Decibels

Published February 2000

From Deci- (10), and bel (after Alexander Graham Bell). A measure of power gain or loss in a sound wave relative to an arbitrarily chosen power level. Equal to ten times the logarithm of the ratio between output power and baselevel power. A difference in one decibel in the power supply to a telephone receiver produces approximately the smallest change in volume of sound which a normal human ear can detect. As applied to speech and sound levels in buildings and factories, dB is a measurement of sound energy ratios on the A-scale (440 Hertz). At 130 dB, sound is painful and deafening. The sound level on a busy city street is 100 dB. The average sound level in a large office is 60 dB.