In this post, we cover some basics - what causes feedback and how to avoid it - as well as tips from some of our favorite audio pros.
Por Shure Notes Editors. Mitarbeiter: John Chevalier, Bill Gibson, Frank Gilbert, June Millington, Dan Murphy
“John had a semi-hollow Gibson guitar. It had a pickup so it could be amplified. We were about to go out and listen to a take when John put his guitar on the amp. He should have turned on the electric guitar.” It was just a tiny bit and John just put it down. -o against the amp when he went "Nnnnnwahhhh!" And we said, "What is this? Voodoo?” “No, it's feedback.” “Wow, that sounds great!” George Martin was there, so we said, “Can we record that?” It was a found object, an accident caused by the guitar touching caused by the amplifier.
– Paul McCartney (Quelle: Many Years From Now, Barry Mile)
It is common knowledge among popular music students that the 1964 recording of The Beatles' "I Feel Fine" was one of the earliest known examples of feedback as a recording effect, although The Kinks and The Who reportedly (and intentionally) used it live appearances. However, for most musicians and engineers, audio feedback is something to avoid.
In this post, we cover some basics - what causes feedback and how to avoid it - as well as tips from some of our favorite audio pros.
What is acoustic feedback?
Acoustic feedback occurs when amplified sound from a speaker travels back into the sound system via an open microphone and is repeatedly amplified. We've all heard it before — it's that sustained ringtone that ranges from a low-pitched rumble to a high-pitched squeak.
what causes it
The simplest PA system consists of a microphone, an amplifier and one or more speakers. Anytime you have these three components, you have an opportunity for feedback. Feedback occurs when sound bounces back from the speakers to the microphone, is amplified again, and sent through the speakers again, like this:
Here's an example: Let's say you place the microphone in front of the speaker as shown here. When you touch the microphone, the touch sound travels through the amplifier, through the speaker, and back into the microphone. This feedback loop happens so fast that it generates its own frequency and creates the howling sound - an oscillation triggered by the sound entering the microphone. Placing the microphone too close to the speaker, too far from the sound source, or simply cranking the microphone volume up too much increases the likelihood of feedback problems.
Pro Tip #1
"The worst are the singers who hold the mic capsule (e.g. rappers who wrap their hand around the mic grille because they think it's cool). This always makes the mic sound awful and very prone to feedback. More importantly, it changes.” The directional characteristics of the microphone essentially change it into an omnidirectional microphone. One trick is to clip everything from 800Hz to 2kHz and compress it. Then hopefully the terrible howling will disappear and the singing will remain understandable. But don't forget that the best way to control feedback is to turn everything off.
– Frank Gilbert, FOH-Ingenieur Park West, The Vic Theatre und The Mayne Stage – alle in Chicago
Suggestions on how to stop the feedback loop
- Move the microphone closer to the desired sound source.
- Use a directional microphone to increase the gain before feedback.
- Reduce the number of open microphones - turn off unused microphones.
- Don't turn up the tone controls indiscriminately.
- Try to keep microphones and speakers as far apart as possible.
- Decrease the speaker output. Move the speaker away from the microphone. Each doubling of this distance can increase the performance of the sound system by 6 dB.
- Move the speaker closer to the listener. Every time this distance is halved, the performance of the sound system increases by 6 dB.
- Use in-ear monitoring systems instead of floor monitors.
- Treat the room acoustically (if possible) to remove hard, reflective surfaces like glass, marble, and wood.
Pro tip #2
“In a well-designed system, unless someone is pointing a mic at a monitor, the annoying nature of high-frequency feedback isn't much of a problem. As long as artists make sure their mics are always kept away from monitors, or specifically.” If you always point the back end of the mic toward the monitor, this shouldn't be a problem.
–Bill Gibson, author of over 30 books, producer, performer and faculty member at the Berklee School of Music
Once these solutions have been exhausted, the next step is to examine themautomatic equalizers and feedback reducers.
A technique commonly used by sound engineers is to 'play' a sound system with a 'playback device'.graphic equalizerTo reduce the level of the feedback frequencies:
- Slowly increase the system level until you hear feedback. Now go to the equalizer and lower the offending frequency by about 3dB.
- If the feedback is a "howl" or "howl," try narrowing the range from 250 to 500 Hz. A "singing" tone can be around 1 kHz. "Whistles" and "squeaks" are usually above 2 kHz. Feedback is very rare below 80 Hz or above 8 kHz. It takes practice to develop an ear to balance a sound system. So be patient.
- After finding the first feedback frequency, turn the system back on until the next frequency is played.
- Repeat the above steps until the desired level is reached, but don't overdo it. Remember that equalizers can only increase the level by a maximum of 3 to 9 dB.
Pro tip #3
"The last time I had feedback was at a small venue where I was on stage. As a musician and audio engineer, I'm an audio engineer's worst nightmare. During the rehearsal, my headphone mic was feedback and the audio engineer kept turning my volume down volume and telling me I couldn't move. I knew the problem was midrange feedback, so I explained to him that if he just lowered the midrange on the EQ, the problem would go away. He explained to me "passionately and assertively" that the only way to get rid of the feedback was for him to turn the volume down and I stood still.
After hearing the first song, I went back to the board, reached over my shoulder, and let go of the midrange. I sang a few notes, looked at him, smiled and walked back to the stage. (Did I mention it was wireless too?) The issue was resolved and we didn't speak after the set, but I know he learned something that night.
–John Chevalier, audio/video professional, author and speaker at InfoComm, NAB and other industry events
Pro tip #4
“If there's one thing I've learned in all my years as a musician, it's that the sound engineer has to be extraordinarily vigilant to protect even the artists' hearing.
