F.A.Q.#5: Soundholes and Bracing Patterns

December 18, 2011

Q: If the soundhole is not in the traditional location at the end of the fretboard, is there a better bracing pattern than the X-brace, in your experience? 

A: The soundhole is where it is, as a matter of tradition rather than critical thought: it’s always been put there. One might put this in terms of history trumping dynamics. History and tradition notwithstanding, the guitar soundhole has a tonal role to play, and I devote an entire chapter of The Responsive Guitar to the mechanical and dynamic functions of the soundhole with respect to brace location.

As far as the mechanical dynamics go, the soundhole in the Spanish guitar is outside of the main vibrating area of the face; it’s isolated from it by a massive brace that acts like a dam, and the comparatively delicate fan bracing on the other side of it does its work without being affected by exactly where, above that dam, the soundhole is. In the steel string guitar, instead, the soundhole is inside the main vibrating area of the face. It represents a mechanical perforation of that plate — and it necessarily weakens it. Imagine a drum head (a vibrating diaphragm) with a great big hole in it, and you’ll be able to grasp one of the principal bad dynamic ideas in the steel string guitar.

As far as bracing placement is concerned, my opinion is that the acoustical work of the bracing is more important than the specific location of the soundhole, and that these shouldn’t be in conflict with one another; therefore, I think there’s more to be said for moving the soundhole “out of the way” than moving the bracing around. Those kinds of judgments depend, of course, on understanding the functions and possibilities of various bracing systems. You don’t just want to move stuff around randomly.

Speaking of tradition vs. critical thought, the Kasha guitars (with the innovative Kasha bracing) were the first ones to focus on the bracing layout first and the soundhole placement second — in spite of how oddball those guitars looked. I give the Kasha people credit for understanding about putting the soundhole in a place where it helps rather than hinders. The soundhole’s dynamic function is to act as a port (as per the discoveries of 18th century Dutch scientist Christian Huygens, which I go into in my book), and as such doesn’t HAVE to be in any particular location. I recommend reading my book if you haven’t already.

Whether or not one moves the soundhole, it’s useful to have an idea of what each bracing layout can do, in terms of its mechanical and vibrational possibilities. Or impossibilities. There’s a logic to each bracing pattern and each one can be tweaked and altered in many ways — some subtly, some radically. And, as I said, part of the challenge is to not put the soundhole where it’ll create a problem. Either way, we’d have to understand how these factors interact before going on to talk about “better” or “worse”… because there are many ways to spoil the efficacy of any blueprint pattern and there are many ways to “get it right”.

But, let’s get back to your question about “X” bracing and soundhole location. The virtue of “X” bracing is that it ties the face together so as to create the possibility of a dominant monopole motion. Now, it won’t work nearly optimally well if the bracing/top are overbuilt and too stiff, or if the plate isn’t properly or consistently tapered, etc., and your job is to learn to do an INFORMED balancing act. Plus, the soundhole is right in the middle of this, sort of like interrupted ceiling beams that are holding up a roof that itself has a great big hole in it.

If you can get comfortable with the idea of relocating the soundhole to somewhere else then you do have to think about what to do with its area of topwood that is newly available as vibrating diaphragm. I mean, you’re creating an empty space bigger than any other empty space on that braced top. You could close the “X” brace up a bit… but that would necessarily open up the bass and treble quadrants, and you’d have to figure out if you were comfortable with that. As I said, it’s all a balancing act. If you didn’t want to mess with the balancing act then you might think about installing one or more finger braces into that space, to tie it into the rest of the bracing. I don’t have a better specific answer for you than this.

My unspecific answer is to think of what your changes might signify in terms of the main modal movements of the top: the monopole, the cross-dipole, and the long-dipole. Mainly, “X” bracing is a recipe for bringing out the monopole; it ties everything together. Fan bracing is a recipe for facilitating cross-dipole; there’s nothing there to prevent or inhibit that mode. Ladder bracing is a recipe for emphasizing long-dipole; it destroys the monopole and the cross-dipole.

So, if you were thinking of closing in the angle of the “X”, you would be justified in suspecting that this will facilitate more cross-dipole: the legs of the “X” would be stiffening the plate in a different way, as a function of their new orientation. So, the equation might look like: (Take away soundhole) + (closing in the “X”) = (more cross dipole). A second equation might be: (remove soundhole and add a bit more topwood) + (leave “X” the same) = (maybe a bit more monopole). Another equation might be: (remove soundhole) + (enlarge the space by spreading the “X” legs out) + (make new bracing accommodations to reinforce this larger space) = (?).

My point is that if you can accept that there’s some actually useful information contained in technical jargon such as “monopole”, “cross-dipole”, and “long-dipole” (which are simply formal words for some basic concepts of top vibration, and hence sound) then I think you can begin to have really interesting ideas about how to problem-solve your next guitar project, and make it better.