Test and Measurement World Terminology Section

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Leq vs TWA | Leq and TWA sound level measurements

This page compares Leq vs TWA and mentions Leq and TWA sound level measurements. Leq stands for equivalent continuous sound level. TWA stands for time weighted average.
Refer basics and types of sound level meters➤.

Both the terms are associated with sound level meters.

Leq-equivalent continuous sound level

Leq stands for average sound pressure over period of time. Like numerical values, logarithmic values can not be added or substracted directly. How Leq measurement is done is mentioned below.

• SLM measure sound level first.
• This level is sampled 16 times.
• Convert these dB samples into sound pressure levels.
• Add these levels and divide by number of samples to obtain average value.
Sound level meters integrate such log values by taking samples at frequent intervals over some period of time. Hence this type is known as integrating SLM.

TWA-time weighted average

As the name suggest TWA uses average of sound level over certain time period. Sound level meters which uses any grade either can be fast SLM or slow SLM type. Fast SLM uses 125 ms time constant while slow SLM uses 1 sec time constant. These time constants are defined in the standard. They are used in both analog and digital SLMs.

Following terms are used in sound level meters.
LAS-Slow, A weighted sound level
LAF-Fast, A weighted sound level
LCS-Slow, C weighted sound level
LCF-Fast, C weighted sound level



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