Chapter 2 — Prepolarized Free-field
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" Microphone Type 4188
Leakage Resistance
Falcon™ Range of Microphone Products
Microphone Handbook
BE1374– 12
2
−
21
Accidentally connecting the microphone to a 200V external polarization will not
damage the microphone. However, the sensitivity will fall by at least 8dB and the
frequency response will change by 1 or 2dB. We do not recommend use in this way.
Warning!
Static electricity can destroy the microphone’s built-in charge.Therefore,
when mounting the microphone on a preamplifier, the housings of the microphone
and preamplifier must be connected before the centre pins make contact. The de-
signs of Brüel&Kjær preamplifiers and sound level meters ensure this.
2.9 Leakage Resistance
The microphone’s leakage resistance is greater than 5×10
8
Ω at 90%RH and 23°C.
2.10 Stability
2.10.1 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 Prepolarized Free-field
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" Microphone
Type 4188 well-suited for surface mounting and for mounting in small couplers as
no mechanical adaptor is required to protect the diaphragm clamping ring. The
microphone can be supported by the diaphragm clamping ring directly on the cou-
pler’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.
2.10.2 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 125°C. Below 125°C, no
changes occur. At 125°C, the sensitivity can be permanently changed within the
first hour by less than 0.1dB. After this, the sensitivity can be permanently
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