BRUEL & KJAER 4188 - Equivalent Volume and Calibrator Load Volume

Chapter 7 — Low-frequency Pressure-field
1
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" Microphone Type 4193
Equivalent Volume and Calibrator Load Volume
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
7
−
20
Maximum Sound Pressure Level
In general, the microphone should not be exposed to sound pressure levels which
produce voltages higher than the maximum input voltage specified for the connect-
ed preamplifier. After an overload, the preamplifier needs time to recover and, dur-
ing this recovery period, you cannot measure validly. The maximum input voltage
for most Brüel&Kjær preamplifiers is
±
50V (with a 130V supply). This voltage is
produced by a nominal Low-frequency Pressure-field
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" Microphone Type 4193 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 Low-frequency Pressure-field
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" Microphone
Type 4193 to levels higher than 171dB (Peak).
7.6 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.
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)
–18.2 5.4 20.7 25.4 161 166
Table 7.4 Dynamic range of the microphone with
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" Microphone Preamplifier Type 2669
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 1Hz to
20 kHz (dB)
< 3% distortion
(dB)
Max. SPL (Peak)
(dB)
–9.9 13.7 29.0 38.2 148 168
Table 7.5 Dynamic range of the microphone with
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" Microphone Preamplifier Type 2669 and
Adaptor UC0211