Acoustic A-Weighting Conversion

 

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.