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I'm trying to understand the effect of X-angle and placement on tone and punch, particularly for guitars with narrower waists. (I'm familiar with the forward-shift and 100 deg X technique for dreads).

The pic below shows 90 deg and 100 deg Xs with my current body profile (see other post), keeping the bridge-wing intersections constant.
- For the 100 deg X, I see that the upper legs tend to run into the waist. I know the waist stiffens/restricts the top, and I'd think the X running into it would restrict this area even more -- i.e., at 100 deg, the upper X anchors itself to narrowest part of the top. (Probably not as significant if the waist were wider.)
- The 90 deg X anchors to the UTB and runs about 2x inboard from the waist as the 100 deg X. So I'd think this would allow the top in this area to be activated more, and if it can move more, then the area below it could move more as well, etc.

The differences in the lower bout seem quite small? (only because I kept the bridge wing intersection constant.)

So for punch and volume, I would think the 90 deg X would be preferred of these two choices. Or is the soundboard around the upper X just not activated much, no matter what X angle is used?

I know conventional wisdom is to do forward shift + 100 deg X for those goals. But since those also move the bridge-intersection much wider, the 100 deg feature itself might not have been the key ingredient, per se?

I've also read X-angle affects lateral-longitudinal stiffness, which affects top modes and tone. Not sure how significant the effect would be for this case.

All feedback appreciated. Has anyone tried experiments with variable X angles?

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David Malicky

i like my X brace upper bout end to tie into the rim just below my upper transvers graft and have the upper arms of the Xbrace pass tangent to the sond hole at 1/4"-3/8" off set. this leads to a forward shiffted Xbrace. I use anything fro 85-95 degree inside splay depending on the body shape I am bracing. here is my bracing patterns for my SJ the splay on the double X pattern is 90 Degrees on the standard X pattern is 87 Degrees inside

A read of "The Responsive Guitar" by Ervin Somogyi will be a help to you with this.

Bump !! .
X-brace angle ! - what are you all using ? and why. why so few answers to this interesting question.

Probably because there is no short simple answer. It's like asking how do you voice a top. Somogyi wrote a 300 page book that can give you some idea of what might happen and why. But it's all part of the system. You might open up the X and slide it forward increasing the sweet area of the lower bout and you might get more bass and volume. But it also depends on all the other factors. At least that's my guess.

Does anyone experiment with this? Who doesn't, unless they are starting out and want to stick with a set of plans.

I think you have the right idea in treating the crossing of the bridge wings as the fixed point (or nearly so) and the anchor point in the upper bout as the variable.

I think you have the wrong idea if you are seeing the braces as a conduit for bringing movement to the upper bout. Spreading the X and bringing the upper anchor point of the arms closer to the waist gives the guitar a deeper sound and allows more top movement, mainly by making the central area below the bridge larger and more flexible.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I move my x up to get a deeper sounding bass. I think spreading out the x frees up flexability to a larger area in the lower bout. It's like moveing up to a bigger speaker in a cabinet or useing a larger drum head, same effect. Thinning the lower x brace on the bass side can help there too.

The X angle effects the pitch relationships between the monopole mode ('main top') and the two dipoles, ad that effects the tone. I just posted some more on this in the 'projecting/enveloping' thread, and don't want to repeat myself.

Good question. I am new to luthier and I would like to know what material, size, shape, and location of each brace affect the sound and volume. If nothing else, someone point to a link that talks about this in depth.
Good question.

Kevin

Braces don't work like that. Read the Somogyi book among others for a start. If it were that simple then we would all be making great sounding guitars. First off you need a target tone you are after.

Thanks for the helpful replies, all. Interesting reading and much to think about. I just received Somogyi's book and am starting into it.

Michael, Thanks for the pics of your SJs. With the somewhat narrower X angles and more vertical LFBs and fingers, how does this design usually come out for enveloping and projecting?

Howard, sounds like my question on experimenting wasn't specific enough... I was looking information on what people have found by varying the x-angle, especially while controlling other variables like bridge-wing intersection. I understand that braces aren't conduits. Thanks for your feedback on X-angles.

I'm not sure my initial post was very clear. Here's another try, again with the assumption that the Xs are pivoted about the bridge wings:
* 90 deg pattern: Mid-upper bout should be relatively loose since upper X legs travel well-inside waist. Lower bout should be slightly stiffer (than 100 deg) since lower X legs are slightly closer together.
* 100 deg pattern: Mid-upper bout should be fairly stiff since upper X-legs are anchored near the waist. Lower bout is slightly looser (than 90 deg).
So my main question is: For punch and volume, is the ~large change in mid-upper bout stiffness more or less important than the small change in lower bout stiffness? I'm guessing that isn't answerable, unless someone has tried a matched-pair experiment with fixed bridge-intersections; if not, maybe a question to think about.

