Whether you're a singer, speaker, technician, audience member, or even an at-home hobbyist, microphone feedback is never a welcomed occurrence. Therefore, preventing and eliminating microphone feedback should be of utmost importance when doing any live sound reinforcement.
Here Are 12 Effective Methods For Preventing/Eliminating Microphone Feedback:
- Do not position the microphone in front of a loudspeaker.
- Point directional microphones away from monitors.
- Turn down the microphone gain and volume.
- Do not cup the microphone.
- Ring out the mic/room with an equalizer.
- High-pass filter the microphone signal.
- Position microphones close to their intended sound sources.
- Isolate the microphone from the floor.
- Find the maximum gain-before-feedback and stay shy of it.
- Use in-ear monitors rather than loudspeaker/foldback monitors
- Reduce the number of open microphones.
- Acoustically treat the room.
Let's discuss each of these methods in more detail and take a deeper look into what microphone feedback actually is in this article!
Table Of Contents
- What Is Microphone Feedback?
- The Sound Of Microphone Feedback.
- The Influencing Factors Of Mic Feedback.
- 12 Methods To Prevent & Eliminate Microphone/Audio Feedback.
- 1. Do Not Position The Microphone In Front Of A Loudspeaker.
- 2. Point Directional Microphones Away From Monitors.
- 3. Turn Down The Microphone Gain And Volume.
- 4. Do Not Cup The Microphone.
- 5. Ring Out The Mic/Room With An Equalizer.
- 6. High-Pass Filter The Microphone Signal.
- 7. Position Microphones Close To Their Intended Sound Sources.
- 8. Isolate The Microphone From The Floor.
- 9. Find The Maximum Gain-Before-Feedback And Stay Shy Of It.
- 10. Use In Ear Monitors Rather Than Loudspeaker/Foldback Monitors.
- 11. Reduce The Number Of Open Microphones.
- 12. Acoustically Treat The Room.
- Eliminating Microphone Feedback In Computers.
- Eliminating Microphone Feedback In Headsets.
- Related Questions.
What Is Microphone Feedback?
Let's start by defining microphone feedback.
Microphone feedback is a type of audio feedback that occurs between a microphone, which acts as an audio input, and an audio output (most often a loudspeaker or monitor).
It is a positive gain loop where the mic signal is amplified and passed through the loudspeaker. The sound from the loudspeaker is then picked up by the mic and amplified further.
This loop happens until the mic channel overloads, causing the loudspeaker to emit a terrible squealing noise.
Microphone feedback is nearly always undesirable. I cannot think of a single scenario where mic feedback would be welcomed. This makes it unlike some other audio feedback loops, such as guitar amplifier feedback, which have creatively found their way into music and other art forms.
So microphone feedback requires a mic and a loudspeaker of sorts (this can be a speaker, headphones, etc.).
Note that the mixer and loudspeaker in the above diagram would be passive. The amplifier may be combined with the mixer (active mixer) or the loudspeaker (active loudspeaker).
To recap, the positive mic feedback loop is a “chicken-and-the-egg” scenario:
- The mic picks up sounds from the environment
- These sounds are converted to mic signals which are sent to the amplifier and loudspeaker(s)
- The loudspeaker passes these signals as sound waves into the environment
- The mic picks up those sound waves in the environment
The Sound Of Microphone Feedback
The sound of microphone feedback is most often described as a shrill squealing, screeching, distorted tone.
The tone of microphone feedback will typically happen at a specific frequency or specific frequencies. Mic feedback may happen at a very low hum or a very high-pitched screech.
The following factors determine the frequency of microphone feedback:
- Resonance frequency of the microphone
- Resonance frequency of the amplifier
- Resonance frequency of the loudspeaker
- Size of the room
- Acoustic material of the room
- Microphone polar pattern
- Loudspeaker emission pattern
- Distance between the microphone and loudspeaker
The Influencing Factors Of Mic Feedback
The factors that influence microphone feedback are:
- Amplification/gain of the microphone signal
- Volume of the loudspeakers
- Distance between the microphone and loudspeaker
- Directionality of the microphone
- Size and shape of the physical space
- Sensitivity of the microphone
- Frequency Response of the microphone
Amplification/Gain Of The Microphone Signal
Applying too much gain to a mic signal will increase the risk of feedback.
