HBK 4231, User Manual

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Chapter 3 – Characteristics
17 Sound Calibrator Type 4231
User Manual
3.9 Construction
To avoid large pressures inside the coupler when you insert a
microphone, there are channels inside the calibrator and in the exterior
casing. These channels also reduce the pressure variations caused by
handling the calibrator. These pressure equalization channels have a
low cut-off frequency to minimise the effect of outside noise.
The coupler volume in the calibrator is shaped like a Helmholtz
resonator and has a resonance frequency of 1 kHz. This makes the
acoustic system efficient and suppresses higher order distortion
components.