincoln Street
Denver CO 80295 Col-
orado. Utah. Wyoming.
Montana. North Dakota.
South Dakota
303-837-3878
EPA Reg ion 9* 215
Fremont Street San
Francisco CA 94105
Arizona. California. Hawaii.
Nevada. Pacific Islands
415-556-1840
EPA Region 10* 1200
Sixth Avenue Seattle
WA98101 'Alaska.
Idaho. Oregon. Washing-
ton 2O6-442-1203
5°
Q) O
=i.
oo
o c
^ in
-05
is
Q) V
u
o
o
n
?.B 3 S.
o 2
T3m T> -H
re -oo 5-
3 S S.
CD
------- |