What is Leq and how is it Measured?

In acoustics, what is Leq, how it is measured and what is it used for?

Leq is the Equivalent Continuous Sound Pressure Level

Equivalent Continuous Sound Pressure Level, or 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 is not an ‘average sound level’, as it sometimes referred to. The equations used to calculate Leq are not calculating a specific average level.

Leq can be described mathematically by the following equation:
Leq 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 equivalent continuous A-weighted sound pressure level determined over time interval Tm is as follows:
Leq Equation
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:
Total Leq Equation


Here are some Sound Meters which measure Leq:


Find out more about Leq and measuring sound on our Noise at Work Regulations Competent Persons Course

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