How to Stop Feedback in Live Sound

Feedback happens when the sound from a loudspeaker reaches a microphone, gets amplified, and is sent back to the loudspeaker, creating a loop that quickly escalates into a howl or screech. The frequency that feeds back is usually the one with the highest gain in the system's response at that point. Room acoustics, speaker placement, and microphone polar patterns all influence which frequencies are most likely to ring.

To eliminate feedback, you must break the loop. This can be done by reducing gain, changing the microphone's position relative to the speaker, or filtering out the offending frequency. SSOUNDS engineers design systems with robust DSP and precise coverage control to minimise feedback potential, but operator technique remains critical.

Proper gain structure ensures that each stage of the signal chain operates at an optimal level without unnecessary noise or distortion. Start by setting the microphone preamp gain so that the loudest expected input peaks around -6 dBFS on the console meter. Then adjust the fader to achieve the desired mix level. Avoid cranking the preamp gain too high, as this increases the system's overall sensitivity and feedback risk.

Use the console's PFL (Pre-Fader Listen) or solo function to check levels before the fader. If you need more output, consider increasing amplifier gain or speaker volume rather than pushing the preamp. SSOUNDS amplifiers feature precise gain controls and limiters that help maintain headroom and prevent feedback from spiralling out of control.

Graphic and parametric equalizers are powerful tools for feedback suppression. The classic method is to ring out the system: slowly raise the gain on a microphone until feedback begins, then use a narrow notch filter to cut that frequency by 3-6 dB. Repeat for other frequencies that ring. Always cut rather than boost to avoid adding gain that could cause feedback.

For monitors, use high-pass filters to remove low frequencies that are not needed for vocal clarity, typically cutting below 80-100 Hz. Also, consider cutting frequencies around 250 Hz to reduce muddiness and 1-4 kHz to tame harshness. SSOUNDS DSP presets include carefully tuned EQ curves that provide a flat, stable starting point, reducing the need for drastic cuts.

Microphone choice and placement are crucial. Cardioid microphones reject sound from the rear, making them ideal for live vocals. Supercardioid and hypercardioid offer even greater rear rejection but have a small rear lobe that can pick up sound from behind. Always position the microphone so that the main speaker or monitor is in its rejection zone.

Encourage vocalists to sing close to the microphone (within 2-4 inches) to maximise the direct-to-reverberant sound ratio. This increases gain-before-feedback. Also, avoid pointing the microphone directly at monitor wedges; instead, angle it so that the null (the direction of least sensitivity) faces the monitor. SSOUNDS engineers often recommend using a high-quality dynamic microphone for its durability and feedback rejection.

Monitor wedges should be placed in front of the microphone, not to the side or behind, and aimed at the performer's ears, not at the microphone. The goal is to provide the performer with enough level without the microphone picking up the monitor's output. Keep monitors as close to the performer as possible so that lower volume levels are needed.

For side fills or drum monitors, use subwoofers sparingly, as low frequencies are omnidirectional and can easily cause feedback. SSOUNDS stage monitors are designed with controlled directivity to minimise spill into microphones. In-ear monitors (IEMs) are an excellent alternative that eliminates monitor feedback entirely.

Modern digital consoles and DSP units offer automatic feedback suppression, but these should be used as a safety net, not a primary solution. SSOUNDS systems include advanced DSP with feedback detection algorithms that can automatically apply notch filters during a show. However, the best approach is to set up the system correctly from the start.

Room acoustics play a role: hard surfaces reflect sound and increase feedback potential. Use drapes, carpets, or acoustic panels to reduce reflections. Also, consider the overall system gain structure: ensure that the main PA is not overdriving the stage area. SSOUNDS line arrays and point-source speakers feature precise pattern control that keeps sound on the audience and off the stage.