Acoustic Guitar Construction

I been thinking...(I know, why not do something worthwhile instead...) about the suggestion that a builder tap-tune a soundboard as part of thinning it so's it 'rings' better than it used to, and therefore would make a guitar made with the tuned soundboard sound better than if it wasn't tuned. I am in the midst of working through designing my first scratchbuilt project and to that end I bought a copy of StewMac's Herringbone dreadnaught which I reduced a bit so as to make a more lap-friendly guitar. The plans call out a top thickness of .100 inches. My question is whether a soundboard's thickness is determined by tap-tuning and if so, is there an implication that the size of the soundboard is irrelevant? If it ain't irrelevant, then should the tap-tuning be done after the soundboard is cut roughly to shape?

Tap-tuning aside, should I be attempting to get my shrunken guitar's top resonating when thumped at roughly the same frequency as the larger original? I'm guessing that a smaller guitar's top needs to be thinner than a larger one, so as to resonate at similar frequencies, as guitar tuning isn't changed in accordance with the guitar's size.

Thanks, folks.

.100" will be fine -- now you have to figure the zillion other things that affect the output, like the size and stiffness of your bracing. Not saying its right or wrong, I'd use 1/4" scalloped braces --- assemble the top to the rim, tap with a dulcimer hammer and shave the braces until I got resonance and decay that suits the sound I have in my ear. Lastly if you want the top more responsive.

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The only things you can really do wrong is have the top too stiff and it will tap like a table top or too fragile and it will imploded. No matter, your project is going to have its own personality -- enjoy that reality and get it done.

There's some science guys on the forum perhaps they will chime in.

One thing that might help you would be to watch a copy of the Ervin Somogyi DVD. It is a well-recorded video of a lecture he gave a few years back on voicing a soundboard, also known as tap tuning. He shows and taps several soundboards and except for one, also shows the progressive thinning of the braces. The final one he just taps, but because it is well-recorded, you can closely listen to the sound of the final tuning for a board he says will be used in one of his guitars. Because all wood is different, the sounds of the various stages struck me as more important than the absolute measurements of the parts anyway, though it is clear in each of the stages where he shows bracing, the braces get thinner and thinner.

As part of the voicing process for his own guitars he also selectively sands (carefully) areas on the top that tap too high along with thinning braces, to get as large and consistent "sweet spot" as possible. He then protects the top aggressively in the rest of the building process so that it gets no dings or scratches that require further wood removal to make look good.

In the Q&A he is asked to show the back side of the final and refuses, saying you should take his annual class to see that, as if that "protected" his trade secrets. However, for me, demonstrating the sound was the trade secret and it is there for everyone to hear. The only hiccup, as far as actual practice goes, is that he clamps his soundboards in a solid mold that holds them firm, as they will be when glued to the sides. Some tap tune with the soundboard held at one of the nodes in free air, which would produce a different sound. Somogyi's use of the mold probably makes more sense than free air, especially if you use rigid molds in the first place. However, and he advocates this, once you have a braced soundboard that sounds right, you set it aside and use it as the measure of each new one you make, instead of using it for an instrument. If you compare the reference with a new effort in free air, that should work pretty well from then on.

In fact, what he attempts to send each student in his class home with is exactly such a reference soundboard, not a finished guitar. If it were not for my caregiving responsibilities, I would happily attend one of his classes myself, just to have his assistance and ear's input into arriving at such a reference for my work.

I would be happy to loan my copy of the DVD if it is of interest to anyone.

I'd love to see that, JOhn.

John, you can put me on the list. I have watched what is available on line and really enjoyed it, but unfortunately it only goes so far. Thanks for the offer,
Jim.

Jim and Dave.

I need your mailing addresses.

Hi John, I've sent you a PM with my info...... I think. Not sure if I did it right. Thanks again for doing this.