HBK 4231, User Manual

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Correction for Sound Field Influence
8 Sound Calibrator Type 4231
User Manual
2) Press the microphone into the opening in the calibrator, see
Fig.2.1.
3) Press the button on the calibrator.
4) Adjust the sensitivity of measuring equipment to read the correct
value.
•
See the relevant instrument user manual for the specific
calibration procedure.
• Refer to Table 1.1 for corrected calibration levels for various
types of microphones and adaptors
• Refer to Table 2.1 for corrected calibration levels for various
types of sound field.
5) Remove the calibrator from the microphone.
6) Switch off the calibrator, or wait for it to stop, before closing the
flap on its case.
2.2 Correction for Sound Field Influence
The sound level produced by the calibrator is 94.0 dB or 114.0 dB (re
20 µPa), when measured as a pressure field in a closed coupler.
However, if you are calibrating a microphone that is going to be used
for free- or random sound field measurements (for example,
microphones used on sound level meters) a small correction is
necessary. This correction compensates for the difference between the
microphone pressure sensitivity that you get with the calibrator, and
the sensitivity in the actual sound field (free or random) in which you
are using the microphone.
Table 2.1 shows the corrected calibration levels obtained with the
calibrator for different sound fields and for different sizes of
Brüel & Kjær microphones.
No correction is required when calibrating microphones which are
used for pressure measurements.