Michael Faraday (1791-1867) started the electronics revolution when he demonstrated that movement of a magnet within a coil of wire indices electricity to flow along the wire (such flow is called electrical current). Microphones and loudspeakers work on this simple principle, which I will demonstrate in class. Both devices contain a magnet and a wire coil that move relative to each other to produce fluctuating electrical current from motion (microphone), or that produce motion from a fluctuating current (loudspeaker). In both cases, the motion is vibration in air, or sound (Units 1 and 2).
How Speakers Work
This video shows how speakers convert an electrical signal into sound. It features a very simple speaker made from a plastic cup, a magnet, and a coil of copper wire.
How Microphones Work
This very brief video shows that a common type of microphone is actually just a speaker in reverse. Sound vibrations cause a wire coil to move within a magnet, which generates an electrical vibration in the wire. This electrical "signal" is a replica of the sound vibrations that produced it, and can be directed to a speaker, which will recreate the sound. The signal can also be preserved for later sound reproduction by directing it to a recorder.
