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 ------- where A(1000) = 0.794
A(1000)
It is convenient to list A-Weighting at nominal octave or 1/3-octave (“third-octave”) frequencies, 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.
At these precise frequencies, the A- and C-Weighting values are as follows:
A, C & U Weighting Table (dB)
Nominal Exact
Frequency Frequency A-Weight C-Weight U-Weight
*
10 10.00 -70.4 -14.3 0.0
12.5 12.59 -63.4 -11.2 0.0
16 15.85 -56.7 - 8.5 0.0
20 19.95 -50.5 - 6.2 0.0
25 25.12 -44.7 - 4.4 0.0
31.5 31.62 -39.4 - 3.0 0.0
40 39.81 -34.6 - 2.0 0.0
50 50.12 -30.2 - 1.3 0.0
63 63.10 -26.2 - 0.8 0.0
80 79.43 -22.5 - 0.5 0.0
100 100.00 -19.1 - 0.3 0.0
125 125.9 -16.1 - 0.2 0.0
160 158.5 -13.4 - 0.1 0.0
200 199.5 -10.9 0.0 0.0
250 251.2 - 8.6 0.0 0.0
315 316.2 - 6.6 0.0 0.0
400 398.1 - 4.8 0.0 0.0
500 501.2 - 3.2 0.0 0.0
630 631.0 - 1.9 0.0 0.0
800 794.3 - 0.8 0.0 0.0
1000 1000.0 0.0 0.0 0.0
1250 1259 + 0.6 0.0 0.0
1600 1585 + 1.0 - 0.1 0.0
2000 1995 + 1.2 - 0.2 0.0
2500 2512 + 1.3 - 0.3 0.0
3150 3162 + 1.2 - 0.5 0.0
4000 3981 + 1.0 - 0.8 0.0
5000 5012 + 0.5 - 1.3 0.0
6300 6310 - 0.1 - 2.0 0.0
8000 7943 - 1.1 - 3.0 0.0
10000 10000 - 2.5 - 4.4 0.0
12500 12590 - 4.3 - 6.2 - 2.8
16000 15850 - 6.6 - 8.5 -13.0
20000 19950 - 9.3 -11.2 -25.3
25000 25120 -37.6
31500 31620 -49.7
40000 39810 -61.8
* There is some reason to believe that a very low frequency rollover frequency of 4 Hz may be appropriate for instruments that are to be used to measure sound affecting humans.