Introduction
Microphones A microphone is what is known as a transducer. A transducer converts one form of energy into another; in a microphones case, acoustic energy (sound) into electrical energy. This basically means that a microphone is the reverse of a speaker driver, which is also a transducer converting electrical energy into sound pressure waves.
The most common type of microphone available is the dynamic mic. A flexibly-mounted diaphragm is coupled to a coil of fine wire. The coil is mounted in the air gap of magnet such that it is free to move back and forth within the gap. When sound strikes the diaphragm, the diaphragm surface vibrates in response. The motion of the diaphragm couples directly to the coil, which moves back and forth in the field of the magnet. As the coil cuts through lines of magnetic force in the gap, a small electrical current is induced in the wire. The magnitude and direction of that current is directly related to the motion of the coil, and the current thus is an electrical representation of the incident sound wave. Dynamic mics tend to be quite rugged, and hence find most of their use in sound reinforcement roles.
Next to the dynamic microphone, the most common type of microphone is the condenser. Basic things you should know about condenser microphones: they need an external power supply. Dynamic microphones do not need this sort of power, but condensers do. Some condenser microphones have a battery attachment that is either part of the microphone housing or on the end of the cable, as part of the connector. Others need power delivered to them through the cable. This power system is known as phantom power. Some mixers provide phantom power, some don't. If they do, there is usually a main phantom switch somewhere. What phantom power does is send a voltage of +48VDC through pins two and three of the microphone cable to the microphone capsule. The return voltage comes back via the shield. Condenser microphones are also slightly less durable than dynamic microphones, so they aren't used as much in on-stage, touring, or reinforcement applications, although some condensers are used for micing drum kits. Mostly, condensers are used in studio applications.
A variant of the condenser microphone is the electret condenser. Electret condenser microphones don't require phantom power to charge the diaphragm (like the condenser), but they do require a power supply for their in-microphone preamplifier. "In-microphone preamplifier" does not mean that they deliver a line-level output; they don't; it's for a sort of "pre-preamplifier." Increasingly, more electret condenser mics use phantom power to power their preamplifiers.
There are several other types of microphones, but they are rarely used in sound reinforcement: Ribbon mics (very, very fragile), and Carbon mics (very bad sound quality; used in telephone handsets although more and more handsets use dynamic mics).
By far the most prominent microphone design is the handheld microphone. These are designed to be held by a speaker or singer or can be clipped onto a stand. Pretty self-explanatory, right? Some attributes it must have, being a handheld mic, are good isolation (from vibrations and handling noise), and the capsule must be protected from being dropped (for that happens a lot); thus the use of the windscreen and rubber shock-mounts. Also featured are stand-mount microphones. These microphones are specifically designed not to be handheld. Shotgun microphones such as those used in video and television sound production are examples of this type. Most microphones of this type are used mainly for studio recording or video production. Sometimes they are used where appearances count, such as a gooseneck mic on television or on a stage. A very popular type in theater sound is the lavalier microphone. Lavalier mics are very small elements that are designed to be pinned directly to clothing or to be hung around the neck on a lanyard. Some new models can be used in the hair, taped to the skin, implanted in the throat, or stuck in the ear. Most lavaliers are electret-condenser, since electret elements can be made very small in size. Lavaliers are used on television broadcasting and in live theater because they are small and unobtrusive. Another type of microphone is the contact pickup. These act similarly to electric pickups (as those found on an electric guitar). They are microphones designed to pick up sound waves in a solid, rather than through the air. They can be used on violins, pianos, mandolins, etc. A new model of contact pickup comes in the form of a flexible strip, and so far has been getting rave reviews. Yet another type of microphone is the pressure response microphone. The commercial name usually given to such microphones is "PZM," for Pressure-Zone-Microphone. This term is a trademark of Crown International, who introduced the technique. The microphone element is placed extremely close to and facing a flat plate. In theory, the microphone samples pressure variations in the tiny air gap between the element and the plate, rather than responding to air velocity. Translation: when the mic is placed on this flat surface, sound from a given sound source is reflected on this surface. The mic element picks up sound directly from the sound source and also picks up the reflections from the surface it is mounted directly over. Since the difference in length (and thus, time) between the reflected sound and the direct sound is very small, the sounds reinforce each other, contributing to the excellent response of these mics. A variant of the PZM is the PCC, the Phase-Coherent-Cardioid (also by Crown). These microphones are pretty much the same as the PZMs, although they have different pickup patterns (polar patterns).
Polar Patterns
The polar pattern (or pickup pattern) is the way in which the microphone element responds to sounds coming in from different directions. There are several different standard patterns.
Omnidirectional elements, as their name implies, pick up sound more-or-less equally from all directions. Omnidirectional mics are used often in studios (where feedback is generally not a problem) and on lavalier microphones (the omnidirectional pattern does not emphasize the resonant chest cavity because the proximity effect does not occur; and the mic can be clipped in different positions without sound quality changing). By far the most popular type of microphone is the cardioid type. The cardioid microphone is most sensitive to sounds coming in on the primary axis, and rejects sounds from the sides and rear of the microphone. The directional qualities of the cardioid make it a natural choice for sound reinforcement, since they help in reducing feedback and increasing system gain. Cardioids tend to have more coloration (audible alterations to the sound) because the cardioid responds to different frequencies differently. This is where the proximity effect comes into play-- cardioid microphones exhibit a tendency to boost the low frequencies if the sound sources is very close to the microphone, which can be a plus with a singer who knows how to control his voice. Another polar pattern encountered is the supercardioid. Although the supercardioid rejects less sound from the sides, it does have a larger rear lobe than the cardioid. Supercardioids are used in special situations where greater side rejection is desired, but some rear pickup may be tolerated. Because of the concentrated forward lobe, they also may "reach" farther than a typical cardioid, and are sometimes used for pickup of distant sources. Similar to, but not identical to the supercardioid, is the hypercardioid. The hypercardioid is very very sensitive at 0 degrees (on-axis), has a somewhat larger lobe at the rear, but rejects almost all sound from the sides. A somewhat more unusual but very useful pickup pattern is the so-called Figure-8 or bi-directional microphone. Bi-directional microphones are most sensitive to sounds coming in from the front or rear of the microphone, and reject sounds from the sides. These mics are useful in, for example, an interview situation (where there are two people facing each other), etc. In recording and reinforcement, they may be used to pick up two adjacent instruments, for instance between two toms on a drum set.
