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I've started on my 4th guitar and really never understood proper bridge placement over the X-Brace, or if there really is a 'proper' to anything in guitar building. I've read an awful lot on the subject but translating that reading to actual practice sometimes has me stumped. I've attached a rough sketch of a small parlor guitar I'm building and wondered if the bridge is located properly. I've intentionally located the end of the bridge over the X and the finger braces under the bridge as well. Any comments criticisms welcome.

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Thanks Todd,

The bridge is located approx. 1/2 the 24.9" scale length from the 12th fret neck joint so I'm not sure how I'd alter that location. I have noticed that some parlor bridges will 'appear' lower on the lower bout but that must be a function of the overall body length below the bridge?

The '90 degree thing' is mostly a function of getting the X under the bridge so I'm not wed to that angle by any means. Is there an optimal angle for smaller guitars? Greater angle will move the X further from the bridge? Lesser moves it closer?

Does having the bridge land over the X-Brace an important factor?

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Todd is talking in relative terms. When he talks about the bridge being back, he means relative to the X. To be more precise, your X is moved forward.



Most (not all) plans position the X so that the back corner of the bridge sits on the brace. This is due to the rotational load on the bridge wanting to lift the back edge. If the back corners land on the brace, you get a little extra support to deal with that stress riser at the back corners. Otherwise you can get a deformation of the top at the back corners of the bridge.

As Todd points out though, you have tied everything together with the lateral brace behind the bridge and that should transfer the load pretty well.

There are structural and tonal implications and I'm only talking about structure.

For myself, I'd open up the X a bit and move it back so that the back corners of the bridge sit on the X but there lots of ways to make it work and yours is probably one of them, depending on the details.

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Thanks so much for the reply Kent, that really clarifies things. And thanks again Todd for the insights.

EDIT: The more I think about it I think I was imagining those forces on the bridge trying to rotate the bridge forward and therefore having the brace under the FRONT corner of the bridge to stop that forward rotation instead of the back corner to help stop the forward lift. Any logic in that thinking?

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Here's a pic of the design with a '100 degree thing' , 'X' shifted rearward and the bridge supported by the 'X' and the finger braces. Looks very stable structurally.

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On the UMGF forum there is a library of Martin guitar bracing photos done by putting a bright light in the guitars and shooting photos. The interesting part of this is the variation of where the bridges land on the X brace. Check it out
http://theunofficialmartinguitarforum.yuku.com/topic/847

Fred

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Fred Tellier
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Yes, the rotation also pushes down on the front edge but moving the bracing back helps support that better too.

I'm always reluctant to get too specific about bracing. There are too many variables. That said, I think your new drawing looks a little off to me. The upper legs of the X typically hit the sides farther above the waist. If it were me, I would close it back up a bit. Maybe something like this pic in the thread that Fred linked to. http://theunofficialmartinguitarforum.y ... NG-LIBRARY

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Thanks Fred,

25 pages wow. I got thru about 10 and saw just about everything I could imagine. There, as usual, doesn't seem to be a real norm or absolute so I'll go with my gut and have tried a couple of different combos but I think I like 96 degrees (for now ha) and the X shifted back just slightly from the original 90 degree design to catch the back corners of the bridge. I also like the idea of the finger braces catching the front corners of the bridge. But of course I have no idea which design I'll finally end up with.

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Good call Kent and I'll adjust accordingly and I know very well how subjective these bracing observations can be but I really appreciate the input. I hope that I have implied clearly enough that I really have no idea what I'm doing so all the help I can get is very much appreciated.

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Todd, I remember that beautiful little parlor that you just posted the sound clip/video of and will take your advice to heart, thank you very much for the help.

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I prefer the first drawing(the one at 90°). In the second, everything is shifted too far back, and I'm concerned with perhaps not having enough support forward of the waist, where it's nicely balanced in the first drawing. If you made the bridge just a wee tad longer(maybe as little as 1/8" to 1/4" longer), you'd have full support across the X braces, too.

