MIL-PRF-87819B
4.6.1.4.3 Disposition of samples. Samples which have been subjected to group C inspection shall not
be delivered on the contract or purchase order.
4.6.1.4.4 Noncompliance. If a sample fails to pass group C inspection (see 3.1), 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 and shipment of the product shall be
discontinued until corrective action that is 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 (see 3.1) 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 responsible
inspection activity and the qualifying activity.
4.7 Methods of inspection.
4.7.1 Visual and mechanical inspections. Products shall be examined to verify that the materials,
design, construction, physical dimensions, marking, and workmanship are as specified in the applicable
4.7.2 Acoustic quality (see 3.5.1). A constant voltage having a value of 1.5 V ± 0.1 V rms shall be
applied at the proper contacts of the connector such that the voltage will be applied to the voice coil
terminals of the earphone elements and the frequency shall be continuously varied from 100 Hz to 4,500
Hz and back to 100 Hz.
4.7.3 Attenuation (see 3.5.2).
4.7.3.1 Qualification attenuation (see 3.5.2.1). The attenuation of the device under test shall be
measured as specified in ANSI S12.42. The MIRE test shall be conducted with additional measurements
at test frequencies of 63, 80, and 100 Hz. Attenuation measurements shall be made on three randomly
chosen headsets. Three fittings and measurements using each headset shall be made for ten subjects.
The mean of all measurements shall be calculated for each test frequency and compared with the
requirements of 3.5.2.1 for compliance. This test shall be accomplished with and without military
eyeglasses. Eyeglasses shall be PIN HGU-4/P Sunglasses, or equal. Following the qualification
attenuation tests, the same product shall be subjected to the flat plate conformance attenuation testing of
4.7.3.2. These results will be retained by the qualification activity for a baseline comparison to
subsequent qualification retention test results (see 3.5.2.2).
4.7.3.2 Conformance inspection (see 3.5.2.2). The test shall be conducted using a Type 1 artificial ear,
acoustic coupler and flat plate as described in the American National Standards Institute, Method for
Coupler Calibration of Earphone, ANSI S3.7. The recommended test fixture is a B&K 4152 Artificial Ear,
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DB 0909 coupler with a brass flat plate that is flush with the top of the coupler and maintains the 6.0 cm
volume of the coupler. A diffuse pink (see 6.8.1) or white (see 6.8.2) noise of 90 dB overall SPL shall be
used as the ambient noise. The open noise field shall be measured using the un-occluded (see 6.8.4)
test fixture. The headset shall be placed on the test fixture and measurements shall be made of the noise
field with the occluded test fixture. The measurements shall be made at the test frequencies of 4.7.3.1
with the exception that measurements at test frequencies of 63, 80, and 100 Hz are not required. The
occluded values shall be subtracted from the un-occluded values to yield the attenuation values. These
attenuation values shall be averaged to yield the baseline attenuation performance.
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