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Sensitivity to Sound Pressure at the Equalization Vent
Ideally, the pressure-sensing microphones used with an intensity probe should only detect the
sound pressure at their diaphragms. In other words, the sensitivity to sound pressure at their
static-pressure equalization vents should be zero.
Microphone Pairs Types 4181 and 4197 are designed to have a very low vent sensitivity. Fig.A.1
shows the difference in vent sensitivity between these microphones which were developed
especially for intensity measurements and conventional measurement microphones that were
previously used for intensity probes. The vent sensitivity is expressed in dB with respect to the
diaphragm sensitivity.
Fig.A.1
Comparison of vent sensitivities of microphones from a Type 4181 pair and a Type 4197 pair. These
microphone pairs have the extra pressure equalization vents (phase correctors). The curve is compared with
the result from a Type 4177, the original intensity microphone pair based on two microphones, Type 4165,
which had no phase correctors. Note that Types 4181 and 4177 are no longer in production.
0
-10
-20
-30
-40
-50
-60
-70
-80
Type 4177 / 4165
Type 4181 & Type 4197
5
2
10
Appendix A
20
50
Frequency (Hz)
100
200
881362/1
31
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