The Basics (and history) of Wireless Microphones
The following article is an excerpt from Shure Notes, Issue #22.
Wireless microphones have become increasingly popular. Sound quality and reliability have improved and costs have decreased. If you are using a wireless microphone for the first time, or you are trying to decide which model to purchase, here’s a basic understanding of how wireless microphone systems work.
Why Use A Wireless Microphone System?
Wireless microphone systems serve one important purpose: to eliminate the cable that connects the microphone (or musical instrument) to the sound system. This gives the user greater freedom to move around, without being restrained by a cable. In general, one wireless system replaces one standard wired microphone in a typical sound system. For example, a wireless system specifically designed for use with electric guitar (or bass) replaces the cable that links the instrument to its amplifier.
System Components and What They Do
A wireless system consists of three main components: an input device, a transmitter, and a receiver. The input device provides the audio signal that will be sent out by the transmitter. It may be a microphone, such as a handheld vocalist’s model, or the lavalier type that is probably worn by your pastor. With wireless systems designed for use with instruments like electricguitars, the guitar itself is the input device.
The transmitter handles the conversion of the audio signal into a radio signal and broadcasts it through an antenna. The antenna may stick out from the bottom of the transmitter or it may be concealed inside. The strength of the radio signal is limited by government regulations. The distance that the signal can effectively travel ranges from 100 feet to over 1,000 feet, depending on conditions.
Transmitters are available in two basic types. One type, called a “body-pack” or “belt-pack” transmitter, is a small box about the same size as a packet of cigarettes. The transmitter clips to the user’s belt or may be worn on the body. For instrument applications, a body-pack transmitter is often clipped to a guitar strap or attached
In the case of a handheld wireless microphone, the transmitter is built into the handle of the microphone, resulting in a wireless mic that is only slightly larger than a standard wired microphone. Usually, a variety of microphone elements or “heads” are available for handheld wireless microphones. All wireless transmitters require a battery (usually AA or 9-volt) to operate.directly to an instrument such as a trumpet or saxophone.
The job of the receiver is to pick up the radio signal broadcast by the transmitter and change it back into an audio signal. The output of the receiver is electrically identical to a standard microphone signal, and can be connected to a typical microphone input in a sound system. Wireless receivers are available in two different configurations. Single antenna receivers utilize one receiving antenna and one tuner, similar to an FM radio. Single antenna receivers work well in many applications, but are sometimes subject to momentary interruptions or “dropouts” in the signal as the person holding or wearing the transmitter moves around the room.
Diversity receivers often provide better wireless microphone performance. A diversity receiver utilizes two separate antennas spaced a short distance apart and (usually) two separate tuners. An “intelligent” ; circuit in the receiver automatically selects the better of the two signals, or in some cases a blend of both. Since one of the antennas will almost certainly be receiving a clean signal at any given moment, the chances of a dropout occurring are reduced.
Most wireless receivers operate on AC power, although small battery-powered models (similar in size to a body-pack transm itter) are available for portable use such as mounting to a video camcorder.
How a Wireless System Works
A conventional wired microphone converts sound waves into an electrical audio signal that travels to the sound system through a cable. A wireless microphone system goes one step further, and converts the audio signal created by the microphone to a radio signal, which is sent to the sound system through the air by a transmitter. The radio signal is similar to those used by television and FM radio stations. The receiver tuned to the same frequency as the transmitter picks up the radio signal, converts it back into an audio signal, and feeds it to the sound system through a short cable. The receiver is usually located near the rest of the sound system.
Each performer or presenter using wireless at a particular location must use a system operating on a different frequency. Wireless systems at one location cannot “share” frequencies because they interfere with each other, just as if two television stations in the same city tried to broadcast on the same channel. If two performers at one location try to use the same frequency at the same time, neither one will be picked up clearly.
Some other common problems in early systems included:
- Signal dropout
- Poor range
- Frequency interference
- Distortion and noise
- Short battery life
- Damaged transmitter connectors and cables
The potential for interference limited the number of wireless systems used simultaneously, until technical advances made it possible to operate literally dozens of systems at the same venue. Today, nearly one half of the microphones that Shure sells are wireless.