MIL-PRF-26542/7B
REQUIREMENTS
Color: Semi gloss black, 27038 in accordance with FED-STD-595.
Component parts: See figure 1.
Microphone element: See figures 1 and 2.
Bracket assembly: See figure 1.
Cord assembly: See figures 1 and 3.
Impedance: 4-6 ohms.
Resistive load: 5 ohms.
Performance:
Sensitivity at ground level: 51.5 ± 3 dB above 1 microvolt (µV), with a Sound Pressure Level input of
115 dB above 20 micropascals (µPa) at 1 kHz, when tested with the microphone sound port .187 inch
± .015 inch (4.75 mm ± 0.38 mm) from, and coaxial with, the opening of the artificial voice.
Sensitivity at simulated altitude: Sensitivity shall be not more than 3 dB below the ground level
sensitivity, when tested at 10,000 feet.
Frequency response: The frequency response of the microphone, compared to the response of 51.5
dB at 1,000 Hz, shall be within the limits shown on figure 4, when tested with the microphone sound
port .187 inch ± .015 inch (4.75 mm ± .38 mm) from, and coaxial with, the opening of the artificial
voice. However, the difference between any two successive readings 100 Hz apart (up to 1,000 Hz)
and 250 Hz apart (above 1,000 Hz) shall not exceed 2.5 dB, under all standard and service
conditions. The response shall fall off at a rate of not less than 3 dB per octave, below 300 dB, and 6
dB per octave above 4,000 Hz.
Distortion: The harmonic distortion in the microphone shall not exceed 4 percent, under standard
conditions, or 5 percent, after being subjected to service conditions.
Pressure equalization: The response of the microphone at 1,000 Hz shall not vary by more than 4
percent, from the reference established at 15,000 feet, while the microphone is subjected to a pressure
increase corresponding to a descent from an altitude of 15,000 feet (16.7 inches of mercury) to sea level
(30.0 inches of mercury) at a rate of 5,000 feet per minute.
Stray magnetic field: The stray magnetic field of the microphone shall not cause more than a 3º
deflection, when placed within 8 inches of a magnetic compass.
Weight: The weight of the microphone shall not exceed 1.5 ounces.
Interchangeability: The equipment should meet the interchangeability requirements, as defined in
MIL-HDBK-5400.
First article and conformance inspection: The microphone assembly shall be tested in accordance with
the tests listed in table I. For First Article Test (FAT), see table I. For conformance inspection, see
groups A and B in table I.
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