MIL-DTL-5794C
The microphone unit shall be placed in an altitude chamber and the pressure inside the chamber reduced
from 30 inches of mercury (approximately sea level) to that corresponding to an altitude of 15,000 feet
(approximately 16.7 inches of mercury). The response of the microphone unit shall be measured at that
simulated altitude. The response of the microphone unit shall also be measured at a frequency of 1,000
Hz while the pressure is being varied at a rate of 5,000 feet per minute (up or down).
4.6.8.3 Response at simulated altitude of 10,000 feet (M-51/UR only) (see 3.6.1.2). The microphone
unit shall be placed in an altitude chamber. The response of the microphone unit at ground level shall be
obtained at 300, 500, 1,000, 2,000, 3,000 and 4,000 Hz. Pressure inside the chamber shall then be
reduced to 20.4 inches of mercury, corresponding to an altitude of 10,000 feet. The response of the
microphone unit shall be taken again at the same frequencies as mentioned above.
4.6.9 Temperature cycling (see 3.6.3). The microphone shall be subjected to the thermal shock test of
method 107, condition A of MIL-STD-202.
4.6.10 Temperature extremes (see 3.6.4).
4.6.10.1 Low temperature. The microphone unit shall be exposed to an ambient temperature of 62
degrees C, for 2 hours. Remove the microphone from the cold chamber and immediately measure the
response under normal room temperature conditions.
4.6.10.2 High temperature. The microphone unit shall be exposed to an ambient temperature of + 71
degrees C, for 2 hours. Remove the microphone unit from the hot chamber and immediately measure its
response under normal room temperature conditions.
4.6.11 Salt atmosphere (see 3.6.2). The microphone unit shall be subjected to the salt spray test in
washed in tap water to remove excess salt deposits and then excess moisture removed. The response
characteristics shall be measured immediately after removal from the salt spray chamber.
4.6.12 Immersion (M-51/UR only) (see 3.5.8). The microphone unit shall be immersed in tap water, at
room temperature to a covering depth of 3 feet for a period of 2 hours. The response characteristics of
the microphone unit shall be measured immediately after removal from the water.
4.6.13 Vibration (see 3.5.6 and 3.6.7). The microphone unit shall be placed in a vertical position on a
vibration machine giving motion in 3 planes; vertical, horizontal and 45 degrees to the horizontal of 0.03
inch amplitude (0.06 inch total excursion), and the frequency of vibration varying from 10 to 50 to 10 Hz
approximately every 3 minutes. The microphone shall be connected in a test circuit providing for a
carbon current of 50 milliamperes. The test shall be conducted for a period of one hour. The current
shall be turned on for 2 minutes and off for 2 minutes alternately for the duration of the test.
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