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I have a few of different OM templates (LMI, Kenneth Michaels Guitars, and one from another source) and they all have the tone bars angled more toward the end block, compared to a set of Martin tracings that I got from John at Blues Creek. The LMI and KMG template have the bars perhaps 1/2 lower than the Martin tracings, but the other one is pretty significant, perhaps an inch to 1 1/4 inch. The spread on the X brace on the Martin tracings is also wider than any of the templates. The x brace is in close to the same location at the top, but wider apart at the bottom. Any thoughts what impact this would have on the sound of the guitar? I've been thinking of making a new template using the tracings from John, but thought I would ask about this first.

Hi Alan,

I'm not sure what you mean by "angled more toward the end block"
Are you referring to the angle of the X ?
I try for about 95 degree X angle.

According to a posting I read several years ago by Mario Proulx, and speaking about an OM , he said the intersection of the X should be 9 to 9 1/2 " from the 14th fret ;
a too far forward X intersection resulted in a muddy tone ;
a too far back X intersection can make the top very stiff.

It works for me,
jack

Actually, it's the tone bars that have been shifted toward the end block on the templates. The top of the tone bar touches the x brace in about the same location as the Martin tracing, but the bottom of the tone bar is shifted more toward the end block.

I would maybe say that they are "fanned out" a bit more in that particular drawing. From what I can gather, if you do fan them out a bit, there is less bracing in one concentrated spot inside the bass lower bout, which can be modified to meet your target sound. For a looser bass, maybe spread them out a bit. For a more focused and controlled low end, run them parallel.

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Thanks Matthew. They really aren't fanned out. They run parallel to each other, just at a different angle from the x brace than those on the Martin tracing.

Ask yourself, "What is the purpose of the face braces?"

Think about it a bit.

You'll know what to do.

the X brace design is the most copied bracing in history. CF Martin designed this in the 1800's. The X brace has evolved a bit over time . The best answer to your question is to build the plots and determine the one you like the best.
The X position , pre war - post war would be 9 inch pre 9 1/2 post war.Angles also were played with . Another thing is the shape of the braces. It isn't just the position. Martin uses 2 sizes 1/4 inch and 5/16 . Moving tone bars will effect tone. You can influence bass and balance.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

You lost me there...appreciate the reply, but I guess that I'm just a little dense. In reality, I suppose that I just asked one of those questions that didn't merit much of a reply.


John....thanks. I do realize that there have been differences over the years and that shifting the tone bars will impact the sound, but was just trying to understand how it might impact the sound. I have the tracings that I got from you and three different templates, all with different tone bar positions, one vastly different. I agree that building one with each position and comparing them would help, but since I can only do this in off hours after my paying job, that would take a very long time. I was hoping to get some guidance on how the position impacts the sound to help me determine which I wanted to try on the next build in order to compare it to those that I have already done. However, again, I do appreciate your response.

Braces that run across the grain add a lot of stiffness to the top in that direction. In theory, then, if you have a top that's floppy across the grain you could change the angle of the braces to make up for that.

The 'scientific' view is that the sound of the guitar is determined by the frequencies, areas, masses and losses of the different resonant modes of the structure and the air in the box. This is often called 'formant theory', since these modes 'form' the tone. Altering the bracing layout alters the relative pitches of the resonant modes, and changes the formants.

Knowing what happens in that sense doesn't always tell you how to get what you want, though. It's not as if we have a recipe that says you need a 'cross dipole' mode that's 15% higher in pitch than the 'main top' mode, with this much mass and so on. At this point in time there are just a few of us more 'left-brain' types gathering data on this sort of thing; we still need to get it all toghether and figure out what it means.

Some of the more traditional minded guys who have built a lot of guitars will have an idea of what heppens on their instruments when they move things around in certain ways. The problem is that, even if they are willing to tell you what it does, it might be hard for you to understand what they mean, since everybody describes these things a little differently. Also, what works for Mario, or for me, might not work the same way for you. In the end, you've got to work out your own salvation on this one.

Thanks Alan (THE Alan). I really appreciate your reply.

I realize that no one can say specifically what the result will be by shifting the tone bars toward the end block, but I was hoping for enough information to make a logical choice on which to use on the next build, rather than leaving it all to chance. Since there are quite a few experts here that have built hundreds of guitars, I was hoping that someone might share their thoughts, or even their speculation, on what the impact might be. After all, someone’s speculation based on their experience is a better starting point than total ignorance. In the end, I guess that this was just one of those questions that isn’t so easy to answer, so I’ll just pick one and give it a try.

By the way, I am in awe of what you do…not only making great guitars, but the scientific approach to how you do it. You’re a legend!

Alan

You might find Somogyi's "The Responsive Guitar" good reading.

Go with John Halls. My 2 cents.

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Formerly known as Adaboy.......

I find this interesting that everyone says that moving these braces will affect the tone but no one has answered the question, which was, what tonal difference will be created with the movement of the tone bars rotating clockwise towards the butt end of the guitar.

I also am interested in what this will do to the top of the guitar.

Fred

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Fred Tellier
http://www.fetellierguitars.com
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Fred Tellier wrote:
"I find this interesting that everyone says that moving these braces will affect the tone but no one has answered the question..."

I suspect that the main reason for that is that nobody knows for sure. You'd have to make a bunch of guitars that were pretty nearly 'identical', only varying that one thing, and analyse the sound statistically, to be able to say for sure that it does one thing or another. Naturally, the more closely you could control the parameters of the experiment, the fewer instruments you'd need to build.

In the extreme, you could 'build' a virtual guitar in a computer model, but these things are always limited in utility, given the processor power that's needed to take everything into account. And, of course, nobody would believe it no matter what the outcome, since it's not a 'real' guitar.

Either way, are you ready to do the experiment?

Fred...glad to hear that you were interested in the question. I was beginning to think that I had just asked a dumb question!

Mr. Carruth,

I suspect you're right - that no one knows for sure. So many variables; so few baselines.

But then what confuses me is that there are a number of luthiers who claim to be able to listen to the desires of a customer and then build a guitar to meet their tone description.

How can that be if something as basic as moving braces is a variable that is not understood?

The braces are just one aspect to it. I'd suggest reading the Somogyi book and you will get some insight on it too .

I suspect most of us just 'tweak' things a bit most of the time. After a while you do get a feel for how a given change will effect the sound, and, of course, those of us who take a more 'left brain' approach might have some numbers to go with that. Over time we've all worked out a design that gives us the sound we like, and will tend to make a lot of small changes that tend in the direction we are trying to go, rather than making one wholesale change. A small alteration in the angle of the tone bars might be one thing you'd do, but normally you would not make a big change because you'd be less sure about the outcome.

I think that voicing has a whole lot of other aspects to it, besides the placement of the tone bars .since most of us could only "request" a certain sound we have already experienced, usualy from factory guitars of another era. choice of woods, and body style, probably has alot more to do with " duplicating " a certain sound of a guitar .with subtle voicing alterations by tone bar placement , among a number if other things . Jody