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Sound measuring (Noise measuring)
Weighting filter after DIN EN 61672-1 2003-10 (DIN-IEC 651)
Calculation: Frequency f → dBA und dBC
Notice: Sound level meters measure the sound pressure level in dBSPL.
Sound pressure is a sound field quantity.
At sound level analyzers the display (attack time tin) is time weighted. There are different settings:
| Slow (S): | tin | = | 1000 ms | |||
| Fast (F): | tin | = | 125 ms | |||
| Pulse (I): | tin | = | 35 ms, | tout | = | 1500 ms |
There is no formula for conversion from dBA to dBSPL and vice versa.
The A-weighting filter curve is defined from 20 Hz to 20 kHz.
dBA: The decibel A filter is widely used. dBA roughly corresponds to the inverse
of the 40 dB at 1 kHz equal-loudness curve for the human ear.
Using this filter, the sound level meter is less sensitive to very high and very low frequencies.
Measurements made with this scale are expressed as dBA.;
dBC: The decibel C filter is practically linear over several octaves and is suitable
for subjective measurements at very high sound pressure levels.
Comparing dBA and dBC
| Relative Response (dB) | Frequency f in Hz | ||||||||
| 31.5 | 63 | 125 | 250 | 500 | 1000 | 2000 | 4000 | 8000 | |
| dB(A) | -39.5 | -26.2 | -16.2 | -8.7 | -3.2 | 0 | 1.2 | 1 | -1.1 |
| dB(C) | -3 | -0.8 | -0.2 | 0 | 0 | 0 | -0.2 | -0.8 | -3 |
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