Acoustic Glossary


Leq, LAeq, LAeq,T : Equivalent Continuous Sound Levels .....

Leq : equivalent continuous sound level is the sound level in decibels, having the same total sound energy as the fluctuating level measured, see the IEC Definition IEC 801-22-16 below.

Leq is also known as the time-average sound level (LAT).

LAeq is the A-weighted, equivalent continuous sound level, in decibels having the same total sound energy as the fluctuating level measured.

LAeq,T is the A-weighted Leq, measured over a specified period of time (T).

Most community and industrial noise measurements are frequency weighted so the LAeq and LAeq,T descriptors are widely used.

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

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 L10, L90, Ln etc., statistical noise levels, over minutes, hours or days as required. The individual meter accuracy is classified in accordance with National and International Standards.

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.

See also LAeq(6h)LAeq(8h)LAeq(16h)LAeq(18h)

Equivalent Continuous Sound Level - formal name for the Leq

Equivalent Continuous Sound Level (Leq) is the average sound level, which over a given period of time has the same total energy as the fluctuating noise and is also known as the time-average sound level

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.

The Equivalent Continuous Sound Level (IEC 801-22-16) should not to be confused with the equivalent continuous sound pressure level (IEC 801-22-11).

See also our sound level calculations page.

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 normalised to 1 second, equivalent to the total sound energy.

Leq 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