As of late, I've been working regular live sound gigs requiring wireless microphones. It's relatively easy to set up wireless systems and have them work properly. However, I thought I'd do some research into how wireless microphone systems work in detail.
So how do wireless microphones work? Wireless mics send their output signals wirelessly via their built-in transmitters. The transmitter will encode the microphone's audio signal into a carrier signal and transmit that carrier wirelessly to the receiver. The receiver will then decode the original mic signal for the connected mic input.
This article aims to provide a brief overview of how microphones work in general, followed by a more detailed inspection of how wireless microphone systems function.
How Do Wireless Microphones Work?
Wireless microphones work nearly the same as wired microphones. There's really only one big difference between the two: the typical “wired” mic has a male XLR output connection and relies on a cable to carry its signal to the mic input. In contrast, the wireless microphone relies on a radio transmitter to broadcast its output signal to a receiver before being sent to a mic input.
Wireless microphones work in tandem with wireless microphone systems. A wireless microphone system is made up of the following three pieces:
Wireless System Piece 1: The Microphone
The microphone part of the system is just like any typical microphone. Wireless microphones come in various transducer/capsule principles (moving-coil dynamic, condenser, and even ribbon dynamic).
Just like any microphone, wireless mics work as transducers, changing acoustic/mechanical wave energy (sound) into electrical energy (audio signal):
- Sound waves vibrate the microphone diaphragm.
- The vibration of the diaphragm is converted to an electrical signal through either electromagnetic induction (dynamic) or the variation in the capsule capacitance (condenser).
- This signal may or may not be amplified within the microphone before the output.
The above is an oversimplification. The point is that the microphone portion of a wireless system is the same as a typical microphone.
For a full explanation of how microphones work, check out my article How Do Microphones Work? (A Helpful Illustrated Guide).
The Microphone Body
Wireless microphones are typically in the style of handheld, lavalier, or headset (there isn't much point in having a stationary studio-grade microphone be wireless, though you never know what you'll need in a given circumstance).
In general, the microphone body of a handheld wireless microphone will be larger than that of a handheld “wired” microphone. This is because handheld wireless microphones have built-in transmitters, and these transmitters require batteries to function wirelessly. Both the transmitter and the batteries take up physical space!
As for wireless lavalier and headset microphones, they aren't truly without wires. The tiny lavalier microphone body that clips onto clothing near a performer's mouth is too small to have a powered transmitter attached to it. Similarly, headsets may become too heavy or bulky if the transmitter is built-in.
Wireless lav mics have a thin cable that leads to a transmitter. Typically these external transmitters are in the form of small belt packs. So wireless lavs aren't truly wireless. However, the belt pack transmitter allows the microphone to be free of a physical connection to its respective mic input on an audio console.
To learn more about lavalier mics, check out the following My New Microphone articles:
• How And Where To Attach A Lavalier/Lapel Microphone
• Best Lavalier Microphones For Interviews, News, And Presentations
• Best Lavalier Microphones For Actors
Much like lavs, wireless headsets also typically have cables to connect them to a belt pack transmitter.
There are plug-in transmitters to further prove the similarities between the microphone portions of wired vs. wireless. These are standalone transmitters that regular microphones can plug directly into. With plug-in transmitters, we can turn practically any microphone into a wireless mic.
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Wireless System Pieces 2 And 3: The Transmitter And Reciever
When discussing wireless systems, it's best to talk about the transmitter and the receiver as one unit (though they are separate pieces).
The transmitter transmits the audio signal produced by the wireless microphone through a specific radio frequency. The receiver receives this specific radio frequency and, therefore, the audio signal.
The wireless microphone and transmitter are free to roam around cable-free. The wireless microphone receiver is typically positioned close to an audio console. The receiver's output is generally connected to the mic input of the audio console via an XLR cable.
Transmitters work by transmitting the audio signal from the microphone through radio waves. The transmitter takes the microphone output audio signal, converts it to a radio signal and broadcasts it through an antenna.
The government regulates the strength of the radio signal from a wireless microphone transmitter to avoid unnecessary interference outside of the practical distance of a wireless microphone system. The distance of a transmitter's effectiveness is typically between 100 to 1,000 feet, depending on conditions.
Wireless microphone system transmitters come in 3 general types:
- Belt pack
Handheld transmitters look like the handles of “regular” microphones and typically attach to specific microphone capsules. In some cases, we may mix and match handheld transmitters and microphone capsules.
Handheld wireless system example: Shure PGXD24/SM58-X8.
Plug-in transmitters are standalone transmitter boxes we plug regular microphones into. These transmitters essentially turn our “regular” microphones into wireless microphones. Some plug-in transmitters even provide phantom power and are compatible with active microphones!
Plug-in wireless system example: Sennheiser XSW-D XLR Base Set.
Belt pack transmitters are sleek and can be hidden easily in clothing, making them fantastic for film and television. These typically require some cabling (a tiny cable) to connect the microphone (typically lavalier or headset) to the transmitter.
Belt/bodypack wireless example: Sennheiser EW 122P G4.
Transmitters nearly all run on batteries rather than wall plug power (why would we remove the audio cable to replace it with a power cable?)
