Acoustic-Electric Feedback: Causes and Cures

Why acoustic-electric guitars howl

An acoustic-electric guitar is a resonant wooden box with a pickup inside. Its top is built to vibrate freely, and that sensitivity is what makes it sound full when you play in a room. When you plug it into an amplifier, the same sensitivity becomes a weakness: any sound that reaches the top, especially from your own speakers, can set it vibrating.

The vibration travels through the bridge to the pickup, which turns it into an electrical signal and sends it to the amplifier. If that signal comes out of the speakers and reaches the top again, the cycle repeats and grows. A sustained howl builds, usually in the low range, and it gets louder the closer the guitar is to the speaker or the higher the volume. Piezo pickups mounted under the saddle amplify the body's motion along with the string's, which is why understanding pickup types helps you predict how a guitar will behave on stage.

Body size and top wood: the physical factors

Feedback is not an electronics defect. It is the physical response of a guitar top to sound pressure. The larger the body and the more freely the top moves, the more speaker energy the guitar absorbs. Martin describes dreadnought and jumbo bodies as producing a loud projective tone with strong bass, which makes them excellent unplugged but more sensitive when amplified. The guitar body shape you choose sets your feedback ceiling before you ever plug in.

Martin also describes parlor guitars as delivering a delicate sound with distinct treble and reduced bass, making them more feedback-resistant on a loud stage. The top wood matters too. Martin explains that the soundboard responds directly to the strings through the bridge, helping shape volume and dynamic range. A solid top is typically more resonant than a laminated top, and that resonance works against you at high volume. If you play live with a band, a guitar with a laminated top or a smaller body can be a pragmatic choice. See solid-top vs laminated-top and acoustic guitar body depth for more.

Using your preamp to stop howl

The controls on your acoustic-electric guitar are your first defense after position and volume. Most onboard preamps include a tone or EQ control, and many add a phase switch. Martin's electronics guide explains that the phase switch reverses the signal 180 degrees, which can decrease feedback and increase bass response. On systems like the Fishman MX-T, the phase switch is described as improving bass response at low volume and suppressing feedback at high volume.

Start by cutting the low-mid frequencies, usually around 200 to 400 Hz, where feedback typically lives. If your preamp has a sweepable mid, dial it back. Then experiment with the phase switch. You may hear a noticeable drop in the howl when the phase is flipped. On some guitars the phase switch also changes bass response, so audition it in context. For a deeper look at the controls on your guitar, read acoustic guitar preamp controls.

Position, EQ, and the soundhole cover

The simplest feedback cure is to move. Stand to the side of your monitor rather than directly in front of it, and keep the guitar top away from the speaker. Even angling the guitar can break the loop. Lower the amp or monitor level, or ask the sound engineer for more of your signal in the house mix instead of the monitor. NIDCD notes that sounds above 85 dBA can cause hearing loss, and a howling monitor can easily exceed that, so protecting your ears matters too.

If you need more stage volume than the guitar can handle with EQ and phase alone, a soundhole cover is the classic mechanical fix. It blocks the sound pressure from entering the body, stopping feedback at its source. You can buy a cover or improvise one from foam, but a purpose-built cover is easy to install and remove. Some players also use a rubber feedback buster that sits on the top. These tools trade a little acoustic resonance for a much higher usable volume, which is often the right trade on stage.

What to pick for your use

If you are buying an acoustic-electric specifically for gigging, weigh the body style and top construction as much as the electronics. A full-size dreadnought with a solid top sounds wonderful unplugged but will fight you at high stage volumes. A smaller body like a concert or parlor, or a guitar with a laminated top, gives up some unplugged projection for feedback headroom. Many stage players choose a cutaway for higher fret access and a preamp with a phase switch and a tuner.

Browse the guides to match your priorities: for all-around performance, see best acoustic electric guitars; for a smaller body that handles volume, check best travel or mini guitars and best 3/4 size guitars; if you prize unplugged tone and can manage feedback with technique, best solid top guitars covers that route.

What to pick for your use

Questions

Why does my acoustic-electric guitar howl only when I play certain notes?

The guitar top resonates strongly at certain frequencies, usually in the low range. When a note matches that resonant frequency, the feedback loop locks on and the howl appears. Cutting those frequencies on your EQ and using the phase switch usually solves it.

Will a soundhole cover completely stop feedback?

A soundhole cover blocks the air pressure that vibrates the top, which removes the main source of feedback. It does not stop all feedback if the monitor is extremely loud or the pickup is very sensitive, but it raises the usable volume significantly.

Does a solid top feed back more than a laminated top?

Yes, in general. Martin describes the top as the main soundboard that responds directly to the strings. A solid top is more resonant, so it also picks up more speaker energy. Laminated tops are less lively, which makes them more resistant to feedback, at the cost of some unplugged tone.

What is the phase switch on my acoustic-electric for?

The phase switch reverses the polarity of the pickup signal 180 degrees. Martin's electronics guide says it can decrease feedback and increase bass response at low volume. It helps because feedback often depends on the phase relationship between the top's vibration and the pickup output.

Can I use a notch filter instead of a soundhole cover?

Yes. Many external EQ units and some preamps have a notch filter that cuts a very narrow frequency band where the howl happens. It works well but requires tuning to the specific feedback frequency. A soundhole cover is a broader, mechanical solution.