What are Magnetic Microphones?
Competing with carbon microphones were magnetic microphones that we know today as dynamic mics. A sound moves a small magnetic coil in and out of a magnetic field. This is just like a speaker except the moving coil makes electric current instead of an electric current making a coil move. The weight and size of the coil is the limiting factor in the quality of the music. A small coil makes for a much better quality microphone, but at a cost of ten times that of the carbon mic.
Variations on the dynamic mic are the Shure Controlled Reluctance element that works by moving an iron pin in and out of a magnetic field changing the shape of the field and causes electrons to move in a coil. Later, the controlled magnetic element seems to be the same idea with a marketing change. They probably changed the name because the word reluctance is a technical word that describes the change of the magnetic field, but has negative connotations in day-today speech.
The magnetic elements work exactly like a guitar pickup except that a thin diaphragm is connected to a wire that moves across the magnetic pickup. These mics can be of very high quality and are designed for recording music. They have a good range from low to medium frequency and accurately record sounds in the human hearing range. The response curve is not exactly the same as a human ear and there are slight differences across different models and manufactures. Shure mass produced a variety of magnetic elements over the years of varying cost and quality.