decibel

Unit of measure used originally to compare sound intensities and subsequently electrical or electronic power outputs; now also used to compare voltages. A whisper has a sound intensity of 20 dB; 140 dB (a jet aircraft taking off nearby) is the threshold of pain.

An increase of 10 dB is equivalent to a tenfold increase in intensity or power. The decibel scale is used for audibility measurements, as one decibel, representing an increase of about 25%, is about the smallest change the human ear can detect.

The difference in decibels between two levels of intensity (or power) L1 and L2 is 10 log10(L1/L 2); a difference of 1 dB thus corresponds to a level of 100.1, which is about 1.026.

Decibel measurements of noise are often ‘A-weighted’ to take into account the fact that some sound wavelengths are perceived as being particularly loud. Typical sound levels in dBA are: pneumatic drill at 1 m/3 ft, 120 dBA; normal conversation, 70 dBA; and limit of audibility, 10 dBA.