Structure

[Dave Bagwill]

Ken Cierp - would you amplify your remarks about bracing - that it is mainly structural? What are the particular 'myths' about bracing that need to be questioned?
"Introduction to the Philosophy of Bracing 101 " :-)
Thanks

[ken cierp]

Keep in mind that I know nothing -- and generally my comments are usually links to those that really do know something or at least have come to their own conclusions.

I will say that I do have a theory regarding the function of a sound board and the associated bracing. Simply look at an audio speaker --- there is a magnetic driver in the middle which moves the cone (diaphragm) that happens to be pretty similar to action of the bridge and strings --- right? Now that cone has no base or treble side, it is just reacting to the magnetic impulses around the entire surface area. If you glue something to the cone --- it will always reduce or distort the output and require more energy to even produce the same volume, but at some level the efficiency of the cone is still reduced. So I would suggest that any piece of bracing is reducing the potential of the sound board and at the very least, the brace configuration does not add any frequency response but merely restricts the output of some frequencies making others more apparent. And again --- Keep in mind that I know nothing.

[Dave Bagwill]

I like that approach. Thanks.
I think you know something, though :-)

[ken cierp]

Thank you Dave.

Another tidbit --- a group experts/scientist/or what ever famously squashed Michael Kasha's bracing and bridge design theory by pointing out that there was no acoustic/sonic bass or treble side of the bridge or the sound board even though he attempted and asserted to have input a stereo signal by cutting the bridge in half.

[John Link]

As far as "theory" goes, I am influenced by Ervin Somogyi. That is, I suspect there is an ideal range of stiffness, both with and across the grain, that yields the most balanced bass/treble response. Too stiff and it moves treble, too loose and it moves bass. This range may also be relevant to maximal volume, because volume depends upon the mass of the soundboard being light by lowering mass for a given stiffness. Bracing (versus just making it solid) also leaves certain areas of the top more flexible and hence responsive than they would be if the top were thick enough to accomplish the stiffness "goal" without them.

The "ideal" that response should be balanced seems somewhat arbitrary to me, though not completely so. For instance, to my ear, 12 strings sound "better", i.e., like a 12 string, if the bias is towards treble. And bluegrass sounds better if using an instrument with a bias to bass. Yet, "acceptable" and even "consistent" seems to have a fairly broad range, given that factory guitars built to numerical thickness specs applied to a range of woods with differing natural stiffness characteristics, produce fairly "branded" sounds. That is, a Martin sounds more or less like a Martin, a Gibson like a Gibson, etc.

I have a top that I drastically over thinned. It is very, very floppy across the grain, cardboard like. I don't think I would ever use it for a real guitar, but want to go ahead and brace it to see what happens, maybe clamp it in a form to get an idea of how it taps out. Because it is ridiculously loose across the grain, ladder bracing seems like the best approach, perhaps not parallel to supply a little more support with the grain, but definitely something that addresses the gross problem. Ah, another project.

As far as I know, there is not much "scientific" evidence to support speculation about soundboard structure beyond the very general. The thing with the speaker cone analogy is that electricity, operating through the magnetic motor in the center, rather precisely controls the amplitude of movement in the rigid part of the cone, nor can we precisely control how far the top can move, as in the Xmax of a speaker design, nor can we have a surround that offers virtually no resistance to the movement of the top, and so on. The speaker cone, because of its geometry, is quite stiff compared to the motion found in the surround (the perimeter of a git) and the motor (the bridge). In a git, there is much less difference in compliance.

Sometimes I think that, unless the player is very, very good, the primary determinants of sound quality are intonation and playability. Even then, the player still makes the major difference. If you want your instrument to sound great, get a great player to play it.

So, speculation is fun, but leaves more questions than it answers. I suppose that is why I wind up going along one of the traditional routes, as opposed to something radical, like Kasha, or even Falcate and lattice, which are less radical. There must be reasons the two major systems of bracing (ladder and X) are dominant.