BRUEL & KJAER 4188 - Leakage Resistance; Stability

Chapter 7 — Low-frequency Pressure-field
1
/
2
" Microphone Type 4193
Leakage Resistance
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Microphone Handbook
Brüel & Kjær
7
−
24
7.9 Leakage Resistance
To maintain the correct polarization voltage on the microphone, the microphone’s
leakage resistance must be at least 1000 times greater than the supply resistance
of the polarization charge, even under the most severe environmental conditions.
This resistance which is generally placed in the preamplifier, is typically 10
9
to
10
10
Ω. Brüel&Kjær microphones have a very high leakage resistance which is
greater than 5×10
15
Ω at 90%RH and 23°C.
7.10 Stability
7.10.1 Mechanical Stability
The microphone’s design with respect to mechanical stability is improved compared
with traditional Brüel&Kjær microphones. The diaphragm clamping ring is less
sensitive to accidental force and the protection grid is significantly reinforced.
Therefore, the microphone can withstand mechanical shocks better than traditional
Brüel&Kjær microphones.
Fig.7.22 Effect of polarization voltage on frequency response. The curves show the difference from
the response with a polarization voltage of 200V (normalised at 250Hz)
940608e
100 1k 10k 100kHz
-2
-1
0
1
2
Response (dB)
2.5
-2.5
Frequency (Hz)
28 V
150 V
250 V