BRUEL & KJAER 4188 - Page 123

Chapter 5 — Free-field
1
/
2
" Microphone Type 4191
Equivalent Volume and Calibrator Load Volume
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
5
−
18
Model 1
C = 0.082 x 10
-12
m
5
/N
L = 253kg/m
4
R = 278x 10
6
Ns/m
5
where C = acoustic diaphragm compliance
L = acoustic diaphragm mass
R = acoustic diaphragm damping resistance
Model 2
V
lf
=11.6mm
3
f
0
=35kHz
Q =0.2
where V
lf
= low-frequency volume
f
0
= diaphragm resonance frequency
Q = quality factor
Calibrator Load Volume
When the microphone with its protection grid is inserted into the coupler of a
calibrator, it will load the calibrator by a volume of 190mm
3
at 250Hz.
Load volume correction to Pistonphone Type 4228 Calibration Level (with
Adaptor DP0776):
+0.02dB
Fig.5.18 Typical equivalent volume (real and imaginary parts) based on mathematical model of
microphone
100 1k 10k 100k
Frequency (Hz)
– 2
0
4
Volume (mm
3
)
940947e
2
6
8
10
12
– V (Im)
V (Re)