In France, the measurement of the spatial sound decay in a room is carried out in accordance with the appendix of the Decree of august 1990 the 30th used for the implementation of the article R. 235-11 of the Labor code and related to the reverberation limitation of working premises or with the standard (which is often preferred) ISO 14257 Acoustics – Measurement and parametric description of spatial sound distribution curves in workrooms for evaluation of their acoustical performance (October 2001).

Production of the acoustic field

The acoustic field is usually produced by an omnidirectional pink noise source.

Measuring equipment

The acoustic measuring equipment generally consists of a sound level meter (with a microphone) and of a calibrator.

ITS omnidirectionnal
noise source

Transfer and analysis software

A transfer and analysis software is generally used, allowing a deferred exploitation of recordings carried out on site.

Evaluation of sound spatial decay

This is the difference in decibels between the sound pressure level in a given octave band and for a microphone position located at a given distance from the reference sound source and the sound power level of the reference sound source in the same octave band.

Determination of the spatial decay of the sound pressure level by doubling the distance

This is the slope, in decibels, of the spatial sound decay curve in a given range, when the source distance doubles.


A value of the spatial decay of the sound pressure level by doubling the distance too small (illustrating excessive reverberation phenomena) can impair the acoustic comfort in some spaces (given their intended purpose) and (in some cases) conformity.