MIL-DTL-83425A
3.4.1.1 Rigid shell. If the rigid shell is made of more than one piece of material, the pieces shall be
permanently joined together. The joining seam shall be smooth. The shape of the rigid shell shall be
rounded and suitable for both the right and the left sides of the head so that the earcup can be worn on
either the left or the right ear. The dimensions of the rigid shell shall conform to the dimensions specified
in Drawing 7136037.
3.4.1.2 Grommet. A grommet shall be installed in the access hole for the electrical conductors to the
earphone. The grommet shall conform to Drawing 60A4277.
3.4.1.3 Attaching and adjusting provisions. A 2-inch-square piece of hook fastener tape shall be
approximately centered on the outside of the rigid shell and securely attached to the rigid shell. Two draw
cords shall be attached to the rigid shell: one on the top and one on the bottom of the rigid shell. Each
draw cord shall be 9 inches ± 0.25 inch (228.6 ± 6.35 mm) long.
3.4.2 Cushion. The cushion shall be designed as an easily replaceable item. The cushion shall
consist of polyurethane foam with a cover that is made of plastic film and heat sealed. The cushion shall
conform to the dimensions shown on Drawing 7136038. The inner seam around the opening for the ear
shall be folded inward during manufacturing, to remove all sharp edges. The cushion shall not be
cemented to the earcup. However; the cushion shall remain attached to the earcup during normal usage.
The cushion shall not be treated in any manner that will cause skin irritation.
3.4.3 Fillers. The fillers shall have a cavity that will accept the H-143/AIC earphone conforming to
MIL-PRF-25670/2. The fillers shall be installed, without gluing to the shell, so that the fillers will not
protrude from the rigid shell and so that the fillers can be removed from the earcup and replaced without
damage to the fillers or any other part of the earcup. The fillers shall not be treated in any manner that
will cause skin irritation.
3.5 Performance
3.5.1 Mechanical stability. After the earcup has been cooled to a temperature of -40 degrees
Fahrenheit and then dropped from a height of 6 (six) feet onto an uncovered concrete floor, the earcup
shall not be cracked or chipped (see 4.5.2).
3.5.2 Sound attenuation. The earcup shall provide the sound attenuation specified in table I
(see 4.5.3).
TABLE I. Sound attenuations.
Group
Frequencies
Minimum group
Minimum single
attenuations (Decibels) 1/
(Hertz)
attenuation (Decibels)
A
23
125
250
B
23
178
500
32
1,000
35
2,000
35
3,000
35
4,000
60
C
6,000
8,000
1/ The minimum group attenuation, for a group, shall be the sum of all
the attenuations measured for all the frequencies listed for the group.
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