# Glossary : sonometry

Sound Pressure Level : Sound Pressure is the difference between the pressure produced by a sound wave and the barometric pressure at the same point in space.

LAeq - A-weighted, equivalent sound level : A widely used noise parameter describing an sound level with the same Energy content as the varying acoustic signal measured. Also written as dBA Leq

Peak Sound Pressure - Lpk : greatest absolute instantaneous sound pressure during a given time interval.

Time Averaged Sound Pressure Level - LAT : the equivalent steady level over a given period of time that contains the same amount of noise energy as the actual fluctuating level.

Lpeak(C) : C-weighted, Peak, Sound Level.

Lday - Day equivalent level : A-weighted, Leq. Sound Level, measured over the 12-hour period 07.00 - 19.00 hours.

Lden - Day-evening-night equivalent level : A-weighted, Leq. noise level, measured over the 24 hour period, with a 10 dB penalty added to the levels between 23.00 and 07.00 hours and a 5 dB penalty added to the levels between 19.00 and 23.00 hours to reflect people's extra sensitivity to noise during the night and the evening.

Daily Exposure Level - LEX,8h : is the Leq - Equivalent Continuous Sound Level corrected for the length of the working shift, in this case 8 hours : Sound Exposure averaged over 8 hours, The Noise at Work Directive 2003/10/EC : defines the following limit and action values:

• Exposure Limit Values: LEX,8h = 87 dB(A) and LCpeak = 200 Pa respectively;
• Upper Exposure Action Values: LEX,8h = 85 dB(A) and LCpeak = 140 Pa respectively;
• Lower Exposure Action Values: LEX,8h = 80 dB(A) and LCpeak = 112 Pa respectively.

LCpeak is the maximum value of the C-weighted, instantaneous noise pressure.

Decay Time : the time taken for the Sound Pressure Level to fall by 60 dB - a million to one

Lmax - Maximum Sound Level : level during a measurement period or a noise event.

Lmin - Minimum Sound Level : during a measurement period or a noise event.

Standardized Impact Sound Pressure Level - LnT : the impact Sound Pressure Level in a stated frequency band, corrected for the standardized reverberation time of 0.5 seconds. Laboratory measurement.