Electric Megaphone

a portable device used to amplify sound. An electric megaphone consists of a microphone that is not very sensitive to acoustic noise, an amplifier that is usually transistorized, and a horn loudspeaker that may have a handle. The microphone, which is usually mounted in the megaphone’s casing, is oriented in such a way that its lowest sensitivity is in the direction of the sound radiation, as viewed from the loudspeaker. The microphone can be moved a certain distance from the loudspeaker by means of an extension cable—for example, when the loudspeaker is mounted on the roof of an automobile. The amplifier’s circuit employs negative feedback and has a powerful push-pull output stage. Power is supplied by storage batteries or by miniature cells. In some electric megaphones, the amplifier can be converted into an audio-frequency oscillator that can produce low-frequency call signals. The weight of a megaphone, including its power supply, is approximately 1.5 kg; its operating range can exceed 250 m.