Introduction to Music Production 12 – Microphones
There are three main types of microphones you will find and use in studios for recording: Dynamic, Condenser, and Ribbon. They are a type of transducer – something that converts energy from one form to another (in this case, sound to electrical signals). A diaphragm inside the microphone vibrates between two poles to create the electrical signal. The type of microphone will determine the size and shape of the diaphragm, as well as how it performs transduction.
Microphones all have 3 dimensional response patterns that determine the optimal way to record. These patterns typically have a ‘cardoid’ (shaped like a heart) shape. Even unidirectional dynamic mics have a cardioid response pattern.
This shows a 3d representation of a dynamic mic with a cardioid pattern. Image source: PearlDrummersForum
Microphones can receive sound from more than one direction. You may find microphones that are bidirectional, tridirectional, multidirectional, and omnidirectional (sound from all sides). These microphones will have different cardioid patterns.
This image shows a 2d representation of different cardioid patterns microphones may have. Source: Garnish Music Production
Moving coil microphones (Dynamic Mics) are probably easiest to understand, because they are basically built like a loudspeaker: A coil is glued to the rear of a membrane, and there is a strong magnet surrounding this coil. When sound waves hit the microphone, the membrane moves to the rhythm of the sound waves, and the coil on its back moves along with it. The relative movement of the coil within its (stationary) magnetic gap induces a small signal voltage in this coil. There’s your microphone, a device that converts sound into an electrical signal. (Neumann)
Dynamic mics are preferred for live settings as well as recording percussion and do not need external power.
Called ‘capacitor microphones,’ condenser mics are the preferred microphone for studios. A condenser capsule is constructed similarly to a capacitor. It consists of a thin membrane in close proximity to a solid metal plate. The membrane or diaphragm, as it is often called, must be electrically conductive, at least on its surface. The most common material is gold-sputtered mylar, but some (mostly older) models employ an extremely thin metal foil. When sound waves hit the diaphragm, it moves back and forth relative to the solid backplate. In other words, the distance between the two capacitor plates changes. As a result, the capacitance changes to the rhythm of the sound waves. Voilà, we have converted sound into an electrical signal. The capsule is too fragile to be connected to other pieces of gear, and the output voltage is quite high, but produces no current because so little energy is stored in this small capacitor. A circuit called an ‘impedance converter’ is a buffer between the capsule and the outside world.
Condenser mics require external power called ‘phantom power’ (+48 volts, most audio interfaces have this). They typically have the widest frequency response and the best transient (bursts of energy) response.
You will likely want to get a shock mount (a mic holder that stops the transfer of vibrations from the mic stand) and a pop filter (a piece that reduces plosives) for a condenser.
Ribbon mics (known as ribbon velocity mics) are microphones that use a thin aluminum, duraluminum, or nanofilm of electrically conductive ribbon placed between the poles of a magnet to produce a voltage by electromagnetic induction. Ribbon mics are typically bidirectional. In a ribbon mic, the light metal ribbon is suspended between the poles of a magnet. As the ribbon vibrates, a voltage is induced at right angles to both the ribbon velocity and magnetic field direction and is picked off by contacts at the end of the ribbon. Ribbon microphones are not as commonly used anymore, but were a very common microphone style before condensers and dynamics became cheaper to produce with better response.
Do not supply phantom power to ribbon microphones, as you can destroy them.