Transducer for converting sound pressure waves into an electrical signal
Microphones are acoustic to electric transducers used for the recording of sound. Mics usually have a number of different specifications and categories which they can be labeled by. All of these should be available within specification documents for a particular micropohone.
Transduction Element
The two major divisions of microphones by transducer are dynamic and condensor.
Dynamic microphones generate electrical signal by magnetic induction. This is either done in a manner similar to a reversed loudspeaker, a technique known as "moving-coil", or by a thin metal ribbon suspended in the magnetic field.
Condensor (or capacitor) microphones generate signal by changes in capacitance between two metal plates, one of which is the diaphragm of the microphone. These microphones require some initial charge, which can be provided either by batteries, an external power supply, or by phantom power.
Polar Pattern
Microphones can also be divided by polar pattern, or the shape of the space in which the microphone is most effective at picking up sounds. Common polar patterns are cardiod, super cardiod, bi-directional or figure-8, and omni-directional.
Cardioid mics get their name from their "heart-shaped" pickup pattern. These mics are also known as unidirectional, as they are most effective at picking up signals directly in front of their diaphragm. They also have the best rejection of signals directly opposite the axis of focus.
Super cardioids have a similar pattern to cardiod mics, but trade a more focused pattern along axis for less rejection at 180º off axis. In this manner, they can be looked at similar to an unbalanced figure-8 mic.
Figure-8 microphones have a pickup pattern that is strong in two directions, with very good rejection perpendicular to its axis. This pickup pattern is often associated with ribbon microphones.
Omnidirectional mics have negligible bias toward any direction in relation to the direction of the diaphragm. The are often used for more ambient recordings, or recordings in which the sound of the space needs to be captured.
Frequency Response
All microphones have a frequency response, which deals with how well the microphone captures sounds at that frequency.
Response Time
The response time is how quickly a microphone can react to transients. Typically condensers have the quickest response times, followed by ribbons, then finally moving coil mics.
