A loudspeaker, or speaker, is a device to convert electrical impulses into sound. It commonly comprises a rigid conical diaphragm attached to a coil held such that it may move backward and forward; within the cylinder of the coil is a fixed permanent magnet. Changes in the current supplied to the coil alter its magnetic field so that it, and the cone, vibrate to produce the compression waves that are sound. High fidelity sets use two or more loudspeakers of different sizes for more accurate reproduction.

A loudspeaker commonly has a permanent magnet (1) to provide a magnetic field in which a coil (2) attached to a fiber cone (3) is held balanced, but is free to move forwards and backwards. A varying electrical current is fed to the coil from the amplifier output, resulting in a varying magnetic flux in the coil. This react with the permanent magnet's field, causing the coil and hence the cone to move back and forth, producing sound.