bel [Alexander G. Bell, Canadian inventor, 1847–1922] , a unit that expresses intensity of sound. It is the logarithm (to the base 10) of the ratio of the power of any specific sound to the power of a reference sound. The most common reference sound has a power of 10−16 watts per square centimeter, or the approximate minimum intensity of sound at 1000 cycles per second that is perceptible to the human ear. An increase of 1 bel approximately doubles the intensity or loudness of most sounds. See also decibel.
