How to Fix Acoustic Guitar Feedback

1 Why Acoustic Guitars Are Prone to Feedback

Acoustic guitars are uniquely susceptible to feedback because of the very feature that makes them acoustic: a large, resonant hollow body designed to amplify string vibrations. When that body is placed near a PA speaker or stage monitor, the sound from the speakers excites the guitar's top, back, and air cavity, causing them to vibrate. The pickup captures these vibrations along with the string vibrations, sends the combined signal to the amplification system, and the cycle repeats, building into an uncontrollable howl or rumble.

The feedback loop is straightforward: speaker output reaches the guitar body, the body resonates, the pickup captures the resonance, the amplification system makes it louder, the louder output excites the body even more, and the cycle accelerates until it reaches a piercing sustained tone. This is the same principle that causes microphone feedback, but acoustic guitars are more problematic because the entire body acts as a resonant membrane rather than a single small capsule.

The frequency at which feedback occurs depends on the guitar's resonant characteristics and the room acoustics. Most acoustic guitars have strong resonant frequencies in the low-mid range between 80 Hz and 300 Hz, which is why acoustic feedback often manifests as a low, booming rumble rather than the high-pitched squeal associated with microphone feedback. However, feedback can occur at any frequency where the guitar body resonates strongly.

The challenge for the performing acoustic guitarist is that the qualities that make a guitar sound wonderful unplugged, a responsive top, a resonant body, and strong projection, are exactly the qualities that make it prone to feedback when amplified. Feedback prevention is about managing this resonance without completely suppressing the acoustic character that defines the instrument's tone.

2 Identifying the Type of Feedback

Low-frequency feedback (below 200 Hz) sounds like a booming rumble that builds gradually. It is typically caused by the guitar's body resonance being excited by bass frequencies from the PA or monitors. This is the most common type of acoustic guitar feedback and often starts subtly before growing into an obvious problem. Low-frequency feedback is harder to notice in its early stages because it can be masked by the bass and drums.

Mid-frequency feedback (200 Hz to 2 kHz) produces a more focused howl or sustained tone. It usually occurs at the guitar's primary resonant frequency, often called the "wolf note." This feedback is more immediately noticeable and can start suddenly when you turn toward a monitor or increase your volume. Mid-frequency feedback is the most disruptive because it sits in the same frequency range as the guitar's fundamental tone.

High-frequency feedback (above 2 kHz) creates a piercing squeal similar to microphone feedback. It is less common with acoustic guitars but can occur with certain pickup systems, particularly those that include a microphone element blended with an under-saddle pickup. The microphone component is susceptible to high-frequency feedback in the same way that a vocal microphone would be.

To identify which type you are dealing with, pay attention to when the feedback starts and what triggers it. Does it build slowly when you face the monitors? That is likely low-frequency body resonance. Does it start immediately when you increase volume past a certain point? That is probably mid-frequency resonance at the guitar's natural frequency. Does it occur only when the blend control favors the microphone element? That is high-frequency pickup feedback. Each type requires a slightly different approach to manage effectively, as we discuss in our live sound basics guide.

3 Positioning and Stage Setup Solutions

The simplest and most effective feedback prevention is strategic positioning on stage. Stand or sit so that the guitar's soundhole faces away from the monitors and PA speakers. If the feedback comes from floor monitors, angling the guitar upward or standing further from the monitor reduces the direct sound energy reaching the guitar body. Even a small change in your orientation relative to the speakers can move you out of the feedback zone.

Place your floor monitor to the side rather than directly in front of you. A monitor positioned at a 45-degree angle to one side delivers sound to your ear while directing less energy toward the guitar body. If in-ear monitors are an option, they eliminate the stage monitor as a feedback source entirely, which is why many professional acoustic performers use in-ear systems.

Reduce the overall stage volume. Feedback occurs when the amplified sound reaching the guitar body exceeds a certain threshold. Every decibel of stage volume reduction increases your feedback-free headroom. This is often a band-wide solution: asking the drummer to play with lighter sticks or brushes, having electric guitarists lower their amp volumes, and keeping the monitor mix minimal all reduce the total stage energy that excites the acoustic guitar body.

