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Power |
The total energy given out by a source, as distinct from its intensity which is the energy crossing a unit area in a unit time. Power is the rate of doing work and is measured in watts. An example of work done by sound is the moving a microphone diaphragm or the tympanic membrane of the ear. However, the ear is sensitive to the rate of energy it receives, and interprets it as loudness.
Sound, however, contains little absolute power; a voice speaking softly may produce as little as 10-12 watts of power. A trombone playing fortissimo produces about 6.4 watts. The energy of a 40-watt bulb falling on an area of 1 cm2 at a distance of 1 cm produces the same energy per second as 1500 bass voices singing fortissimo.
Compare: Amplifier, Amplitude, Dynamic Range, Sound Intensity, Sound Pressure, Volume.
Power level is measured in decibels. See table below and Appendix D.
|
Power ratio |
Decibels |
Current or voltage ratio |
Decibels |
|
1 |
0 |
1 |
0 |
|
2 |
3.0 |
2 |
6.0 |
|
3 |
4.8 |
3 |
9.5 |
|
4 |
6.0 |
4 |
12.0 |
|
5 |
7.0 |
5 |
14.0 |
|
6 |
7.8 |
6 |
15.6 |
|
7 |
8.5 |
7 |
16.9 |
|
8 |
9.0 |
8 |
18.1 |
|
9 |
9.5 |
9 |
19.1 |
|
10 |
10 |
10 |
20 |
|
100 |
20 |
100 |
40 |
|
1,000 |
30 |
1,000 |
60 |
|
10,000 |
40 |
10,000 |
80 |
|
100,000 |
50 |
100,000 |
100 |
|
1,000,000 |
60 |
1,000,000 |
120 |
Table for conversion of power ratios to decibels.
In an electrical circuit, power equals the voltage times the current, as established by Ohm's Law. See also: Root Mean Square.