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Sounds can be measured using absolute units of energy or pressure, e.g.
watts per unit area or millibars, but these numbers become very large and impractical.
Thus the Decibel (dB) system was developed. Sound is expressed in terms of logarithmic
ratio between two values, usually the intensity or pressure of the sound being
measured and a reference intensity or pressure. The formula for calculating a logarithmic
ratio, or level, in decibels is expressed as:
Using the logarithmic ratio we can compress the entire range of audible
sound pressure into a convenient scale of 0 to 140 dB.
Common Sounds
This decibel (dBA) table compares some common sounds and shows
how they rank in potential harm to hearing. In many industries, workers
are exposed to dangerous noise levels. This is particularly true in the
construction, lumber, mining, steel and textile industries.
| SOUND |
NOISE
LEVEL (dBA) |
EFFECT |
| Boom Cars |
140 |
|
| Jet Engines
(Near) |
140 |
|
| Shotgun Firing |
130 |
|
| JET TAKEOFF (100-200
Fl.) |
130 |
|
| Rock Concerts
(Varies) |
110-140 |
Threshold of Pain (125 dB) |
| Oxygen Torch |
121 |
|
| Discotheque/Boom Box |
120 |
Threshold of Sensation (120
dB) |
| Thunderclap (Near) |
120 |
|
| Stereos (Over 100 Watts) |
110-125 |
|
| Symphony Orchestra |
110 |
Regular Exposure of more
than 1 minute risks permanent hearing loss (over 100 dB) |
| Power Saw (Chain Saw) |
110 |
| Jackhammer |
110 |
| Snowmobile |
105 |
|
| Jet Fly-over (1000 Ft.) |
103 |
|
| Electric Furnace Area |
100 |
No more than 15 minutes
of unprotected exposure recommended (90-100 dB) |
| Garbage Truck / Cement Mixer |
100 |
| Farm Tractor |
98 |
| Newspaper Press |
97 |
|
| Subway / Motorcycle (25 ft.) |
88 |
Very annoying |
| Lawn Mower / Food Blender |
85-90 |
Level at which hearing damage (8 hrs.)
begins (85 dB) |
| Recreational Vehicles / TV |
70-90 |
|
| Diesel Truck (40Mph, 50 Ft.) |
84 |
|
| Average City Traffic Noise |
80 |
Annoying; interferes with conversation;
constant exposure may cause damage |
| Garbage Disposal |
80 |
|
| Washing Machine |
78 |
|
| Dishwasher |
75 |
|
| Vacuum Cleaner |
70 |
Intrusive; interferes
with telephone conversation |
| Hair Dryer |
70 |
| Normal Conversation |
50-65 |
|
| Quiet Office |
50-60 |
Comfortable (under 60 dB) |
| Refrigerator Humming |
40 |
|
| Whisper |
30 |
Very quiet |
| Broadcasting Studio |
30 |
|
| Rustling Leaves |
20 |
Just audible |
| Normal Breathing |
10 |
|
| |
0 |
Threshold of normal hearing
(1000-4000 Hz) |
Since the sensitivity of the ear to sound is not the same
for all frequencies, weighting or attenuating filters are included in the
sound level meter's circuits to simulate the ear's response. A noise
level meter gives an instantaneous measurement of the noise present, but
cannot measure the duration of the exposure. To measure the amount
of noise a person is exposed to over a period of time, a "dosimeter"
or an integrated sound level meter must be used. Sources for above
include the American Medical Association and the Canadian Hearing Society
of Ontario. Decibel table developed by the National Institute on Deafness
and Other Communication Disorders, National Institutes of Health, Bethesda,
Maryland 20892. January 1990.
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