Norsonic nor1251, Пользовательская документация

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If the level or frequency needs to be re-adjusted, this can be
done by adjusting the corresponding potentiometer. The loca-
tion of the adjustment potentiometers are shown in the Fig.
on page 9. Note that the access to the potentiometers may
have been blocked by a sealing mark.
The level should be measured with a working standard
microphone type WS2 (according to IEC61094–4) where the
pressure sensitivity at the working frequency of your calibra-
tor is known with a sufficiently high accuracy.
Microphone Effective Front Volume Corrections
Various types and makes of microphones may have different
effective front volume. Due to its working principle, the Nor-
1251 has a large effective coupler volume. The variations in
sound pressure level due to variations in effective front vol-
ume among microphones is therefore for most applications
insignificant.
The calibrator is adjusted with the ½” adaptor for an equiva-
lent microphone volume of 250 mm³, which corresponds to
most ½” measuring microphones with protecting grid mounted
like the Norsonic types 1220, 1225 and 1230. If the actual
microphone has a volume deviating from this reference vol-
ume, the accuracy may be improved by applying a volume
correction. The typical sensitivity for the level change is
+0.0003 dB/mm
3 at 1000 Hz. Hence, if a ½” microphone with
an effective front volume of 150 mm³ is used, the level in the
coupler will typically decrease by 0.03dB because of the
100mm³ volume reduction.
If no adaptor rings are used, the nominal effective front
volume for no correction is 1333 mm³. This corresponds to most
1” measuring microphones with the protection grid mounted.
Removing the rear cover will alter both the level and the frequency!
Note that the level and frequency will be altered slightly when the sound calibrator is operated without its rear cover.
Whenever adjusting the level and/or the frequency, this must be taken into account.
0,0
[dB]
0,1
-0,1
100 0 200 300 400 500 mm 3
Calibrator sound pressure level change [dB] as a function of
the microphone load volume for ½” microphones