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Microphones and Vent Sensitivity
Type 4297 has been designed to work with Microphone Pair Types 4197 and 4181, which have an
extremely low sensitivity to sound pressure at the equalisation vents due to their patented
acoustical filters. When microphones are inserted into the calibrator, their diaphragms are
exposed to the sound pressure in the calibrator, but their pressure-equalization vents are not.
Type 4297 cannot be used to measure the pressure-residual intensity index with pairs of
conventional microphones as they have vent sensitivities several orders of magnitude higher
than that of Types 4197 and 4181.
Fig.1.4
Typical intensity and sound pressure levels measured with 12 mm spacer using the arrangement shown in
Fig.1.2. The pressure-residual intensity index spectrum is characteristic of the sound intensity measurement
system and is obtained by subtracting the intensity spectrum from the pressure spectrum
90
SPL in Coupler
80
70
60
Intensity Level in Coupler
50
40
30
20
Pressure-Residual Intensity Index
10
0
10
100
Frequency (Hz)
CHAPTER 1
Introduction and Description
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