Chapter 7 — Low-frequency Pressure-field
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" Microphone Type 4193
Sensitivity
Falcon™ Range of Microphone Products
Microphone Handbook
BE1379– 12
7
−
5
These text files can be viewed on Microsoft
®
Windows™ using the Brüel&Kjær
Microphone Viewer program (BK–MIC.EXE) supplied on the disk. They can also be
accessed by a suitable spreadsheet for further processing or printing.
Brüel&Kjær Microphone Viewer must be installed before use (see section 1.3.5).
7.1.4 Adaptor UC0211
Adaptor UC0211 is for use of Low-frequency Pressure-field
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" Microphone Type
4193 with microphone preamplifers Types 2669 and 2639. The adaptor lowers the
electrical lower-limiting frequency (the –3dB point) of the microphone/preamplifer
combination to 0.1Hz (see section 7.3.2 and section 7.3.4).
The adaptor’s capacitance is 100pF and it increases the preamplifer’s input capaci-
tance.
In addition to extending the microphone/preamplifer combination’s frequency range,
the adaptor also:
●
Lowers the sensitivity (see section 7.2)
●
Increases the inherent noise (see Table 7.4)
●
Reduces the 3% distrotion limit (see Table 7.4)
●
Slightly changes the frequency response due to varying input capacitance with
frequency (see Fig.7.20 and section 7.3.1)
7.1.5 Recommended Recalibration Interval
With normal handling of the microphone and any associated instrument,
Brüel&Kjær recommends that the microphone be recalibrated every 2 years.
Low-frequency Pressure-field
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" Microphone Type 4193 is very stable over this
period (see section 7.10 to section 7.12). Improper handling is by far the most likely
cause of change in the microphone’s properties. Any damage which causes improper
operation can probably be detected using a sound level calibrator. In many cases,
the damage can be seen by carefully inspecting the protection grid and diaphragm.
7.2 Sensitivity
7.2.1 Open-circuit Sensitivity
The open-circuit sensitivity is defined as the sensitivity of the microphone when not
loaded by the input impedance of the connected preamplifier (the termination is
described in IEC1094–2). The sensitivity is measured for the individual microphone
at 251.2Hz and stated on the microphone’s calibration chart (see section 7.1.2) and
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