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A Weighting

This is the most generally used filter when making overall noise measurements. The attenuation of the sound signal with an A-weighted filter corresponds to the fact that the human ear is not as sensitive to sound of the lower frequencies as it is at the higher frequencies.

The A weighting curve approximately follows the equal loudness curve of 40 phons.

The 40 phon curve shown in red and the inverted (40dB-A weighting) A-weighting curve shown in blue.

The inverted A weighting curve was calculated based on the fact that the A-weighting is 0dB at 1000Hz and the 40 phon curve is 40dB at 1000Hz, therefore, these two points coincide.

The A-weighting value in decibels as a funcion of frequency is given by:

W_A = weighting to be applied, dB; f = frequency, Hz

: Enter frequency and level in either dB or dB(A) to get conversion and weighting or frequency only to get weighting.

The following are tabulated standard A weighting values for the 1/3 Octave centre frequencies.

Frequency Hz	A weighting dB	Frequency Hz	A weighting dB
20	-50.5	800	-0.8
25	-44.7	1000	0
31.5	-39.4	1250	0.6
40	-34.6	1600	1
50	-30.2	2000	1.2
63	-26.2	2500	1.3
80	-22.5	3150	1.2
100	-19.1	4000	1
125	-16.1	5000	0.5
160	-13.4	6300	-0.1
200	-10.9	8000	-1.1
250	-8.6	10000	-2.5
315	-6.6	12500	-4.3
400	-4.8	16000	-6.6
500	-3.2	20000	-9.3
630	-1.9

where s is the complex variable.