Wireless microphone
A wireless microphone, or cordless microphone, is a microphone without a physical cable connecting it directly to the sound recording or amplifying equipment with which it is associated. Also known as a radio microphone, it has a small, battery-powered radio transmitter in the microphone body, which transmits the audio signal from the microphone by radio waves to a nearby receiver unit, which recovers the audio. The other audio equipment is connected to the receiver unit by cable. In one type the transmitter is contained within the handheld microphone body. In another type the transmitter is contained within a separate unit called a "bodypack", usually clipped to the user's belt or concealed under their clothes. The bodypack is connected by wire to a "lavalier microphone" or "lav", a headset or earset microphone, or another wired microphone. Most bodypack designs also support a wired instrument connection. Wireless microphones are widely used in the entertainment industry, television broadcasting, and public speaking to allow public speakers, interviewers, performers, and entertainers to move about freely while using a microphone without requiring a cable attached to the microphone.
Wireless microphones usually use the VHF or UHF radio frequency bands since they allow the transmitter to use a small unobtrusive antenna. Cheap units use a fixed frequency but most units allow a choice of several frequency channels, in case of interference on a channel or to allow the use of multiple microphones at the same time. Frequency modulation is usually used, although some models use digital modulation to prevent unauthorized reception by scanner radio receivers; these operate in the 900 MHz, 2.4 GHz or 6 GHz ISM bands. Some models use antenna diversity to prevent nulls from interrupting transmission as the performer moves around. A few low cost models use infrared light, although these require a direct line of sight between microphone and receiver.
History
Various individuals and organizations claim to be the inventors of the wireless microphone.From about 1945 there were schematics and hobbyist kits offered in Popular Science and Popular Mechanics for making a wireless microphone that would transmit the voice to a nearby radio.
Figure skater and Royal Air Force flight engineer Reg Moores developed a radio microphone in 1947 that he first used in the Tom Arnold production "Aladdin on Ice" at Brighton's sports stadium from September 1949 through the Christmas season. Moores affixed the wireless transmitter to the costume of the character Abanazar, and it worked perfectly. Moores did not patent his idea, as he was illegally using the radio frequency 76 MHz. The producers of the ice show decided that they would not continue using the device; they would rather hire actors and singers to perform into hidden microphones to "dub" the voices of the other ice skaters, who would thus be free to concentrate on their skating. In 1972 Moores donated his 1947 prototype to the Science Museum in London.
Herbert "Mac" McClelland, founder of McClelland Sound in Wichita, Kansas, fabricated a wireless microphone to be worn by baseball umpires at major league games broadcast by NBC from Lawrence–Dumont Stadium in 1951. The transmitter was strapped to the umpire's back. Mac's brother was Harold M. McClelland, the chief communications architect of the U.S. Air Force.
Shure Brothers claims that its Vagabond 88 system from 1953 was "the first handheld wireless microphone system for performers." Its transmitter used five subminiature vacuum tubes and could cover an area from , using FM at a carrier frequency of 2.1 MHz. At about the same time, Donald E. Thomas at Bell Labs described an experimental transmitter that used a single point-contact transistor as both oscillator and modulator and whose signal could be picked up by any commercial FM receiver.
In 1957, the German audio equipment manufacturer Sennheiser, at that time called Lab W, working with the German broadcaster Norddeutscher Rundfunk, exhibited a wireless microphone system. From 1958 the system was marketed through Telefunken under the name of Mikroport. The pocket-sized Mikroport incorporated a dynamic moving-coil cartridge microphone with a cardioid pickup pattern. It transmitted at 37 MHz with a specified range of.
The first recorded patent for a wireless microphone was filed by Raymond A. Litke, an American electrical engineer with Educational Media Resources and San Jose State College, who invented a wireless microphone in 1957 to meet the multimedia needs for television, radio, and classroom instruction. The main transmitter module was a cigar-sized device that weighed, contained the microphone and circuitry including four junction transistors, and was suspended around the user's neck in lavalier fashion by a cord that also carried the antenna wire. Vega Electronics Corporation manufactured the design in 1959, producing it as a product called the Vega-Mike. The device was used by the broadcast media at the 1960 Democratic and Republican National Conventions. It allowed television reporters to roam the floor of the convention to interview participants, including presidential candidates John F. Kennedy and Richard Nixon. Litke's patent was granted in May 1964, assigned to Vega Electronics.
