BRUEL & KJAER 4188 - Effect of Humidity; Effect of Vibration; Effect of Magnetic Field

Chapter 6 — Pressure-field
1
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2
" Microphone Type 4192
Effect of Humidity
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Microphone Handbook
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6
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6.13 Effect of Humidity
Due to the microphone’s high leakage resistance, humidity has, in general, no effect
on the microphone’s sensitivity or frequency response. The microphone has been
tested according to IEC68–2–3 and the effects of humidty on the sensitivity at
250Hz and the frequency response have been found to be less than 0.1dB at up to
95% RH (non-condensing) and 40°C.
6.14 Effect of Vibration
The effect of vibration is determined mainly by the mass of the diaphragm and is at
its maximum for vibrations applied normal to the diaphragm. A vibration signal of
1m/s
2
RMS normal to the diaphragm typically produces an equivalent Sound Pres-
sure Level of 65.5dB for a microphone fitted with Protection Grid DB3421.
6.15 Effect of Magnetic Field
The effect of a magnetic field is determined by the vector field strength and is
normally at its maximum when the field direction is normal to the diaphragm. A
magnetic field strength of 80A/m at 50Hz (the test level recommended by IEC and
ANSI) normal to the diaphragm produces a typical equivalent Sound Pressure Lev-
el of 16dB. Higher frequency components in the microphone output become domi-
nant at field strengths greater than 500 to 1000A/m.
Fig.6.28 Typical variation in sensitivity at 250Hz from that at 101.3kPa as a function of ambient
pressure
1 10 100 1000Ambient Pressure (kPa)
– 6
– 4
0
Response (dB)
940761e
– 2
2
4