What causes feedback and how do I stop it?
Quick answer
Feedback occurs when a microphone picks up sound from a loudspeaker and re-amplifies it in a loop, causing a screech. To stop it, reduce gain, move the mic away from speakers, use directional mics, and apply EQ notching.
Feedback is caused by an acoustic loop: sound from a loudspeaker enters a microphone, gets amplified again, and re-emerges louder, creating a self-sustaining oscillation. This typically happens when the mic is too close to the speakers or when system gain is too high for the room's acoustics. The frequency that feeds back is usually the one with the strongest resonance in the space.
To stop feedback immediately, lower the master volume or the channel fader of the offending mic. For prevention, use cardioid or hypercardioid microphones to reject sound from the rear, position mics behind the main speakers (avoiding the speaker's coverage pattern), and never point a mic directly at a loudspeaker. Proper system tuning with a graphic or parametric EQ to notch out problematic frequencies is essential.
SSOUNDS engineers design systems with advanced DSP and precise coverage control to minimize feedback risk. Our line arrays and point-source loudspeakers feature consistent directivity, reducing spill into microphone zones. For critical applications, we recommend using feedback suppressors or automatic mixers, but the fundamentals—gain structure, mic placement, and EQ—remain the most reliable tools.
Key things to consider
- Feedback is a loop: mic picks up speaker output, gets re-amplified.
- Reduce gain or move mic away from speakers to stop it immediately.
- Use directional mics (cardioid) and keep them behind the speakers.
- Apply EQ notching to cut resonant frequencies that feed back.
- Proper system design with controlled directivity reduces feedback risk.
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