Loudspeaker

A loudspeaker, commonly called a speaker, is an electroacoustic device that converts an electrical audio signal into sound, typically by using a voice coil that moves within a magnetic field to vibrate a diaphragm or cone. Working essentially as the reverse of a microphone, the modern moving-coil dynamic loudspeaker was invented in 1925 by Chester W. Rice and Edward W. Kellogg, whose key innovation was tuning the device mechanical parameters to give it a comparatively flat frequency response, distinguishing their design from earlier, less successful attempts at loudspeaker design.