Decibel

Decibel, pronounced DEHS uh behl, is a unit used in comparing sound pressure, voltage, power, and other related acoustical and electrical quantities. Its symbol is dB. A decibel equals one-tenth of a bel, a unit named for the Scottish-born inventor and scientist Alexander Graham Bell.

In acoustics, the decibel is frequently used to compare the intensity or pressure of sound with fixed reference levels. For measuring intensity, the most common reference level is 10 to the power of -12 watts per square meter. This level equals 0 decibels. The common reference point for sound pressure level is 2 X 10 to the power of -5 pascals. Thus, a sound pressure level of 60 decibels means that the sound pressure is 60 decibels above the reference level.

Sound at a level of 10 decibels is barely audible to the normal human ear. The level of sound pressure in a quiet room may be about 40 decibels, but a level of 70 decibels would be considered noisy. Sound at the 70-decibel level transmits 1,000 times as much energy as sound at 40 decibels.

Contributor: Thomas D. Rossing, Ph.D., Prof. of Physics, Northern Illinois Univ.

Decibel

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