Sound intensity is measured on the decibel scale (dB), with a decibel being
of 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 to
and 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
