How to Control Feedback on Stage

Dealing with feedback can be extremely frustrating and a never-ending task unless you know a few of the basic principles for live performances. This article will explore two different types of feedback and explore the solutions to help eliminate the problem.

Speaker Placement

The first type of feedback is where the main sound system speakers are feeding back through your microphones. A live performance can be ruined by this, but there are a few ways to prevent feedback.

The best practice is to always position your speakers in front of your microphones. If you were to stand above the stage looking down, you will want your microphones to be behind the front of the speakers. Feedback is caused when the amplified sound is picked up by the microphone. So, by simply positioning your microphones behind the speakers you can eliminate most feedback issues. However not every room is the same and there are other variables to consider.  

You may have no issues when you are rehearsing but when you play a gig the overall volume of your sound system may be pushed louder to cover an audience in a large venue. This is where improper positioning during your rehearsals can fool you into thinking your speaker placement is adequate. This is why it is important to know what proper placement should be for a live performance. Another variable is the room itself. Perhaps you rehearse in a room that has plenty of absorbing materials such as curtains, foam sound dampening and carpet. Absorption in a room can help reduce feedback. However, you do not have control over the materials on stage, on the floor or on the ceiling. Even with proper microphone positioning you can still experience feedback if you have elevated your main speakers to be too close to structures on the ceiling that can reflect problem frequencies into your microphones.

Feedback issues with both high and low frequencies can occur when your main speakers’ sound is bouncing off a low ceiling and/or exposed HVAC metal ductwork as seen in many bars and breweries. It may be necessary to decrease the height of the main speakers, so the sound does not bounce off the ceiling. It may also be necessary to roll off low frequencies to reduce low frequency feedback. In one such instance this author has found the MONITOR setting on Carvin Audio’s SCx12A 1000W Active 12-Inch Main/Monitor to help control low frequency and high frequency feedback on main loudspeakers at a low ceiling performance. The room was prone to low frequency build-up so the MONITOR setting was a solution to the issue.

SCX12A 1000W Active 12-Inch Main/Monitor with DSP

Floor Monitor Feedback

Floor monitor feedback is the other primary frustration. One important factor to consider is the type of vocal microphone being used in relation to the physical position of the monitor on the floor. Most people use a dynamic vocal microphone similar to a Shure SM58 or beta58. These and other similar dynamic microphones offer good rejection which means they are not designed to pick up sound from the back of the microphone. However, the beta58 does have more side rejection than rear rejection. You can see this in the polar pickup pattern. This means it will tend to feedback if you do not place your monitor accordingly. If you are experiencing feedback with this type of microphone the solution is to slide your monitor slightly left or right of center of your microphone position - thereby moving the monitor to the side where the beta58 has better rejection. As with the main speakers, monitors can also experience feedback due to lack of absorbing materials on stage. If you know a venue has hard floors or a hardwood stage, it may be beneficial to take a small rug or some sort of floor mat to place under your monitor. Once again, the Carvin SCx12A Main/Monitors offer a MONITOR internal circuit that reduces feedback.  

Improper gain settings can also play a role in causing feedback when a soft vocalist is needing the microphone preamp to be dialed to an extreme level. The microphone becomes ultra-sensitive to more frequencies than normal when the gain is set too high. A potential solution in this scenario is to reduce the microphone preamp gain and lower other mic channels to match this level and use the gain at the active loudspeakers and monitors to increase the audible volume. Proper gain staging can reduce feedback issues.

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