Description

This article is from the Acoustics FAQ, by Andrew Silverman with numerous contributions by others.

8.1 Formula for A weighting

A weighting can be found from the following formulae

For A-weighting: A(f) =
                              12200^2 f^4
------------------------------------------------------------------
(f^2 +20.6^2) (f^2 +12200^2) (f^2 +107.7^2)^0.5 (f^2 +737.9^2)^0.5

The weighting in dB relative to 1000Hz is now given by

                  A(f)
          20 lg -------        note: A(1000) = 0.794
                A(1000)

In tables, octave and third-octave frequencies are given as nominal values, for example 1250 Hz or 2500 Hz. Ideally weightings should be calculated for the exact frequencies which may be determined from the formula 1000 x 10^(n/10), where n is a positive or negative integer. Thus the frequency shown as 1250 Hz is more precisely 1258.9 Hz etc

 

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