Larson Davis 831C-FFT, Reference Manual

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SoundAdvisor Model 831C C-8
A-Weighting
: A filter that adjusts the amplitude of a frequency spectrum (20 Hz to 20 kHz) to be
perceived the same way the human ear does when exposed to low levels of sound. This weighting
is most often used for evaluation of environmental sounds. See table below.
B-Weighting
: A filter that adjusts the amplitude of a frequency spectrum (20 Hz to 20 kHz) to be
perceived the same way the human ear does when exposed to higher levels of sound in the lower
frequencies (below 1 kHz). This weighting is sometimes used for musical listening purposes. See
table below.
C-Weighting
: A filter that adjusts the amplitude of a frequency spectrum (20 Hz to 20 kHz) to be
perceived the same way the human ear does when exposed to high levels of sound. This weight-
ing is most often used for evaluation of machinery and mechanical sounds. See table below.
Flat-Weighting
: A filter that does not adjust the amplitude of a frequency spectrum. It is some-
times an alternative selection to A, B, and C-weightings.
Z-Weighting
: Similar to a flat-weighting curve, this is a bandpass filter that does not adjust ampli-
tude in the range of 10 Hz to 20 kHz.
Table C.4 Frequency Filter Response
Center Frequencies,
Hz
Weighting Network Frequency
Response
1/3
Octave
1 Octave A B C
20 -50.4 -24.2 -6.2
25 -44.7 -20.4 -4.4
31.5 31.5 -39.4 -17.1 -3.0
40 -34.6 -14.2 -2.0
50 -30.2 -11.6 -1.3
63 63 -26.2 -9.3 -0.8
80 -22.5 -7.4 -0.5
100 -19.1 -5.6 -0.3
125 125 -16.1 -4.2 -0.2
160 -13.4 -3.0 -0.1
200 -10.9 -2.0 0
250 250 -8.6 -1.3 0
315 -6.6 -0.8 0
400 -4.8 -0.5 0
500 500 -3.2 -0.3 0
630 -1.9 -0.1 0
800 -0.8 0 0
1000 1000 0 0 0
1250 0.6 0 0
1600 1.0 0 -0.1
2000 2000 1.2 -0.1 -0.2
2500 1.3 -0.2 -0.3
3150 1.2 -0.4 -0.5
4000 4000 1.0 -0.7 -0.8
5000 0.5 -1.2 -1.3