MIL-PRF-26542 Microphone, And Microphone Assemblies, Dynamic General Specification ForThis specification covers the general requirements for moving coil, noise-canceling dynamic microphones. The products described herein are used in oxygen and gas-masks, and headset-microphones \(boom-mounted and protective-shield mounted\). These parts provide communications within moderate to high noise environments, at ground level and altitude, as specified, and meet established United States Air Force sensitivity standards \(see 6.1\).

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MIL-PRF-26542F

4.5.9 Talk-out (see 3.5.11). Each microphone shall be given a talk-out test. The tester shall talk

separately into the front and back sound ports of the microphone with equal loudness and with lips

touching the moisture barrier guard. The tester shall wear a good quality headset which is connected to

the microphone through a suitable amplifier and shall listen to his own voice to determine if there is a

difference in sound level, when he is talking into either the front or back sound port of the microphone and

to ensure that the microphone is functioning in a satisfactory manner. The amplifier used in this test shall

not contain automatic gain control or other circuits that will compensate for low microphone output.

4.5.10 Dielectric withstanding voltage (see 3.5.12). Following the initial impedance readings as stated

below, the product shall be tested in accordance with method 301 of MIL-STD-202. The following details

shall apply:

a. Test voltage: 250 volts.

b. Nature of potential: 60 Hz ac.

c. Points of application: Between one terminal and the external surface of the microphone case with

the use of a metal bracket or equivalent provided by the manufacturer.

4.5.11 Interchangeability (see 3.5.13). All mechanical dimensions shall be gauged or measured to

determine conformance to the physical interchangeability requirements of 3.5.13. When a dimension is

not within the specified or design limits, it shall be considered a major defect.

4.5.12 Thermal shock (see 3.5.14). Following the initial readings and examination as stated below, the

equipment shall be tested in accordance with method 107 of MIL-STD-202. The following details shall

apply:

a. Special mounting: The microphone element shall be mounted on the boom.

b. Test condition letter; A.

c. Measurements before and after test: Visual examination, frequency response at ground level, and

impedance at 1,000 Hz.

4.5.13 Humidity (see 3.5.15). Following the initial readings and examination as stated below, the

equipment shall be tested in accordance with method 507 of MIL-STD-810. The following details shall

apply:

a. The number of 48-hour cycles for this test is 5 (five).

b. The temperature/humidity levels shall be 60 degrees "C" and 95 percent, respectively.

c. Measurements after test: Before and within 1 (one) hour after the test, the frequency response at

ground level shall be measured, the impedance at 1,000 Hz shall be determined; and the

microphone shall then be examined for evidence of damage.

4.5.14 Drop (see 3.5.16). Following the initial readings and examination, the equipment shall be

dropped 12 (twelve) times at random from a height of 6 (six) feet onto concrete faced with 0.125 inch

thick asphalt tile. The impedance at 1,000 Hz, sensitivity, and frequency response characteristics of the

microphone element shall be measured and a mechanical inspection shall be made before and after

completion of the tests.