Selecting Microphones for Wireless

No one type of microphone is best for all situations. Microphones vary widely in size, shape, sound quality, acoustic characteristics and other details. In some situations it may be necessary to conceal the microphone, in others this is unimportant, or even undesirable. Personal preferences are also important. Performers and presenters may greatly prefer one type or model of microphone over others. The time spent making the right choice will pay off every time the wireless system is used.

The first decision is whether to use a handheld transmitter or a body-pack transmitter. Handheld transmitters include both the microphone element and the radio transmitter in one package and are similar in appearance to wired vocal microphones. They are a good choice for vocal performances, live interviews and situations where the transmitter is passed from person to person. Many performers are accustomed to controlling the loudness and sound quality of their performance by varying the distance between the microphone and their mouth, so a handheld transmitter is likely to be preferred. Of course, a "handheld" model also can be mounted on a conventional mic stand.

Body-pack transmitters use external microphones, so they are more flexible and adaptable than handheld transmitters. Some vocalists use headworn microphones with body-pack transmitters, leaving their hands free to play an instrument or to enhance their dance performances. Body-pack transmitters are also sometimes used with musical instrument microphones and other specialized types of microphones and pickups. In most cases, however, body-packs are used with miniature microphones which are clipped onto clothing on the chest or concealed near the mouth. This arrangement is widely used for newscasts, TV and film production, the theater, TV interviews, presentations and many similar applications.

Two basic types of microphones are available for use with wireless: dynamic microphones and electret condenser microphones. Dynamic microphones use magnetic elements that convert sound into small electrical signals in a manner that is basically the reverse of that used by loudspeakers to convert electrical energy into sound. Dynamic microphones are rugged, reliable, inexpensive and have a "warm" sound quality desirable to many vocalists.

Electret condenser microphones use an element with a thin membrane (diaphragm) connected to an electronic circuit. Membrane motion caused by sound pressure is sensed by the electronic circuit and converted into a usable electrical signal. Condenser microphones have smooth, extended frequency response and a clarity and definition not usually found in dynamic microphones. They can also be miniaturized, making them especially suitable for lavalier use.

Both dynamic and condenser microphones can be designed to be directional or omnidirectional. Directional microphones receive sound more efficiently from one direction than from others. This is useful when it is desired to pick up sound from greater distances or to de-emphasize unwanted external sounds. Omnidirectional microphones receive sound equally well from all directions. This is desirable in many situations, such as for lavalier microphones which cannot be directly in front of the mouth.

Handheld transmitters almost always use directional vocal microphones, which may be either dynamic or condenser. In many cases, a particular wireless system is only available with one type of handheld transmitter and one type of microphone element, usually dynamic. More expensive systems may offer a choice of either dynamic or condenser elements. Dynamic microphone elements tend to sound warmer and more mellow; condenser elements tend to have a wider and smoother frequency response and greater clarity. Before selecting a handheld wireless system, it is very important to listen to it carefully to make certain that the sound quality is pleasing. As with wired vocal microphones, the choice can be very much a matter of personal taste.

Body-pack transmitters have a microphone connector and may be used with many different types of microphones. The most popular choice is a lavalier microphone, which may be either directional or omnidirectional. Because condenser microphone elements can be made considerably smaller than dynamic microphones, no modern lavalier microphones have dynamic elements. Omnidirectional lavalier microphones are smaller and usually less expensive than similar directional units.

Omnidirectional lavalier microphones work well in most situations and are more popular than directional types. Except when external noise is a problem, this type of microphone is easy to use and provides excellent sound quality. Directional lavalier microphones are useful where feedback is a potential problem, where the external noise level is high or where reverberation and echo are troublesome. However, they tend to change in sound quality and level if the wearer turns his or her head away.

A headworn microphone can provide excellent rejection of external noise without the drawbacks of ordinary directional microphones. A directional element is normally used in headworn microphones, providing good rejection of external noise. The microphone is also close to the mouth, allowing the gain to be turned down, further reducing outside noise. In addition, because the microphone is attached to the head, instead of some location on the chest, the sound quality does not change as the user's head turns.

Microphones are often used with musical instruments such as saxophones, trumpets, reed instruments and acoustic guitars. Special mounting adapters are available to position the microphone correctly on the instrument. Because of the very high sound levels created by brass instruments, special overload-resistant microphones are normally required.

Many other types of microphones can also be used with wireless body-pack transmitters. Boundary microphones, which provide greatly improved intelligibility in many sound reinforcement and conference room situations, are often used with body-packs to avoid the need for unsightly and inconvenient microphone cables. Similarly, body-pack transmitters are often used with miniature gooseneck podium microphones, eliminating the necessity for distracting and possibly unsafe cables.

In fact, many types of conventional microphones can be used with wireless by means of a simple adapter cable. Among these are dynamic and battery-powered condenser vocal microphones, podium microphones and shotgun (line) microphones. However, condenser microphones that require external (phantom) power will not work directly with wireless body-pack transmitters.

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