AT&T engineer C.G. Hensley got the idea for the loudspeaker when he thought about what would happen if he made a telephone receiver really big. Loudspeakers were first used in public address systems (along with the microphone and the vacuum tube amplifier) and only for the human voice. But as loudspeakers improved, they were used to broadcast music. Today, loudspeakers are as fundamental to rock as the electric guitar and the semi-tranced bass player.