MIL-DTL-5794C
4.6.2.3.4.1 Set oscillator for maximum driver response. The oscillator shall be set at that frequency
between 1,000 and 3,000 Hz, at which the response of the driver is maximized.
4.6.2.3.4.2 Set driver output sound pressure level. The driver input voltage shall be adjusted at that
frequency, to 127 dB sound level (the maximum sound pressure level developed during conditioning
shall, therefore, not exceed 127 dB).
4.6.2.3.4.3 Determine reference conditioning voltage. The oscillator frequency shall be changed to
1,000 Hz without disturbing the output control of the oscillator. The voltage read on output meter 2 on
figure 5, shall then be taken as the 1,000 Hz reference conditioning voltage.
4.6.2.3.5 Adjust input voltage. The driver input voltage shall be adjusted at 1,000 Hz to the value
required for conditioning (see 4.6.2.3.4.3).
4.6.2.3.6 Perform conditioning sweep cycles. The oscillator frequency shall be continuously varied
from 1,000 to 3,000 and returned to 1,000 Hz audio frequency range 3 times at a rate of approximately
one complete sweep in 2 seconds.
4.6.2.3.7 Adjust oscillator to zero. At the conclusion of the third sweep cycle, the oscillator output
voltage shall be gradually reduced to zero.
4.6.2.3.8 Delay before response measurements. Approximately 2 seconds shall elapse, before
starting response measurements in a specific test run.
Caution: The microphone unit shall not be disturbed by loud clicks from the driver unit, noises,
vibrations, or accidental bumps during "conditioning" or measurements of response, resistance or
thermal noise.
4.6.2.4 Response measurement. After the microphone unit under test has been conditioned in
accordance with the above procedure, the sound level, determined as specified in 4.6.2.2 shall be
applied. The response (output level) of the microphone unit shall be determined for each test frequency.
Measurements shall start at 200 Hz and progress through each successively higher test frequency up to
4,000 Hz. The sound output from the driver shall be left on in changing the oscillator from one test
frequency to the next, but the sound input to the microphone unit shall not exceed 115 dB in effecting the
changes in frequency. This shall not be construed as prohibiting the use of push-button frequency control
in production testing, provided that substantially equivalent results are obtained.
4.6.2.5 Response curves. The response curves of the microphone units, based on the contractor's
test data, shall be plotted on 20 divisions per inch (total 120 divisions) by two 4.5-inch cycles, semi-
logarithmic graph paper. The axis of ordinates shall cover the range of from + 10 to + 70 dB. Each
vertical division shall be 0.5 dB. Resistance, thermal noise and signal-to-noise ratio values for the
microphone units shall also be shown on the curve sheets. It is necessary that the total time for taking
the response curve does not exceed 3 minutes in order that the carbon button may not completely lose its
conditioning.
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