Acoustic Glossary


Leq, LAeq, Equivalent Continuous Sound Level : Definitions, Terms, Units, Measurements ..


is the sound level in decibels equivalent to the total sound energy measured over a stated period of time


is the sound level in decibels equivalent to the total A-weighted sound energy measured over a stated period of time.

Most community and industrial noise measurements are A-weighted so the LAeq descriptor is 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 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 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. 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 formal IEC definition directly below

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. The 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.

Not to be confused with IEC 801-22-11, equivalent continuous sound pressure level
Equivalent Continuous Sound Level is also known as the Leq
Equivalent Continuous Sound Level is also known as the Time-average Sound Level (LAT)

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 - the more detailed explanation
SEL : Sound Exposure Level = Leq normalised to 1 second, equivalent to the total Sound Energy.

Related Terms •
CNEL : Community Noise Equivalent Level
LAIeq : A-weighted, Impulse, Leq, Sound Pressure Level.
LCeq : C-weighted, Leq, Sound Pressure Level
Lday : Day equivalent level
Lden : Day-evening-night equivalent level
Ldn : Day-night equivalent level
LEX,8h : Daily Exposure Level
LEP,d : Daily Personal Noise Exposure -
LEP,w : Weekly Personal Noise Exposure
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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