back buzz(?) on classical. Likely causes?

[Simon Magennis]

I am not sure if I am using the correct term. What I am referring to is a "rattle" which happens when you finger a string on a fret and the string hits the previous fret with a rattling noise. So for example, finger the 12 fret and the buzz/rattle happens on the 11th. It is not a buzz while playing, just rattles as you put your finger in position on the next fret. I am getting this on the the 8th or 9th fret thru to the 13th or 14th on some classicals I have built. It effects the E and A strings primarily and a little on the D. I believe it started happening when I change the way I did the frets. Originally I put the fretboard on and then cut the slots freehand in situ. Now I cut the slots before gluing on the fretboard and even partially fret it. I put little or no relief in the fretboard.

So what is the most likely cause? Need more relieve in the fretboard? Bad gluing technique? Fret levelling not agressive enough? Overall neck geometry. Fretboards are IR.

[Bob Gramann]

Back buzz can be really sensitive to relief. I have found that changing the relief just a little can fix the problem. I have seen it happen in some classicals when the humidity changes. I make mine with a double-action truss rod even though that's not standard for classicals. You need a little relief.

[Michael Lewis]

After gluing your slotted fingerboard do you level the surface, or just go ahead and put frets in? Do you check for relief? Get a straight edge at least 18" long, I find 24" very useful for things like thin plus setting neck angles. Also a set of feeler gauges, and a fret rocker. Measure the relief with the straight edge and feelers, this will tell you how much and where the relief is, and the rocker will tell you if any frets are high in relation to the others.

A lot depends on your fret work, ( all frets even, sufficient relief, etc.)

[Simon Magennis]

Thanks guys. A couple of very useful tips there. I will refret two of the "offenders" and put in some more relief in the process and see if that solves the problem.

[Alain Moisan]

Hi Simon,

The problem may not be caused be not enough relief. A nut slot too deep also causes back buzz. Try raising the nut a bit and see if you get the back buzz again.

Also, if the problem is caused by not enough relief, you don't need to refret. You can just induce a relief by fret leveling it. Sure you will have lower frets in the middle of the neck, but by just a few thousands. It is much easier to do than a complete refret.

.02$