MIL-PRF-25670B
3.4.8 Color. Color shall be as specified (see 3.1).
3.5
Performance
3.5.1 Frequency response. (see 4.5.2) The frequency response at ground level (see 3.1) and,
when specified, at altitude (see 3.1), shall be within the limits specified in the frequency response
range.
3.5.1.1 Smoothness of frequency response curve. The response in the 1,000 to 5,000 Hz range
shall not vary by more than ±3 dB within any 500 Hz increment.
3.5.2 Sensitivity. (see 4.5.3) The sensitivity shall be as specified (see 3.1).
3.5.3 Impedance. (see 4.5.4) The impedance at 1,000 Hz, measured at 20 °C, and between 100
Hz and 3,000 Hz shall be within the specified limits (see 3.1).
3.5.4 Harmonic distortion. (see 4.5.5) The harmonic distortion shall not exceed the specified
percent (see 3.1).
3.5.5 Dielectric withstanding voltage. (see 4.5.6) There shall be no arcing or breakdown between
the points of contact.
3.5.6 Stray magnetic field. (see 4.5.7) The stray magnetic field of the earphone element shall
cause no more than the specified deflection (see 3.1) of a magnetic compass at the distance as
specified (see 3.1).
3.5.7 Effect of stray magnetic field on the earphone element. (see 4.5.8) The earphone element
shall suppress noise due to a stray magnetic field by not generating a discernible signal.
3.5.8 Speech Intelligibility. (see 4.5.9) The intelligibility scores shall meet or exceed 95 percent
for an ambient sound pressure noise level not exceeding 75 dB Overall Sound Pressure Level. The
elements shall be installed in standard headsets meeting MIL-PRF-87819, and tested in a
representative operating Intercommunication Set AN/AIC-25(), or equivalent.
3.5.9 Endurance. (see 4.5.10) The frequency response and sensitivity shall not vary more than
±3 dB from the initial readings recorded in accordance with 3.5.1 and 3.5.2, respectively. Following
the test, the harmonic distortion shall be as specified (see 3.5.4).
3.5.10 Moisture resistance. (see 4.5.11) The product shall resist degradation in performance due
to moisture penetration, and the frequency response, sensitivity, harmonic distortion, and dielectric
withstanding voltage shall be as specified in 3.5.1, 3.5.2, 3.5.4, and 3.5.5, respectively. There shall
be no loosening or deformation of parts or other damage due to exposure to moisture.
3.5.11 Barometric pressure (reduced). (see 4.5.12) The product shall resist degradation in
performance due to barometric pressure, and the frequency response and sensitivity shall not vary
more than ± 3 dB from the initial readings recorded in accordance with 3.5.1 and 3.5.2, respectively.
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