| Inside Home |
25 |
45 |
| Inside Office |
35 |
50 |
| Inside Airplane Cabin |
75 |
85 |
| Inside Factory |
65 |
100 |
| Talking @ 3 ft |
55 |
65 |
| Shouting @ 3 ft |
75 |
85 |
| Clothes Dryer @ 3 ft |
55 |
65 |
| Vacuum @ 3 ft |
65 |
80 |
| Chain Saw @ 3 ft |
100 |
120 |
| Clothes Washer @ 3 ft |
55 |
75 |
| Car @ 25 ft @ 65 mph |
70 |
80 |
| Airplane @ 1000 ft |
95 |
110 |
| Traffic @ 300 ft |
40 |
60 |
| Rural Ambient |
25 |
35 |
 Sound powers
for the following equation in dBA units are referenced to a picowatt (10-12 W).
Where: W1, W2 = sound power in similar units of watts
The threshold of pain for the human ear is usually taken to be around 120 dBA.
One of the best compilation of noise power level data can be accessed in Chapter 5
of the Occupational Safety and Health Administration's
OSHA Technical Manual website.
Loudness is the subjective human response to sound. It depends primarily on sound
pressure but is also influenced by frequency. Three different internationally standardized
characteristics are used for sound measurement: weighting networks A, C, and Z (or
"zero" weighting). The A and C weighting networks are the sound level meter's means
of responding to some frequencies more than others. The very low frequencies are
discriminated against (attenuated) quite severely by the A-network and hardly attenuated
at all by the C-network. Sound levels (dB) measured using these weighting scales
are designated by the appropriate letter (i.e., dBA or dBC). The A-weighted sound
level measurement is thought to provide a rating of industrial noise that indicates
the injurious effects such noise has on human hearing and has been adopted by OSHA
in its noise standards (OTM/Driscoll). In contrast, the Z-weighted measurement is
an unweighted scale (introduced as an international standard in 2003), which provides
a flat response across the entire frequency spectrum from 10 Hz to 20,000 Hz. The
C-weighted scale is used as an alternative to the Z-weighted measurement (on older
sound level meters on which Z-weighting is not an option), particularly for characterizing
low-frequency sounds capable of inducing vibrations in buildings or other structures.
A previous B-weighted scale is no longer used.
The following tables present examples of some common noise sources.
| Military Jet @ Takeoff w/Afterburner |
50 |
Carrier Flight Deck |
140 |
128x |
| Civil Defense Siren |
100 |
|
130 |
64x |
| Commercial Jet @ Take-off |
200 |
|
120 |
32x Threshold of Pain |
| Pile Driver |
50 |
Rock Music Concert Inside NY Subway |
110 |
16x |
| Ambulance Siren Newspaper Press Gas Lawn Mower |
100 5 3 |
|
100 |
8x Very Loud |
| Food Blender Prop Plane Flyover Diesel Truck |
3 1,000 150 |
Boiler Room Printing Press Plant |
90 |
4x |
| Garbage Disposal |
3 |
Higher Limit of Urban Ambient Sound |
80 |
2x |
| Passenger Car, 65 mph Living Room Stereo Vacuum Cleaner |
25 15 10 |
|
70 |
0x (reference) |
| Normal Conversation Air Conditioning Unit |
5 100 |
Data Processing Center Department Store |
60 |
1/2x |
| Light Traffic |
|
Large Business Office Quiet Urban Daytime |
50 |
1/4x |
| Bird Calls (distant) |
|
Quiet Urban Nighttime |
40 |
1/8x |
| Soft Whisper |
5 |
Library and Bedroom at Night Quiet Rural Nighttime |
30 |
1/16x |
| |
|
Broadcast and Recording Studio |
20 |
1/32x Just audible |
| |
|
|
10 |
1/64x |
| |
|
Picowatt (10-12 W) power level |
0 |
1/128x Threshold of hearing |
| Source: Compiled by Kimley-Horn and Associates, Inc., for
the San Diego County government |
The networks evolved from experiments designed to determine the response of the
human ear to sound, reported in 1933 by a pair of investigators named Fletcher and
Munson. Their study presented a 1,000-Hz reference tone and a test tone alternately
to the test subjects (young men), who were asked to adjust the level of the test
tone until it sounded as loud as the reference tone. The results of these experiments
yielded the frequently cited Fletcher-Munson, or "equal-loudness," contours shown
in the chart below.
Fletcher-Munson Contours, OSHA
|
