Microphone Sensitivity Adjustment - Telex Airman 850 Maintenance And Overhaul Manual

28 Maintenance
3. Calibrate a lab microphone.
4. Place the calibrated lab microphone 1/4 inch (6mm) above an artificial mouth
5. Connect a signal generator to the artificial mouth.
6. Adjust for an output of 74dB SPL at 1kHz @ 1/4 inch from the opening to the
7. Remove the lab microphone.
8. Position the headset microphone 1/4-inch (6mm) above the output of the
NOTE:
9. Measure the output of the headset microphone with a digital volt meter.
The output measured should be -51 ±3dBV.
5.1.1.1 Measure current of 12V Power Supply

5.1.2 Microphone Sensitivity Adjustment

If the sensitivity of the microphone does not meet the requirements from section
5.1.1 on page 27, readjust the sensitivity.
To adjust microphone sensitivity, do the following:
(Bruel and Kjaer type 4219).
lab microphone.
artificial mouth.
The acoustic hole in the boom mic should be aligned with the center of the
artificial mouth opening.
The current should be 4mA ±1mA with sound pressure supplied to the mic
and ANR turned on.
The current should be less than 1mA without sound pressure supplied to
the mic and ANR turned off.
>Turn the gain adjustment control in the microphone housing, using a small
screwdriver. For more information, see Figure 13.
>Clockwise adjustment increases output level.
Airman 850 Headset, Boom Microphone Gain Adjustment Location
FIGURE 13.
Gain Adjustment
Airman 850