How to Stop Feedback in Live Sound

Feedback occurs when a sound from a loudspeaker is picked up by a microphone, re-amplified, and cycled through the system, creating a loop that builds into a sustained tone. This loop is most likely at frequencies where the system's gain exceeds the acoustic isolation between the mic and speaker. Common contributors include high gain settings, resonant room acoustics, poor mic placement, and monitor positioning that directs sound directly into the mic's pickup pattern.

The feedback frequency is determined by the resonant peaks in the system—typically the room's natural modes, the speaker's frequency response, and the mic's proximity to reflective surfaces. Understanding this loop is the first step to breaking it.

Proper gain structure ensures that each stage of the signal path operates optimally without excessive amplification. Start by setting microphone preamp gain so that the loudest expected input peaks around -6 dBFS on your mixing console. Avoid cranking the preamp to compensate for low mic output; instead, ensure the mic is positioned correctly and the source is loud enough.

After setting input gain, adjust faders to achieve a balanced mix without pushing the master output into clipping. Overloading the input stage creates distortion and reduces headroom, making feedback more likely. Use the console's metering to maintain healthy levels throughout the chain—aim for average levels around -12 dBFS on the master bus.

Equalization is a powerful tool for feedback suppression, but it must be applied surgically. Use a graphic or parametric EQ to identify and cut the specific frequencies that ring. Start with a narrow bandwidth (high Q) and boost a small amount to locate the feedback frequency, then cut it by 3-6 dB. Repeat for each offending frequency.

Avoid excessive cuts that degrade sound quality. Instead, focus on notching out only the problematic frequencies. For monitors, use a high-pass filter to remove low-end rumble below 80 Hz, and consider a low-pass filter above 12 kHz to reduce sibilance pickup. SSOUNDS systems include built-in DSP with feedback suppression algorithms, but manual EQ remains essential for fine-tuning.

Microphone placement and selection directly impact feedback susceptibility. Use directional mics (cardioid, supercardioid) for vocals and instruments to reject sound from the rear and sides. Place the mic close to the sound source—within 6 inches for vocals—to maximize direct sound over ambient noise.

Avoid pointing the mic directly at monitor speakers or main PA enclosures. For vocalists, train them to maintain consistent distance and angle. If using multiple mics, keep them spaced apart to reduce phase cancellation and cumulative gain. Wireless systems should have antennas positioned away from speakers to avoid RF interference that can mimic feedback.

Monitor speakers are common feedback culprits because they sit close to microphones. Place monitors in front of the mic's null point—typically the rear of a cardioid mic. For floor monitors, position them so the mic's axis is at 90 degrees to the speaker's axis. Use wedge angles to direct sound toward the performer's ears, not the mic.

Keep monitor levels as low as possible while still being audible to the performer. Use the 'ringing out' technique: slowly increase monitor gain until feedback begins, then cut the offending frequency with EQ. Repeat until you achieve the desired level without feedback. In-ear monitors (IEMs) are a superior alternative, eliminating monitor feedback entirely.

Room reflections and resonances amplify feedback potential. Treat the space with absorptive materials on walls and ceilings to reduce flutter echoes. For permanent installations, use acoustic panels. In temporary setups, drape heavy curtains or use portable baffles.

System tuning with measurement software (e.g., SMAART) helps identify problematic frequencies before they cause feedback. Apply parametric EQ cuts to the main PA and monitor outputs based on room measurements. SSOUNDS systems offer FIR filtering for precise phase alignment, reducing comb filtering that can exacerbate feedback.