Chapter 5 — Free-field
1
/
2
" Microphone Type 4191
Effect of Ambient Pressure
Falcon™ Range of Microphone Products
Microphone Handbook
BE1377– 12
5
−
25
The effect of temperature on the free-field response (see Fig.5.25) of the microphone
is the sum of the following effects:
●
the calculated effect of the change in the speed of sound due to temperature on
the 0°-incidence free-field correction
●
the measured change in the actuator response due to temperature (see Fig.5.23).
5.12 Effect of Ambient Pressure
The microphone’s sensitivity and frequency response are affected by variations in
the ambient pressure. This is due to changes in air stiffness in the cavity behind
the diaphragm, and changes in air mass in the small gap between the diaphragm
and the back plate. The effects are shown in Fig.5.26 to Fig.5.28.
Fig.5.25 Typical variation in 0°-incidence free-field response with
Protection Grid DB3421 (normalized at 250Hz) as a
function of temperature, relative to the response at 20°C
(see Fig.5.7) over the temperature range defined by
IEC651
Frequency (Hz)1 k 10 k
1.0
Response (dB)
– 1.5
– 1.0
– 0.5
0.0
0.5
500 Hz
1.5
940809/1e
50 k
– 10°C
50°C
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