MIL-DTL-9415B
3.4.2.3.2 Sensitivity variation. The average sensitivity of the loudspeaker over the frequency bands specified
herein shall not differ from the initial sensitivity by more than 1 dB as a result of any or all of the environmental tests
(see 3.14).
3.4.2.3.3 Response-frequency characteristic. The response-frequency characteristic of the loudspeaker shall be
between two parallel horizontal lines 10 dB apart from 300 Hz to 6000 Hz, with the exception that above 3000 Hz,
one dip and one peak, if less than 0.10 octave wide, may pass through the limits provided that the amount by which
the dip or peak extends beyond the limits does not exceed 3 dB. One-tenth of an octave shall be considered as 0.10
of the linear length of 1 octave scaled on the semi-logarithmic paper on which the response-frequency characteristic
is drawn (see 4.5.2.1.4).
3.4.2.3.4 Response-frequency characteristics variation. The acoustic response of the loudspeaker shall not differ
from the initial acoustic response at corresponding frequencies by an amount greater than that indicated in table II as
a result of service condition tests.
TABLE II. Response frequency.
Change from initial Response in Decibels dB
Test
During Immediately
1 Hour
24 Hours
Test
After Test
After Test After Test
Extreme operating temperature
1
1
1
0
Temperature cycling
-
1
1
0
Pressure cycling
3
3
-
0
Vibration
-
0
-
0
Shock (15g)
-
0
-
0
Humidity
-
5
-
1
Fungus resistance
-
5
-
1
Salt spray
-
5
-
1
All tests above
-
-
-
3
After the explosive decompression test or gun blast test, the loudspeaker shall show no degradation in acoustic
response greater than 2 dB at any frequency between 300 Hz and 5,000 Hz and none greater than 5 dB at any
frequency between 5000 Hz and 6,000 Hz.
3.4.2.3.5 Directional characteristics. The sound pressure measured in any plane 3 feet away from the
loudspeaker in a free field at the indicated angles with respect to the principal axis shall not deviate from the sound
pressure measured on the principal axis by an amount greater than the values shown in table III for the frequencies
indicated (see 4.5.2.1.7).
TABLE III. Sound pressure.
Sound Pressure Deviation (dB)
Frequency (Hz)
15º
30º
500
0.5
1.0
1,000
1.0
2.0
2,000
2.0
4.0
4,000
2.0
4.0
6,000
3.0
6.0
3.4.2.3.6 Linearity. The acoustic output of the loudspeaker shall not deviate from a linear function of the input
voltage by more than 1 dB when subjected to the linearity test specified herein (see 4.5.2.1.8).
3.4.2.3.7 Distortion-frequency characteristic. The harmonic distortion in the acoustic output of the loudspeaker
shall not exceed the values given in table IV for the frequency ranges and inputs indicated (see 4.5.2.1.9).
7
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