Looking for plans - 8 string guitar

[Hans Mattes]

I built a couple of harp guitars in the last 18 months. The first turned into a "learning experience." The second works well but convinces me that a harp guitar (at least in my clumsy hands) is useful only for a limited range of music. The good news: it has LOTS of sustain. The less-good news: It ALWAYS has lots of sustain -- and, unlike with a piano, one can't lift off the sustain pedal. As a result, it can work well with slow ballads but not as well with lively tunes.

[Dave Bagwill]

Wow. I really like that, Hans!
Would you happen to have a pic or two of the top bracing?

General question - what is the difference in sound between a 25" long string tuned to low D, and a 12" string tuned to the same note? This string would be unfretted, and tuned only to low D.

Such as:

[Hans Mattes]

Here's a picture of the bracing I used for the harp guitar. The "harp neck" is a 1" dia. carbon fiber tube (1/16" wall) that's epoxied to the tailblock, the headblock, and the harp headstock. (I built a simple jig to assure that those elements remained aligned as the epoxy set.) As ever, my builds include a floating fretboard that allows adjustable neck angle (for the conventional, played neck). While the adjustable neck requires several more steps in the build, it GREATLY simplifies the construction process as adjustment of the string height above the fretboard can be done at anytime (and without removing the strings). No more concern over whether the straight edge grazes the bridge, etc. The bracing is quite light as the carbon fiber tube carries much of the string load while keeping the headblock and tailblock in proper position to one another. The bracing is still required to control bellying of the soundboard at the bridges.

[Dave Bagwill]

Thanks Hans. Some nice design elements in there!

[Hans Mattes]

Dave: Responding to your suggestion about using very short (e.g., 12") scales for the fretless strings of a harp guitar, I checked the string tension calculator at www.tension.stringjoy.com (which seems to be one of the more flexible string tension calculators on the net). The challenge of a low tuning (e.g., D2) with short strings is the need for very heavy strings to allow acceptable string tension. To tune a 12" string to D2 would require a 0.115" diameter string (available as a bass guitar string) to get the tension up to 20 lbs. If you are willing to accept a tension as low as 12 lbs., a 0.090" string could be used. I won't speculate on what the volume and tone consequences might be. It could be worth an experiment.

[Dave Bagwill]

Hans: good information, thanks. I may experiment with that a bit. I just need the note and a bit of sustain, not much.
Good tip on that website!
I need to figure out what a C2 note would require. Probably that .090 would do it.