Chapter 4 — Free-field
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" Microphone Type 4190
Equivalent Volume and Calibrator Load Volume
Falcon™ Range of Microphone Products
Microphone Handbook
BE1376– 12
4
−
17
produced by a nominal Free-field
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" Microphone Type 4190 at a Peak level of
154dB (re 20µPa).
The microphone will maintain its charge up to a Peak level of 159dB (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
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" Microphone Type 4190 to levels
higher than 159dB (Peak).
4.6 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.4.18 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)
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3
-octave band
at 1 kHz (dB)
A-weighted (dB) Linear 20Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–24.3 –0.7 14.6 15.3 148 159
Table 4.3 Dynamic range of the microphone
Lower Limit Upper Limit
1 Hz bandwidth
at 1 kHz (dB)
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3
-octave band
at 1 kHz (dB)
A-weighted (dB) Linear 20Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–23.6 0.0 15.0 17.0 147 154
Table 4.4 Dynamic range of the microphone with
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" Microphone Preamplifier Type 2669
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