## The Decibel Scale

Sound intensity is measured on the decibel scale (dB), with a decibel beingof a bel. This is a logarithmic scale, needed because human hearing is sensitive to a wide range of sound intensities. Th decibel scale compares any given sound intensity with the intensity of sound at the threshold of hearing – the quietest sound that a person can hear, taken to be equal toand labelled

Mathematically, the intensity level in decibels is given by

The intensities of some sounds on the decibel scale is shown below.

Example: The sound intensity near to a plane about to take off is

The sound intensity in decibels is