Norsonic nor1218, Instruction Manual

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4 Chapter 3
Microphone calibration
Microphone calibration
The Nor1218 can be calibrated with a sound calibra-
tor for ½” microphones without the need for special
couplers. We recommend using Nor1251 (1000 Hz) or
Nor1253 (250 Hz).
Unscrew the upper part of the Nor1218 to gain
access to the microphone cartridge. Mount the
calibrator slowly and carefully while turning the calibrator
and switch it on. See figure.
If the calibrator frequency is 250 Hz, adjust the
reading to be the level stated for the calibrator, e.g.
124,0 dB for Nor1253 with 124 dB specified level.
If the calibrator frequency is 1000 Hz, adjust the
reading to be 0,1 dB below the stated calibrator level,
e.g. 113,9 dB for Nor1251 calibrator with a stated level
of 114 dB.
This is only valid if the frequency response
correction is turned off. For the Nor131 and Nor139 the
frequency correction is turned off, when entering into
the calibration menu. Perform calibration and calibrate
the microphone as a normal free field microphone. I.E.
-0.1 dB if using a 1000 Hz calibrator. When leaving
the calibration menu, you will observe that the level
measured with the calibrator on, is different from what
obtained in the calibration mode. This is correct, and
is due to the frequency correction added. If horizontal
reference axis is selected, the signal will be about
0.1 dB higher than the calibrated signal, if vertical
reference axis is selected the signal will be 0.3 dB
lower than the calibrated level. This does not apply if
you calibrate with a 250 Hz calibrator since there is no
correction added at this frequency.