I have had an acoustic guitar howl at me through a monitor wedge more times than I can count, usually two bars into a song I cannot stop to fix. Feedback with an acoustic on stage is almost always the guitar’s own top and soundhole acting as a resonant chamber that the PA is pumping right back into. The fix is rarely one thing. It is a stack of small corrections, and the order matters because the cheap ones should happen before you spend money.
First, move your position relative to the monitor and the mains, not the volume knob. Feedback needs a loop between speaker and top, so before anything else, angle the guitar’s soundhole away from the wedge, or step back a foot from where it’s aimed. I have killed a screaming feedback loop just by turning forty-five degrees on a small stage in Pittsburgh where the wedge was six feet from my knees. This costs nothing and takes five seconds, so it goes first every time.
Second, cut the low mids on your EQ, not the whole tone. Acoustic feedback usually rings between 100 and 300 Hz, right where the body resonance and the room’s low end overlap. On a stage box or your preamp’s EQ, notch down around 150 to 200 Hz before you touch the highs, which is where your presence and pick attack actually live. If your preamp has a built-in notch filter, use it before you start carving with a graphic EQ at the board. The Fishman Aura, for instance, ships with
a feedback eliminator that defaults to a 100Hz notch filter at -14dB with a quarter-octave bandwidth
, and you can trigger it to hunt down the offending frequency automatically. That is a specific, purpose-built tool doing exactly the job a generic EQ sweep does by hand, just faster.
Third, flip the phase switch if your preamp has one. Many pickup systems, including several Fishman and LR Baggs preamps, include a polarity or phase invert switch specifically because reversing phase can cancel out the frequencies causing the loop without touching your tone at all. It is a one-button experiment, so try it before you reach for anything more invasive.
Fourth, block or stuff the soundhole. A soundhole cover, the kind of rubber or foam disc that fits into the hole and reduces the cavity’s resonance, cuts feedback significantly because it disrupts the very chamber that is ringing. These run under fifteen dollars and are the classic fix for anyone who plays a hollow-body acoustic loud and close to a monitor regularly. I keep one in my gig bag next to the capo.
Fifth, and this is the one people skip, mute the strings you are not using with your palm or a hair tie behind the nut. Sympathetic string vibration adds energy to the loop, and a folded cloth or elastic band across the headstock strings, or a firmer palm mute on rests, takes that extra ringing out of the equation. It is free and it works alongside everything above rather than replacing it.
Do these in order, cheapest and fastest first, because half the time the room and your stance solve it before you ever touch a knob.
