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hi,
i was wondering if anyone has ever made, or heard of anyone making a classical guitar with a mahogany top? or any other hardwood for that matter?

and if so, how did sound??

any help would be greatly appreciated :]


robbie

Hi, Robbie. Welcome to OLF. I would bet that someone has done it, at some time. I'm not aware of one specifically, but surely someone has. As is often said, "There is nothing new in guitars." I know that there are plenty of Ukes with hardwood tops, Koa, Mahogany, etc., and they seem to work.

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Waddy

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Sound Clips of most of my guitars

I kind of doubt it would work too well. Luthiers go to great lengths to obtain the best stiffness to weight ratios on classical soundboards, and a hardwood top is the opposite choice.
On a guitar I finished a while ago it happened that at the same average thickness of 2.5mm, the spruce top and the rosewood back measured almost the same in terms of deflection testing. I think one was 5 and the other 5.5mm. (this is while a slightly lower density piece of spruce can move 8mm). Of course, the rosewood plate was weighting double!

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Alexandru Marian wrote:
"On a guitar I finished a while ago it happened that at the same average thickness of 2.5mm, the spruce top and the rosewood back measured almost the same in terms of deflection testing."

Yes, I've had East Indian Rosewood test out with the same Young's modulus along the grain as some spruce samples, so it would have the same stiffness at the same thickness. But, of course, rosewood usually has twice the density of spruce.

And that's the problem, in a nutshell. Whatever we use for the B&S, we try to make the top as light as possible. The thing that limits the top thickenss is the stiffness necessary to withstand the bridge torque over time. Since the stiffness of a plate varies as the cube of the thickness, it's usually better to use a low density wood: even if the Young's modulus is low you can leave it thicker, and end up with a lighter top.

So there's the clue; find a low density hardwood. One that I have often thought of loking into is South American Cedar, AKA cedro. It varies a lot, of course, but some of the lighter stuff has decent stiffness and very low density. It can look a lot like mahogany, and would work well with 'hog B&S. Most hardwoods have much higher cross grain stiffness than softwoods, too.

Another that might work would be butternut. I tested one set of long- and cross-grain strips some while ago, and the density was on the low side for softwoods. Sadly, so were the Young's modulus values. Still, it might be worthwhile to poke around a bit and try to find some better stock.

The whole task would be easier if you were making a steel string. With more power to work with, and much more power in the high frequency range, weight becomes less of an issue. It's like a car: if you've got a small engine you need to keep the car light if you want accelleration and top speed. Accelleration = high frequency response, more or less, and top speed is like loudness or 'carry'.

Two thoughts:
a) What about spruce for the back and sides? I know it's been done, but only by pictures; anyone have any idea how the thing sounds? How about balancing the neck with the uber light body?

b) What if one were doing a double top with the honeycomb NASA stuff? You could make the top plates really thin and light. Would it be viable to try a hardwood then?

Kyle

I've played an all spruce D quite often, it was the shop guitar (a prototype) where I worked for a while. If I recall it is sitka B&S with a red spruce top. It sounded quite nice, comparable to a mahogany guitar in tone and weight.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Kyle Vandewart asked:
"b) What if one were doing a double top with the honeycomb NASA stuff? You could make the top plates really thin and light. Would it be viable to try a hardwood then?"

Sure. When I started fooling around with double top construction I made some test panels using standard .5mm mahogany veneer, and Nomex. They ended up quite light and stiff. You would not get a top as light as if you used spruce skins, but it would be lighter than a solid spruce top, possibly by quite a lot. The neat thing is that you can get all sorts of veneers: anybody for an ebony top? How about a 4-piece matched walnut crotch veneer?

I think too that it could work with a doubletop style construction, but I wonder about longevity? Sure, the nomex is likely doing a good job at backing the veneer up, but by how much?
I heard some saying that in a double top, the outer skin makes most of the tone characteristics, so it would be an interesting experiment. Now, who would be willing to build one?

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