ACOUSTIC
A-WEIGHTING CONVERSION
Introduction:
A-weighting is a commonly used
family of curves relating to the measurement of Sound Pressure Level. A-weighting
is applied to measured sound levels in an effort to account for the relative loudness
perceived by the human ear. The A-weighting curve reflects the 40 phon curve
from the Equal Loudness Contour or Fletcher Munson curves. The unit of
A-weighted Sound Pressure Level is expressed in dB(A).
Formula:
To add A-weighting,
Level in dB(A) = Level in dB +
A-Weighting value
To remove A-weighting,
Level in dB = Level in dB(A) -
A-Weighting value
A-Weighting conversion table (To add A-weighting):
1/1 Octave band
|
Frequency
Bands (Hz) |
A-Weighting
Values |
|
31.5 |
-39.4 |
|
63 |
-26.2 |
|
125 |
-16.1 |
|
250 |
-8.6 |
|
500 |
-3.2 |
|
1000 |
0 |
|
2000 |
1.2 |
|
4000 |
1 |
|
8000 |
-1.1 |
|
16000 |
-6.6 |
1/3 Octave band
|
Frequency
Bands (Hz) |
A-Weighting
Values |
|
12.5 |
-63.6 |
|
16 |
-56.4 |
|
20 |
-50.4 |
|
25 |
-44.7 |
|
31.5 |
-39.4 |
|
40 |
-34.6 |
|
50 |
-30.2 |
|
63 |
-26.2 |
|
80 |
-22.5 |
|
100 |
-19.1 |
|
125 |
-16.1 |
|
160 |
-13.4 |
|
200 |
-10.9 |
|
250 |
-8.6 |
|
315 |
-6.6 |
|
400 |
-4.8 |
|
500 |
-3.2 |
|
630 |
-1.9 |
|
800 |
-0.8 |
|
1000 |
0 |
|
1250 |
0.6 |
|
1600 |
1 |
|
2000 |
1.2 |
|
2500 |
1.3 |
|
3150 |
1.2 |
|
4000 |
1 |
|
5000 |
0.5 |
|
6300 |
-0.1 |
|
8000 |
-1.1 |
|
10000 |
-2.5 |
|
12500 |
-4.3 |
|
16000 |
-6.6 |
|
20000 |
-9.3 |
Single Value Determination:
Once levels of each frequency
band are A-weighted, those A-weighted levels can be added logarithmically in
order to obtain a single overall level value. For example, if there are n level
values from S1, S2, …, Sn, the total level S is given by,
S = 10*log10{10^(S1/10) +
10^(S2/10) + … + 10^(Sn/10)}
Note:
A-Weighting can only be
applied on spectral data, i.e., each Octave frequency band carries a weighting
factor. A single unweighted level value cannot be directly A-weighted. For
example, a single overall value of 80dB cannot be converted in dB(A) due to
lack of spectral information.
