What to do about resonance?

[Pscheoverdrive]

I'm not talking about tone, here... I'm talking about single-item resonance that occurs when an item is exposed to a specific frequency and starts to vibrate at that frequency (think Memorex's old ad with a wine glass in front of a speaker).

I noticed with one guitar I built for myself that it'd feedback like nuts whenever I played low D. It wasn't too terrible on the clean (kinda boomy, but livable), however, when I was playing a larger gig, I had to avoid playing that low D when I had any kind of distortion on, or else the monitor would break up and I'd drown out the bassist...

I was playing a Les Paul Standard at the same gig this past year, and I got the same thing, but it was with C...

So, now I'm working on another build, and I'm wondering what you high-end guitar builders do about this kind of thing? What can you do to add/subtract weight without altering the body much? Or do you just tune the weight of the guitar to resonate at some frequency below/above the range of the guitar?

[HerrRentz]

Eliminate parallel surfaces on the body front to back.

[Pfeister]

What kind of guitar is the first one?

What you're experiencing is similar to a wolf tone in a cello. It's a sympathetic resonation and has more to do with your strings than the body or neck. In a cello, the part of the string under the bridge can resonate loudly and sound like a howl (hence "wolf tone"). That sympathetic resonation is caused by another sound in the same frequency that's making the string vibrate (it's coming from the amp, in your case). It's not really the guitar resonating; it's the string reacting to the loud amp.

I'd bet the guitar that had the problem with C has a different scale length or string gauge than the LP.

[Pscheoverdrive]

@ HerrRentz: How is that supposed to help? What's that supposed to accomplish, and how does it do so?

@ Pfiester: It was a knock-off Randy Rhoads w/Floyd Rose. Your theory sounds pretty reasonable... However, I don't seem to have this problem with some of my other guitars. What would you suggest as a solution to the guitars with the issue?

[Terry McInturff]

With all due respect,

Not to "make a mountain out of a molehill" but, by my reading of the OP it seems a deep topic indeed...one that involves the acoustical nature of the electric guitar. This is a topic that I have brought up previously on a few occasions.

By my reading of the OP, it seems that our friend is referring to the propensity of a guitar to really "get excited" at a certain frequency. This is all tied up in the acoustical nature of the chassis.

There is the better part of a career tied up in answering this (if my reading of the OP is correct). Ive at times tried to answer such queries, but this time Im curious to read the replies from the other builders. There are some well regarded folks here who ought to be able to contribute.

[Pscheoverdrive]

^ Yep... You're right. I only posted this b/c it's a big problem, albeit an interesting one.

When you play a C on that Les Paul, the sustain grows in volume until you hit feedback. It 'obliterates everything' in the words of my bassist.

[Terry McInturff]

Play that guitar in a highly reflective room such as a bathroom, in order to make the acoustical nature easier to hear. Then, see how C sounds.....

Possibly one certain position of C is most likely to "take off"..however...other C positions may well have a bit of a different sounding sustain too. How about C @ the 13th fret on the B string? As it sustains does the overtone series seem to support an especially rich sustain?

Is there a neighboring note that seems reluctant to ring out?

Its all about the primary resonant freq's of the chassis.

Looking forward to the pro builders input. Big topic.

[Pscheoverdrive]

Unfortunately, that Randy Rhoads knock-off has a broken headstock and is currently stripped of all hardware... And the Les Paul isn't mine, so it's not in my possession right now, so I can't test those.

But... I was pretty annoyed both times, so I played around a bit and if I started a bend a half step lower, I'd get the resonance as I approached that specific frequency. It didn't matter if I played the C or D on the low E string, or on the A string. If I played higher up, the resonance was a little present (the guitar was happy), but it didn't create a problem. Just made a sweet note with a lot of sustain.

[HerrRentz]

Originally Posted by Pscheoverdrive

@ HerrRentz: How is that supposed to help? What's that supposed to accomplish, and how does it do so?

@ Pfiester: It was a knock-off Randy Rhoads w/Floyd Rose. Your theory sounds pretty reasonable... However, I don't seem to have this problem with some of my other guitars. What would you suggest as a solution to the guitars with the issue?

It's supposed to eliminate standing waves.

[Pscheoverdrive]

:S If you eliminated standing waves, you would have no sound from your guitar. The strings' vibration is a first-order harmonic standing wave.

Eliminating parallel surfaces would not accomplish that, anyways.