MIL-DTL-18239E(AS)
3.4.1 1,000 Hz sound pressure output. The normal sea level sound pressure versus
frequency characteristics of the earphone shall be 103 ± 2 db above a reference level of 0.0002
dyne per square centimeter with 1 milliwatt rms power at 2,000 Hz applied to the earphone
terminals when tested in accordance with 4.7.1.
3.4.1.1 Sound pressure output versus frequency. The normal seal level sound pressure
versus frequency characteristics of each earphone shall not deviate from the 1,000 Hz response by
more than the values shown in table I when tested in accordance with 4.7.1.
TABLE I. Deviations of sound pressure versus frequency.
Frequency in Hz
Deviations (in db)
Minimum
Maximum
100 to 2,500
-3
+3
2,500 to 3,000
-3
+3
3,000 to 7,000
-7
+6
3.4.2 Temperature cycling. The sound pressure versus frequency characteristics of the
earphone unit shall not vary more than 3 db from normal seal level performance at any frequency
between 100 and 7,000 Hz after being subjected to 5 temperature cycles ranging between 55 °C
and +85 °C, when tested in accordance with 4.7.2.
3.4.2.1 Temperature extremes. The sound pressure versus frequency characteristics of the
earphone unit shall not vary more than 3 db from normal seal level performance at any frequency
between 100 and 7,000 Hz after exposure to temperature of 55 °C and +55 °C, when tested in
accordance with 4.7.3.
* 3.4.3 Ambient pressure cycling. The sound pressure versus frequency characteristics of the
earphone unit shall not vary more than 1 db from normal seal level performance at any frequency
between 100 and 7,000 Hz after being subjected to 5 cycles of ambient pressure ranging between
3.4 and 30 inches of mercury when tested in accordance with 4.7.4.
* 3.4.3.1 Response at specific ambient pressures. The sound pressures versus frequency
characteristics of the earphone unit shall not vary more than 4 db from normal seal level
performance between 100 and 1,000 Hz when subjected to an ambient pressure of 13.75 inches of
mercury, nor more than 12 db at an ambient pressure of 3.4 inches of mercury when tested in
accordance with 4.7.5.
3.4.4 Impedance. The impedance of the earphone at 1,000 Hz shall be 15 ± 2 ohms when
tested as required by 4.7.6. At any frequency between 100 and 7,000 Hz the impedance shall not
vary from the 1,000 Hz value by more than 20 percent when tested in accordance with 4.7.6.
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