What is Leq and how is it Measured?

What is Leq? How it is measured? And what is it used for?

Leq (or LAeq) is the Equivalent Continuous Sound Pressure Level

Equivalent Continuous Sound Pressure Level, or Leq/LAeq, is the constant noise level that would result in the same total sound energy being produced over a given period.

LAeq is a fundamental measurement parameter designed to represent a varying sound source over a given time as a single number. This number is a measure of the energy contained within the sound at the point of the receiver. This is useful in terms of the potential for sound to damage or disturb and is extensively used in environmental noise standards as well as many other regulations and documents.

Read our Managers Guide to Noise at Work and freshen up your knowledge.

The Maths

It can be measured in either A, C or Z (Linear) modes, but you should remember that it’s not an ‘average sound level’, as it sometimes referred to. In the equation used to calculate Leq it’s important to remember that this doesn’t calculate a specific average level.

Leq can be described mathematically by the following equation:
Leq Equation

  • 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 equivalent continuous A-weighted sound pressure level determined over time interval Tm is as follows:
Leq Equation

In practice, it is possible to take Leq readings in durations as short as 5 minutes, so long as your sound meter provides all variations of noise emissions. As with any sample of data, the more you have the more accurate your results.

For this reason we’d recommend longer than 5 Leq measurements to ensure greater accuracy.

How to add Leq values together

Adding Leq values requires taking an anti-log of each value.

The addition can be performed as shown:

Learn about Leq and measuring sound on our Noise at Work Regulations Course

Here are some Sound Meters which measure Leq:

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