Gain and amplification are essential to strengthen a microphone's signal so that it plays through the loudspeaker at a reasonable level.
In the case of live sound reinforcement, there are two gain stages for the microphone signal to go through:
- Mic level to line level (gain applied at the mic input of a mixer or other audio device).
- Line level to speaker level (gain applied so the signal is strong enough to move the loudspeaker diaphragm properly).
To read an in-depth article on the different audio levels, feel free to check out my article Do Microphones Output Mic, Line, Or Instrument Level Signals?
Gain should first be set so that there is no distortion in the signal (no clipping).
Then, finding the gain-before-feedback of a microphone within your sound system is a good idea. Once found, reduce the gain to a safe amount below the gain-before-feedback threshold.
Volume Of The Loudspeakers
Similar to proper gain staging, the loudness or volume of the loudspeakers play a big role in microphone feedback.
The “volume of the loudspeakers” really has to do with amplifying the post-mic-gain signal, which we touched on in the above point. However, I thought it would be good to reiterate it here.
Let's say all the levels are healthy and the microphone(s) with well in a mix, but you're still experiencing microphone feedback. In this case, the overall volume of the loudspeakers is likely too high for the acoustic space and should come down to help reduce or eliminate the risk of microphone feedback.
Distance Between The Microphone And Loudspeaker
The distance between the mic and loudspeaker is a critical factor for gain-before-feedback. This is especially important to consider for handheld microphones since their distance to the nearest loudspeaker often changes.
Basically, the closer a microphone is to a playback source (a loudspeaker in our example), the stronger the sound waves of that playback source. Stronger sound waves yield stronger mic signals. This is a recipe for microphone feedback!
This factor is explained with the inverse-square law:
“The inverse-square law states that the intensity of a sound wave (in the air) is inversely proportional to the square of the distance from the sound source. Thus, sound intensity decreases 50% or ~6 dB for every doubling of distance from the sound source. This is worth knowing for better mic placement.”
– Definition From My Microphone Terminology/Glossary Page
Directionality Of The Microphone
The directionality (polar pattern) tells us the direction(s) in which a microphone is the most sensitive to sound.
Microphones with cardioid polar patterns are by far the most commonly used mics in live sound reinforcement. They provide excellent isolation of sound sources and relatively high gain-before-feedback.
The cardioid polar pattern (as seen in the graph) is unidirectional. It is most sensitive to on-axis sounds (0°); less sensitive to the sides (about -6 dB @ 90° and 270°), and has a null point to its rear (180°).
Looking at the above picture, we can see that the rear null point of a cardioid microphone will effectively reject the sound from the foldback monitor.
In the scenario described above, a cardioid microphone reduces the risk of feedback while retaining the sensitivity where the microphone is pointing (away from the foldback monitor and loudspeaker).
If we were to place an omnidirectional microphone on the mic stand in the above picture, we'd have a much greater risk of microphone feedback. This is because the rear of an omni mic is equally as sensitive as the front (and all other directions).
Therefore, the omnidirectional mic would present much more risk of feedback.
For an extremely detailed look into microphone directionality, check out my article The Complete Guide To Microphone Polar Patterns.
Size And Shape Of The Physical Space
The size, shape, and even the boundary material (floor, walls, and ceiling) of a room will affect microphone feedback.
The smaller the room, the stronger the sound reflections will be. Strong reflections increase the risk of feedback even if the microphone and loudspeaker are positioned in ideal locations. This is because sound waves are able to reflect off closer surfaces and travel less distance before reaching the microphone.
