Effect of 'Tapering' Braces on Tap Tone?

[LHawes]

Curious what those with more experience know about the effect of tapering braces on tap tone and overall tone of the guitar? The obvious answer might be to taper them and note any difference but my ears may not be sensitive enough to really tell or may experience some placebo effect after doing so.

The current top and its bracing have a pretty nice tap tone and I'm pretty happy with it and yet I see hundreds of guitar top bracing with square topped braces that seem to sound fine. I believe the logic to tapering the tops of braces is to reduce weight while having minimal effect on the structure.

So what do/would you expect to hear after tapering the braces? Minimal and don't sweat it? Or enough of a difference to make the effort worth the time?

[Bruce Sexauer]

Braces are structural beams, and there is a “right” amount to handle the job for each of them. Some of us, and I am one, approach the issue as strictly structural, others worry about the pitch of the plate when tapped. Since it changes completely when glued to the rims, I don’t understand their concern. I work as though structure integrity (good joinery) and just the right amount of that structure is what counts.

Removing material from a plate or its braces lowers the the tap pitch, and it is easily heard by almost anyone, I imagine. While there are audible tonal differences between the different styles of bracing, it’s really about how much structure. IMO, of course.

[Fathand]

When you say tapering braces, are you talking about mid 1940s Martin style tapered bracing or are you talking about shaving scalloped bracing?

[LHawes]

Originally Posted by Fathand

When you say tapering braces, are you talking about mid 1940s Martin style tapered bracing or are you talking about shaving scalloped bracing?

Thank you for the reply and apologies for the confusing thread title but what I meant to ask was about tapering or the rounding the top of the braces instead of leaving them squared off, not the general taper towards the sound board edges. I've read that a 'parabolic' shape of the braces may be ideal but have seen many braces that are left square with fine sounding guitars.

[LHawes]

Originally Posted by Bruce Sexauer

Braces are structural beams, and there is a “right” amount to handle the job for each of them. Some of us, and I am one, approach the issue as strictly structural, others worry about the pitch of the plate when tapped. Since it changes completely when glued to the rims, I don’t understand their concern. I work as though structure integrity (good joinery) and just the right amount of that structure is what counts.

Removing material from a plate or its braces lowers the the tap pitch, and it is easily heard by almost anyone, I imagine. While there are audible tonal differences between the different styles of bracing, it’s really about how much structure. IMO, of course.

Thank you Bruce and I'm trying to wrap my head around your reply as I'm not the sharpest tool in the shed. If I understand your response is it accurate to say, through your experience that braces should/could be designed to handle the structural needs of the guitar no matter the 'tap tone' those braces might create? And through that same experience discovered that too little or too much structural strength within the bracing structure is what matters to the overall quality of sound the guitar might produce? Too little structure resulting in a weakened top and too much resulting in perhaps not enough movement?

And of course I've watched the obligatory Dana Bourgeois top voicing videos ( https://www.youtube.com/watch?v=bNchJIfT2O8 ) where he hand voices his tops, and most certainly doesn't ignore the structure but seems more focused on getting certain tones etc. through that voicing. And after re-watching I see that he seeks changes in the tap tone through the 'tapering' I was trying to describe which basically answers my question.

Also brings up another question that probably requires a new topic or a forum search as to how many builder here use a tap tone method or are more focused on structural considerations, or both?

Thank you again for taking your time to reply.

[redir]

Rounding off the braces will reduce weight, a bit, while retaining full strength. It's traditional too.

[Alan Carruth]

I've been told that the weight difference between using, say, a triangular brace section, and one that is rectangular but rounded off on top, is minimal so long as you've worked them to the same stiffness. The triangular one might be a bit taller, but I suspect that's about it.

Since it's most likely impossible to make 'matched' guitars that sound the same in blind tests (I've tried!) making any definitive pronouncements on such variations is speculative at best, when it's not BS. There's simply no way, short of a major study involving a couple of hundred instruments and using nearly insane quality control, to get anywhere near an answer, and I suspect it would come up with a non-significant difference ("bigger study needed"). Who's interested enough to pay for this? That's the basic reason we spend so much time on line debating this stuff.

[Bruce Sexauer]

When doing research, particularly in the internet, it is possible to find pictures and and opinions that support just about anything. Combined with the “fact” that just about any style of guitar concept works adequately, at least for a while, it can be difficult to sort the wheat from the chaff.

