MIL-PRF-25670B
TABLE VI. Group C inspection.
Inspection
Requirement
Test method
Number of sample
paragraph
paragraph
units to be inspected
Subgroup 1
Endurance
3.5.9
4.5.10
2
Subgroup 2
Moisture resistance
3.5.10
4.5.11
2
Fungus 1/
3.5.6
4.5.17
2
Visual and mechanical
3.3, 3.4, 3.6, and 3.7
4.5.1
2
examination
1/ Test is to be performed
if certification is not provided (see 4.5.17).
4.4.2.1.2 Failures. If one or more sample units fail to pass group C inspection, the sample
shall be considered to have failed.
4.4.2.1.3 Noncompliance. If a sample fails to pass group C inspection, the manufacturer
shall notify the qualifying activity and the cognizant inspection activity of such failure and take
corrective action on the materials or processes, or both, as warranted, and on all units of product
which can be corrected and which were manufactured under essentially the same materials and
processes, and which are considered subject to the same failure. Acceptance of the product shall be
discontinued until corrective action, acceptable to the qualifying activity, has been taken. After the
corrective action has been taken, group C inspection shall be repeated on additional sample units (all
inspections, or the inspection which the original sample failed, at the option of the qualifying activity).
Group A and group B inspections may be reinstituted; however, final acceptance and shipment shall
be withheld until the group C inspection has shown that the corrective action was successful. In the
event of failure after reinspection, information concerning the failure shall be furnished to the
cognizant inspection activity and the qualifying activity.
4.4.2.1.4 Disposition of sample units. Sample units which have been subjected to group C
inspection shall not be delivered on the contract.
4.5
Methods of examination and test.
4.5.1 Visual and mechanical examination. Earphone elements shall be examined to verify that
the design, physical dimensions, weight, marking, and workmanship are in accordance with the
applicable requirements (see 3.3, 3.4, 3.6, and 3.7).
4.5.2 Frequency response. (see 3.5.1) The earphone element shall be mounted as shown in the
test circuit (see figure 1). Adjust the output from the audio oscillator to 1 mW at 1 kHz as measured by
the electronic voltmeter (voltmeter No. 1). Measure the frequency response over the specified range
(see 3.1). The output signal shall be recorded in the dB value above 0.0002 dyne/cm2.
4.5.2.1 Automatic recorder. If the acoustic output is recorded on an electro-mechanical graph
recorder, the minimum writing speed shall be 10 inches per second, the maximum chart speed shall
be 30 inches per minute, and the writing speed and chart speed shall be noted on the graph paper.
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