User manual

28
Specifications
Diffuse Field Correction Factors
A diffuse sound field is characterized by the sound arriving at
the receiver from all directions with more or less equal prob-
ability. The M2230, M2211, M2215 and M4261 are free-field
equalized measurement microphones. The default frequency
response refers to a 0° sound incidence. The diffuse-field fre-
quency response is calculated by averaging the directional char-
acteristics; this results in a reduction at the high frequencies.
The individual third-octave band correction values for diffuse-
field conditions are documented in the following table. The di-
rectional response of the M2230 is described in the appendix.
Example:
The sound pressure level in a diffuse sound field shall be •
determined. The display of the XL2 with the M2230 reads
80.0 dBA for the 20 kHz third-octave band.
The diffuse sound level is now calculated from the sum •
of the XL2 measurement value and the correction value
(80.0 dB + 8.7 dB = 88.7 dB).
This correction is not necessary using a diffuse
field equalized measurement microphone.
Nominal
Frequency
[Hz]
1/2”
Microphone
M2230, M2211, M2215
[dB]
1/4”
Microphone
M4261
[dB]
<63
63
80
0.0
0.0
0.0
0.0
0.0
0.0
100
125
160
0.0
0.0
0.0
0.0
0.0
0.0
200
250
315
0.0
0.1
0.1
0.0
0.0
0.0
400
500
630
0.1
0.1
0.1
0.0
0.1
0.1
800
1000
1250
0.2
0.2
0.3
0.1
0.1
0.1
1600
2000
2500
0.4
0.5
0.6
0.1
0.1
0.2
3150
4000
5000
0.8
1.1
1.4
0.2
0.3
0.5
6300
8000
10000
1.9
2.5
3.4
0.7
1.0
1.4
12500
16000
20000
4.6
6.4
8.7
1.9
2.5
3.2