Many/most builders start out copying something something they’ve run into, and it takes a good many guitars before any clarity comes along, and even then many builders aren’t able or willing to rise to mastery, preferring to stick with the comfort of the middle path. There’s nothing wrong with that, but it does not lead to greatness.

The traditional acoustic guitar, as a system, has not fully evolved despite its long time popularity in our society. I do not mean to include radical departures like Taylor’s new bracing system or the Ryan (in my opinion) inspired system Martin just released, but mean the more conservative ladder and X systems we all know.

When I look at pictures of guitar bracing, I see two things that seem overwhelmingly obvious to me. One is that many peoples system are grossly over-braced. The other is that the distribution of the top braces is unnecessarily uneven.

The first means not only unnecessary structure, but also weight (enertial energy) which is a big deal in a limited energy system driven by a guitar string. As an example: why do so many builders put a large scallop peak in the first tonebar right below the bridge? The bridge itself is doing more that needed to stiffen the top in that location. There are many of these poorly thought through aspects in popular guitar design, just waiting to be addressed.

The second issue, distribution, often leaves unevenly sized areas of the top brace free, begging for those areas to vibrate at specific frequencies, introducing uneven response, something we often call “wolf tones”. This is less of an issue when top thickness is large, but as we thin the top to where great response is possible, shiftIng structural tasks to the braces, their distribution becomes paramount.

So, brace shape and tapered or straight are the tip of an iceberg, and there are many solutions, all of which work, kind of. Adequate structure and minimum weight are the normal goals, and looking at cost conscious factory bracing systems probably won’t get you the answers you seek.

IMO, of course. There are pictures of my work in my ongoing blog-thread in the AGF Custom Shop which illustrate my current thing, if you are interested.

[LHawes]

Thank you so much for sharing your wisdom and expertise re: guitar building! Very insightful and helpful. Am very interested in following your blog post in the custom shop forum but can't seem to locate such an animal. Would you be so kind as to share a link to same? Thank you again.

[BlueBowman]

Here ya go: https://www.acousticguitarforum.com/...=679724&page=4

[Howard Klepper]

Keeping it just to the OP's question as clarified:

The stiffness of a beam is directly proportional to its width, but is proportional to the cube of its height. So clearly a taller, thinner brace can get the same stiffness as a lower, wider brace at a fraction of the weight.

The width of the brace where it joins the top does, however, affect how securely it glues. A great majority of builders don't take the width of the glue surface any thinner than 1/4". And some abide by Martin's 1930's "Golden Age" width, which is nominally 5/16" (but really often a little thinner). I aim about midway between those two fractions--around .285+/-".

To both assure good gluing, and at the same time take advantage of the cube of the height rule for stiffness in order to keep weight down, builders taper braces from the bottom (glue edge) to the top. There are very few free lunches to be had in building a guitar, which is a quite well-developed instrument. But compared with leaving the sides of the brace orthogonal to the glue surface and their tops flat, tapering them from bottom to top is money for nothing--a no brainer.

The exact shape is not critical, but the taper should begin as close to the glue surface as possible, or else there is unnecessary weight being left. Some people use a triangular shape, but IMO that loses so much width near the top that it loses part of the stiffness advantage that comes from height (most of the work in providing stiffness comes from the wood that is furthest from the center height of the brace). So IMO the ideal shape is a taper that begins as low (close to the top) as you can make it, and ends up rounded on top. The cross-section will resemble a parabola, but 99.9% (or more) of the "parabolic" talk you hear is just an attempt to make something done by intuition sound as if it has been done with analytic geometrical precision. I have asked builders who purport to make this shape parabolic to say what is the quadratic equation for graphing their parabola. None has ever responded.

[Bruce Sexauer]

Although braces are often referred to as “parabolic”, it seems Hyperabola- bolic mIght be closer.

[LHawes]

Originally Posted by BlueBowman

Here ya go: https://www.acousticguitarforum.com/...=679724&page=4

THANK YOU!

[Bruce Sexauer]

The supplied link represents the last day or two of an ongoing 10 year plus build thread. Because this forum limits the number of posts in a given thread, the series of threads are mostly linked both directions from their 1st and near last posts. Occasionally, a moderator closes the thread before I put the forward link in, but that’s enthusiasm for you! There has been ongoing metamorphosis in my concept over that period, but it is subtle. I arrived at something resembling my current thinking over 20 years ago, and have been building guitars professionally for 56 years. That means it took me several hundred instruments over a 36 year period to sort things out, not that I’m done growing.

[phavriluk]

Structural integrity is a necessity, and balancing tone to structure is an art. No easy answers.