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Hi, I'm new to the site. I have been building guitars for a few years so am quite new at this, comparatively speaking. I started with a kit guitar then stated learning to build from scratch. I have always loved the look of ALL mahogany guitars. So I decided to try one for myself. My question is, is there anything different I should be concerned with when building a Mahogany soundboard. What sort of thickness should I be looking for? Or any qualities specific to Mahogany that I should be concerned with before I start making the top?

Welcome Chris

Folks were just discussing thicknessing tops. I'd think the same rules apply to mahogany. That's where I'd start

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First a qualifier: I haven't actually built any hog top guitars, but the next one will be so I've been putting some thought into it. I have built quite a few assorted all mahogany dulcimers, zithers, and weird experimental instruments.

In theory, mahogany and spruce have about the same MOE, so they should be thicknessed the same regardless of the difference in density.

In practice, the outstanding mahogany (or koa) topped guitars that I've played all have had very thin tops. Based on this, I'd go with a very thin top, even if it requires a double X or something to not belly too much. First guess would be about .100", or maybe .090" for a smaller guitar.

cmarr6

I have built with Sitka tops, WRC tops, a Koa top, a Mahogany top, a redwood top and a half Sikta/ half WRC top. I treated all those tops the same. I have a deflection test that I perform as I am thinning the tops and I use the same test no matter the top material. It seems to work for me but I am not recommending that you use my method. Someone else here on the forum will probably come up with a much better solution. Just thought I would give you one answer to your question. - Mike

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guitarsbygiltzow.com

I've not heard that theory!

The frequency at which anything vibrates is a function of both its stiffness (MOE, Young's modulus) and its mass (governed by density) with frequency being proportional to SQRT(stiffness/mass). So if you want guitars to resonate at particular frequencies you need to consider both. In this forum post I write about how I approached the issue with a koa guitar. If you want the responsiveness of a spruce guitar, you have to reduce the mass of a hardwood top, which means taking it thinner, but then you loose a lot of stiffness (proportional to the thickness cubed), so that has to be put back in with some efficient low mass, high stiffness bracing; a CF reinforced lattice in this case.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Obviously (or not) I was thinking in terms of deflection of the soundboard under the string load, not the frequency at which it vibrates. You are right of course, in looking at the bigger picture. What you say is pretty much confirmed by my experience.

In the end it seems that we are both saying to go with a thin soundboard, and use some sort of clever bracing scheme to support the thin top and put the stiffness back in.

Up to this point in my building, I have not been very "scientific" and am not naturally that way. I prefer the old school method of building by "feel". Although the deflection concept seems appealing. I read the post about top thicknessing. I plan on building a deflection jig and start there. Trevor, that bracing on that Koa guitar is awesome. Might have to try something similar. Thanks