TB 9-4931-413-50
(1) Position sound-level calibrator (table 2) securely over test instrument
microphone, making sure that microphone is seated properly over lip of coupler.
NOTE
Step (2) below is for model 1551-C only.
(2) Set test instrument attenuator switch to 130 CAL and WEIGHTING switch to
CAL. Test instrument meter will indicate in center of white area marked CAL. If not,
perform b(1) below.
(3) Set attenuator switch to 110.
(4) Energize sound-level calibrator and adjust frequency to 500 Hz.
Test
instrument will indicate between 112.8 and 114.8 db. If not, perform b(2) below
(5) Repeat (2) through (4) above, as applicable, several times until correct
indications are obtained on meter.
NOTE
Throughout this procedure, pressure corrections should be
made to sound-pressure-level readings, using pressure
correction chart (fig. 1), according to the nearest 1000-foot
elevation above sea level of the calibration site.
b. Adjustments
(1) Adjust microphone sensitivity adjustment (fig. 2) until meter pointer indicates in
center of white area marked CAL.
(2) Adjust CAL control (screwdriver adjustment on front panel of model 1565-A)
until meter indicates 113.8 db.
8. Frequency Response
a. Performance Check
(1) Position test instrument controls as indicated in (a) through (c) below:
(a) METER BATTERIES switch to FAST (not applicable to model 1565-A).
(b) WEIGHTING switch to C (CF).
(c) Attenuator switch to 110 db.
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