Microphone Types And Pick-up Patterns
James A. Putnam
Dennis L. Trunk
Although it's possible these days to record music directly from instruments, software synthesizers and other sources without the use of a microphone, sooner or later you're going to need at least one, and probably several, in your home studio. Vocals, acoustic instruments and certain kinds of recording techniques require them. To decide what mics to buy, it helps to know the basic kinds available.
One way to classify microphones is by type. In home studios, these three microphone types are the most commonly used:
Condenser mics use a thin conductive diaphragm in combination with a charged plate to translate sound into an electrical signal which must then be amplified. The plate must be charged by a voltage source, such as a battery or phantom power. Condenser mics are known especially for their accurate reproduction of mid-range and treble frequencies. Although they are often more sonically sensitive than dynamic mics, they are also more delicate.
Small diaphragm condenser mics, because of their excellent high-frequency response, are frequently used for drums and percussion, for acoustic string instruments, and for picking up acoustic ambience.
Large diaphragm condenser mics, which combine excellent high-frequency response with a warm, full sound, are often used for vocals and horns.
Dynamic mics use a moving wire coil suspended in a magnetic structure to translate sound into an electrical signal by means of electromagnetic induction. Unlike condenser mics, they don't need a voltage source and they are more rugged.
Small diaphragm dynamic mics, largely because of their sturdiness, are often used on stage for both vocals and instruments, but they are also commonly used in home and professional studios.
Large diaphragm dynamic mics are typically used with brass or bass instruments, as well as guitar amps, in order to reduce the distortion these instruments can cause because of their high sound pressure output. The trade off is less sensitivity to higher frequencies.
Ribbon mics have a thin aluminum ribbon suspended in a magnetic field. Although they are very sensitive to sound nuances and have a wide frequency response, they are also very fragile and expensive. And because of their low voltage output, they require more pre-amp gain.
Microphone Pickup Patterns
Microphones can also be classified by their pickup patterns. These three are the most often used in the home studio:
Bi-directional (figure-eight) mics pick up sound directly in front of and directly behind the mic, but not the sound on either side of the mic. Their frequency response is generally excellent, but because they are sensitive to ambient sound, they can be difficult to use and should be used only in a good acoustic environment. They are usually placed above an instrument, but not too close.
Cardioid mics are designed to pick up sound directly in front of the mic and are usually pointed at a vocalist or instrument for best effect. Because they are less sensitive to sound on either side of the mic or behind it, they are especially useful in poor acoustic environments, such as many home studios.
In spite of their popularity, they are not problem-free. Sounds from behind the mic are only reduced in volume, not completely cut off, and the frequency response to sounds from the back and sides can vary. Even the pick-up pattern can vary by frequency. In regard to bass frequencies, for example, most cardioids can be considered omni-directional. In addition, these mics have a characteristic known as the "proximity effect," which means that the closer the mic is placed to the sound source, the more the bass frequencies will be emphasized. This can increase the richness and fullness of a voice or instrument, but it can also cause a muddying effect if the mic is placed too close. Because of the "proximity effect," some cardioid mics have a built-in lowcut filter switch.
Supercardioid and hypercardioid mics are a variation. In general, they are even less sensitive to sound on either side of the mic and have a more consistent frequency response.
Omni-directional mics are the simplest - they pick up sound from every direction. They usually have a very good frequency response, and in a quality acoustic environment, they can be the best choice for reproducing an open, ambient sound.