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 TM 55-1905-220-14-9
4-47.3. LOUD HAILER- MAINTENANCE INSTRUCTIONS
(f) The pistol-grip handle is secured to the driver unit-horn assembly with screws. It contains the
trigger switch, a toggle switch to transfer from internal batteries to external storage battery connection, and a
receptacle for external power cable plug. These handle components and the wiring are readily accessible by
the removal of the plate on one side of the handle.
(g) In additional to the two control switches referred to, a volume control is mounted on the rear
housing directly under the microphone grille. This control permits reducing the amplification of the system. This
may be necessary when the loud hailer is used in enclosed areas, as the reflection of sound is such areas may
cause the loud hailer to squeal or howl.
(2) Quick Reference Data.
(a) Electrical ratings - rated power output is 10 v.a. at 10% distortion or less.
(b) Input impedance - 400 ohms.
(c) Output impedance - 16 ohms.
(d) Amplifier voltage gain - 47 db
(e) Power supply - Eight 1.5 v Type BA-30 dry cell batteries in series providing 12 volts of internal
supply, or an external 12 v storage battery. In lieu of BA-30 dry cells, commercial types, such as D-99 or No.
950 flashlight cells, may be used.
b. Operation.
(1) Functional Operation.
(a) The loud hailer is a self-contained assembly consisting of a microphone and amplifier, a
loudspeaker, and a battery supply. It is essentially a portable p.a. system with a microphone connected to the
amplifier input and the loudspeaker connected to the amplifier output. The amplifier is activated for use by
operation of the trigger switch in the pistol grip handle. Speech signals from the microphone are amplified and
impressed on the loudspeaker.
(b) In conventional p.a. systems a microphone cannot be placed in close proximity to a
loudspeaker when both are connected to the same amplifier, as uncontrollable howling and squealing will
occur. This is caused by acoustic feedback of sound energy from the loud- speaker to the microphone of the
system. This loud hailer, however, is specially designed to eliminate this undesirable acoustic feedback to the
greatest practical extent by balancing out a sufficient
4-1193
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