Acoustic Glossary


Leq, LAeq, Equivalent Continuous Sound Level ...

Leq., LAeq. and LAeq,T

Sound Levels usually vary over time. Leq is the equivalent continuous sound level in decibels, equal to the total sound energy measured over a stated period of time. Leq is also known as the time-average sound level (LAT).

LAeq is the A-weighted, equivalent continuous sound level in decibels usually measured over a stated period of time, denoted LAeq,T where T is the measurement time.
Most community and industrial noise measurements are A-weighted so the LAeq descriptor is widely used

Early sound level meters had a very limited dynamic range, so if the noise levels fluctuated by more then 20 dB during a measurement the accuracy was in doubt. They also used exponential averaging circuits (Fast, Slow etc.) which helped the operator average the meter fluctuations by eye, but introduced another accuracy limitation.

Modern class 1, integrating sound level meters monitor a wide range of fluctuating levels faithfully and the digital linear averaging circuits record and display the Leq (average energy) time histories and the L10, L90, Ln etc., statistical noise levels, over minutes, hours or days as required.

Leq is widely used, but not widely understood - click here for a more detailed explanation.

Leq is normally based on an exchange rate of 3 dB. An 8-hour Leq is also known as LEP,d = LEX,8h.

Leq is the 'common' name for the equivalent continuous sound level, see the IEC definition below

Equivalent Continuous Sound Level

Equivalent Continuous Sound Level is the average sound level which over a given period of time has the same total energy as the fluctuating noise.

Equivalent Continuous Sound Level Definition IEC 801-22-16, logarithm of the ratio of a given time-mean-square, standard frequency-weighted, sound pressure for a stated time period, to the square of the reference sound pressure of 20 μPa. Equivalent continuous sound level in decibels is ten times the logarithm to the base ten of that ratio.
Note 1 : if a frequency-weighting is not specified, the A-frequency weighting is understood.
Note 2 : in principle, exponential time weighting is not involved.

Equivalent continuous sound level should not to be confused with equivalent continuous sound pressure level.

See also our sound level calculations article

Short Leq

Short Leq is the preferred modern method of storing sound levels and displaying the true time history of noise events and all other sound levels during any specified period of time. The resulting 'time histories', typically measured in 1/8 second intervals may then be used to calculate the 'overall' levels for any sub-period of the overall measurement time.

See also integrating sound level meters
Leq (equivalent continuous sound level) - a more detailed explanation
SEL (sound exposure level) - the Leq normalized to 1 second, equivalent to the total sound energy.

Related Terms
CNEL - community noise equivalent level
Lday - day, equivalent sound level
Lden - day-evening-night, equivalent sound level)
Ldn - day-night equivalent sound level
LEP,d - daily personal noise exposure level
LEP,w - weekly personal noise exposure level
LEX,8h - daily noise exposure level
Noise Dose
Sound Energy
Sound Level and Integrating Sound Level Meters
Sound Exposure
Sound Pressure
See also the IEC Definition of Level

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