Feedback Prevention in Live Sound: Strategies That Work

Feedback prevention in live sound requires understanding the physics of acoustic feedback and applying multiple strategies simultaneously. No single technique eliminates feedback risk entirely; effective prevention combines proper equipment selection, strategic placement, and active management throughout the performance.

Understanding How Feedback Occurs

Acoustic feedback develops when a closed loop exists between a microphone and a speaker. Sound from the speaker enters the microphone, amplifies through the signal chain, exits the speaker louder than before, re-enters the microphone, and cycles continuously. The result ranges from subtle coloration to howling screech depending on severity.

The frequency that feeds back depends on multiple factors: microphone sensitivity at various frequencies, speaker output characteristics, room acoustics and resonances, and distance between microphone and speaker. Different frequencies reach feedback threshold at different gain levels.

Gain before feedback describes the amount of amplification possible before any frequency sustains and grows. The goal of feedback prevention is maximizing gain before feedback while maintaining natural sound quality.

Microphone Selection and Technique

Microphone polar patterns significantly affect feedback susceptibility. Cardioid microphones reject sound from the rear, making them standard choices for live vocals. Supercardioid and hypercardioid patterns offer tighter front pickup with some rear sensitivity—useful when monitor placement can avoid the rear lobe.

Dynamic microphones like the Shure SM58, Sennheiser e835, and Electro-Voice ND767a handle high sound pressure levels and resist feedback better than most condensers. Their reduced high-frequency sensitivity compared to condensers also means less susceptibility to harsh feedback frequencies.

Microphone technique matters tremendously. Singers working close to the microphone receive stronger direct signal relative to ambient sound, improving gain before feedback. Proper technique keeps the microphone pointed at the mouth, not toward monitors or main speakers.

Handheld microphone handling creates problems when performers cup the microphone grille. This common mistake compromises the polar pattern, turning a feedback-resistant cardioid into a feedback-prone omnidirectional. Educating performers about proper technique prevents this issue.

Speaker and Monitor Placement

Main speaker placement should position the loudspeakers ahead of microphones in physical space. Sound travels from the stage toward the speakers, then into the audience—not back toward the performers. Speakers placed beside or behind performers create direct feedback paths.

Monitor wedge positioning takes advantage of microphone rejection patterns. Cardioid microphones reject sound from directly behind, making monitor placement at the performer’s feet, aimed upward toward their ears, optimal. The monitor projects into the microphone’s null zone.

Side-fill monitors covering wide stage areas need careful aiming to avoid spilling into vocal microphone pickup patterns. Angling side-fills slightly toward center stage while maintaining performer coverage minimizes direct sound reaching front-facing microphones.

Distance from microphones to speakers affects feedback potential. Greater distance reduces the sound level reaching the microphone from the speaker. Even small increases in separation distance can significantly improve gain before feedback.

Equalization-Based Prevention

Graphic equalizers reduce feedback-prone frequencies across the entire signal path. The ringing out process identifies these frequencies before performance, allowing preemptive cuts. Each microphone-monitor combination may require different treatment.

High-pass filters remove low-frequency content that contributes to feedback, particularly room resonances and proximity effect buildup. Filtering below 80-100 Hz on vocal microphones eliminates problematic low frequencies without affecting vocal tone.

Parametric EQ offers more precise feedback control than graphic EQ. Narrow notch filters at specific feedback frequencies affect minimal adjacent content. Digital mixers often include parametric EQ with enough bands for multiple feedback notches.

System EQ on main outputs addresses room-related feedback issues. Room modes that reinforce certain frequencies can push those frequencies toward feedback at lower gain. System EQ cuts compensate for room anomalies.

Gain Structure Optimization

Proper gain structure throughout the system maximizes signal-to-noise ratio without creating unnecessary headroom problems. Input gain should bring microphone signals to appropriate level with channel faders near unity.

Monitor sends should start conservatively, increasing only as performers request more level. Starting with lower levels and building up prevents immediate feedback while establishing usable baseline levels.

Fader riding during performance maintains appropriate levels as conditions change. A vocalist moving away from the microphone may need increased channel level, but this increases feedback risk. Awareness of the trade-off guides decisions.

Active Management During Performance

Despite thorough preparation, feedback threats emerge during shows. Performers move, monitor requests increase, and room conditions change as audiences arrive. Active monitoring and quick response prevent embarrassing feedback howls.

Recognizing pre-feedback conditions allows intervention before full howl develops. A sustained ringing quality or tonal coloration indicates a frequency approaching feedback threshold. Quick fader reduction or EQ adjustment maintains control.

Channel muting when sources are inactive prevents unnecessary feedback paths. Unused vocal microphones represent feedback risk without contributing to the mix. Muting between uses improves overall stability.

Communication with performers about monitor levels helps manage expectations. Explaining that excessive monitor levels cause feedback and degrade audience sound encourages reasonable requests. Most performers prefer slightly lower monitors to embarrassing feedback.

Technology-Assisted Prevention

Automatic feedback destroyers detect and notch feedback frequencies using digital signal processing. Products from dbx, Behringer, and Sabine track feedback as it develops, applying narrow notch filters automatically. These devices provide safety net protection when manual control misses a problem.

Digital mixer processing often includes feedback detection and suppression features. Allen & Heath, Yamaha, and other manufacturers build these capabilities into their digital consoles. While convenient, manual control typically produces better tonal results.

In-ear monitoring systems eliminate stage monitors, removing the primary feedback source. Performers hear their mix through earphones rather than wedge monitors. This approach dramatically improves gain before feedback at the cost of added complexity and reduced room ambiance for performers.