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, creating a high-pitched squeal. To stop it, reduce gain, reposition microphones away from speakers, use directional mics, and apply EQ notching with a graphic equalizer.
Feedback is caused by an acoustic loop: sound from a loudspeaker enters a microphone, gets amplified again, and repeats until the system oscillates at a resonant frequency. This typically happens when the microphone is too close to the speaker, gain is too high, or the room has reflective surfaces that reinforce certain frequencies.
To stop feedback, start by lowering the overall gain or volume. Move microphones further from speakers and behind them if possible. Use directional (cardioid) microphones that reject sound from the rear. Apply a graphic equalizer to notch out the feedback frequency—cut 3–6 dB at the offending band. SSOUNDS DSP systems include automatic feedback suppression tools that detect and notch frequencies in real time.
In live sound, proper system tuning is essential. Ring out the system before the event: slowly raise gain until feedback occurs, then notch that frequency. Repeat until stable. Also, avoid placing microphones in front of subwoofers and use high-pass filters to remove low frequencies that don't contribute to vocals. SSOUNDS line arrays and point-source systems are designed with controlled directivity to minimize spill into microphones.
Key things to consider
- Feedback is a loop: mic picks up speaker output, gets re-amplified.
- Reduce gain first; reposition mics away from speakers.
- Use cardioid mics and keep them behind the main speakers.
- Apply EQ notching at the feedback frequency (cut 3–6 dB).
- Use high-pass filters and ring out the system before show.
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