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Old 03-24-2013, 01:53 PM
KevinLPederson KevinLPederson is offline
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Quote:
Originally Posted by Alan Carruth View Post
One of the interesting things about bracing is how little it does to the sound.

The actual main function of bracing is to add stiffness to the top to allow it to withstand the torque of the bridge, without adding too much weight. It's interesting to note that an unbraced top off the guitar will vibrate in much the same way as a braced one. If you simply left it thick enough to have the requisite stiffness, it would have much the same timbre as a properly braced top, but the mass of the thick top would cut down on power a lot. In this respect, a good bracing design is one that doesn't do too much: that 'keeps out of the way' of the top, so to speak.

IMO, it's more important to get the bracing working well with the top than it is to use a particular brace pattern. Good guitars can be made with a wide range of bracing patterns if they're done well, and anything done badly makes a bad guitar.

That said, different bracing schemes do sound different. Several years ago I made a 'matched pair' of maple Small Jumbos with different top bracing, and took them to a luthier convention. There, I had as many people as possible try them out without telling them what the difference was, and asked them which they liked better. In two cases out of three these experienced builders preferred the one with 'double-X' bracing over the 'standard' top by a slight margin. It was really interesting to hear the guesses people gave as to what they thought the difference was. When I told one maker that the guitar she preferred had double-X bracing, she exclaimed: "But that doesn't WORK!" I shrugged.

In most traditional designs, both the top and the braces are taking at least some of the load, but this is not the case so much with some of the modern designs. The Smallman 'lattice', which is more or less like Charles' next to the last photo, takes almost all of the load on the carbon/balsa bracing, with the veneer thickness top being there mostly to fill in the gaps and push air. I think of this as 'distributed bracing'. The use of high tech materials cuts down on the overall weight of the top. Some 'sandwich' tops have been made that also delete the bracing entirely, or nearly so.

To the extent that a 'different' braving system actually works differently, it will alter the tone of the guitar from the expected one. As often as not this is a disadvantage in a world where there is a lot of existing music that people will want to play on the new instrument. On the other hand, a well designed and executed 'different' bracing scheme can make a very nice instrument, and be a decided marketing advantage.

Finally, to the OPs question:
You have to remember that most bracing schemes were not 'designed' in any rational way. They are mostly the outcome of seat-of-the-pants engineering and a lot of cut and try. Given enough time this sort of evolutionary process can get you a pretty well optimized system, but there will be a lot of failed experiments along the way. We mostly don't see those, of course; the luthiers bury them.

It's also really hard to say in many cases what a particular brace 'does' that's different from all the others. In a general sense, as I tell my students, the edge of the top at the upper block is primarily about structure, and the lower edge, at the tail block, is about tone. It usually does not make a lot of difference to the sound if you remove wood from the bracing above the bridge, and lightening the bracing below the bridge does not affect the strength as much.

Every scheme is a compromise: we want low weight and high stiffness: mobility to produce sound and stability over time for playability. You can't have everything you want, and each choice you make comes with a cost. In the end, there's at least as much 'art' in this as 'science'. A good top is not so much the prose of a technical paper, where each brace has a well-defined purpose, as poetry, where it all works together to produce meaning. A successful maker knows how to work with both aspects.
Well stated Alan. Thank you.

Kevin.
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