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ALPHA ARRAYS - SOME BASIC RULES
ALPHA SERIES USER MANUAL V1.0
DATE: 14/01/00 18:27
Hygrometry and Temperature - Air Absorption
Under usual conditions, air absorption increases when relative humidity decreases and 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
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
Air absorption over a 50m distance; t=10°C-20°C-30°C
The speed of sound C varies with temperature according to the formula below:
273
t
20
C
+
°
=
Where t° is the temperature in °C
The delay time between two sources spaced at a distance d is then:
∆
t = C/d
20
100
1k
10k
20k
-40.00
-30.00
-20.00
-10.00
0.0
10.000
Frequency (Hz) / Attenuation (dB)
