Ear sensitivity varies according to frequency but also sound intensity. Weighting curves (A, B and C), designed to reproduce the frequency response of the human ear on sound level meters, have been standardised (ISO recommendation R 1761). Nowadays, only curve A is used for environmental measurements.
The order of 23 January 1997 establishing the measurement method to be used in all cases, refers to the so-called “short equivalent levels” method defined by AFNOR standard NF S31-010 “Characterisation and measurement of environmental noises – Specific measurement methods” (December 1996), which is the most commonly used method in the environmental domain. It requires a specifically adapted sound level meter. All modern sound level meters are now designed to use this method.
This method does not measure the level equivalent to the noise considered but a succession of consecutive equivalent levels referred to as “short” because they are measured over a duration generally ranging from 1 to 10 s, stored in the sound level meter and subsequently processed on a computer by appropriate software.
Treatment methods are based on prevention:
Order of 20 August 1985 relative to airborne noise emitted into the environment by classified installations for environmental protection
Order of 23 January 1997 relative to the limitation of the noise emitted into the environment by classified installations for environmental protection
AFNOR standard NF S31-010