U, M12606-01 and M12606-02, unencased, permanent magnet loudspeakers with a 2-watt normal \(4-watt peak\) input. These loudspeakers are fungus-, and immersion-resistant, and have a voice coil impedance of 8 ?? 1 ohms. The cone and spider are made of polyamide-based phenolic material \(see 6.1\).

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MIL-DTL-12606E

FIGURE 6. Measurement of impedance by direct reading method.

4.7.4 Dielectric withstanding voltage (see 3.4.3). The loudspeaker shall be tested in accordance with method 301 of

MIL-STD-202. The following details shall apply:

a. Test voltage � 400 volts.

b. Nature of potential � 60 Hz, AC.

c. Points of application � The test voltage shall be applied between one of the voice coil terminals and the loudspeaker frame;

simultaneously, the voice coil shall be excited with a minimum of 2.85 volts root mean square (rms) at 300 Hz.

4.7.5 Acoustic quality (see 3.4.4). A constant voltage having a rms value of 4.00 � .1 volts shall be applied to the voice coil terminals

and the frequency varied continuously from 300 to 7,000 Hz and back to 300 Hz. For M12606-01, the frequency shall be varied

continuously from 400 to 6,000 Hz and back to 400 Hz.

4.7.6 Frequency response.

4.7.6.1 Type LS-445/U and M12606-02 (see 3.4.5.1). The loudspeaker shall be mounted in a test cabinet (see figure 7) and placed 3

feet from a calibrated Western Electric Type 640AA (or equal) condenser microphone and amplifier. The microphone shall be placed on

the axis of the loudspeaker. A constant voltage having a rms value of 4.00 � .1 volts shall be applied to the voice coil terminals and the

frequency varied continuously from 300 to 7,000 Hz. The acoustic output shall be recorded on a direct-writing strip graph chart using an

automatic plotter or curve tracer, with a minimum writing speed of 10 inches per second and a maximum chart speed of 30 inches per

minute. Or, at the option of the manufacturer, point-to-point measurements may be made, every 50 Hz from 300 to 600; every 100 Hz

from 600 to 1,500 Hz; every 250 Hz from 1,500 to 2,000 Hz; every 100 Hz from 2,000 Hz to 2,500 Hz; every 250 Hz from 2,500 to 3,000

Hz; every 500 Hz from 3,000 to 7,000 Hz, with the data record and a graph drawn (see figure 4).

4.7.6.2 M12606-01 (see 3.4.5.2). The loudspeaker shall be mounted in a closed 5 x 5 x 3 inch test cabinet with suitable 2-3/4 inch

diameter loudspeaker opening and placed 3 feet from a calibrated Western Electric Type 640AA (or equal) condenser microphone and

amplifier. The microphone shall be placed on the axis of the loudspeaker. A constant voltage having a rms value of 4.00 � .1 volts shall

be applied to the voice coil terminals and the frequency varied continuously from 400 to 6,000 Hz. The acoustic output shall be recorded

on a direct-writing strip graph chart using an automatic plotter or curve tracer with, a minimum writing speed of 10 inches per second and

a maximum chart speed on 30 inches per minute. Or, at the option of the manufacturer, point-to-point measurements may be made every

50 Hz from 400 to 600 Hz; every 100 Hz from 600 to 1,500 Hz; every 250 Hz from 1,500 to 2,000 Hz; every 100 Hz from 2,000 to 2,500

Hz; every 250 Hz from 2,500 to 3,000 Hz; and every 500 Hz from 3,000 to 6,000 Hz, with the data recorded and a graph drawn (see

figure 5).