How to Stop Feedback in Live Sound

Feedback occurs when a microphone picks up sound from a loudspeaker, which is then re-amplified in a loop. The loop builds until the system oscillates at a specific frequency, producing that piercing howl or low rumble. Three factors determine feedback potential: the gain before feedback (how much you can turn up before it rings), the frequency response of the system and room, and the physical relationship between microphones and speakers.

In practice, feedback happens when the sound from a monitor or main PA reaches a microphone at a level equal to or greater than the direct sound source (voice or instrument). The system then amplifies its own output. Every room has resonant frequencies that ring longer and are more prone to feedback—these are the frequencies you'll need to notch out.

Proper gain structure is your first line of defense. Set your input trims so that the signal is strong but not clipping, and avoid excessive gain at any stage. A common mistake is boosting the channel fader to compensate for a weak input level, which raises the noise floor and reduces headroom before feedback. Instead, ensure your microphone preamp delivers a healthy signal (around -18 dBFS for digital consoles) and use faders only for mixing, not gain correction.

On monitors, start with all aux sends at unity and bring up the channel fader to a reasonable mix level. Then gradually increase the aux send until you get enough monitor volume, but never push the aux send beyond the channel fader level—that's a recipe for feedback. If you need more monitor level, consider moving the monitor closer to the performer or using a more directional microphone.

Graphic and parametric EQ are your primary tools for feedback elimination. The classic approach is to ring out the system: slowly raise the master volume or monitor send until feedback begins, then use a narrow notch filter (high Q) to cut that frequency by 3–6 dB. Repeat until you achieve the desired level without feedback. On a graphic EQ, identify the offending band and pull it down gently—avoid deep cuts that affect tonality.

For monitors, use a separate EQ on each monitor mix. Start with a high-pass filter around 80–100 Hz to remove low-end rumble that eats headroom. Then apply subtle cuts at frequencies that ring in the room. Be careful not to over-EQ; too many cuts can make the system sound thin. Modern DSP, like that in SSOUNDS amplifiers, allows precise parametric filtering that can be tuned per zone or monitor wedge, giving you surgical control without compromising overall sound quality.

Microphone choice and placement dramatically affect feedback susceptibility. Cardioid and hypercardioid patterns reject sound from the rear and sides, making them ideal for live vocals. Position the microphone so that the performer's mouth is close (within 2–4 inches) to maximize direct-to-reverberant ratio. For instrument miking, use close-miking techniques and aim the microphone's null (the direction of least sensitivity) at the nearest monitor.

Teach vocalists to work the mic: they should sing directly into the capsule, not off-axis. If a singer cups the grille, they destroy the polar pattern and invite feedback. Also, avoid placing microphones directly in front of monitor wedges; instead, angle the monitor so its coverage passes behind the mic. In larger systems, using a microphone with a tighter pattern (like a supercardioid) can buy you several dB of gain before feedback.

Monitor placement is critical. Wedges should be positioned so that the performer hears themselves without the microphone being in the direct line of fire. Typically, place the monitor directly in front of the performer, angled upward, and slightly off-axis from the mic's rear lobe. For multiple monitors, avoid covering the same area with overlapping coverage—use separate mixes and position wedges to minimize spill between them.

In-ear monitors (IEMs) are the ultimate feedback solution, but when wedges are necessary, consider using subwoofer arrays or cardioid sub configurations to reduce low-frequency buildup on stage. SSOUNDS line array systems and point-source enclosures are designed with consistent directivity control, which helps maintain stable monitor levels even in challenging acoustic environments. For permanent installations, acoustic treatment (absorption, diffusion) can reduce room reflections that contribute to feedback.

Automatic feedback suppressors (like those built into some DSP units) can be useful in fast-paced situations, but they should be used sparingly—they often apply too many cuts and degrade sound quality. A better approach is to use a real-time analyzer (RTA) to identify resonant peaks in the room and apply targeted EQ. Modern digital consoles allow you to set up dynamic EQ that only cuts when feedback is detected, preserving tone during normal use.

System tuning with measurement software (e.g., SMAART, SysTune) lets you align the PA and monitors to the room's acoustics. By measuring transfer functions, you can see exactly where feedback loops occur and apply precise filters. SSOUNDS engineers use advanced simulation tools to predict system behavior before setup, reducing the guesswork. For touring systems, create a baseline EQ preset for each venue type and fine-tune during soundcheck.