The common name for an electroacoustic transducer is 'speaker'. Speakers are simple devices that convert electrical signals into sound. Speakers are composed of three main parts; a magnet, coil and cone. There is a permanent magnet that is attached to the housing at the back of the speaker. Then a coil rests over the magnet and is attached to the cone. The cone is simply a rigid material that allows the coil to produce sound. When current passes through the coil a magnetic field is created. The magnetic field repels the permanent magnet and causes the coil to moved forward or backward rapidly. The vibration is amplified by the cone.