Nexo Alpha System - Manual (Page 18)

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P 18
USER MANUAL
VERSION :1.01
DATE : 06/10/10
3.3.4. H YGROMETRY AND T EMPERATURE - A IR A BSORPTION
Under usual conditions, air absorption :
− increases when relative humidity decreases ;
− increases when temperature decreases.
Air absorption gives a linear attenuation, i.e. a constant value of loss of dB per meter : if 1 dB is lost from
10 to 20 meters, 2 dB will be lost from 20 to 40 meters, 4 dB from 40 to 80 meters and so on...
The tables below list these values for normalised frequencies, and various values of relative humidity and
temperature :
At 20°C :
[dB] loss / meter Up to 1 kHz 2 kHz 4 kHz 8 kHz 16 kHz
RH 20% 0 0.02 0.06 0.20 0.66
RH 50% 0 0.01 0.03 0.08 0.27
RH 80% 0 0.00 0.02 0.05 0.17
Air absorption over a 50m distance ; RH=20%-50%-80%
At RH 50% :
[dB] loss / meter Up to 1 kHz 2 kHz 4 kHz 8 kHz 16 kHz
10°C 0 0.01 0.04 0.13 0.43
20°C 0 0.01 0.03 0.08 0.27
30°C 0 0.01 0.02 0.06 0.19
Air absorption over a 50m distance ; t=10°C-20°C-30°C
20 100 1k 10k 20k
-40.00
-30.00
-20.00
-10.00
0.0
10.000
Frequency (Hz) / Attenuation (dB)
20 100 1k 10k 20k
FREQ(Hz)
-40.00
-30.00
-20.00
-10.00
0.0
10.000
LEVEL(dBV) AUDIO PRECISION vs 17 JUL 97 19:30:05