MIL-PRF-25670B
- Room ambient, +15 °C to +35 °C.
a. Temperature
b. Pressure
- Normal atmospheric.
c. Humidity
- Room ambient up to 90 percent relative humidity.
All acoustical measurements shall be made above a reference level of 0.0002 dyne/cm2. All
acoustical testing shall be made in a free-field environment. (A `free field environment' is one which
simulates free-field conditions to the extent that the inverse-pressure versus distance law should hold
within ± 1 dB at all frequencies for which measurements are made. Ambient noise shall not change
the measurements more than ± 1 dB.)
4.3 Qualification inspection. Qualification inspection shall be performed at a laboratory
acceptable to the Government (see 6.3) on sample units produced with equipment and procedures
normally used in production.
4.3.1 Sample size. Six (6) earphone elements shall be subjected to qualification inspection.
4.3.2 Inspection routine. The sample shall be subjected to the inspections specified in table I, in
the order shown. All sample units shall be subjected to the inspections of group I. The sample shall
then be divided equally into two groups of three units each, and subjected to the inspection for their
particular group.
TABLE I. Qualification inspection.
Inspection
Requirement
Test method
paragraph
paragraph
Group I
Visual and mechanical examination
3.3, 3.4, 3.6, and
4.5.1
3.7
Frequency response
3.5.1
4.5.2
Sensitivity
3.5.2
4.5.3
Impedance
3.5.3
4.5.4
Harmonic distortion
3.5.4
4.5.5
Dielectric withstanding voltage
3.5.5
4.5.6
Stray magnetic field
3.5.6
4.5.7
Effect of stray magnetic field on the
3.5.7
4.5.8
earphone element
Speech Intelligibility
3.5.8
4.5.9
Endurance
3.5.9
4.5.10
Group II
Moisture resistance
3.5.10
4.5.11
Group III
Barometric pressure (reduced)
3.5.11
4.5.12
Thermal shock
3.5.12
4.5.13
Vibration, high frequency
3.5.13
4.5.14
6
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