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Controlling Feedback

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Another one in my "Stupid questions about archtops" series.. How would you go about controlling feedback in high gain situations without stuffing the thing with a pillow or adding an ES-335 style sustain block? I'm a metal guy, so I'll be playing metal on this thing (go on, ask why I want a hollowbody :D ). I don't use that much gain but probably enough to get a good squeal going wherever I stand onstage.

What is it about a hollowbody that actually makes them so feedback prone? I've never seen this adequately explained. Is it the added body vibration being transferred to the pickup? Is it sound echoing through the chamber? Is it magical trolls? :D

I've seen jazz guys like George Benson tape up the f-holes to prevent feedback. That gives me two ideas. One is to just not use f-holes at all, but I don't want to do that since I want a good acoustic voice too. The second is to make removable f-hole inserts that I can use at shows. But is there a better way I don't know about? Maybe a partial block just under the pickup?

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Make a semi, and don't put F-holes in it. My semis are blocked firmly under the bridge (piece of wood) and with a healthy amount of wood by the neck joint, and have a top that's carved inside and out (about 6mm-1/4" all 'round, not tuned in any way). Sustain is great, they sound difference from solidbodies, and they have very controllable feedback.

Why you get feedback probably has to do with the increased resonance you get with a thin top and large open cavities, the pickups themselves vibrating in their pickup rings/with the top, etc. F-holes seem to make things worse, probably because they 'free' parts of the plate to vibrate even more, possibly even 'pump' some air, although this is purely conjecture on my part. The cause is just the crazy amount of signal from an amp driving strings and body at a frequency that the resonance is reinforced (positive feedback loop).

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I don't want a semi-hollow. Like I said, I've never liked their unamplified tone and that's as important to me with this guitar as the amplified tone is.

I ran across a couple of interesting ideas from Daniel Slaman and Steve Andersen. What Slaman does is leave the underside of the upper bout uncarved. This way when he installs the pickup there's still wood under it. Andersen's Electric Archie is similar but it's just the area right under the center that's left uncarved. I might try something like that.

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Feedback at moderate to high gain is the reason solid and semihollow guitars were invented in the 50s. Hollowbody and real loud just don't mix unless you're a long way from your amp or you take steps to make the guitar act a good bit less like a hollowbody, and then why would you need a hollowbody?

Gibson invented semihollows to reintroduce some of the resonance (amplified) of a hollow guitar, but the reason hollowbodies are relatively loud unamplified is that the top is free to vibrate. It's the vibration of the top, not the strings, that makes the volume. That's also, mostly, why they feed back: sympathetic vibration of the top in all its resonant frequencies. So any kind of contraption that hinders the top's vibration is going to 1) reduce feedback, and 2) kill unamplified tone. Sadly you can't have it both ways.

By the way, it's not only the top's vibration that leads to feedback; I have a custom-made semihollow where the center block does not extend all the way to the back. The back's freedom to resonate gives the guitar a super tone, but it's way more prone to feedback than my ES-335 -- and way less so than my hollow Casino.

Good luck...


Edited by ccbryan
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