Amplifying An Acoustic Guitar – How To Prevent Feedback

If you’ve played on stages before, you’re probably well aware of the sonic nuisance that is feedback. In this blog, we explain how you can counter feedback and keep the ears of your audience members from bleeding.

Feedback

Imagine yourself on stage. You’ve got your trusty acoustic guitar and you’re ready to accompany the singer for a tearjerker of a ballad. The room’s packed full of people and you’re having a great time until suddenly a squealing sound pops up and intensifies. *eeEeeeEEeEEeeeeeHHHHHHHH!* Everyone in the audience immediately covers their ears and the flow and magic of the show vanish instantly. The song’s been hijacked by the devil called feedback and, want it or not, you’re the one to blame. Well, sort of. Technically, it’s your guitar that causes the feedback. Anyone who’s ever miked up or plugged in an acoustic guitar has probably dealt with it. Feedback is a common phenomenon that can only be averted if your gear or sound tech cooperates.

Feedback Pops Up at Around 440Hz

Before we dive in a little deeper, let’s take a quick look at how acoustic feedback is caused. Simply put, feedback is formed when the sound produced by a speaker is sent back through the instrument or microphone it’s amplifying, which is then sent through the speaker again, creating what’s known as a ‘feedback loop’. This vicious cycle creates an increasingly loud, piercing noise as a result: feedback. The fact of the matter is that hollow-body guitars resonate the most at around the 440 Hertz mid-range mark, which is the same frequency as the A note. If the song you’re playing contains a lot of As and you need to let them ring out, the risk of feedback increases. To wipe out any on-stage feedback, you can either use the palm of your hand to dampen string vibration or get off your stool and walk away from your amp or monitor.

Pro tip: never aim your speaker at the sound hole of your guitar and make sure there’s enough distance between you and your monitor. Try setting up your amp or monitor next to you or facing away from the guitar so that the sound enters either your left or your right ear.

Damping The Strings With Your Hands

If you play an electro-acoustic guitar, you can try to quickly turn down the volume or tweak the bass pot of any two-tone control set-up or the mid-range pot in case your guitar has a more extensive EQ section. No matter the option you pick, you’re forced to remove your hand from the strings to work the controls. Nine times out of then, by the time you remember to mute the strings with your hand, feedback is already rearing its ugly head.

Guitar-builders and makers of amplifiers and other guitar-focussed gear actively brainstorm solutions to tackle the issue at hand. Some guitars, like models by Ovation, feature a ‘bulgy’ back designed to reduce internal sound hole resonance. As far as Ovation guitars go, the downside – if you even want to call it that because it really all depends on personal preference – is that you get a slightly ‘unusual’, acoustic foundation sound.

Sound Hole Covers Reduce Feedback… and Sound Quality

Fortunately, there are cheap tools available that can be used to significantly reduce sound hole resonance. We’re talking about special covers that form-fit the sound hole of your guitar and seal it off. All sound hole covers, which you’ll find with names like screeching halts, feedback busters, suppressors and pushers, are essentially different takes on a rubber cap.

Unfortunately, sound hole covers are only compatible with electro-acoustic guitars, because fitting one to an acoustic guitar means you can no longer use a sound hole pickup or microphone to amplify your sound.

Equaliser or Feedback Destroyer

If you’ve got the support of a sound tech during your gigs, they could help out. Since acoustic feedback stems from mid-range frequencies, your sound tech should be able to slam the brakes on the mids via their mixing console. There are plenty of sound technicians who panic as soon as feedback pops up and quickly cut out the sound. That’s not exactly an ideal solution, but luckily there’s gear that can help them out.

Some sound techs use a graphic EQ, or even an electronic feedback destroyer in some cases. Using a graphic equaliser, you can very accurately single out and eliminate the frequency that’s causing the feedback. These bits of kit are highly effective when it comes to countering feedback while maintaining solid live sound.

There’s even equipment that automatically knocks out feedback: so-called feedback killers, suppressors, destroyers or eliminators. These devices search out and remove feedback-causing frequencies, either by suppressing them across a narrow frequency band, by phase-reversing any malicious frequencies, or by applying a high-pass/low-cut or notch filter.

If you know of any additional tricks of the trade that help counter feedback, feel free to share them in the comment section below!

How to Change the Strings of Your Acoustic Guitar How Can I Connect a Guitar to a Computer? How Many Strings Does a Guitar Actually Have? How to Change the Strings of your Classical Guitar Acoustic or Electric Guitar? Where’s the Best Place to Start? Which Acoustic Guitar Do You Need in Your Life? Steel-String or Classical?