BRUEL & KJAER 4188 - Distortion

Chapter 2 — Prepolarized Free-field
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" Microphone Type 4188
Dynamic Range
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
2
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18
Distortion
The distortion is determined mainly by the microphone but, at the highest opera-
tion levels, the preamplifier also contributes to the distortion (see Fig.2.19).
The distortion is dependent on the capacitance parallel to the microphone. It in-
creases with increasing capacitance. The distortions given in Table 2.2 and Table
2.3 are valid for a parallel capacitance of 0.5pF. The distortion is measured at
100Hz but can be assumed to be valid up to approximately 5kHz (that is, where
the diaphragm displacement is predominantly stiffness-controlled). Distortion meas-
urement methods for higher frequencies are not available.
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
Fig.2.19 Typical distortion characteristics of the microphone, both
open-circuit and with
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" Microphone Preamplifier Type
2669
0.1
1
0.01
940400e
155145135125
Distortion (%)
SPL (dB)
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Harmonic
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Harmonic