Microphones come in a few basic types, based on their method of operation. Dynamic microphones are simple, magnet-based devices that excel at capturing louder sources. The more complex class of condenser microphones require external power but are much more sensitive. Ribbon microphones employ a thin strip of metal suspended in a magnetic field.
Main Microphone Types
Dynamic microphones do not require external power, since they use simple passive components to turn acoustical energy into electrical energy. Dynamics tend to be less sensitive than condensers, but can typically handle higher sound pressure levels.
Moving Coil microphones, like the Shure SM57, are the most common dynamic mics and are built like a tiny speaker cone, with a thin diaphragm attached to a coil of wire surrounded by a magnet. When sound waves strike the diaphragm an electrical signal is created as the coil moves inside the magnetic field.
Ribbon microphones, like the Cascade Fat Head, employ a thin strip of metal suspended in a magnetic field. As the ribbon moves with changing air pressure it disturbs the magnetic field, producing signal. These types of mics were incredibly popular from the mid-1930s through the 1950s.
Condenser microphones always require external power and function like a capacitor, with two charged elements (a fixed plate and a thin moving diaphragm). The diaphragm moves in response to sound waves, creating an electrical signal from the changing capacitance between the elements.
Large-diaphragm condensers like the Audio-Technica AT4040 have diaphragms measuring about one inch or more in diameter and are usually a side-address design. Their large surface area can capture a lot of acoustical energy, providing excellent signal-to-noise ratio.
Small-diaphragm condensers such as the Neumann KM-184 feature diaphragms about half-an-inch or smaller and are often pencil-shaped with an end-address design. Their low-mass elements are easily moved by the air, allowing them to accurately capture transient sounds.
Other Types
Electret condensers are used in cell phones and other devices where a continuous voltage isn’t practical, when space and weight are limited, or to reduce costs. Instead of external power, part of the element itself is made from a permanently charged material.
Carbon microphones are found in old telephones and public address systems and use granules of carbon to produce an electrical signal when compressed by air pressure. Because of their rudimentary design, carbon microphones produce a limited frequency range and significant noise.
Contact microphones aren’t actually microphones at all, but rather mechanical transducers. They use piezoelectric materials, which create an electrical signal as they contract and expand when placed on a vibrating surface.
Polar Patterns
Some microphones are more sensitive to sound coming from certain directions based on their design. Some have just one pattern while others feature multiple switchable patterns achieved by combining multiple capsules. Common options include:
Omnidirectional microphones pick up sound equally from all directions.
Cardioid microphones pick up best from the front, decrease in sensitivity around the sides, and have a null point at the back which rejects sound.
Supercardioid and Hypercardioid patterns are similar to cardioid but sacrifice the null point for a narrower focus and more side rejection. Shotgun mics are an extreme variant with an especially narrow focus.
Figure-eight means a microphone is equally sensitive to sound coming from each side. All ribbon mics have this pattern due to their construction, and condenser mics can have this pattern by combining two opposite-facing elements.
Application
A critical part of the recording process is selecting the best microphone and positioning for a given source. While there are no hard and fast rules, several common practices are often followed. For instance, dynamic mics are often used up close on louder sources like guitars and drums because they can handle high sound pressure levels, while condensers are popular on acoustic instruments and vocals for capturing detail and clarity with lower noise.
While it may seem obvious to use a bright-sounding mic on a treble-heavy guitar amp or a mellow ribbon mic on a baritone singer, a good rule of thumb is to do the opposite and complement the source’s timbre with a microphone that balances it. For example, ribbon mics are often used on brass instruments to soften their extreme overtones. Using multiple microphones on a source is a way to get the best of all worlds, blending them to taste.