What I question are the fan braces. Why do you wish to use this system? It's heavier and more complex than necessary. On such a small body, we easily get away with just one rear tone bar, and if you want a symmetrical system, keep the transverse brace behind the bridge plate, and add one more about 2" below that one. Or do a second, smaller and shorter "X" brace in place of the tone bars...

You can also make the bridge plate narrower, but you need to be positive about the bridge placement if you do so.

But if you went ahead with drawing #1 as it sits today, methinks you'd have a fine little guitar. Just keep everything light and 'free'.

Thanks so much for the reply. I see your point and very easy to make the bridge longer as it hasn't been built yet.



I cannot explain why I have a 'thing' for fan bracing and why I can't understand 'tone bars' they just don't make sense to me. And please remember I am very new to guitar building so i need to work though my version of errors and fumbles but for some reason I like the idea of the sound 'fanning' out along those braces from the bridge. That's my story etc. etc.



Excellent as I haven't gotten there yet either.



Light and Free, Light and Free!

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I like the first drawing better too. Just fan the X to 93 degrees or so and make your bridge longer. I've built a bunch of size 2's like that with about 6.7" bridges. They've held up well and people like them. It'll be interesting to see what the fan braces do to the sound.

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What fan braces do on a classical guitar is help bring out the treble response which is often the weakness of nylon strings. That's something a small steel string guitar doesn't need. Quite the opposite. With a small steel string guitar you want to help bring out the bass. So I would avoid fan braces unless they are very small. I'm with Grumpy on this, one well-placed tone bar and you're good to go on a small guitar.

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Thanks so much for the post and pictures Terence - worth a thousand words. This surprises me a bit but for the first time I can understand the potential tonal logic behind a 'tone bar' and if I am interpreting the purpose and the picture correctly that single tone bar opens the base side of the sound board and tightens the treble side in no uncertain terms. Warming up to the tone bar idea and I know it's been the staple of guitar building since the late 1800's but some part of me wants to try something different no matter the cost but in this case it may be a fool's game to try and re-invent the wheel.

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Thanks Ken. I have a fan braced steel string and I'd say it's quite treble heavy - always wondered why. I wonder if graduated fans (heavy on the treble side lighter on the base side) might have the same effect as a well place tone bar? Still in the design stages so anything can happen between here and the actual placement of braces.

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This has nothing to do with bracing, but if that line through the center of the saddle is your scale length line, the bridge needs to go back about 1/8".

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The bridge? Or bridge and saddle both back 1/8"? That's probably another topic about bridge/saddle placement re: scale length but very much appreciate the observation.

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I much prefer using fan braces behind the bridge to control the monopole/bass response rather than tone bars. Lots of ways to skin a cat and all that... I've had decent results with tone bars, and just awful results with a second X or a lateral brace below the X like a Larrivee, but 2 or 3 fans starting just below the bridge pin holes have always worked very well for me.

One downside to using fans is that over time they tend to telegraph through a light top. I wonder if that's part of why tone bars evolved to be what they are today.

Have you used fans on a smaller guitar as well?

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Depends on what you mean by 'small'... This is pretty typical; the body is right at 14" wide at the lower bout and about 18" tall. Like I said, there's lots of ways to skin a cat; my way is certainly not the only way but it works for me.

Actually, just the saddle. It needs to be behind your scale length line. You could, and probably should move both.
I just wanted to point that out, since you seem to be refining the bridge placement to the point that moving it 1/4" could be significant.

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That probably has more to do with the amount of clamping pressure and how it effects the cellular structure of the wood. One has to pay attention to clamping "just enough".

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I find this "print-through" more a function of the stiffness of the plate. So, for example, a fan brace aligned with the long grain of the top will print through much more than the same fan brace glued cross grain to the same top. A handy rule of thumb is to keep your braces at an angle of >15 degrees to the long grain direction, if you can, as this usually introduces enough extra stiffness to reduce the print-through by quite a lot. Not always possible of course, in which case wider, lower braces of the same stiffness help, if you can put up with the extra mass.

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I found Randy Muth's explanation of what he calls his XTC bracing system to be quite thought -provoking ...http://www.rsmuthguitars.com/XTC.php