Non-musical harmonic vibration

Chiefbigeasy · March 2015

My in-every-other-way-fantastic Alves de Puga DR 670 has developed some sort of intermittent harmonic distortion when I strum a loud six string harmonic at the twelfth fret. As the volume decreases, the distortion fades away. I seem to have isolated the note at D. I was hearing what I thought was fret noise when I played the D note on the third string and on the second string as well during single note solos.

I have tried pressing pressing and lifting the tailpiece during the noise to see if there is some sort of vibration happening against the top of the guitar. I looked for other vibrating wood on the surface at the bridge and found nothing loose. I've inspected the guitar and I see no hairline cracks developing anywhere as of yet. I was wondering if bracing from the interior coming loose could cause this kind of symptoms. The strings are silk and steel and relatively new; haven't noticed any breaking surface or separation of coils.

I characterize the sound as a mild dirty distortion, very subtle though, and only occurring at three aforementioned locations.

Haven't brought the guitar into my local luthier yet, but that's probably the next step. Any thoughts or experience in these matters? Thanks advance for any suggestions.

Russell Letson · March 2015

Try putting some sort of damping material between the bridge and the tailpiece and across the strings north of the nut. Those short lengths can produce annoying, mosquito-like harmonic whines. Some players weave a length of piano or Autoharp felt in those places (Michael Dunn, if I recall correctly), and repairman Marty Reynolds put a nice muting device on one of my archtops--a confection of wood and felt that clips across the south-of-the-bridge segment. A length of sew-on (non-sticky-back) Velcro will serve the same purpose.

Chiefbigeasy · March 2015

That's the sound: mosquito-like harmonic whines. Tried dampening the strings from the tailpiece to the bridge last night: no difference. I'll try the upper string lengths tonight. Must say, however, I hear the sound most pronounced coming from the sound hole, or at least projected from there.

HCQ · March 2015

See if the bridge feet are not slightly tilted on the guitar's top. Just gently rock the bridge back and forth, (neck to tail piece), till it doesn't move anymore or make any little squeaking noise. Then you the bridge is seated properly

Chiefbigeasy · April 2015

Problem solved. Luthier diagnosed problem as upper nut was a little too high and some sort of vibration was happening at fret zero. He lowered that nut just a smidgen and that seemed to solve the vibration issue. He also replaced the felt underneath the tailpiece with leather, and he placed small leather rounds around each string post beneath where the string threads through the post so that the ball end of each string sit on a small piece of leather. (Don't like the way those little pieces look, so will remove them next time and see if that makes any difference.)

Chiefbigeasy · April 2015

Problem returned with a vengeance on a different note harmonic, but solved after all.

Luthier had adjusted truss rod to reduce relief and straighten neck. The result was a vibrating truss rod in the neck (thanks for your help Michael and past forum commenters regarding vibrating truss rods). Returned and put some torque on the truss rod and the vibration disappeared. The neck is now dead straight and the action is a bit lower as well. I think I've lost a little bit of volume, or maybe I'm compensating by playing a little softer.

Nevertheless, I'm wondering if most players like a little relief in the neck or do you like a dead straight neck?