Soft dB I-Track User guide - Manual (Page 19)

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It is strongly recommended to perform an amplitude calibration and a phase mismatch
compensation calibration prior to the measurement of the PI residual. Enabling phase mismatch
compensation increases the PI residual and the dynamic capability of the instrument.
Some PI Residual calibrators require a certain time to equilibrate the pressure in the calibration
chamber after the insertion of the microphones.
Microphone Spacer
The microphone separation is an important parameter in the sound intensity evaluation from the
pressure gradient. In order to provide precision measurement of sound intensity, the microphone
separation distance must be carefully selected in function of frequency range.
The input configuration allows defining the selected microphone spacer. It also provides a
reminder tool to select the appropriate spacer. If a single spacer doesn’t provide a bandwidth
which is large enough to appropriately evaluate the sound intensity over the whole frequency
range, the measurement must be repeated using different spacers and combined afterwards.