Average sound level, sound exposure level, and noise dose

The practical enforcement of any specification concerning sound, whether for the sound output of a sonar or the insulation of a house against aircraft noise, is facilitated by the reporting of sound measurements in the fewest possible ways. The possible ways are those covered by definitions of terms and measurement procedures available in internationally accepted standards. Definitions are here offered for three recently developed quantities; means of calculating one from the others are described. Average sound level is a sound level that is typical of the various levels that exist at a certain place during a stated period of time; technically, average sound level is the level of a time-mean-square A-weighted sound pressure, unless some other rule of averaging is specified; it may be called equivalent sound level; the unit is the decibel. Sound exposure level is the level of sound accumulated during a stated time interval or event; unless another rule of integration is specified, sound exposure level is the level of the time integral of squared A-weighted sound pressure; the unit is the decibel. Noise dose is the duration of a specified constant sound level that would lead to the same sound exposure level as an actual time-varying sound; noise dose is expressed usually as a fraction or percentage of a specified duration, like eight hours.