Spruce top with Mahogany braces?

[Dave Bagwill]

Ok, a strange question. Would it be worthwhile to brace a spruce top with mahogany braces? Why/why not? Has it been tried?

[Herman]

If you want to add mass to the top, then yes.
Herman

[Hans Mattes]

I'm with Herman on this.

Spruce is a favorite wood for stringed instrument tops (including bowed instruments) because it is stiff and light. Guitar tops are braced because they need to be stiffer than a thin top allows, and using a thicker top would make it too heavy to provide adequate sound volume. Bracing. then, should be chosen to complement the characteristics of the top. My last few builds (OM or a bit smaller) have used redwood tops (similar to spruce) with spruce bracing -- I'm pleased with the sonic results. (I do use a construction technique that allows significantly lighter bracing than a traditional (e.g., Martin-style) guitar.

As long as we're on this topic, I am disappointed to see the widespread use of guitar bracing that strongly tapers brace cross-sections, going from a relatively wide base, where glued to the soundboard, to a much narrower peak. That runs counter to the idea that braces should be constructed to maximize stiffness-to-weight. Strongly tapering the brace's cross-section lowers the EFFECTIVE height of much of the brace (stiffness is proportional the the cube of the height -- but ONLY where it actually IS high) and only removes a small faction of the weight. Not a good trade-off. Though not as visually esthetic (how much do we care about what the inside of the top looks like?), pursuing maximum stiffness-to-weight suggests a rectangular cross-section, tall with a narrow base. If one only wants a light bracing, however, that can mean such a narrow base that it's hard to clamp with a go-bar deck without the brace tipping over. I've compromised by using braces about 0.2" wide and 0.4" tall with rather limited tapering and that seems to work well.

[John Parchem]

I use spruce, best stiffness to mass of any of the woods.

[Dave Bagwill]

Hans - that's an interesting post. Would you have a picture of a top braced with those narrow footprint braces?
I have used .25" braces on a couple of D-35 type guitars and the sound was fine.
When I had a chance to examine a friends new Goodall, I was surprised to see the following advanced techniques : none. The x-braces, scalloped and the tone braces also, 5/16" at the gluing surface and just about the same on top - not a lot of narrowing going on there. And it sounds very good.
But I have an excellent guitar from Herman Arendsen that uses Lowden 'Dolphin' bracing, and those braces are pretty thin on the top, and it sounds great also.
If it wasn't so much work I'd try lattice bracing as Greg Smallman uses.
John How's ladder braces look HUGE - but his guitars sound very good as well.

[Hans Mattes]

Dave: Attached is "a picture of a top braced with those narrow footprint braces" destined for a J-185 style build. It's a torrified spruce top, with a bridgeplate for a fan-fret build (24.1"-25.6" scale length). The soundhole reinforcement is a thinned bit of spruce from another soundboard (grain direction--east/west), tapered on its outer edge. The bridgeplate is also tapered along edges not glued to braces. The intent of the tapering is similar to the intent of (most of) the brace layout -- minimize acoustic impedance changes that the soundwave in the top sees as it propagates from the bridge across the soundboard. The intent is to get the maximum energy spread across the soundboard -- to utilize the full soundboard area for radiation and to maximize the opportunity for harmonic resonances. The only significant braces not following this goal are the two glued to the bridgeplate, as they're intended to control static tipping of the bridge against the pull of the strings. All other braces (except the two small tone bars in the upper bout) point away from the center of the bridge to minimize their cross section as seen by the propagating sound wave. Though the brace pattern has some similarity to X bracing, it's not nearly as strong/stiff, but doesn't need to be as the soundboard in my builds is NOT a structural element holding the neck in place. (More on that is available if anyone is interested.)

[Dave Bagwill]

Thanks Hans!
So. none of the braces are let into the kerfing, no brace touches another, there is no upper transverse brace, and no long 'continuous' brace.
I see the reasoning behind each of those features. Am I wrong in thinking that a more or less symmetrical layout like this should give a balanced tone? The long monopole, for instance, will not be as accented as a traditional x-brace, right?
Do you radius all the braces, or is the upper bout left flat?

Very interesting. Do you cantilever the neck?