Microphones in which the voltages are varied by an electromagnet; such as, ribbon or velocity microphones, dynamic or moving-coil microphones, and reluctance or moving-vane microphones.

• Ribbon or velocity microphones are those in which electric output depends on the velocity of the air particles that form a sound wave; examples are a hot-wire microphone and a ribbon microphone in which the conductor is a thin ribbon of aluminum alloy moving perpendicularly in a magnetic field. It is strongly directional and can be used to reduce unwanted side noise.
• Dynamic or moving-coil microphones consist of moving-conductor microphones in which the flexible diaphragms are attached to a coil positioned in the fixed magnetic fields of a permanent magnet.
• Reluctance or moving-vane microphones consist of diaphragms acted upon by sound waves that are connected to armatures which vary the reluctance in magnetic fields each of which is surrounded by a coil.