Chapter 5 — Free-field
1
/
2
" Microphone Type 4191
Equivalent Volume and Calibrator Load Volume
Falcon™ Range of Microphone Products
Microphone Handbook
BE1377– 12
5
−
17
produced by a nominal Free-field
1
/
2
" Microphone Type 4191 at a Peak level of
166dB (re 20µPa).
The microphone will maintain its charge up to a Peak level of 171dB (re 20µPa).
Above this level, the diaphragm and back plate short-circuit. If this occurs, the
microphone needs one or two minutes to recharge before it is ready to measure
validly. We recommend not to expose Free-field
1
/
2
" Microphone Type 4191 to levels
higher than 171dB (Peak).
5.6 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 a complex equivalent volume. This makes it easier to
evaluate the effect of microphone loading on closed cavities or acoustic calibration
couplers.
The real and imaginary parts of the equivalent volume shown in Fig.5.18 are in
parallel. They are calculated from a simple R–L–C series model of the microphone
which gives the best overall approximation of the microphone’s diaphragm imped-
ance.
The Models
The following equivalent models are valid at 101.325kPa, 23°C and 50%RH:
Lower Limit Upper Limit
1 Hz bandwidth
at 1 kHz (dB)
1
/
3
-octave at
1kHz (dB)
A-weighted (dB) Linear 20Hz to
40 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–19.0 4.6 20.0 21.4 162 171
Table 5.3 Dynamic range of the microphone
Lower Limit Upper Limit
1 Hz bandwidth
at 1 kHz (dB)
1
/
3
-octave at
1kHz (dB)
A-weighted (dB) Linear 20Hz to
40 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–16.5 7.1 21.4 25.8 161 166
Table 5.4 Dynamic range of the microphone with
1
/
2
" Microphone Preamplifier Type 2669
To Next Page
Loading...
