How to Prevent Feedback in Live Sound
What Causes Feedback in Live Sound?
Feedback happens when sound from a speaker re-enters a microphone, gets amplified again, and loops back through the system. That loop creates the high-pitched squeal or low rumble you hear at live shows. The microphone picks up its own amplified signal, which gets louder each time it cycles through.
Three factors control this: microphone placement, speaker position, and gain structure. Move a mic closer to a speaker and you increase the chance of feedback. Turn up the gain too high and you push the system past its stable threshold. The room itself matters too — hard surfaces reflect sound back toward microphones, while carpets and curtains absorb it.
Understanding this loop is the first step. Once you know what feeds the cycle, you can break it at multiple points.
Microphone Selection and Polar Patterns
Your microphone's polar pattern determines what it hears and what it rejects. A cardioid pattern picks up sound from the front and rejects sound from the sides and rear. Point a cardioid mic at a vocal and position monitors behind it — the pattern naturally reduces monitor bleed.
The Shure SM58 is a cardioid dynamic microphone that has become the standard for live vocals precisely because of this rejection characteristic. Its pattern isolates the vocalist while minimizing stage noise and monitor spill. The SM57 uses the same capsule design and offers identical feedback rejection for instruments.
Supercardioid patterns take this further. They have a tighter front pickup angle and stronger side rejection, though they do pick up some sound directly behind the capsule. The Shure Beta 58A uses a supercardioid pattern that provides higher gain before feedback than the SM58, making it better suited for loud stages with monitors in front of the performer.
Dynamic microphones handle high sound pressure levels without distortion, which makes them more forgiving in feedback-prone situations than condensers. A dynamic mic won't overload when a monitor gets too loud. Condensers like the Audio-Technica AT2020 are more sensitive and deliver more detail, but that sensitivity means they pick up more stage noise and require careful gain management. Use condensers in live settings only when you have controlled stage volume and need the extended frequency response they provide — acoustic performances, quieter venues, or situations where the extra detail justifies the added risk.
Omnidirectional and figure-8 patterns pick up sound from multiple directions. Avoid them in live sound unless you have a specific reason and total control over stage volume.
Microphone Placement Techniques
Keep microphones as far from speakers as possible. That sounds obvious, but stage layouts often force compromises. If you must place a monitor near a mic, angle the monitor so its coverage pattern aims away from the capsule. A cardioid mic's null point is directly behind it — position the monitor there.
Get the sound source close to the microphone. A vocalist working the mic at 2 inches requires less gain than one singing from 12 inches away. Less gain means more headroom before feedback. The inverse square law works in your favor here — doubling the distance from mic to mouth requires four times the gain to maintain the same level.
Avoid placing microphones in front of speaker cabinets. This seems basic, but in cramped stages with backline amps and drum kits, mics end up pointing at sound sources they shouldn't hear. Angle instrument mics away from the PA mains. Use your ears during soundcheck — walk the stage with headphones on the board's monitor send and listen for what each mic picks up.
Gain Structure and EQ Strategies
Set your gain correctly. Start with the preamp gain on your mixer or interface. Raise it until the signal hits a healthy level on the meter — aim for peaks around -12dB to -6dB. If you need more volume in the house, raise the fader. If you need more in the monitors, raise the aux send. Don't compensate for weak fader levels by cranking the preamp gain. That's where feedback starts.
Ring out the system before the show. Play pink noise or music through the mains at performance volume. Slowly raise the master fader until you hear the first hint of feedback. Use a parametric EQ to find that frequency — sweep a narrow cut through the spectrum until the feedback stops, then apply a 3-6dB reduction at that frequency. Repeat for the next resonant frequency. Stop after addressing 3-4 problem spots — over-EQing makes the system sound hollow.
Cut frequencies rather than boost them. Boosting adds energy to the system and pushes you closer to feedback. If vocals sound thin, cut low-mids on everything else rather than boosting highs on the vocal mic. Subtractive EQ gives you more gain before feedback than additive EQ.
High-pass filters are essential. Most vocal mics don't need anything below 80Hz. That low end just adds stage rumble and eats up headroom. Engage the HPF on every channel that isn't a kick drum or bass guitar.
Monitor Positioning and Stage Volume
Wedge monitors should sit directly in front of the performer, angled up toward their ears. The mic should be behind the monitor's coverage pattern. If a performer moves around, they'll step into the monitor's throw and feedback becomes inevitable. Coach performers to stay in their zone.
In-ear monitors eliminate most feedback issues because they don't project sound into microphones. The tradeoff is cost and the learning curve for performers used to wedges. If you can make the switch, do it.
