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 the 'common' name for the equivalent continuous sound level, see the IEC definition below
● 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.
See also our sound level calculations article
See also • Integrating Sound Level Meters
Leq • Equivalent Continuous Sound Level - the more detailed explanation
SEL • Sound Exposure Level = Leq normalized to 1 second, equivalent to the total sound energy.