DeciBel

A customary logarithmic measure most commonly used (in various ways) for measuring sound.Sound is measured on a logarithmic scale. Informally, if one sound is 1 bel (10 decibels) "louder" than another, this means the louder sound is 10 times louder than the fainter one. A difference of 20 decibels corresponds to an increase of 10 x 10 or 100 times in intensity. The beginning of the scale, 0 decibels, can be set in different ways, depending on exactly the aspect of sound being measured. For sound intensity (the power of the sound waves per unit of area) 0 decibel is equal to 1 picoWatts per Metre Squared. This corresponds approximately to the faintest sound that can be detected by a person who has good hearing. For sound pressure (the pressure exerted by the sound waves) 0 decibels equals 20 micropascals RMS, and for sound power 0 decibels sometimes equals 1 picoWatt. In all cases, one decibel equals ≈ 0.115129 neper.

-- QUDT