sympathetic vibrations

[GDAE]

This is actually a guitar question, but I've experienced it to a lesser extent on mandolins, too.

I have a guitar that has a really resonant A string. I can be picking on the G and B strings, and the A resonates longer than either of them, and rather loudly too...to the point it could be distracting.

What causes this? What can I do about it?

Thanks

[Wes Brandt]

Do you mean the a note itself, on the a string plucked open? That A is getting close the body chamber resonance peak of a smaller guitar and notes will naturally get louder as they approach that pitch. Some of that is to be expected.

That would be my first guess, since I don't know what you have. Its also possible that the nut or saddle shaping for clean "breakaway" for the g and b are not quite right but are both right for the a string.

I wouldn't use the term sympathetic vibration... which usually refers to one string setting off related frequencies, octave, 5th etc on another string. Think Sitars. Or open tunings for that matter.

[GDAE]

Thanks for responding, Wes. What I mean is that the A string resonates fairly loudly even if it's not being plucked at all...for example, I'm picking on the upper three strings, not hitting the A string at all, but it resonates in sympathy with the others to the point it is a bit distracting. It is a parlor guitar.

What would be the appropriate term?

Thanks.

[Wes Brandt]

Are you using an open tuning by chance?

A bit more... is this a high quality guitar or a lesser one?

The way you describe it above sympathetic is the correct term... not that I'm a correctness fanatic.

[GDAE]

It's all solid woods, well put together...I wouldn't call it a lesser guitar. No open tuning, just standard tuning.

Thanks....

[Wes Brandt]

Try loudly humming (or some kind of vocalizing) some notes into the sound-hole and see where it resonates... try starting at A-110 and "slur" the pitch up and down several half steps...you should find a pitch where the box obviously resonates... try it with the strings dampened too. It may well be right at A, which I then would say is the problem. I can't remember the resonance modes for guitar tops, but if one of the significant modes is resonating at or near very near the same note or octaves of that, it could explain it even more as they combine... ( Do you know how it's braced? would that be a 12 fret neck, 0 size?)

[GDAE]

I did indeed find that it really resonates right on the A-110. However, with the strings dampened, it doesn't ring out, of course.

It's a 12 fret, x-braced, 0(ish) size.

Since that seems to be the note of the natural body resonance, does that mean there's nothing to be done about it?

[eastmountain]

Since that seems to be the note of the natural body resonance, does that mean there's nothing to be done about it?

Yes. Send the guitar to me ASAP and get a new guitar. I'll keep it at my house and I promise you never hear that resonance again.

[John Flynn]

I had a similar problem with my Rigel mandolin when I first got it. Some things helped to some degree:
1. Different strings - experiment with different sets.
2. Visit to the luthier - he tried a few things that helped, not sure what they were, sorry.
3. Learn to ignore it - the audience can't hear it as much as you can and if you really get into a tune, you'll find it never rings out long enough to be a problem.
4. Wait - after a few years of playing it, the problem mostly went away onmy instrument.

[Wes Brandt]

Usually the body resonance is not a problem and then, there is that little thing about once you notice some "flaw", it can become more important than it really is (I've seen it many times)... but check out this link-

http://www.phys.unsw.edu.au/music/guitar/patterns.html

It's easy to imagine one of the modes of the top is at an A also... the first one at A110 for a small guitar? Or an octave above? Then the resonance would be that much more exaggerated. Then you might even say you have a "wolf note"...

You could find some luthier who has a frequency generator setup who's into working with modes who could test it. The body resonance could be raised by opening the sound-hole and the top resonance moved by adding braces or taking away brace material. Not exactly a typical repair.

Also if there really is that problem and I was the maker, I would surely want to know about it (don't want to make the same mistake again) and cover it under warranty

[GDAE]

Thanks for the info...I think I'll take it to my local luthier, as I think you've gone a bit beyond me, Wes.

John, another friend told me it went away on his, too...so maybe it is something time will take care of, as well.

And Eastmountain...it's not THAT big a problem! ;-)