How to Fight Acoustic Guitar Feedback Using EQ

If you have ever performed as an acoustic guitarist in a band, you know soundchecks can be a headache. After plugging your fancy acoustic into a DI box (which is plugged into a channel on the house mixer), you turn up and strum a G chord only to be assaulted by a cacophony of ringing feedback. Why does this happen?

Same settings as the last show, same cables, same everything. Meanwhile, your electric guitarist is blaring away in sonic bliss, grinning ear-to-ear because his rig sounds just like it did last night and the night before. Meanwhile, your tone is thin, uninspiring, and ultimately very un-acoustic. You’re bummed. What can you do?

Step 1: Know Your Limits

Understanding the limitations of your instrument with regard to amplification is the first step in achieving a better live sound. Acoustic guitars can be significantly more difficult to amplify than electrics, due in part to the fact that they are completely hollow and provide the perfect recipe for feedback.

Step 2: Understanding Your Guitar’s EQ

Certain qualities on an acoustic guitar dictate the overall responsiveness of the different frequencies that are produced when the instrument is strummed.

Depending on the type of tonewoods used and the quality of their construction, one guitar may possess a more midrange dominant sound, for example, while another might highlight the high and low ends, having a less pronounced midrange characteristic.

No matter what type of guitar you have, discerning the natural frequency response of your instrument can be the first clue to understanding how it will sound when plugged in and which EQ adjustments you will need to make to compensate for its natural character.


Step 3: Understanding A Room’s EQ

Similar to an acoustic guitar, a performance venue is essentially just a hollow box that produces sound. The band is playing, perhaps the patrons are drinking and talking noisily at the bar. All of these things build sonic pressure within the walls of the building and, just like with an acoustic guitar, certain frequencies can resound more prominently than others.

In a live setting, your acoustic guitar is essentially a complex and highly resonant box within the larger resonant box that is the music venue. To resist feedback or achieve any semblance of sonic harmony when amplifying your guitar in this scenario, all of the resonant frequencies at play in the room must be managed through EQ.

Now, if you are lucky enough to have a house sound tech, any adjustments on the mixer may be out of your control. You do, however, wield the power of your own instrument’s EQ bands. Remember the fancy DI that you spent all that money on? Here’s where it pays off.

Step 4: Nice DI! Now Use It...

Now that we’ve determined what we are working against as acoustic players, let’s turn some knobs. Even the most basic preamp/DI will feature EQ parameters for Hi, Lo, and Mid.

Often, these knobs will be fixed at a predetermined frequency. However, on more advanced equipment – such as the LR Baggs Venue DI – you retain a more comprehensive set of parameters, as well as the ability to choose specifically which midrange frequencies you are boosting or cutting.

I cannot overstate the importance of this feature. Taking the time to make adjustments to these knobs and listening critically to the ways they shape your tone can be a game changer. Not only can they be used to fight feedback, but should you find your instrument lacking punch or definition amongst other bandmates, a more extensive set of mid-range EQ can be an invaluable asset.

Step 5: Notch Filter

Though not an option on every stage DI, a notch filter can also be invaluable as it serves one basic function: kill feedback. Essentially a narrow band cut that you can sweep across a wide band of frequencies, notch filters are the quickest means of dialing out those nasty resonant frequencies that muddy your tone and distract from an otherwise great performance.

It’s not uncommon to find notch filters on higher-end DIs and acoustic amplifiers. The Fishman Loudbox series, for example, utilizes a handy notch filter in lieu of adjustable mid-range parameters. When combined with independent phase switches on each channel, it accounts for all of the frequencies at which an acoustic guitar could produce unwanted resonance and feedback.

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