MIL-DTL-16225C
3.6.3 Input impedance. A transformer, capable of handling 10 watts, shall be included in each unit,
which shall provide for changing the input impedance from 600 ohms to 1,200, 1,800, 2,400, or 3,000
ohms when the impedance is measured at 1,000 Hz. A tolerance of ± 10 percent will be permitted on
these impedance values.
3.6.4 Acoustical efficiency. The acoustical efficiency of the loudspeaker shall be such that, with an
input of 1.00 watt to the voice coil with the frequency varied between 950 and 1,300 Hz, the acoustical
pressure shall average at least 1 Pascal (Pa) along the sound axis, at least 0.9 Pa at 10 degrees off the
axis, and at least 0.7 Pa at 25 degrees off the axis. These values shall be based upon pressure
measurements on the sound axis made at a distance of 6 feet from the mouth of the loudspeaker and off-
axis measurements made at four equally spaced points around the periphery of a circle whose plane is
normal to the sound axis with the points of measurements 6 feet from the center of the loudspeaker
mouth (see figure 2).
3.6.5 Volume control. The loudspeaker shall be provided with a volume control having the following
characteristics:
3.6.5.1 Minimum attenuation. Minimum attenuation shall occur in the full clockwise position of the
control.
3.6.5.2 Maximum attenuation. Maximum attenuation shall occur in the full counter-clockwise position
of the control and shall be at least 30 decibels (dB) below the audio output at the minimum attenuation
position of the control, for all audio frequencies.
3.6.5.3 Attenuation and shaft rotation. The attenuation with respect to shaft rotation shall be linear
within ± 6 dB over approximately three-quarters of the range. The attenuation shall be spread over not
less than 75 percent of the angular rotation of the control.
3.6.6 Distortion. Distortion shall not exceed 10 percent r.m.s., when measured at the frequencies
specified in 4.4.4.
3.6.7 Acoustical quality. The loudspeaker shall withstand the acoustical quality test specified in 4.4.5.
During this test, there shall be no buzzing, rattling, or other spurious sounds in the acoustic output of the
loudspeaker, which will degrade the quality of reproduced speech.
3.6.8 Insulation resistance. Insulation resistance shall be not less than 100 megohms, when
measured with a 500-volt source as specified in 4.4.6.
3.7 Mechanical details and construction.
3.7.1 Dimensions. The dimensions and external physical characteristics of the loudspeaker shall be in
accordance with Drawing RE-C-49041.
3.7.2 Weight. The weight of the loudspeaker unit, including transformer and volume control, shall not
exceed 10.5 pounds.
3.7.3 Mounting. The loudspeaker shall be designed for mounting to any vertical surface, such as
bulkheads, or to the overhead by the addition of a right angle bracket. It is not required that the
contractor provide the right angle bracket.
3.7.4 Terminal tube entrance. A cable clamp shall be provided on the interior of the mounting base to
support all incoming audio lines. The entrance for the terminal tube shall be enclosed and protected
against the entrance of moisture, and shall be so constructed as to permit ready access to the terminals
for the connection of the leads. Entering tube and cable will be Government-furnished.
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