Wireless Microphone Systems
How Wireless Microphone Systems Work
As an audio technician, I have witnessed a revolution in the conference industry.
Just about everybody wants a wireless microphone — “like the ones they use on TV”.
As sound quality and reliability have increased and cost has decreased, wireless microphone systems have become very popular. They have thrived for one important reason: eliminating the microphone cable connection frees you to walk across the stage, among the audience, (and, sometimes, out the door). This gives the presenter greater mobility, flexibility, and — with the wireless, hands-free models — the ability to talk with your hands!
So what is a Wireless Microphone System?
A wireless microphone system is usually made up of three components:
- the microphone (either handheld or handsfree),
- a transmitter, and
- a wireless receiver.
In the case of a handheld microphone, the transmitter is built into the microphone itself.
For the handsfree microphone, a short cable connects it to a body pack transmitter. This unit usually looks like a transistor radio and has a clip for attaching to a pocket or belt. This configuration is used for a number of “handsfree” microphones, lapel (or lavaliere) mics, collar mics and headband mics
How does a wireless microphone system work?
First the microphone provides the audio signal.
A conventional wired microphone converts sound waves into an electrical audio signal that travels to the PA 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 (UHF/VHF) or an Infrared signal.
Then the transmitter broadcasts that signal through an antenna.
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 TV remote control. The transmitter clips to the user’s belt or may be worn on the body.
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. All wireless transmitters require a battery (usually a 9-volt alkaline type) to operate.
The job of the receiver is to pick up the signal broadcast by the transmitter and change it back into an audio signal.
The output of the receiver is electrically identical to a standard microphon signal, and can be connected to a typical microphone input in a PA system or a closed system headset.
Wireless receivers are available in two different configurations: Single Antenna or Diversity.
Single antenna receivers utilize on 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 through "dead spots" in a room.
Diversity receivers 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 greatly reduced.
NOTE: Each performer or presenter using a wireless system 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 radio stations in one 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. The technicians at AudioLink can assist with selecting the appropriate frequencies for your needs.
Choosing the wireless system which is right for you!
Choosing a wireless microphone 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 lavaliere or lapel /tie-clip microphone and body-pack transmitter (for lecturers or stage actors)
- a headband microphone and body-pack transmitter (for singers/dancers or aerobics instructors)
For example, UHF is more expensive but has a wider range of operating frequencies. Then too, there is a school of thought that infrared systems are more secure than FM systems. This may have been true in the past, but with more modern technology both are subject to interception and the real decision comes down to personal preferences and the operating environment. (e.g. infrared is limited to line of sight broadcast, while FM systems may be subject to frequency interference).
Transmitter choices often revolve around the difference between UHF, VHF and infrared.
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 source of radio frequency interference.
How a Wireless System Connects to your PA System
A wireless system connects to the rest of your PA 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. The output jack of the receiver simply connects to the same input on the audio mixing console, mixer/amplifier or PA system.Because each user may be talking or singing at a different volume, each wireless system must be connected to a separate input on the PA system so that the level of each wireless microphone can be adjusted individually. Depending on the type of input connections that your PA system has (XLR or 1/4 inch), you may need an adapter cable to properly interface the output of the wireless receiver to the input of the PA system.
Ask us at AudioLink about what type of connectors, if any, you’ll need.
Next month I’ll be focusing on a particular type of transmitter/receiver system that incorporates both digital and analog features.