Chapter 7 — Low-frequency Pressure-field
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Frequency Response
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Microphone Handbook
Brüel & Kjær
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7.3.4 Low-frequency Response
The low-frequency response (see Fig.7.3) is the typical response with the vent ex-
posed to the sound field. If the vent is not exposed to the sound field, the sensitivity
increases from 0dB at the reference frequency (251.2Hz) to approximately 0.2dB at
1Hz.
For applications where the vent is not exposed to the sound field, take care to
ensure proper static pressure equalization to prevent static displacement of the
diaphragm.
The microphone’s low-frequency response is common for all types of sound field.
The microphone’s lower limiting frequency (–3dB) is between 10 and 50mHz with
the vent exposed to the sound field. If used with Adaptor UC0211 and
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phone Preamplifier Type 2669, the microphone’s lower limiting frequency (–3dB) is
below 0.1Hz with the vent exposed to the sound field. The ibdividual microphone’s
lower limiting frequency (–3dB) is stated on its calibration chart.
7.3.5 Free-field Response
The microphone’s free-field correction curves are shown in Fig.7.6 and Fig.7.8.
These corrections are added to the microphone’s actuator response obtained using
Electrostatic Actuator UA0033 in order to determine the free-field response at any
angle of incidence. The typical free-field response at 0° incidence with and without
the protection grid are shown in Fig.7.7 and Fig.7.9.
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