Wireless microphone systems send their output signals wirelessly via their built-in transmitters. The transmitter encodes the audio signal from the microphone into a carrier signal and transmits this wirelessly to the receiver. The receiver then decodes the original microphone signal for the connected microphone input.
The aim of this article is to provide a brief overview of how wireless microphone system works in general.
How Do Wireless Microphone Systems Work?
Wireless microphones work the same way as wired microphones. There’s really only one big difference between the two: the typical “wired” microphone has an XLR output connector and uses a cable to carry its signal to the microphone input.
In contrast, the wireless microphone relies on a radio transmitter to send its output signal to a receiver before sending it to a microphone input. A wireless microphone system consists of the following 3 parts:
The microphone part of the system is like any typical microphone. Wireless microphones are available in different converter/capsule principles (moving coil dynamics, condenser, and even ribbon dynamics).
Like any microphone, wireless microphones also work as converters and convert the energy of acoustic/mechanical waves (sound) into electrical energy (audio signal):
- Sound waves vibrate the membrane of the microphone.
- The vibration of the membrane is converted into an electrical signal by electromagnetic induction (dynamic) or by varying the capacity of the capsule (capacitor).
- This signal may or may not be amplified in the microphone before output.
Wireless microphones are generally handheld, tie, or headphone types (it makes little sense for a studio-grade stationary microphone to be wireless, although you never know what you might need in certain circumstances.
In general, the microphone body of a wireless handheld microphone is larger than that of a “hardwired” handheld microphone. The only reason is that handheld wireless microphones feature a built-in transmitter that requires batteries to function wirelessly.
Wireless microphones have a thin cable that leads to a transmitter. Typically, these external transmitters come in the form of small belt packs. Wireless lavas are therefore not really wireless. However, the transmitter on the belt allows the microphone not to be physically connected to its corresponding microphone input on an audio console.
There are devices called plug-in transmitters to further prove the similarities between the wired and wireless microphone parts. They are stand-alone transmitters to which ordinary microphones can be connected directly. With pluggable transmitters, we can turn virtually any microphone into a wireless microphone.
The transmitters work by transmitting the audio signal from the microphone over radio waves. The transmitter picks up the audio output signal from the microphone, converts it into a radio signal, and sends it via an antenna.
The government regulates the radio signal strength of a wireless microphone transmitter to avoid unnecessary interference beyond the practical distance of a wireless microphone system. The effective distance of a transmitter is generally between 100 and 1000 feet, depending on the conditions.
There are 3 general types of wireless microphone system transmitters:
- Handheld: Handheld transmitters look like the handles of “normal” microphones and are usually attached to special microphone capsules. In some cases, we can combine handheld transmitters and microphone capsules.
- Plug-in: Plug-in transmitters are independent transmitter boxes into which we plug common microphones. These transmitters essentially transform our “normal” microphones into wireless microphones.
- Belt Pack: Belt Pack transmitters are stylish and easy to hide in clothing, making them a fantastic product for film and television. These usually require at least some cables (a small cord) to connect the microphone (usually a tie or headphones) to the transmitter.
Basics of Wireless Microphone Radio Frequency Transmission:
Virtually all wireless microphone systems use FM (frequency modulation) and require around 200 kHz bandwidth (for indoor modulation). To have this bandwidth, the radio frequency bands used to send wireless microphone signals are generally:
- FM (very high frequency) = 30-300 MHz
- UHF (ultra-high frequency) = 300 MHz – 3 GHz
Wireless microphones that operate on VHF are usually tuned to a signal frequency. This makes them easy to install, but difficult to use if there is RF interference nearby at the set frequency.
Newer wireless microphones often use UHF. However, these frequencies are also regulated in their range, and thus the 300 MHz – 3 GHz are not fully available. This regulated area is known as the “television band”.
- In the United States, the regulated television band is 470 MHz to 614 MHz
- In Europe, the regulated television band is 470 MHz – 790 MHz
Like the RF force/distance regulations, these regulations are introduced to minimize interference with other RF communications.
Wireless microphone receivers efficiently receive the radio frequency of the microphone transmitter and convert it back into an audio signal. The receiver decodes the desired audio signal and must be connected to a microphone level input of an audio console.
For the wireless system to function properly, the receiver must be set to receive the same radio frequency that the transmitter is transmitting. In VHF systems, these values are usually set so that a transmitter works properly with its receiver. In UHF systems, these frequencies are generally variable and it is up to us to ensure that the frequency being transmitted matches the frequency of the receiver.
Wireless systems are of 3 main types and relate to how the receiver receives the transmitted radio signal. These are:
- The diversity
- True diversity
System receivers without diversity have an antenna to receive the signal from the transmitter. These are seldom found in the quality receivers available on the market today.
The receivers of the diversity system have two antennas that are closely spaced from one another. Both are linked to a single receiver. The wireless connection only takes place between a transmitting antenna (microphone side) and a receiving antenna (receiver side). If the signal strength at one antenna connection falls below an acceptable value, the receiver switches to the other antenna. This change is blind and often improves a bad signal connection, but sometimes it makes a bad connection worse.
The receivers of the true diversity system use two separate antennas, each connected to a separate receiver module. The receiver circuit reads both antenna signals and selects the best of the two. At least one of the antennas must receive a clean signal in order to ensure a clean signal transmission with a reduced risk of failure.
Also Read: Jabra Elite Sport Wireless Earbuds