MIL-DTL-5794C
4.6.2.6 Response measurements (individual tests). Prior to making response measurements, the
microphone unit shall be conditioned as specified herein or according to some other specifically approved
method, which will produce equivalent results. Each microphone units shall be subjected to response
tests at not less than 6 (six) approved frequencies, such as 400, 1,000, 2,000, 3,000, and 4,000 Hz. The
specified frequencies to be used will be determined by the procuring activity on the basis of tests made
on the first article samples and information gained in the initial stages of production. Sweep or band
frequency tests may be employed provided the contractor demonstrates the suitability of such tests to the
procuring activity. The method of testing and the selection of frequencies shall be such that they will truly
indicate the overall response characteristics and output level of the microphone.
4.6.3 Microphone unit resistance (see 3.5.3). The microphone unit resistance shall be measured at
the time the 1,000-Hz response is being determined, as specified in 4.6.2.4, by the voltmeter-ammeter
method and meters M-1 and M-3 read simultaneously utilizing the circuit shown on figure 3.
4.6.4 Signal-to-noise ratio test (see 3.5.4).
4.6.4.1 Noise spectrum. By means of suitable apparatus similar to that detailed on figure 6, or equal,
and the test circuit on figure 7, or equal, provision shall be made for the production of the noise spectrum
shown in table VII at an rms sound pressure of 115 dB above a reference level of 20 µPa, as measured at
the microphone diaphragm. The "noise" source shall be a loud speaker capable of producing a sound
pressure of 115 dB above a reference level of 20 µPa at the rear as well as the front of the microphone
and the loudspeaker shall be located as far away from the microphone as practicable. The calibrating
microphone shall be mounted in the test rig, in the box, 0.25 (¼) inch from the mouth of the signal
speaker, which shall be short-circuited during adjustments of the noise spectrum.
4.6.4.2 Signal spectrum. By means of the apparatus as set up previously, provision shall also be
made for the production of the following signal spectrum shown in table VIII, at an rms sound pressure of
115 dB above a reference level of 20µPa. The "signal" source shall be the driver unit. The calibrating
microphone shall be positioned 0.25 (¼) inch directly in front of the driver unit.
TABLE VII. Noise spectrum.
Frequency
Sound pressure in dB relative
Hz
to sound pressure
at 130 Hz
40
0
70
0
130
0
300
-5
600
-9
1,000
-13
2,000
-17
3,000
-19
4,000
-21
16
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