Since sound waves reflect off surfaces, the shape of the room matters for mic feedback, too. The more square or rectangular a room is, the stronger the standing waves will be (the sound wave frequencies that have wavelengths equal to the length of two parallel boundaries).
Standing waves cause a boost at their frequencies within the room and will increase the risk of feedback at those same frequencies.
Finally, the material of the boundaries is important to mic feedback. A room with absorptive soundproofing surfaces will be less likely to have mic feedback problems than a room with reflective surfaces.
Sensitivity Of The Microphone
Sensitivity ratings tell us how strong a microphone's output signal will be when subjected to a given sound pressure level.
Basically, the greater a mic's sensitivity, the less gain it will need to get to line level. Therefore, all other things being equal, sensitive mics are more prone to feedback than less sensitive mics.
For a great read on microphone sensitivity, check out my article What Is Microphone Sensitivity And Why Does It Matter?
Frequency Response Of The Microphone
A mic's frequency response plays a large enough role in feedback that it's worth mentioning here.
Condenser microphones often have flat frequency responses and can pick up a wide range of frequencies. This, in theory, makes them more sensitive to microphone feedback across the entire audible frequency spectrum.
Microphones with coloured frequency responses (many dynamic mics are coloured) often won't cover the full range of audible frequencies. This makes them, theoretically, less prone to microphone feedback.
However, coloured mics are often more sensitive to certain frequencies than others. These bands of increased frequencies make them more susceptible to feedback at those frequencies than flat mics.
For more information on microphone frequency response, read my Complete Guide To Microphone Frequency Response (With Mic Examples).
12 Methods To Prevent & Eliminate Microphone/Audio Feedback
With all that said, let's get into the top 12 methods to prevent and/or eliminate microphone feedback. Once again, they are:
- 1. Do Not Position The Microphone In Front Of A Loudspeaker
- 2. Point Directional Microphones Away From Monitors
- 3. Turn Down The Microphone Gain And Volume
- 4. Do Not Cup The Microphone
- 5. Ring Out The Mic/Room With An Equalizer
- 6. High-Pass Filter The Microphone Signal
- 7. Position Microphones Close To Their Intended Sound Sources
- 8. Isolate The Microphone From The Floor
- 9. Find The Maximum Gain-Before-Feedback And Stay Shy Of It
- 10. Use In Ear Monitors Rather Than Loudspeaker/Foldback Monitors
- 11. Reduce The Number Of Open Microphones
- 12. Acoustically Treat The Room
1. Do Not Position The Microphone In Front Of A Loudspeaker
Positioning a live microphone in front of a public address or sound system loudspeaker is a recipe for microphone feedback.
When setting up your loudspeakers and microphones, be aware of their positions and the directions in which they point.
If you are using handheld mics, do your best to ensure the performer holding the handheld mic doesn't walk in front of or point the mic at the speakers.
Live sound venues and stages are set up with the loudspeakers pointing away from the stage and in front of any live microphones.
2. Point Directional Microphones Away From Monitors
Foldback monitors present a direct contradiction to the previous point.
Monitors are used in live sound reinforcement situations to help performers hear themselves by providing specific audio mixes.
Monitors are loudspeakers that are positioned on stage and point toward the performers.
With vocalists, this means we point the monitor at the ears, even though the microphone is in the same direction.
This is where directional microphones become essential.
As mentioned, the cardioid directional pattern is the most popular among live reinforcement microphones. This is largely due to its rear (180°) null point.
The cardioid microphone effectively rejects sounds from its rear. This is essential for vocal mics for the following reasons:
- The monitor can be pointed at the null point of the cardioid mic.
- The vocalist can sing into the microphone while simultaneously hearing her vocal mix.
This doesn't only go for vocals, though. When miking other instruments and sound sources, be aware of where the monitors and loudspeakers are and try to position your directional mics accordingly.
To read more about the cardioid directional pattern, check out my article What Is A Cardioid Microphone? (Polar Pattern + Mic Examples).
3. Turn Down The Microphone Gain And Volume
This would have been number one on this list had I not decided to start with setup techniques.
