Chapter 2 — Prepolarized Free-field
1
/
2
" Microphone Type 4188
Equivalent Volume and Calibrator Load Volume
Falcon™ Range of Microphone Products
Microphone Handbook
BE1374– 12
2
−
19
produced by a nominal Prepolarized Free-field
1
/
2
" Microphone Type 4188 at a Peak
level of 158dB (re 20µPa).
The microphone’s distortion increases smoothly as a function of sound pressure
level until the diaphragm’s displacement becomes so large that it hits the back
plate. When this occurs (at a Peak level of 157dB), the output voltage is clipped.
We recommend not to expose Prepolarized Free-field
1
/
2
" Microphone Type 4188 to
levels higher than 157dB (Peak).
2.6 Equivalent Volume and Calibrator Load Volume
Equivalent Volume
For some applications it is practical to express the acoustic impedance of the micro-
phone diaphragm in terms of an equivalent volume. This makes it easier to evalu-
ate the effect of microphone loading on closed cavities or acoustic calibration
couplers.
The typical equivalent volume of Prepolarized Free-field
1
/
2
" Microphone Type 4188
is 65mm
3
.
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 208mm
2
at 250Hz.
Load volume correction to Pistonphone Type 4228 Calibration Level (with
Adaptor DP0776):
+0.02dB
Lower Limit Upper Limit
1 Hz bandwidth
at 1 kHz (dB)
1
/
3
-octave band
at 1 kHz (dB)
A-weighted (dB) Linear 20Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–24.5 –0.9 14.2 14.5 146 157
Table 2.2 Dynamic range of the microphone
Lower Limit Upper Limit
1 Hz bandwidth
at 1 kHz (dB)
1
/
3
-octave band
at 1 kHz (dB)
A-weighted (dB) Linear 20Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–21.7 1.9 15.8 20.1 146 157
Table 2.3 Dynamic range of the microphone with
1
/
2
" Microphone Preamplifier Type 2669
To Next Page
Loading...