Stage volume is your enemy. Loud guitar amps, drum kits without shields, and bass rigs cranked to 11 all bleed into vocal mics. That bleed reduces your available gain before feedback. Ask the band to turn down. Use amp isolation cabinets or move backline off stage. Put the drummer behind a shield. Every dB of stage volume you eliminate is a dB of headroom you gain.
Side fills and drum fills add controlled stage volume without pointing speakers at microphones. A side fill aimed across the stage gives the band a sense of the mix without creating a feedback trap. Keep side fill volume reasonable — it's for vibe, not for hearing every detail.
Feedback Suppression Tools
Automatic feedback suppressors detect feedback frequencies and apply narrow notch filters in real time. These processors listen for the rapid amplitude increase that signals a feedback loop, identify the offending frequency, and cut it before it becomes audible. They work as a safety net during performances when a performer moves unexpectedly or a monitor gets bumped, but they shouldn't replace proper gain structure and placement. If your suppressor is constantly triggering, you have a fundamental setup problem.
Graphic equalizers give you fixed-frequency control across the spectrum. A 31-band graphic EQ on your monitor sends lets you address problem frequencies specific to each mix. The bands are typically spaced at 1/3-octave intervals, which means you're cutting a fairly wide range around the center frequency. This works for broad resonances but lacks precision for narrow feedback spikes. Parametric EQs offer adjustable bandwidth and frequency, making them more surgical for feedback control.
Notch filters cut a very narrow frequency range by 20dB or more. Use them only for persistent feedback that survives normal EQ adjustments — a room resonance at 315Hz that rings no matter what you do, or a monitor sweet spot that always feeds back at 2.5kHz. Apply notches sparingly. Each one removes a slice of your frequency response, and stacking too many makes the system sound hollow and unnatural.
Digital mixing consoles often include built-in feedback suppression algorithms that combine detection with parametric filtering. These systems can be set to manual mode, where they identify problem frequencies but wait for you to apply the cut, or automatic mode, where they engage filters on the fly. Manual mode is better for soundcheck and system tuning. Automatic mode serves as insurance during the show.
Soundcheck Best Practices
Start with all faders down and all aux sends off. Bring up one channel at a time. Set the preamp gain, then raise the fader to a unity position. Add monitor send gradually until the performer says it's loud enough. If you hit feedback before they're satisfied, you have a placement or pattern problem — fix that before adding more gain.
Walk the stage during soundcheck. Listen for sympathetic resonances — drums that ring when the bass plays, cymbals that sing when the guitar hits certain notes. Gate or dampen those sources. They're not feedback, but they eat up headroom.
Check microphone cables and connections. A loose XLR or a cable with a broken shield can introduce noise and instability. Swap out any cable that looks damaged.
Test at performance volume. A system that's stable at soundcheck levels can fall apart when you push it for the show. If the band says "we'll be louder tonight," believe them and plan accordingly.
Our Recommendations
These microphones offer strong feedback rejection for live sound applications. Each uses a directional polar pattern to isolate the source and minimize stage bleed.
The SM58 and SM57 both use cardioid patterns with excellent off-axis rejection. The Beta 58A's supercardioid pattern provides even tighter side rejection, giving you more gain before feedback on loud stages. The AT2020 is a condenser option for controlled environments where you need more detail than a dynamic mic provides — just keep stage volume in check.
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FAQ
Why does feedback happen more with certain microphones?
Microphones with omnidirectional or wide polar patterns pick up sound from all directions, including speakers. Cardioid and supercardioid mics reject off-axis sound, which reduces the chance of the speaker-to-mic loop that causes feedback. Condenser mics are also more sensitive than dynamics, so they require less gain but pick up more ambient sound.
Can you completely eliminate feedback in live sound?
You can minimize it to the point where it's not an issue, but you can't eliminate the physics. Feedback happens when gain exceeds the system's stability threshold. Proper mic placement, appropriate polar patterns, controlled stage volume, and correct gain structure keep you well below that threshold. Automatic feedback suppressors add a safety margin but don't replace good technique.
How do I stop feedback in monitors without ruining the mix?
Start by positioning monitors correctly — directly in front of the performer with the mic behind the coverage pattern. Use a parametric EQ on the monitor send to cut only the frequencies that feed back, typically in narrow bands. Don't scoop out wide frequency ranges or the monitor will sound thin. If you're still fighting feedback, reduce stage volume or switch to in-ear monitors.
Does room acoustics affect feedback?
Hard surfaces like concrete, glass, and bare walls reflect sound back toward microphones, increasing the chance of feedback. Rooms with carpeting, curtains, and acoustic treatment absorb reflections and give you more headroom. In a reflective room, you may need to reduce overall system gain or add more aggressive EQ cuts to maintain stability.