That question applies most to the monopole mode, which I understand (from Alan's posts) is probably the main sound producer. Maybe an optimum for the monopole: use the 90 deg X to help the mid-upper bout, and simply shave more off the far ends of the lower X legs to keep the lower bout loose. I see the other modes are more complex, both because the mid-upper bout may not be that active (cross-dipole) and because their frequencies are affected by the longitudinal/lateral stiffness, and thus X-angle.

Thanks, Alan, for the ref to your other posts--very helpful. If a 90 deg X is used, how effective would it be to place the LFBs and fingers more horizontal, to restore lateral stiffness, so the dipole frequencies are similar to a 100 deg X? I'm guessing the X-angle dominates the long-lat stiffness balance, though?

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David Malicky

Mark Blanchard has built more guitars, and done more data mining on them than I have, and I have to agree with him when he says: "The top is the sound". It's sometimes dismaying to see how _little_ effect you can have with the bracing.

There are a lot of folks who will say with some assurance that altering the X angle by a certain amount will have a given result. I'm not that sure. When I think about what it would take to real data on this sort of thing my eyes sort of glaze over. Identical guitars are tough to make, and most of us will never make enough of one model to count as a statistically viable sample for the purposes of digging out these sorts of small differences, I think.

It would be a lot of fun to hijack, say, Taylor's plant for a few weeks, get in a crew to do some intensive wood testing, and then build a lot of dimensionally identical instruments with known wood. You could then alter the brace angles on the next batch and do it all again. Then, with the test crew working overtime, and a good statistics guy or three, you might get someplace.

IMO, to paraphrase Mark Blanchard, the lower bout is the sound. Or 90% of it. I've never worried about the mid-upper bout region, but maybe you are seeing something I didn't see.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I find that changeing the woods, braceing, and body size to be the main factors that control tone.Changeing the X angle is a nother design element that can manipulate the tone.Voiceing doesn't really do much to control tone.

Howard Klepper wrote:
"IMO, to paraphrase Mark Blanchard, the lower bout is the sound. Or 90% of it."

I tell my students that the upper edge of the top, at the neck block, is all about structure, and the lower edge, at the tail block, is all about sound, and it sort of shades from one to the other.

In Chladni tuning the braces above the bridge have very little effct on the mode shapes, and you spend a lot of time fine tuning the lower ends of the X baces and the tone bars, particularly the lower one in a normal Martin-style top.

Mark Groza wrote:
"Voiceing doesn't really do much to control tone."

I guess it depends on what you mean by 'tone'. I agree that, once you've decided on a body size and shape you have pretty much established the basic shape of the tone of the instrument. Wood choice shades it, but doesn't usually have enough pull to alter it in any basic way: a rosewood Dread and trhe mahogany one will both have more of a 'Dread' than a 'Jumbo' sound.

Voicing effects the quality of the tone rather than the character, IMO. A lot of the bass response has to do with how strongly the top and back work togehter, and I think of treble clarity and such as depending very much on the way the braces work with the top. Sometimes you can go from a 'bad' tone to a 'good' one with a few shavings off the right brace, but what's changed is not the basic character, but things like the balance, clarity, and eveness of the tone.

Anyway, that's my story and I'm sticking with it....

Wow, Kevin, that is a huge question. There are many great books and DVDs that can help you out there. Many of our forum sponsors have plans of different guitars which will answer your size, shape and placement questions. I can safely say that spruce is the most common brace material with almost any strong, lightweight wood being used by someone somewhere with success.

If and when you find out what each brace does, post it here and you will have lots of readers........

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It's not the miles ahead, it's the stone in your shoe


In Markham,Virginia

Kevin asked:
"I am new to luthier and I would like to know what material, size, shape, and location of each brace affect the sound and volume."

The question itself shows that you're new to this: it just doesn't work like that. There is no one brace that always controls, say, the response of the B string on the first five frets, or makes the whole guitar louder or more 'punchy'.

Several years ago I built a more or less' matched pair' of classical guitars, one with Brazilian rosewood B&S and the other with oak, to get an idea of the influence of the wood properties on the tone. It turned out that the back on the oak guitar was a fair amount heavier than the BRW back, although otherwise, in terms of 'tap tones' and so on, they were very similar. The tops were much more closely matched.

When I made measurements of how hard it was to drive the tops I got a bit of a surprise: it took more power to get the top on the oak guitar to a given amplitude than it did on the BRW one. This, despite the fact that the tops weighed the same, and had the same tap tones (and, therefore, very much the same stiffness). The only thing I could think of that could have been slowing it down was the heavier back. Basically, the top couldn't get moving unless it got the back moving: the two work together. How much more likely is it that the braces on the top have to work as a unit?

Thanks all -- very helpful replies. Yes, I'd like to think I was on to something, but I don't really know what it would amount to. It sounds like the gains of a loose mid-upper bout are likely to be small. But I'm curious enough that I'll go ahead with the 90 deg... might help, probably can't hurt.

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David Malicky

Well ask the some 30 members here that have built off my plans (OLF-SJ) but seriously the SJ projects nicely. It is by far my best seller the double X brace tends to tune brighter than the standard X but you can do a lot with it.