bullhorn, loud-hailer - a portable loudspeaker with built-in microphone and amplifier

electro-acoustic transducer - a transducer that converts electrical to acoustic energy or vice versa

P.A., P.A. system, PA system, public address system, PA - an electronic amplification system used as a communication system in public areas

intercom speaker, squawk box, squawker - the loudspeaker on an inter-com or public address system

tannoy - a loudspeaker

tweeter - a loudspeaker that reproduces higher audio frequency sounds; "the sound system had both tweeters and woofers"

woofer - a loudspeaker that reproduces lower audio frequency sounds