HBK 4231, User Manual

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Information for Pattern Evaluation Tests
14 Sound Calibrator Type 4231
User Manual
3.7 Information for Pattern Evaluation Tests
Ambient Sound Pressure Level
To ensure correct SPL and distortion values of the calibrator, it is
recommended to perform these measurements with an ambient
sound pressure level below 74 dB SPL lin.
Reference Orientation and Setting for RF Emission and
Immunity Test
Opening for external microphone must face away from RF antenna.
Calibrator must operate at 94 dB SPL.
3.8 How the Calibrator Works
The calibrator uses a feedback loop based on a reference microphone
(see Fig.3.3). Using this technique, the calibrator is highly stable and
almost insensitive to variations in static pressure and temperature. The
reference microphone has been specially developed for this purpose
and is optimised for stability, independence of temperature and
pressure at the 1 kHz calibration frequency.