4 Soundhole Covers and Feedback Busters

Soundhole covers are rubber or foam discs that fit inside or over the soundhole, blocking the primary pathway through which sound energy enters the guitar body. They are the most popular physical solution for acoustic guitar feedback and are remarkably effective, often providing 6 to 10 dB of additional feedback headroom, which can be the difference between a manageable and an unmanageable stage situation.

The trade-off is tonal. Covering the soundhole changes the guitar's acoustic resonance, typically reducing bass response and altering the "airiness" of the tone. The degree of tonal change depends on the cover's design: full covers that seal the soundhole completely provide maximum feedback prevention but the most tonal alteration. Partial covers with strategically placed openings offer a compromise, reducing feedback susceptibility while preserving more of the natural acoustic tone.

Popular options include the Feedback Buster (a simple rubber disc), the Planet Waves Screeching Halt (a self-adhesive cover), and various third-party options in different sizes. Make sure the cover fits your guitar's soundhole diameter snugly; a loose cover can vibrate and create its own noise. Most standard dreadnought guitars use a soundhole diameter around 100mm, but smaller-bodied guitars and concert-sized guitars may need different sizes.

For players who resist soundhole covers for aesthetic reasons, internal foam padding placed inside the guitar body can reduce resonance without being visible. Lightweight foam or acoustic damping material placed loosely inside the body absorbs some of the internal resonance that contributes to feedback. This approach is less effective than a soundhole cover but offers a more cosmetically acceptable alternative for performance situations where appearance matters.

5 EQ and Notch Filter Techniques

Equalization is your most precise tool for fighting feedback without significantly altering your overall tone. The key technique is the notch filter: a narrow, deep cut at the specific frequency where feedback occurs. Because feedback happens at a specific resonant frequency, you can cut that frequency surgically while leaving the rest of your tone intact.

To find the feedback frequency, slowly increase your monitor volume during soundcheck until feedback begins. As soon as you hear the onset of feedback (before it builds to full strength), identify the frequency using a parametric EQ. Sweep a narrow band across the frequency spectrum while boosting slightly; the feedback frequency will jump out dramatically when you hit it. Then apply a narrow cut of 6 to 12 dB at that frequency. This process is called "ringing out" the system.

Many acoustic guitar preamps include a built-in notch filter specifically designed for feedback suppression. Units from brands like LR Baggs, Fishman, and Grace Design include one or two adjustable notch filters that you can tune to your guitar's specific feedback frequencies. These purpose-built tools are more convenient than carrying a separate parametric EQ pedal and are designed specifically for the acoustic guitar's frequency range.

Automatic feedback suppressors are electronic devices that detect feedback frequencies and apply notch filters in real time. While convenient, they can sometimes cut frequencies that are not actually feedback, dulling your tone unexpectedly. Manual notch filters that you set during soundcheck provide more predictable results. If you play the same guitar at various venues, the feedback frequency is usually consistent because it is determined by the guitar's body rather than the room, so once you find your guitar's problematic frequency, you can preset the notch filter for every gig.

6 Choosing the Right Pickup System for Feedback Resistance

Under-saddle piezo pickups are the most feedback-resistant acoustic guitar pickup type because they respond to the string's vibration at the saddle rather than the body's air vibration. Since they are in direct contact with the strings and largely insensitive to airborne sound, they can operate at higher volumes before feedback occurs. The trade-off is that piezo pickups can sound thin or "quacky" compared to the guitar's natural acoustic tone.

Magnetic soundhole pickups detect string vibration magnetically, similar to electric guitar pickups, making them highly resistant to acoustic feedback. They produce a tone that is warmer than piezo but more electric-sounding than the natural acoustic tone. For feedback-prone performance environments, magnetic soundhole pickups offer excellent volume headroom with minimal risk of feedback.

Internal microphone systems capture the most natural acoustic tone but are the most feedback-prone because they respond to the same airborne vibrations that cause feedback. Many modern acoustic pickup systems blend a microphone with a piezo or magnetic element, giving you control over the mix. In feedback-prone situations, reducing the microphone blend and relying more on the pickup element solves the feedback problem at the cost of a less natural tone.