How to control feedback in a sound system (2023)

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.

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:

"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

“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.

"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

“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.

"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.