Simply reducing the microphone gain or volume of the mic channel in the audio mixer is the fastest and easiest way to eliminate feedback with that mic.
Depending on your mixing style, the audio sends you're using (pre or post-fader), and other factors, you may want to adjust the gain rather than the volume or vice versa.
To put it simply, once everything is set up a running, the easiest way to quickly eliminate mic feedback is to quickly turn down the offending microphone.
4. Do Not Cup The Microphone
This tip is for the vocalists that use handheld microphones.
Cupping the microphone basically means you wrap your hands around the grille (top) of the mic. Although it may look cool, it effectively turns your directional live vocal mic into an omnidirectional mic.
Omnidirectional mics are sensitive to sound from all directions (in our example, this would mean the mic picks up sound from the vocalist, foldback monitor, and even the reflections of the loudspeakers around the room).
The change in polar pattern happens because cupping the mic blocks the rear ports of the microphone.
Blocking the rear ports means that no sound will affect the rear of the mic diaphragm.
When sound waves only interact with one side of the diaphragm, an omnidirectional polar pattern is produced.
This makes omnidirectional mics very prone to feedback, making cupping the microphone a poor technique when trying to avoid mic feedback.
5. Ring Out The Mic/Room With An Equalizer
Basically, this technique filters the room's resonant frequencies out of the sound system mix. By pulling out the room's resonant frequencies, we reduce the effects that standing waves have on microphone feedback. Filtering these sensitive, room-specific resonances allows more gain and volume before feedback.
There are 3 common types of equalizers used in live sound reinforcement to rid of mic feedback:
- Graphic EQ.
- Parametric EQ.
- Automatic Feedback Reducers.
A graphic EQ has set gain faders for frequency bands across the audible frequency spectrum. High-quality graphic EQs typically have 31 bands.
To ring out the room, a sound technician will find the offending band and reduce its gain.
For more information on graphic EQ, check out my article The Complete Guide To Graphic Equalization/EQ.
A parametric EQ has a sweepable frequency and Q (bandwidth of the boost or cut).
With a parametric EQ, a sound technician can sweep a boost across the frequency spectrum until an offending frequency is found and then cut that offending frequency.
For more information on parametric EQ, check out my article The Complete Guide To Parametric Equalization/EQ.
Automatic Feedback Reducers
As the name suggests, automatic feedback reducers adjust their EQs automatically to reduce the risk of feedback.
Automatic feedback reducers are a joy to work with when handheld, wireless, or other moving microphones are being used because they'll adjust their EQ as the mic moves relative to the sound system.
To learn more about audio EQ, check out my article The Complete Guide To Audio Equalization & EQ Hardware/Software.
6. High-Pass Filter The Microphone Signal
This is similar to method number 5 since it has to do with equalization.
Simply high-passing a microphone can greatly reduce the likelihood of feedback. This is particularly true if that mic is not shock-mounted, positioned close to the stage, or in a particularly bass-heavy region.
If the microphone is not intended to capture a bass-heavy sound source, applying a high-pass filter will likely benefit the mix, and it will certainly reduce the risk for feedback.
For more info on microphone high-pass filters, check out my article What Is A Microphone High-Pass Filter And Why Use One?
7. Position Microphones Close To Their Intended Sound Sources
Close-miking a sound source provides isolation and less microphone bleed from other sound sources and noise in the environment.
This allows us to capture a more direct sound and apply less gain to get a strong, clean signal. Less gain and less bleed from the loudspeakers mean less risk of feedback!
An additional benefit is that, oftentimes, the sound source will not be right in front of a loudspeaker, and so close-miking the source will also mean that we're positioning mics away from the sound system.
For a related article I wrote on microphone placement, check out Top 23 Tips For Better Microphone Placement.
8. Isolate The Microphone From The Floor
Isolating a microphone from any vibrating body is a good idea.
