Introduction:
A microphone is in most cases (with the exception of instruments with a line out) the first link in the recording chain, its job is to convert sound into an electric signal. As the microphone is the link in the chain, it is very important that it is not the weakest. If your signal sounds bad here, there’s not a whole lot you can do to save it. As there are not only many types of microphones available but also many microphone techniques, it is important to understand the basic principles behind them so that when the time comes you can decide which microphone is the right choice for a given situation.
How a microphone works
Though there are numerous types of microphones, all of them have the following in common: They convert differences in air pressure (i.e. sound) into an electrical signal which varies in voltage amplitude and frequency analog to the original sound. The differences in air pressure created by sound cause a diaphragm inside the microphone to vibrate. These vibrations are translated into electrical signals, which represent the original sound. The method used to translate the vibrations into electrical energy varies depending on what type of microphone is being used.
Dynamic microphones
A dynamic microphone consists of a thin diaphragm, to which a coil of wire is attached. This coil is surrounded by a magnet. When sound reaches the diaphragm it begins to vibrate, in turn causing the coil to move back and forth inside the magnetic field. This process induces a varying current in the coil.
Due to the fact that the diaphragm has to move a coil, the frequency response on most dynamic microphones is not all that great. Particularly quiet or high frequency signal are not depicted as well as with other forms of microphones. One advantage dynamic microphones do have is that they are relatively sturdy, making them ideal for rough situations such as live performances. Due to the lower sensitivity, such microphones are also more resilient to feed back.
Condenser Microphones
In a condenser microphone the diaphragm acts as on plate of a capacitor. As sounds moves the diaphragm, the voltage maintained across the capacitor changes with the vibrations of the air creating a varying current.
One large benefit of a condenser microphone over a dynamic microphone is that there is no heavy coil fixed to the diaphragm, so the microphone is much more true to the actual sound. The diaphragm being only very thin and light, the frequency response of such devices is very good. However, due to the fact that a condenser microphone works with a capacitor, it requires some form of power supply. This can either be supplied by battery or by phantom power, supplied to the microphone via XLR cable (microphone cable).
Condenser microphones, being highly sensitive, are still only rarely seen on live performances, but are definitely a preferred choice for studio recordings.
Piezo microphones
A piezo microphone uses the Piezoelectric effect to convert vibrations into an electric signal. The diaphragm of this microphone is attached to a crystal. When the crystal vibrates is creates an electrical signal.
Directionality
Omnidirectional
Bi-directional
Cardioid
Hypercardioid
ShotgunRed dot represents microphone, lines indicate sensitivity in respective direction
A microphone's directionality or polar pattern indicates how sensitive it is to sounds arriving at different angles about its central axis. The polar pattern represents the area of points that produce the same signal level output in the microphone if a given sound pressure level is generated from that point.
An omnidirectional microphone is sensitive to sound coming from any direction. A unidirectional microphone is sensitive to sounds from only one direction. The most common form of unidirectional microphone is a cardioid microphone, for example the SM 58 from Sure. Unidirectional microphones have the benefit, that they only take in sound from a certain direction. This can be very helpful when trying to eliminate ambient noise.