MIL-PRF-26542F
3.5.8 Effect of external magnetic field (see 4.5.6). The sensitivity of the microphone to an external 400
Hz magnetic field shall not be more than 25 percent of that of a coil consisting of 123 turns of No. 34
enameled wire closely wound in a single-layer solenoid upon a nonconductive, nonmagnetic mandrel
0.500 inch in diameter, placed in the same magnetic field.
3.5.9 Stray magnetic field (see 4.5.7). Unless otherwise specified (see 3.1), the stray magnetic field of
the microphone shall cause no more than a 5 degree deflection of a magnetic compass at a distance of
12 inches.
3.5.10 Linearity (see 4.5.8). The output of the microphone shall be a linear function of the sound
pressure input to the microphone in the range of inputs from 74 dB to 114 dB inclusive, relative to 20 µPa
at any frequency within the specified frequency response range (see 3.1). A 20 dB increment in acoustic
input shall yield a 20 dB ± 1 dB increment in the voltage output.
3.5.11 Talk-out (see 4.5.9). There shall be no subjective difference in the output of the microphone by
talking into the front and the back sound ports with equal loudness and with lips touching the moisture-
barrier guard.
3.5.12 Dielectric withstanding voltage (see 4.5.10). The product shall operate safely at its rated
voltage, and withstand momentary over-potentials due to switching, surges, and other similar
phenomena. It shall be capable of withstanding a voltage higher than its rated voltage, for a prolonged
period of time, between mutually insulated portions of the product and between insulated portions and
ground. This shall not result in either arcing or breakdown of insulation. Following such exposure, the
impedance shall change not more than 1 ohm or 5 percent from the initial measured value, whichever is
greater.
3.5.13 Interchangeability (see 4.5.11). Like units, assemblies, subassemblies, and replaceable parts
shall be electrically and mechanically interchangeable. Design tolerances shall permit parts,
subassemblies and assemblies to be used without regard to the source of supply or manufacturer.
3.5.14 Thermal shock (see 4.5.12). The product shall resist degradation in performance due to
exposure to extremes of high and low temperatures, and to the shock of alternate exposures to these
extremes, such as would be experienced when parts are transferred to and from heated shelters in arctic
areas. Following such exposure, the product shall exhibit the following performance:
Visual examination:
No evidence of physical damage which would cause a malfunction.
Sensitivity and frequency
No more than ± 3 dB variation at any frequency, when referenced to the
response:
initial response.
No more than ± 1 ohm or 5 percent variation from initial reading,
Impedance:
whichever is greater.
3.5.15 Humidity (see 4.5.13). The product shall resist degradation in performance due to exposure to
extremes of a warm, humid atmosphere, resisting such defects as corrosion, biological growth, material
property changes due to moisture penetration, and effects of condensation. Following such exposure, the
product shall exhibit the following performance:
Visual examination:
No evidence of physical damage which would cause a malfunction.
Sensitivity and frequency
No more than ± 3 dB variation at any frequency, when referenced to the
response:
initial response.
No more than ± 1 ohm or 5 percent variation from initial reading,
Impedance:
whichever is greater.
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