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Noise Measuring Technology

Working Group 1.63

Free Field Microphone Calibration

The sound pressure unit of a calibrated primary standard microphone is transferred to a tested microphone by a substitute procedure.

The technical measuring process is the comparison between two sound-pressure-proportional microphone voltages at constant sound pressure, using the substitute voltage procedure.

Standard and tested microphone are both exposed to the same sound pressure level ( 84 dB, sine with f= const. ) in an approximate free sound field.

Reference conditions are:

Temperature 23,0 ºC, atmospheric pressure 101,3 kPa and relative humidity 50%.

The temperature and humidity of the low reflection chamber used for free field calibration is stabilized to reference environmental conditions.


Measurement uncertainties for single frequency ranges in dB (re 1 V/Pa)

Frequency range in Hz

Measurement uncertainty in dB

25 - 80 0,4
100 - 5.000 0,2
6.300 - 10.000 0,3
12.500 - 20.000 0,4


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