Speakers

A loudspeaker (or "speaker", or in the early days of radio "loud-speaker") is an electroacoustic transducer that produces sound in response to an electrical audio signal input. In other words, speakers convert electrical signals into audible signals. ... The most popular speaker used today is the dynamic speaker. The dynamic speaker operates on the same basic principle as a dynamic microphone. ... Where high fidelity reproduction of sound is required, multiple loudspeakers may be used, each reproducing a part of the audible frequency range. Miniature loudspeakers are found in devices such as radio and TV receivers, and many forms of music players. Larger loudspeaker systems are used for music, sound reinforcement in theatres and concerts, and in public address systems. Speakers are typically housed in an enclosure which is often a rectangular or square box made of wood or sometimes plastic. [Loudspeaker. Wikipedia]