Sick and tired of dealing with microphone cables? Ever thought of going wireless? Well, don’t get too excited just yet, because there may be things you would want to consider first, before making the jump. If you are interested in becoming a live sound engineer someday, then you need to ask yourself this – What is a Wireless Microphone?
The reason I mentioned “live sound” is because in my experience, the technology that we will be discussing about in today’s article, is also often used during live events, as part of a live sound reinforcement system. Thus, I will be focusing more on the operating principles of wireless microphone systems. Are you intrigued yet? Then lets begin!
Wireless? So What is it Exactly?
Simply put, a wireless microphone is a microphone that doesn’t require a physical cable to be connected directly to a pre-amplifier. Also called “radio microphone”, it is designed with a battery-powered radio transmitter in the microphone body itself, which will transmit the audio signal from the mic (via radio waves) to a nearby receiver unit, which will receive the audio.
This receiver unit will then transmit the audio signal to other audio equipment, usually via “balanced” cables such as XLR. Wireless microphones are commonly used in the entertainment industry, television broadcasting, and in any live event that involves public speaking or musical performances. Users are able to move about freely while using wireless microphones.
There are a variety of standards, frequencies and transmission methods used in order to facilitate a wireless microphone’s cable-less connection. For instance, wireless transmission can be done via radio waves using ultra high frequencies (UHF) or very high frequencies (VHF), FM, AM, or various digital modulation schemes.
There are also cheaper models that use infrared light. These types require a direct line of sight between the microphone and the receiver, unlike costlier radio frequency models. Some infrared models use only a single fixed frequency, but the more advanced ones have “user selectable” frequencies, to avoid interference and allow several microphones to be used simultaneously.
Let us now look at the topics we will be touching on:
- Transmission method
- Product types
- Bandwidth and spectrum
- Advantages vs disadvantages
Wireless microphone systems that are used professionally, transmits audio in VHF or UHF radio frequency, and have true diversity reception (two separate receiver modules, with an antenna each). This design helps to eliminate “dead spots” (caused by phase cancellation) and other negative effects caused by the reflection of the radio waves on walls and surfaces within the room.
You will find that some models are designed with an adjustable “gain” parameter on the microphone itself, in order to accommodate different sound sources, such as loud instruments or quiet voices. This feature actually helps to prevent “clipping”.
It is also important to take note of models which have an adjustable “squelch” control. This silences the output when the receiver unit is not getting a strong signal from the microphone, instead of reproducing noise. When you adjust the “squelch”, the threshold of the signal quality or level will be attenuated.
Although wireless microphones may only operate within a limited frequency band, some high-end systems can support over 100 mics used simultaneously. However, these systems are more expensive due to more complex component specifications, design and construction. This is one of the major reasons for the price differences between various wireless systems.
In general, there are three types of wireless transmitters:
- Handheld – It resembles a typical wired microphone, but will usually have a bigger body to accommodate the built-in transmitter and battery pack.
- Plug-In or Slot-In – These are cube-style transmitters, that are attached to the bottom of a typical microphone (with XLR connector), hence effectively making it wireless.
- Bodypack – This is a small box-type unit that houses the transmitter and battery pack, but not the microphone itself. It is usually attached to clothing or on the body and is connected to the headset or lavalier microphone via a thin wire.
The common types of wireless receivers are as follows:
- True Diversity – Every one of these receiver units is housing two radio modules with two dedicated antennas (one for each module).
- Diversity – Each receiver unit houses one radio module with two antennas (the second antenna may not be obviously visible).
- Non-Diversity – Each receiver unit only has one antenna.
True diversity is the technology used in most quality receivers. It uses two antennas, spaced at least a few inches apart, each receiving the same signal from the transmitter. The signal strength received by both antennas (connected to two separate radio modules) will be constantly measured, and the receiver will switch to the antenna with the stronger signal.
Diversity receivers are unable to monitor the signal strength of both antennas simultaneously, due to both antennas being connected to only a single radio module (unlike true diversity). If the audio signal is weak, the receiver will switch antennas blindly, without knowing the signal strength on the other antenna, until the switch is complete.
Bandwidth and Spectrum
The majority of wireless microphone systems today, operate in the UHF television band. In the United States, this band ranges from 470 MHz to 698 MHz. Other countries such as Great Britain, have a similar UHF TV band ranging from 470 MHz to 790 MHz. Generally, wireless mics operate on unused TV channels, allowing one to two mics per megahertz of spectrum available.
Do take note that most wireless microphone systems use wideband FM modulation (a method of radio broadcasting that uses frequency modulation “FM” technology), which requires approximately 200 kHz of bandwidth. Since FM technology have relatively large bandwidth requirements, wireless microphone operations are effectively restricted to VHF and above.
Advantages vs Disadvantages
The idea of having a wireless microphone system may be enticing to most people. However, before you make the decision to acquire one for yourself, you should consider the pros and cons of wireless systems in general.
- Greater freedom of movement for the user (performer or speaker).
- No cabling problems, typically exhibited by wired microphones due to constant movement.
- No “tripping hazards” due to the absence of cables.
- Microphone is electrically isolated, thus nullifying “ground loops” between microphone and other electrical instruments on stage.
- May have a very limited range (a microphone cable can run up to 300 ft or 100 meters). Some wireless systems have a shorter range, but higher-end ones can have a higher range.
- Wireless transmission may interfere with other radio equipment or other radio microphones, although many models now include frequency-synthesized, switch-selectable channels.
- Battery life may be shorter than a typical condenser microphone due to power requirements of the transmitting circuitry, and extra circuitry features, if any.
- The possibility of “Noise” or “dead spots” (places where it doesn’t work, especially in non-diversity systems)
- Limited number of operating microphones at any given time and place, due to the limited number of radio channels (frequencies).
We have come to the end of this article. I hope this has been educational and have given you folks a greater insight on the intricacies of wireless microphone technology.
Do leave comments or questions below, and share this article with your friends!