Chapter 7 — Low-frequency Pressure-field
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" Microphone Type 4193
Stability
Falcon™ Range of Microphone Products
Microphone Handbook
BE1379– 12
7
−
25
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 Low-frequency Pressure-field
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" Micro-
phone Type 4193 well-suited for surface mounting and for mounting in small cou-
plers 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
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.
7.10.2 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.
Note:
Special adaptors (inserted between the microphone and preamplifier) must be
made for high-temperature applications in order to protect the preampifier from
heat conduction and radiation.
7.10.3 Long-term Stability
Over a period of time, the mechanical tension in the diaphragm will decrease due to
stretching within the foil. This mechanism, which, in principle, causes an increased
sensitivity, is, however, very weak for the microphone. Measurement of this mecha-
nism is not possible at room temperature.
At present, no exact value can be given for the microphone’s long-term stability but
measured changes at high temperatures indicate that Low-frequency Pressure-field
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" Microphone Type 4193 is more than 10 times more stable than traditional
Brüel&Kjær microphones. This indicates typical changes of less than 1dB in 5000
years.
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