My most recent incident of bad feedback was caused by the sound engineer manipulating the gain stage without letting us know - after we got to a good spot. The resulting screeching feedback changed everything - nothing but pain filled the space between our ears. A lot of people forget that EQing something can result in a change in loudness — at that very frequency.
Of course, the equalizer can easily solve volume problems. Simply take a moment to identify the offending frequency or group of frequencies - band members will protect their ears, of course - and "forensically" remedy the problem, solving the problem immediately. A hall of mirrors, isn’t it?”
– June Millington, lead singer of FANNY, musician and songwriter, co-founder ofTER
automatic feedbackReducers are very useful in wireless microphone applications. Remember that microphone placement is critical to avoiding feedback and there is a great temptation to deviate from the ideal microphone position when using wireless. If the performer gets too close to a speaker, feedback occurs; A good feedback reducer can catch and eliminate feedback faster than an audio engineer.
Pro Tip #5
"The best 'equipment' a sensible man has is his ears. Learn to identify the ringing frequency by blindly asking, 'What is this frequency?' Tests with a sine wave generator or test tone generator. Have someone pick a tone and see if you can identify the frequency. This is a great workout to identify the frequency of the howling feedback problem and how I've learned to tame the feedback. "
– Dan Murphy, Director of Sound Engineering, Lakeside Church
NOTE: Do not rely solely on an equalizer/feedback reducer to provide sufficient additional output in a sound system where the microphones and speakers are very close together. You probably won't get the results you want.See our post for more informationEQ IQ: A Brief Introduction.
Davida Rochman has been an employee of Shure since 1979. She studied speech communications and never thought that her first job out of college would lead to a lifelong career marketing microphones instead of speaking into them. Today, Davida is Corporate Public Relations Manager responsible for PR activities, sponsorships and fundraising programs that overlap with Shure at the corporate and industry levels.
Feedback is most likely to occur when a microphone is in front of the loudspeaker. You can reduce the likelihood of feedback by placing the speakers ahead, toward the audience, of the microphone. 2 – When mic is behind speaker it cannot pic up sound – No Feedback!How do I reduce the feedback on my computer speakers? ›
- Avoid placing microphones near to the loudspeakers.
- Place microphone as close to the sound source as possible, rather than increasing the volume of the microphone.
- Use directional microphones, such as cardioid or supercardioid.
A feedback control system consists of five basic components: (1) input, (2) process being controlled, (3) output, (4) sensing elements, and (5) controller and actuating devices. A final advantage of feedback control stems from the ability to track the process output and, thus, track the system's overall performance.What is feedback control technique? ›
In a feedback control system the controller takes the decision on how to act on the final control element by considering the error between the actual value of the controlled variable and its expected set point value, according to the control algorithm or control law used.What frequency causes feedback? ›
A "singing" tone may be around 1 kHz. "Whistles" and "screeches" tend to be above 2 kHz. Very rarely does feedback occur below 80 Hz or above 8 kHz. It takes practice to develop an ear for equalizing a sound system, so be patient.What is the best EQ adjustment? ›
600 Hz–3,000 Hz (Mids)—the range that humans can hear the best. The majority of the sound of vocals is here, so EQing this range represents the perfect equalizer settings to play with if you want to affect someone's voice. 3,000 Hz–8,000 Hz (Upper Mids)—most audiophiles handle this range with care.How do I reduce speaker interference? ›
- INPUT. ✓ Remove your audio source devices one by one. ✓ Replace audio cables one by one. ...
- MIXER / AMPLIFIER. ✓ Connect your audio source device into another input. ...
- OUTPUT. ✓ Remove your speakers one by one. ...
- EXTERNAL INTERFERENCE. ✓ Use a Radio Frequency Interference (RFI) filter.
Move your speakers at least 2-3 feet away from the nearest wall. This will minimize sound reflections, which can negatively impact playback clarity. Adjust speaker angle (toe-in). Angle your speakers inward so they're pointed towards the listener - more specifically, at a point directly behind the listener's head.Should speakers be behind you or in front of you? ›
Speaker positioning within the room
The most significant mistake people make is to place their speakers along the wall behind them. Instead, speakers should be placed in front or close to your listening spot (ideally less than 1m away).
Speakers Causing Feedback
The microphone picks up sound from the speakers, and then it is played back through the computer's speakers. This can cause feedback, echo, and other sound issues. If the microphone input is activated in the Volume Control, sound picked up by the microphone is played through the speakers.
Turn down the gain on your amp or guitar.
There should be at least two knobs on the face of your guitar. One of these should be the gain. Turn this counter-clockwise to reduce the gain. You can keep the gain at three-fourths max or less on both your amp and guitar to prevent feedback.
The speakers are too close to the microphone. The speaker volume is turned up so as the microphone hears the speakers. You have a very sensitive microphone.What causes feedback in sound system? ›
Simply stated, feedback occurs whenever the sound entering a microphone is reproduced by a loudspeaker, picked up by the microphone, and re-amplified again and again. The familiar howl of feedback is an oscillation that is triggered by sound entering the microphone.What are the examples of feedback control? ›
An example of feedback control is when a sales goal is set, the sales team works to reach that goal for three months, and at the end of the three-month period, managers review the results and determine whether the sales goal was achieved.What is an example of feedback control system? ›
An example of a feedback control system is the central heating and air conditioning system for a home, or building. A thermostat or temperature sensor is the feedback sensor that measures the room temperature and compares it to the desired temperature or set point, calculating a difference or error.What is sound feedback setting? ›
You use this setting when you watch TV at night and do not want a high-volume channel to appear during zapping. Sound feedback. If you choose this option, the TV plays a sound when you select a menu or option.