Outdoor Microphone System - Page 15
G.R.A.S. Sound & Vibration
4.2 Pistonphone
If actuator calibration results give rise to suspicion by showing abnormal variations, i.e. in
excess of 0.4 dB (temperature coefficient accounted for), after a warm-up period of at least one
hour, a Pistonphone calibration is advisable.
A calibration using a Pistonphone (or Sound Calibrator) requires first removing the windscreen
from the Outdoor Microphone System and mounting a special adapter in its place: no other
parts need be removed.
Use Adapter RA0009
1
for Type 41AM
Use Adapter RA0041
1
for Type 41CN
Note: remove the black plastic cone from the rain-protection cap only if a Sound Calibrator
is to be used.
The RA0009/RA0041 consists of a support tube with a close-fitting collar which holds together
the two halves of a split coupler. The two halves of the split coupler are engraved with a
common number to show that they are correctly matched. The correction values supplied with
each RA0009/RA0041 must be applied to the nominal value for the Pistonphone or Sound Cali
-
brator used (+ means add, – means subtract).
When using a Pistonphone, apply any barometric correction in the normal way. The Piston
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phone/Calibrator must be fitted with a coupler for 1-inch microphones.
Once the windscreen has been removed, mount the adapter as follows (refer to Fig. 4.2):
Fig. 4.2 Mounting the Adapter RA0009/RA0041
1
The Adapter RA0009/RA0041 is not included with the Outdoor Microphone System Type 41AM/41CN but is available on sepa
-
rate order.
Fig. 4.1 Calibration Control Box AC0001
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2
3
4
1
