The diagnosis was a high spot in the region of "frets" 14-18, for the first and second strings. On careful inspection, the bottom lip of the fingerboard was partly the culprit, it was also partly the general slope of the board above the octave. These tolerances are tight!
The diagnostic sanding (60-grit and 150-grit) was done with strings in place; once all notes were ringing clear, I took strings off and more gratuitously sloped off the end of the board. When satisfied, I finished up with 220, 400, and 600-grit paper. The board is certainly not perfect, you can see that right away, but since this is a bit of work in progress and an experiment to begin with, I'm pretty happy with progress thus far. Before restringing, I did manage to get a couple of photos of the fingerboard, which I'd meant to do before:
Yeah, 600-grit sandpaper is pretty nice. I'd never seen unfinished wood shine before these projects. (It was after these photos that I wiped on the linseed oil.)
Restringing this time was another experiment. The first iteration had a marvelous warm buzz (what Dave Sweeney called the "mwah" sound, which is exactly right), but the top two strings were so light (.012 for the E and .010 for the G) that I thought I should try some heavier ones to see if I could get a little more sound. What I did, so as not to risk overtensioning my little kit's system, was to go to heavier gauge strings all around, and then tune everything down a whole step. So, I used the following for this experiment
- 6th string: .059 bronze wound, tuned to Bb1
- 5th string: .048 bronze wound, tuned to F2
- 4th string: .038 bronze wound, tuned to C3
- 3rd string: .022 nickel wound, tuned to G3
- 2nd string: .014 plain, tuned to D4
- 1st string: .012 plain, tuned to F4
Boy, interesting observations there. First: the .059 for the Bb is floppy, and the instrument does seem to have a hard time responding to it. Curiously, the .054 string seemed to work fine for the low C previously. Quite a difference. Next, those first two strings really do sound better being a little thicker. That point is well-taken. Finally, I noticed that a lot of the "mwah" was missing, at least the first time the strings were brought up to pitch.
I started thinking about this, and it's quite possible that multiple things are at work. First, the thicker strings may simply ride a little higher in the nut/saddle notches, and be enough higher off the board that the natural buzzing is affected by it. Probably it's also that the fingerboard has indeed been relieved by the sanding.
Some of that "mwah" is coming back as things settle in, or perhaps it's because of how I'm playing it. I also have considered the roundwound strings. Ultimately, I am still interested in either flatwound electric strings, or possibly the original idea, nylon. (That would really require some more work on nut and saddle!) But...I wonder how much of this buzzing sound is actually coming from the roundwound strings. I've heard that the "Jaco growl" may have been partly due to his use of roundwound strings, and I'll admit, that's not a bad sound to have available...
One way or the other, it's given me a lot to think about. Current plan is to play like this for a while, and then at my next string change, polish up the fingerboard once again and put on the "light" electric flatwounds to see what they sound like. The plan there is for the following:
- 6th: .056 flatwound, tuned to C2
- 5th: .042 flatwound, tuned to G2
- 4th: .024 flatwound, tuned to D3
- 3rd: .018 plain, tuned to A3
- 2nd: .013 plain, tuned to E4
- 1st: .011 plain, tuned to G4
I figure that if the action/setup sounds good with the lightest strings, I'll have done with the instrument what I am capable of doing as a luthier, and by then I'll have enough evidence to decide how I want to string in the longer term.
For now, we'll try whole-step-down, heavy strings, and see how it goes!