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What is Leq Sound Level?

Primary Software: LabVIEW Toolkits>>Sound and Vibration Toolset
Primary Software Version: 4.0
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
The Sound and Vibration Toolkit has a VI named SVL Leq Sound Level.vi that returns a value called "Leq Sound Level". What is Leq Sound Level and what does it represent?

Solution:
Leq is a symbol that represents “Equivalent Continuous Noise Level”. Usually the signal that you are measuring is varying in amplitude. You can calculate the sound pressure (noise) level of an imaginary continuous signal, within a given time interval, that would produce the same energy as the fluctuating sound level that you are measuring.

The calculation is relatively simple; the Leq algorithm just divides the integrated sound pressure by the total duration of the signal. The result is expressed in dB.

  • Leq = equivalent continuous sound pressure level [dB]
  • p0 = reference pressure level = 20µPa
  • pA= acquired sound pressure in Pa
  • 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. If you want to calculate Leq across a certain band you must first filter the data to isolate the frequency band of interest. Here is an example:
The VI SVL Leq Sound Level.vi is often used in conjunction with an A-Weighting Filter to calculate equivalent continuous A-weighted sound pressure level.


Equivalent continuous A-weighted sound pressure level is widely used around the world as an index for noise. It is defined as "the A-weighted sound pressure level of a noise fluctuating over a period of time, expressed as the amount of average energy." The result is expressed in dB(A), which gives a reasonable approximation of the human perception of loudness.

Related Links:
KnowledgeBase 1ESGFH0O: Third Octave Analysis with the NI 4551/NI 4552 Dynamic Signal Analyzer (DSA) Instrument
NI Sound and Vibration Toolkit

Attachments:


Leq_Equation.JPG - Leq_Equation.JPG
LeqVI.JPG - LeqVI.JPGLeq_pic.JPG - Leq_pic.JPG

Report Date: 11/22/2006
Last Updated: 12/12/2008
Document ID: 43LD037E

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