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. It also helps to know upfront that a guitar with just a piezo under the saddle behaves differently than one running a blended pickup-and-mic system, because the mic element adds a second, more feedback-prone signal path that some of these fixes only partly address.
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. The catch is that this trick assumes you can actually move, and at a seated coffeehouse gig on a riser with a monitor wedge parked at your feet, you sometimes cannot. In that setup, the better ask is to have the engineer tilt the wedge downward or push it a foot further away rather than trying to twist around on a barstool.
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. That range is not arbitrary. A typical dreadnought’s main air, or Helmholtz, resonance sits around 100 Hz, while the top plate’s own wood resonance usually lands somewhere between 185 and 200 Hz, and those two overlapping peaks are exactly what a monitor loop latches onto. 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 default setting lines up almost exactly with where the air resonance sits, which is no coincidence. 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. Outboard boxes carry this too. The LR Baggs Para Acoustic DI, a pedal a lot of working players keep on their board regardless of what pickup is in the guitar, has its own phase switch for exactly this reason. It is a one-button experiment, so try it before you reach for anything more invasive. The caveat is that on a blended system like the Baggs Anthem or the Fishman Rare Earth Blend, where a piezo and an internal mic are mixed together, flipping phase can cancel feedback but also thin out the woody character the mic was there to add in the first place, so you are sometimes trading tone for stability rather than getting both for free.
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. D’Addario’s Feedback Buster is the one you will see in most gig bags, sold in a couple of sizes to match different soundhole diameters, and it pops in and out in a couple of seconds between sets. The trade-off between rubber and foam versions is worth knowing: rubber seals tighter and kills more feedback, while foam breathes a little and leaves slightly more of the guitar’s natural openness intact. 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.
