MIL-DTL-12606E
4.6.2.1.1 Sampling plan. Group C inspection shall be performed once every 12 months on 6 sample units selected, without regard to
their quality, from units produced during the preceding 6 month period or each 1,000 units, whichever occurs first. Each inspection
sample shall include approximately the same number of loudspeakers from each of the different styles (LS-445/U, M12606/01, or
M12606/02) produced and to be tested. The sample shall be divided equally into two groups and subjected to the tests of subgroups 1
and 2 of table V.
TABLE V. Group C inspection.
Inspection
Requirement
Method
paragraph
paragraph
Subgroup 1 (3 sample units)
Immersion resistance
3.4.7
4.7.8
Endurance
3.4.8
4.7.9
Subgroup 2 (3 sample units)
Cold resistance
3.4.9
4.7.10
Heat resistance
3.4.10
4.7.11
Moisture resistance
4.7.12
3.4.11
Bounce
4.7.13
3.4.12
4.6.2.1.2 Failures. If one or more units fail to pass group C inspection, the sample shall be considered to have failed.
4.6.2.1.3 Disposition of sample units. Sample units which have been subjected to group C inspection shall not be delivered on the
contract or order.
4.6.2.1.4 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 conditions, with essentially the same
materials, processes, etc, and which are considered subjected to the same failure. Acceptance and shipment 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 inspection, or the inspection which the original sample failed, at the option of
the qualifying activity). Groups A and B inspection 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.
4.7 Methods of inspection.
4.7.1 Visual and mechanical examination. The loudspeaker shall be examined to verify that the materials, design, construction,
physical dimensions, marking, and workmanship are in accordance with the applicable requirements (see 3.2, 3.3, 3.5, and 3.6). Unless
otherwise specified (see 6.2), the defects shall be classified as specified in table VI.
4.7.2 Voice coil polarity (see 3.4.1). A dc potential of 3 to 10 volts shall be applied to the voice coil terminals, with positive polarity
applied to the terminal adjacent to the red mark, and the direction of motion of the voice coil shall be observed.
4.7.3 Voice coil impedance (see 3.4.2). The loudspeaker shall be supported on the side opposite the cone. There shall be no
obstruction within 3 feet of the front of the cone. Voice coil impedance shall then be determined as specified in 4.7.3.1, 4.7.3.2 or by test
equipment capable of determining the ratio of input voltage to input current at a given frequency, at the option of the manufacturer.
4.7.3.1 Direct reading method. The voice coil terminals shall be connected in series with a 10 ± .10-ohm resistor ® across the output
of a low impedance 1000-Hz signal source (ET) (see figure 6). A voltmeter shall be placed across R, and ET set so that ER equals 1 ± .01
volt. A voltmeter shall be placed across R, and ET set so that ER equals 1 ± .01 volt. The voltmeter shall be removed, placed across the
voice coil terminals, and a reading taken. The voltmeter reading should be multiplied by 10, to determine the impedance in ohms. (The
voltmeter will measure the impedance divided by 10.)
4.7.3.2 Resistance to substitution method. The voice coil terminals shall be connected in series with a variable resistance across the
output of a low impedance 1000-Hz signal source. The voltage drops across the voice coil and the variable resistor shall be determined
with an electronic voltmeter. The value of the variable resistor shall be adjusted until the voltage drops are equal, and the resistance of
the variable resistor shall than be measured with a resistance bridge or other suitable equipment. The voice coil impedance shall be
considered as numerically equal to the measured value of resistance of the variable resistor.
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