Before talking about the receivers, let's discuss a few basics of RF transmission.
Basics Of Wireless Microphone Radio Frequency Transmission
Practically all wireless microphone systems use FM (frequency modulation) and need roughly 200 kHz bandwidth (to modulate within). To have this bandwidth, the radio frequencies bands utilized for sending wireless microphone signals are typically either:
- VHF (Very High Frequency) = 30-300 MHz
- UHF (Ultra High Frequency) = 300 MHz – 3 GHz
Wireless microphones operating with VHF are typically set to one signal frequency. This makes them easy to set up but difficult to use if there is nearby RF interference at the set frequency.
Newer wireless microphones often operate at UHF. However, these frequencies are also regulated in their range, so the 300 MHz – 3 GHz is not entirely available. This regulated range is known as the “television band.”
- In the U.S, the regulated television band is 470 MHz – 614 MHz
- In Europe, the regulated television band is 470 MHz – 790 MHz
Like the RF strength/distance regulations, these regulations are put in place to keep interference with other RF communications to a minimum.
Wireless mics operating in these television bands often have the option to change their transmitted frequency. This makes it easy to avoid nearby RF interference and to use multiple wireless mics at a time.
The transmitter and receiver must be set to the same radio frequency for the wireless microphone signal to be sent correctly. The transmitter can be thought of like its own little radio station sending out the audio from the microphone. The receiver must be set to accept the specific radio waves to “hear” the microphone.
Interference may happen if other transmitters are sending out the same radio frequency. This is called RF interference and can be avoided with quality wireless systems that allow us to change the transmitted frequency.
Wireless microphone receivers effectively receive the radio frequency of the microphone transmitter and convert it back to the audio signal. The receiver decodes the desired audio signal and should be connected to a mic level input of an audio console.
Once again, for the wireless system to work correctly, the receiver must be set to receive the same radio frequency the transmitter is transmitting. In VHF systems, these values are typically set so that one transmitter works with its coinciding receiver. In UHF systems, these frequencies are usually variable, and it's up to us to ensure the transmitted frequency matches the receiver's frequency.
Wireless systems come in 3 main types and have to do with how the receiver receives the transmitted radio signal. They are:
- True diversity
Non-diversity system receivers have one antenna to receive the signal from the transmitter. These are rarely found in any quality receivers on the market today.
Diversity system receivers have two antennas spaced a short distance apart. Both are connected to a single receiver. The wireless connection only happens between one transmitter antenna (at the mic end) and one receiver antenna (at the receiver end). If the signal strength drops below an acceptable level on one antenna connection, the receiver will switch to the other antenna. This switch is done blindly, and so it often improves a bad signal connection, but sometimes it makes a bad connection worse.
True Diversity system receivers utilize two separate antennas, with each connected to a separate receiver module. The receiver circuitry reads both antenna signals and selects the better of the two. At least one antennae should receive a clean signal, creating a clean signal transfer with reduced chances of dropouts.
Receivers are almost always stationary devices, and so they're typically powered via wall plug AC. However, there are battery-powered belt pack receivers available as well.
Let's Recap How Wireless Mics Work Versus ‘Wired' Mics
Wired microphone signals follow this basic path:
- The wired microphone outputs a balanced audio signal to an XLR cable
- The XLR cable carries the balanced audio signal to the mic input
Wireless microphone signals follow this basic path:
- The wireless microphone outputs an audio signal to its connected transmitter
- The transmitter sends this audio signal wirelessly through radio waves
- The receiver is tuned to receive these radio waves and audio signals
- The receiver outputs the balanced audio signal via an XLR cable
- The XLR cable carries the balanced audio signal to the mic input
From the basic descriptions above, we see that wireless mic systems replace the mic cable.
Pro tip: Do not forget batteries when using a wireless microphone system!
The Benefits Of Going Wireless
There are numerous benefits of using wireless microphone systems over “wired” setups.
The advantages of wireless microphones include:
- Less/no cable (fewer trip hazards, and no potential tension/pulling between the microphone and console)
- Increased mobility of the microphone (both for a performer and for passing the mic around to various people)
- Cleaner signal since the audio doesn't travel through any length of cable
The Cons Of Going Wireless
As with anything, there are also disadvantages of using wireless microphone systems over “wired” mics.
The disadvantages of wireless microphones include:
- The transmitter's need for batteries (and the subsequent static noise many receivers output when the transmitter dies or is turned off)
- The possibility for radio interference to intercept the signal (we don't want to pick up audio from anything but the specified microphone)
What's the difference between audio frequencies and radio frequencies?Audio/sound frequencies range from infrasound (<20 Hz) through the human audible range (20 Hz – 20 kHz) to ultrasound (>20 kHz). Radio frequencies range from 3 Hz – 3 THz. Sound is mechanical wave energy and can only travel through a medium. Radio waves are electromagnetic and do not need a medium.
Related articles: How To Connect A Wireless Microphone To A Computer (+ Bluetooth Mics).
Choosing the right microphone(s) for your applications and budget can be a challenging task. For this reason, I've created My New Microphone's Comprehensive Microphone Buyer's Guide. Check it out for help in determining your next microphone purchase.