Chapter 6 — Pressure-field
1
/
2
" Microphone Type 4192
Leakage Resistance
Falcon™ Range of Microphone Products
Microphone Handbook
BE1378– 12
6
−
21
6.9 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.
6.10 Stability
6.10.1 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.
The sensitivity change of the microphone is less than 0.1dB after a free fall of 1m
onto a solid hardwood block (re IEC68–2–32).
This improved mechanical stability makes Pressure-field
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2
" Microphone Type 4192
well-suited for surface mounting and for mounting in small couplers as no mechani-
cal adaptor is required to protect the diaphragm clamping ring. The microphone can
be supported by the diaphragm clamping ring directly on the coupler’s surface. Any
force of less than 5Newtons will cause a change in sensitivity of less than 0.005dB.
This makes the microphone well-suited for fitting in small, plane wave couplers
used for reciprocity calibration and any other small coupler with a well-defined
volume.
6.10.2 High-temperature Stability
The diaphragm is made of a stainless steel alloy. The alloy has been carefully
selected and is very resistant to heat. This means that the diaphragm tension (and
therefore the sensitivity) remain the same, even after several hours’ operation at
high temperature.
The microphone has been tested at temperatures up to 300°C. Below 170°C, no
changes occur. At 170°C, the sensitivity can be permanently changed within the
first 10hours by less than 0.025dB. After this, the sensitivity can be permanently
changed within the next 100hours by a similar value. At 300°C, the sensitivity can
be permanently changed within the first hour by +0.4dB. After this, the sensitivity
can be permanently changed within the next 10hours by less than +0.4dB.
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