Introduced in 1958, the Sony CR-4 wireless microphone was being recommended as early as 1960 for theater performances and nightclub acts. Animal trainers at Marineland of the Pacific in California were wearing the $250 device for performances in 1961. The 27.12 MHz solid-state FM transmitter was capable of fitting into a shirt pocket. Said to be effective out to, it mounted a flexible dangling antenna and a detachable dynamic microphone. The tube-based receiver incorporated a carrying drawer for the transmitter and a small monitor loudspeaker with volume control.
Another German equipment manufacturer, Beyerdynamic, claims that its Transistophone, which went into production in 1962, was the first wireless microphone.
The first time that a wireless microphone was used to record sound during filming of a motion picture was allegedly on Rex Harrison in the 1964 film My Fair Lady, through the efforts of Academy Award-winning Hollywood sound engineer George Groves.
By 1971, wireless microphone products for amateurs and hobbyists were available. Radio Shack offered a microphone/transmitter module that proved to be vulnerable to capacitive detuning as a user moved around and mingled with crowds. One solution was to build on a final RF amplifier stage, which the module lacked, though Litke had already anticipated the problem and included one in his patent.
Wider dynamic range came with the introduction of the first compander wireless microphone, offered by Nady Systems in 1976. Todd Rundgren and the Rolling Stones were the first popular musicians to use these systems live in concert. Kate Bush is regarded as the first artist to have had a headset with a wireless microphone built for use in music. For her Tour of Life in 1979 she had a compact microphone combined with a self-made construction of wire clothes hangers, to free her hands for expressionist dance performances. Her idea was adopted for live performance by other artists such as Madonna and Peter Gabriel.
Nady joined CBS, Sennheiser and Vega in 1996 to receive a joint Emmy Award for "pioneering development of the broadcast wireless microphone".
Techniques
The professional models transmit in VHF or UHF radio frequency and have 'true' diversity reception, which eliminates dead spots and the effects caused by the reflection of the radio waves on walls and surfaces in general..Another technique used to improve the sound quality, is companding. Nady Systems, Inc. was the first to offer this technology in wireless microphones in 1976, which was based on the patent obtained by company founder John Nady.
Some models have adjustable gain on the microphone itself to be able to accommodate different level sources, such as loud instruments or quiet voices. Adjustable gain helps to avoid clipping and maximize signal to noise ratio.
Some models have adjustable squelch, which silences the output when the receiver does not get a strong or quality signal from the microphone, instead of reproducing noise. When squelch is adjusted, the threshold of the signal quality or level is adjusted.
Products
, Audio Ltd, Audio-Technica, Electro-Voice, Lectrosonics, MIPRO, Nady Systems, Inc, Samson Technologies, Sennheiser, Shure, Sony, Wisycom and Zaxcom are all major manufacturers of wireless microphone systems. They have made significant advances in dealing with many of the disadvantages listed above. For example, while there is a limited band in which the microphones may operate, several high-end systems can consist of over 100 different microphones operating simultaneously. However, the ability to have more microphones operating at the same time increases the cost due to component specifications, design and construction. That is one reason for such large price differences between different series of wireless systems.Generally there are three wireless microphone types: handheld, plug-in and bodypack:
- Handheld looks like a 'normal' wired microphone, may have a bigger body to accommodate the transmitter and battery pack.
- Plug-in, plug-on, slot-in, or cube-style transmitters attach to the bottom of a standard microphone, thus converting it to wireless operation.
- Bodypack is a small box housing the transmitter and battery pack, but not the microphone itself. It is attachable to clothing or on the body and has a wire going into a headset, a lavalier microphone or a guitar.