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I'm building #3, and it's my own idea, design. I want to scallop the braces, and was watching the Obrian video on LMI about how he scallops his braces. He claims that the peaks of the braces should be 3" from the edge of the top, at the "node" location. The other guitar plans I've used, and the guitars I own, don't have the peaks 3" from the edge.

Is this just his way of doing it? Anyone ever hear the same thing? Can anyone recommend some other reading or videos on the subject of scalloped braces?

Thanks

Sean

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First things first - Why do you want to scallop the braces? If you understand that then maybe you will know where to put them.

BTW - I have never heard a reason to put peaks on braces that I understood. Maybe there is a good reason that I have not heard. I never put a peak on braces because I don't see a need or reason to have a sudden change in stiffness in the brace that these peaks create.

YMMV

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Sean : The high peak of the brace creates a node at that location. To me the important thing at the end of the brace is the gradual fall away so the edge of the sound board is allowed to move and not constrict the vibrations of the top. Don't get too up tight about that 3" dimension.The height of the brace at the lining is much more important.
Tom

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A person who has never made a mistake has never made anything!!!

I want to scallop them because some of the best guitars that I have heard and played have scalloped braces. From what I've read this effects the sound by allowing more movement, especially on the bass side. I just thought, that since other luthiers put peaks on their braces, or high points if you want to call them that, I would do the same. Just trying to learn here. Thanks.

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change isn't synonymous with improvement
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Thanks Tom, I will pay attention to that. I was planning on bringing them down to about 1/16" at the lining. I appreciate your advice.

Sean

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change isn't synonymous with improvement
instagram.com/bucketguitars/

I recommend Kent Everret and Al Carruth's DVD's on voicing guitars, although personally, I'm in the camp where I never want any abrupt changes in stiffness anywhere on the soundboard system (so scalloping is out); I use "fair curve" bracing (some call this parabolic bracing, but in reality, the curves are nowhere near true parabolae).

Dave F.

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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

I think many people (myself included) find that scalloping the main X near the bridge plate gives good 'thump'. Not too much though--leave at least 1/4" - 5/16" of brace height there. I leave 13/32", as 5/16" seemed muddy for my builds. And I think Somogyi's advice to keep the scalloping reasonable is good (the cube rule says even a little scallop drops the stiffness a lot).

If you scallop, you usually get peaks. In general, a peak won't create a node there -- node and anti-node locations are pretty consistent for guitar bodies. The node line of the 'main top' mode does happen to fall near the typical lower X peak, but that node line is due to the momentum balance between the top/sides/back. If a peak has reasonably gentle slopes (i.e., adding broad stiffness and not just mass at a point), it should increase the frequency of any mode that has an anti-node near it. The lower peaks on the main X are probably helpful to keep the cross-dipole frequency relatively high, but I don't know if there's any experimental evidence on that.

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David Malicky

I'm with Steve....meaning that I'm not big into scalloping braces.........but, there's all kinds of methods to arrive at good tone.................and there's also a bunch of different definitions of good tone.


With that said, find the nodes. Hold the top up by holding it on the unshaped X brace. Grab or pinch it from the top of the brace, to the outside of the top. Move the point you're holding it in and out while tapping, until you find the node. By holding it you'll be damping it, but if you're holding it at the node location it will magically ring, instead of being damped by you holding it. Mark that location, then go the the other leg. This location may move a little as you shape the braces, but it won't move much.

Disclaimer, I'm certainly not an expert, and I don't read books or watch DVD's. YMMV.

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Back in January of 2010 during a slow period, I posted a thread about voicing/bracing and the question of where the peaks end up came out. Check it out.

viewtopic.php?f=10101&t=25759

Couple great reply's from Al Carruth and Ervin Somogy that I found enlightening. Especially Ervin's post about the origins of scallops.

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Rob

David82282 makes a very good point about the location of the nodes on finished instruments....

The location of the node lines around the top have more to do with the inertia of the top and back/sides than anything else...

If you are the sort who likes to fool with Chladni patterns on your finished instruments - Putting the peaks close to those nodes certainly won't hurt....

And.. if you are building a fairly conventional design (Like say a Martin pattern) out of "Standard" materials - the blueprint peak locations are probably a fine starting point....

Thanks