LAeq is the A-weighted Leq sound level.
LAeq,T is the A-weighted Leq sound level, measured over a specified period of time (T)
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 sound 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 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
Equivalent Continuous Sound Level (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. Also known as the time-average sound level
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 the equivalent continuous sound pressure level.
See also our sound level calculations article