unit expressing the relative intensity of a sound. The intensity in bels is the logarithm (to the base 10) of the ratio of the power of the sound to that of a reference sound. Ordinarily, the reference sound is assumed to be one with a power of 10-16 watts per sq cm, approximately the threshold of a normal human ear at 1000 hz.
Origin: a.G. Bell, Scottish-U.S. Scientist, 1847-1922