Loudspeaker

特許 権利維持 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 first primitive loudspeakers were developed as accessories to telephone systems in the late 1800s, but electronic amplification by vacuum tube beginning around 1912 made loudspeakers truly practical, and by the 1920s they were used in consumer products; radios, phonographs, and theater sound systems for talking motion pictures.