Leq is the constant noise level that would result in the same total sound energy being produced over a given period. It can be measured in either A, C or Z (Linear) modes.

Leq can be described mathematically by the following equation:

Where:

• Leq is the equivalent continuous linear weighted sound pressure level re 20µPa, determined over a measured time interval Tm (secs)
• P(t) is the instantaneous sound pressure of the sound signal
• P0 is the reference sound pressure of 20µPa

When the instantaneous A-weighted sound pressure (PA) of the sound signal is introduced the the equivalent continuous A-weighted sound pressure level determined over time interval Tm is as follows:

In practise when measuring noise it is possible to take Leq readings, with your instrument, of short duration, ie <5 minutes, providing all variations of noise emissions are covered. If the measured environment changes greatly then the longer the Leq measurement is taken the more accurate the measurement.

Adding Leq values requires taking an anti-log of each value. The addition can be performed as shown: