MIL-PRF-25670/2C
REQUIREMENTS:
Dimensions and
configuration:
See figure 1.
Weight:
1.25 ounces, maximum.
C
Color:
The back case shall be dull black, or an equivalent low-contrast, dark color,
while the front cover shall be either clear, anodized aluminum or black, in
order to indicate the versatility of the parts' use in both ground-level and
altitude applications.
C
Breather:
If the earphone element includes a breather hole in the back case, either
as a hydroscopic breather, or a pressure equalization port, it shall be no
more than .125 inches in diameter.
5o maximum, measured at a distance of 12 inches.
Stray magnetic field:
Frequency response range:
100 to 5000 Hz.
Frequency response:
H-143/AIC:
At ground level :
Within the limits specified in figure 2. The response in 1000 to 5000
Hz shall not change by more than ± 3 dB in any 500 Hz limit.
At altitude:
Within the characteristics shown on figure 3 and in the response
envelope on figure 4.
C
H-143A/AIC:
At ground level:
Within the limits specified in figure 5.
Within ± 5 dB of the ground level response at an altitude of 15,000 ft, up
At altitude:
to 3500 Hz.
Sensitivity:
105 ± 3 dB at 1kHz at ground level; 100 dB minimum at 1 kHz at an
H-143/AIC:
altitude of 25,000 feet.
C
H-143A/AIC:
102 dB minimum at 1 kHz at ground level.
Impedance:
19 ± 2 Ω.
at 1000 Hz -
Shall not exceed 22 Ω.
between 100 to 3000 Hz -
Harmonic distortion:
between 100 and 2000 Hz - 3%, maximum.
between 2000 and 5000 Hz - 5%, maximum.
Speech Intelligibility:
In accordance with MIL-PRF-25670.
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