Operates on the electromagnetic principle, just like the electro-mechanical loudspeaker. A flexibly-mounted diaphragm is coupled to a wire coil (voice-coil). The coil is mounted in the air gap of the magnet (moving freely up and down). Sound striking the diaphragm, the diaphragm surface vibrates in response. The diaphragm is coupled directly to the coil and the coil moves too (in the magnetic field). Moving in the magnetic field, an electrical current is induced in the wire of the coil. The magnitude and direction of that current is directly related to the motion of the coil, and the current is an electrical representation of the sound wave. No pre-amplifier is needed for this type of microphones.
The condenser microphone is an electrical system that depends upon variations in the internal capacitance (a thin metallic membrane and the stationary back plate). The diaphragm of the condenser microphone is the negatively charged plate of the capacitor. Sound waves moving the diaphragm cause a synchronous change of the capacitance of this capacitor. By moving the plates closer together, the electrostatic attraction between the plates increases. This causes a flow of current back to the positive plate and vice versa. As the sound wave changes, the electrical current changes simultaneously.
For best performance also gold transducer cases for optimum conductivity and high resistance to corrosion and humidity are used.
It works similar to the condenser microphone, but the condenser plate is made from an electret material to provide the polarizing voltage. It consists of a very light diaphragm (moving plate) and back plate (stationary or static plate) and has a permanent charge implanted into it.
The principle of operation is that sound waves moving the diaphragm cause the capacitance between it and the back plate to change synchronously, this induces an AC voltage on the back plate. They don't require phantom power to charge the diaphragm (like the condenser), but they do require a power supply for their in-microphone preamplifier.
There are two common types:
Foil Electret Condenser Microphones, the electret material is the diaphragm itself.
Back Electret Condenser Microphone, the electret material is the back plate.
Front Electret Condenser Microphone, the electret material is the inside of the case of the microphone.
Here the air moved by the sound moves a metallic ribbon arranged in the magnetic field of the microphone head. The movement generates a voltage between the ends of the ribbon which is proportional to the velocity of the ribbon. It is also called a "velocity" microphone.
The ribbon microphone design first gained popularity in the early 1930s and remained the industry standard for many years.
For most ribbon microphones at a distance of less than six feet, the proximity effect starts. This effect made the ribbon microphone very preferred to produce a full, rich voice for announcers. A disadvantage is the large size of this type of microphone.