Introduction to Wireless Mics

Wireless microphones have become increasingly popular as their sound quality, reliability, and cost have improved. This article is intended for people who are using a wireless microphone for the first time, or who are trying to decide which model to purchase to suit their particular needs.

It provides a basic understanding of how wireless microphone systems work and what level of performance can reasonably be expected from them.

Why Use A Wireless Microphone System?

Wireless microphone systems serve one important purpose: to eliminate the cable which connects the micro phone (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 a lavalier "tie-clip" type. With wireless systems designed for use with electric guitars, 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 directly to an instrument such as a trumpet or saxophone. 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 a 9-volt alkaline type) to operate.

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 transmitter) 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 (a theater, church, or school, for example) must use a system operating on a different frequency. Wireless systems at one location cannot "share" frequencies because they would 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. This potential for interference limits the number of wireless systems that can be used simultaneously at one venue. Reputable manufacturers and dealers of wireless systems can assist with selecting the appropriate frequencies for your needs.

Choosing a Wireless System

Choosing a wireless system is really a series of choices relating to the individual components (input device, transmitter, and receiver) that make up the system, and their suitability for your specific application.

The input device and transmitter are chosen based on the source to be miked. For example, some typical input device/transmitter combinations and their applications are:

· a handheld microphone with built-in transmitter (for vocalists)

· a lavalier or "tie-clip" microphone and body-pack transmitter (for lecturers or stage actors)

· a headworn microphone and body-pack transmitter (for singer/dancers, aerobics instructors, etc.)

· an instrument microphone and body-pack transmitter (for horn or woodwind players)

· a short cable and body-pack transmitter (for connection to an electric guitar, bass, or keyboard)

The process of selecting the microphone component of your wireless system (in terms of pickup pattern, frequency response, etc.) is the same as for selecting a wired microphone to be used in the same application. The fact that a microphone is wireless does not eliminate the need to consider acoustic issues such as proper microphone and loudspeaker placement to minimize feedback, for instance.

Choosing the type of receiver - single antenna vs. diversity - is more a function of where the wireless system will be used, rather than what it will be used for. Single antenna receivers perform well when operating distances from transmitter to receiver are short, or in environments where the likelihood of signal dropouts is low. Diversity receivers should be chosen whenever operating distances may be longer, when the transmitter user may walk behind walls or through doorways, or in environments where the potential for dropouts is greater due to the presence of metal structure or external sources of radio frequency interference.

How a Wireless System Connects to your Sound System

A wireless system connects to the rest of your sound system in the same way that a standard wired microphone connects. Almost all wireless receivers put out a signal that is electrically identical to that of a wired microphone, so the output jack of the receiver simply connects to the same input on the audio mixing console (or mixer/amplifier) where - the microphone had been connected. A wireless system designed for electric guitar replaces the cable from the guitar to the amplifier. A short cable connects the guitar to the transmitter, and another short cable connects the receiver's output jack to the input jack on the guitar amplifier.

Because each user may be talking, singing, or playing at a different volume, each wireless system must be connected to a separate input on the sound system so that the level of each wireless microphone can be adjusted individually. Depending on the type of input connections that your sound system has, you may need an adapter cable to properly interface the output of the wireless receiver to the input of the sound system. Your local wireless system dealer can usually provide the proper adapter if necessary.

For more information, please contact Shure, Inc.

Reprinted with permission from Shure, Inc. All Rights Reserved