Classical - 5 and 7 fan bracing.

[Bax Burgess]

What is the audible difference? Additionally, how does symmetric bracing compare to asymmetric bracing?

[charles Tauber]

Nobody knows for sure. There are too many variables at play to isolate one - such as 5 vs. 7 braces - to say this causes that. However, there are lots of theories and beliefs.

Brace height and width probably matter as much or more as the number of braces.

Ramirez, many years ago, introduced a slanted cross brace that created asymmetry with progressively shorter fan braces on one side. The theory was that it "tightened-up" the treble side of the top, though no one has proven that there is such a thing as a "treble side" and a "bass side", but it sounds nice/plausible.

Guitar design remains largely empirical - one tries "stuff" and sees how that works, or doesn't, for the one trying it. What works for one maker doesn't necessarily work for another, particularly with so many other variables, such as top thickness, variable thickness of top - thinner at the edges, thinner on the "treble side" than the "bass side", thicker in the upper bout ...

Think of it this way. Suppose there were 50 things that you could change about a single design. Each of those 50 things has numerous options or possibilities. One maker might use 30 of the same things as another maker, but the other 20 that are different results in a different sounding instrument. Attempting to state that one of those 20 different things is the reason that the first maker's guitar sounds like this and the other maker's guitar sounds like that is mostly conjecture.

[Bruce Sexauer]

Assuming there is a perfect degree of structure for supporting the tension of the strings and yet offering ideal response etc., this structure is part top and part braces. More top means Less brace, more brace allows (demands) more top. If the structure is in the top, the frequency of the braces (number) can be less because the top is better able to bridge the gap between the braces, and then on the other hand, more braces are required if the top is thin, but they do not have to be as robust. It has been shown that the more the structure is carried in the top, the more the necessary assembly weighs.

THEREFORE: Assuming perfect structure, a 5 brace top would have less quick response, more sustain, and a satisfying but less open tone.

CAVEAT: No two makers are likely to fully agree about “perfect structure”, thus the assumption is not valid.

[Bax Burgess]

Now with the properties of carbon and glass fiber, will there be clarity, predictable measurables?

[Alan Carruth]

It all depends on how it's done.

In theory you could make a top thick enough to stand up to bridge torque with no braces. A braceless top actually vibrates in much the same way as one with bracing, just at different frequencies. If the torque was kept low enough (the strings are really close to the top, like a couple of mm)you might not need to make the top all that thick. Good luck playing it.

Because they're (relatively) taller and narrow braces add stiffness faster than they add mass. That's why we use them; to make the top stiff enough without making it too heavy. In terms of stiffness you could get what you want from one big one right in the middle and be done with it. The problem there is that it's a big lump, both of mass and stiffness. It would make a top that didn't vibrate smoothly. Remember, you're trying for something that works like a a top with no bracing, but with less weight.

To get the top to work that way we distribute braces around in different arrangements. There is a wide variety of brace patterns in use in classical guitars; 'way more than you'd think from such a 'conservative' bunch. Every pattern establishes a different pattern of mass and stiffness in the top, and thus alters the way the top vibrates and produces sound. For example, many Flamenco guitars use braces that are the same as those in classicals, but they leave out the two outer ones. This makes the 'wings' of the top more flexible, and is one element in the 'punchy' sound. They get away with less bracing and a thinner top by lowering the string height at the bridge. This is not simply a function of having fewer braces, but rather of the way the brace stiffness is distributed.

Putting more braces of the same size closer together adds more stiffness and reduces the load that the top itself carries, as Bruce points out. The reducto ad absurdum of this is the 'lattice' top, where the load is taken by a grid of bracing and the top itself is simply a membrane in between them to move air.

As Charles says, with all the variables involved it might be impossible to demonstrate a consistent effect from something like a simple change in brace count, so long as the overall amount of wood in the braces stays more or less the same(more braces = narrower and closer together with the same height). OTOH, the brace pattern and profiling is one of the things that establishes a makers 'tone', even though it's only one of many co-dependent variables. The 'right' value for any one of those variables depends to some extent on what all of the others are. With each new piece of wood you're starting from scratch.

[Bax Burgess]

I couldn't be more satisfied/appreciative of/with these replies. Three explanations, differing in style, in concert.