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Wireless Microphone Theory

Quote: "There is nothing in the world worse than a cheap wireless system," Hosch says. "It's scary when your future is hanging on a $ 1.98 battery. Anytime you can, you should get someone to use a wired mic over a wireless system." Scheirman adds, "and just remember that even the best wireless microphone system, a $10,000 system, is almost as good as a mic cable." (From TCI, May 1993, page 25).

A wireless microphone system is a small-scale version of a typical commercial FM broadcasting system. In a commercial broadcasting system, a radio announcer speaks into a microphone that is connected to a high-power transmitter in a fixed location. The transmitted voice is picked up by an FM receiver and heard through a speaker or headset.

In a wireless microphone system, the components are miniaturized but the same principles apply. The transmitter is small enough to fit into the microphone handle or into a small pocket-sized case. Since the microphone and transmitter are battery powered, the user is free to move around while speaking or singing into the mic. The transmitted voice is picked up by a receiver that is wired to a speaker.

Two types of microphones are available with wireless mic systems: the handheld mic, with a transmitter in its handle; and the lavalier mic, which is small enough to be concealed as a lapel pin or hung around the neck. Lavalier mics are wired to miniature body-pack transmitters, which fit into a pocket or clip onto a belt. There is also a transmitter, designed by Lectrosonics, which accepts any three-pin XLR input and acts as a wireless mic-- then you can use any mic you want with the transmitter.

Wireless microphones are widely used today in television and video production. They eliminate the need for stage personnel to feed cables around cameras, props, etc. For location film production, as well as ENG (Electronic News Gathering) and EFP (Electronic Field Production), wireless mics make it possible to obtain usable first take sound tracks in situations that previously required post-production dialogue looping. The cost saving can be significant.

Handheld mics are used by performers on camera where they provide the freedom needed to move around the stage and gesture spontaneously. They are used by speakers and entertainers who need to pass the mic from one person to another. In concerts, hand-held wireless mics permit vocalists to walk and dance around the stage and even into the audience without restriction and with no chance of shock in the event of rain.

Lavalier mics are used in game shows, soap operas and dance routines. They eliminate the need for boom mics and help to alleviate visual clutter. Lavalier mics are used by MCs, panelists, lecturers, clergy, stage actors, and dancers because they can be concealed easily and provide hands-free mobility. Some lavalier transmitter models have high impedance line inputs that accept cords to create wireless electric guitars.

Technology in the early 1970s introduced the integrated circuit compandor which was incorporated into wireless mics to reduce noise. At about the same time, the FCC authorized the use of frequencies in TV channels 7-13 for wireless mics. Thus the wireless microphone's most serious problem, radio interference from other services, was virtually eliminated. Later, the application of diversity reception minimized the problem of dropouts (transmission losses due to cancellation of radio waves), greatly improving system reliability.

Today's wireless mics perform almost as well as conventional wired mics. In the 1980s, wireless mics were manufactured with an improved dynamic range and smaller transmitters, a result of better compandor integrated circuitry and advanced circuit design techniques. A variety of standard microphones with different sound characteristics is available.

There are no international standards for wireless mic radio frequency allocations. Performance is not controlled for transmitter power limits, frequency stability, or RF bandwidth occupancy. Wireless mics could therefore, theoretically, operate at any frequency. Certain frequency bands are more commonly used. In the United States, the FCC regulates the operation of wireless mics at specified frequency bands.




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