Sound doesn't only travel through the air; it also travels through the stage and venue. Therefore, isolating your microphones from the floor and other vibrating bodies will help to reduce the risk of mic feedback.
Microphone stands will provide some isolation.
Many live-purpose microphones will have internally shock-mounted capsules/cartridges.
Shock mount microphone clips can also be used to decrease the likelihood of microphone feedback.
To read more about properly attaching your microphones to mic stands, check out my article How To Attach A Microphone To A Microphone Stand.
9. Find The Maximum Gain-Before-Feedback And Stay Shy Of It
Once the microphones and the room are properly equalized in the monitor and main mixes, we can really start to find the sweet spots for each microphone.
During soundcheck or rehearsal, find the gain-before-feedback threshold of each microphone under normal circumstances.
This means during a normal and expected performance volume, push the mic gain up until the mic begins to feedback. That is the normal gain-before-feedback threshold.
Now, because performances are dynamic, pull the gain back a few decibels to have a “safety net” when the performance ramps up.
This built-in buffer will make life a lot easier for the audio technician. When the performance gets louder, there won't be an urgent need to bring down multiple mic levels to avoid microphone feedback.
10. Use In-Ear Monitors Rather Than Loudspeaker/Foldback Monitors
In-ear monitors are an alternative to foldback monitors. They are like special headphones that fit inside the performers' ears.
Removing the foldback monitors (loudspeakers) from the stage effectively reduces the noise and improves the gain-before-feedback of all the stage microphones.
Related article: The Complete Guide To Balanced Armature IEMs/Earphones
11. Reduce The Number Of Open Microphones
Having more open microphones means more signals going to the sound systems and more opportunities and positions for mic feedback to occur.
Less is often more when miking stages. By reducing the number of microphones on stage (or at the very least the number of microphones that send signals to the sound system at a given time), we will greatly reduce the chance of feedback.
Reducing the number of open mics also allows for faster troubleshooting if feedback was to occur.
12. Acoustically Treat The Room
This is the last method on our list since it isn't always in our direct control. It is directed more toward venue owners and people with jam spaces.
Acoustically treating a room can be broken into two main points:
- Applying dampening foam to the surfaces.
- Introducing odd angles to the room structure.
The aim of acoustic treatment is to reduce reflections and standing waves. This reduces the amount of sound that enters the microphones and improves the effectiveness of proper mic and loudspeaker positioning.
Eliminating Microphone Feedback In Computers
The built-in microphones and speakers in laptop computers are often very close to one another (due to the restrictions of the computer design).
If your computer is feeding back, mute the speaker output to immediately rid of the squealing.
It's not advised to monitor a built-in computer mic with built-in speakers.
If you absolutely need to monitor the mic input, try using the headphone output and monitoring with headphones. With the headphones in your ears, there should be no risk of mic feedback.
Otherwise, it's a matter of muting the built-in microphone send to the built-in speakers. These options will be in the audio preferences of whatever computer software you're using.
For more information, check out my article How To Stop A Microphone Feedback Loop In A Computer.
Eliminating Microphone Feedback In Headsets
Feedback in headsets typically happens when the headset is off someone's head, and the headphone muffs are not closed together. If the mic is too close to an open headphone and the headset is monitoring itself, feedback is likely to occur.
If the headset is properly positioned on someone's head, it generally will never feedback.
To eliminate the potential for feedback with a headset, you'll have to mute the monitoring of the microphone in the headphones.
To reduce the risk while still monitoring, make sure to turn the volume down or off when you take the headset off your head.
What causes wireless microphone feedback? Microphone feedback is caused by the same factors, whether the mic is wired or wireless. The main causes are likely the mic's gain, the speakers' volume, and/or the positioning of the mic(s) and speaker(s) relative to one another.
How do I stop microphone feedback on my computer? The most likely cause of mic feedback in a computer is having the built-in microphone live while the built-in speakers are turned up. Changing the audio input or output from within the system can quickly solve this issue. It could be as easy as plugging in a pair of headphones to switch the output.
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.