What is Leq Sound Level?

Updated May 3, 2018

Reported In

Software

  • LabVIEW Sound and Vibration Toolkit

Issue Details

NI Sound and Vibration Software has a VI named SVL Leq Sound Level.vi that returns a value called Leq sound level [dB EU]. What is Leq sound level and what does it represent?

Solution

Leq represents a value known as Equivalent Continuous Sound Level. Usually the sound pressure level (SPL) you are measuring varies in amplitude over time. Leq, on the other hand, is the imaginary constant SPL that would produce the same energy as the fluctuating sound level you are measuring over a given time interval. 

Additional Information

The equation to calculate Leq divides the integrated, normalized sound pressure by the duration of interest of the signal. The result is expressed in units of decibels:
  • Leq = equivalent continuous sound pressure level in dB
  • p0 = reference pressure level (typically 20 µPa)
  • pA = acquired sound pressure
  • t1 = start time for measurement
  • t2 = end time for measurement

It is important to note that the Leq calculation is performed on time domain data, so the resultant sound level does not represent any specific band of frequencies. To calculate Leq across a certain band, you must first filter the data to isolate the frequency band of interest. The example below uses the SVL Leq Sound Level.vi in conjunction with an A-weighted filter to calculate the equivalent continuous A-weighted sound pressure level of a signal:
 

Equivalent continuous A-weighted sound pressure level is a common measurement used in industry to characterize noise levels in loud environments. The result is expressed in dB(A), a weighted decibel scale that filters frequency components to roughly imitate the hearing profile of the human ear.

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