My harp mic-the lovely 540D, is a controlled-magnetic mic. How is it different than a dynamic mic?
A controlled magnetic element is a variation of a dynamic element.
In the controlled magnetic (also called controlled reluctance) element:
1) the magnet is stationary,
2) the wire coil is stationary,
3) the metal diaphragm moves a ferrous rod that disturbs the magnetic field,
4) thus causing an output signal in the wire coil.
The controlled magnetic element was developed during World War II. It was a very rugged design that could stand up to military use. Shure discontinued the last controlled magnetic microphone in the early 1980's.