MIL-DTL-5794C
TABLE VIII. Signal spectrum.
Frequency
Sound pressure in dB
Hz
relative
to sound pressure
at 130 Hz
130
0
300
+7
600
+8
1,000
+5
2,000
-3
3,000
-7
4,000
-9
4.6.4.3 Measurement of the signal-to-noise ratio.
4.6.4.3.1 Connection to test circuit. The microphone under test shall be mounted in its test rig with its
front grid 0.25 (¼) inch from the mouth of the signal speaker. The microphone shall be connected to the
test circuit.
4.6.4.3.2 Measurement of the signal-to-noise ratio. The short-circuit current shall be as specified in
4.6.2.3.2. The short-circuit switch shall be opened and the noise spectrum applied for 3 seconds. The
noise spectrum shall be removed and the signal spectrum applied for 3 seconds and the output of the
microphone shall be measured. The signal spectrum shall be removed and the noise spectrum applied
for 3 seconds and the output of the microphone measured. The signal-to-noise ratio shall be the quotient
of these values.
4.6.5 Burning noise (see 3.5.5). The output of the microphone unit due to burning noise shall be
measured in the circuit shown on figure 3. After the microphone unit has been conditioned according to
the procedure given, it shall remain still and without signal input for 30 seconds. The maximum output, as
indicated on Meter M-2 of the test circuit during the 10-second interval immediately following the 30-
second period, shall be the measure of the burning noise.
4.6.6 Positional characteristics. Response measurements shall be made with the microphone
mounted at angles of + 90 degrees (face up) and 90 degrees (face down). The angles shall be
measured in vertical plane between the sound source-microphone axis and the horizontal.
4.6.7 Moisture resistance (see 3.6.5). The microphone shall be subjected to the humidity resistance
test of method 106 of MIL-STD-202, except that step 7 shall not apply.
4.6.8 Altitude.
4.6.8.1 Pressure cycling (M-6A/UR only) (see 3.6.1.1.2). The microphone unit shall be subjected to 5
varying pressure cycles. Each pressure cycle shall consist of 30 minutes at 3.4 inches of mercury
(approximately 50,000 feet) and 30 minutes at 30 inches of mercury (approximately sea level). The
pressure transition shall be approximately 5,000 feet per minute. The response characteristic of the
microphone unit shall then be measured.
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