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I have been wondering about the forward shifted X-brace and when you would want to do it...

It might not be appropriate a times... perhaps with redwood or cedar top? ...perhaps not with a 12 fret design?

What are your thoughts on when to shift the X-brace forward? ...and when not to...?

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Steve, this is the guideline I go by to determine the x-brace location effect. Add that to the other parameters of your build to give an "idea" of what the tone tendency will be (others may not agree with the below).

Forward Shifted – 1” from edge of sound hole, allows for more bass

Standard – 1 ½” from sound hole edge, even tempered

Rear Shifted – 1 ¾” from sound hole edge, more focused, treble and mid heavy, can be driven harder

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"I've been had again"
Tim Benware
Creedmoor, NC

Steve, here's link to an article on the Stew Mac site about this very topic.
http://www.stewmac.com/How-To/Online_Resources/Building_Instruments/Banjo_Killer_The_scoop_on_forward_X_bracing_for_greater_guitar_volume_.html

Ken

I used the layout for the one and only dread I've built. Turned out very nice. I liked it enough to use pretty much the same bracing layout for a 16" lower bout that I call a concert model. I haven't, but would use it for other top woods. I can't see a disadvantage but I am far from an expert on such matters. I would be interested to hear what others say.

I was thinking that maybe a 12 fret already moves the position of the bridge into the center of the lower bout and the forward shifted X might be too much... A stiff spruce top could bennefit from the forward shift, but maybe cedar or redwood could perhaps loose definition. ...just thinking (maybe too hard...).

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

No, I think that's pretty much it.

I do think it is more logical to think of forward shift in terms of the X position relative to the bridge, rather than the sound hole. Relative to the soundhole is the traditional way to describe it, but only works for traditional shapes. It doesn't really define the structural relationships.

The way I see it: the X arms crossing the upper corners of the bridge and exiting the sides is forward shifted, X arms exiting across the lower corners of the bridge is standard, and X arms crossing the back of the bridge is rear shifted.

Not true. The bridge and the bracing move together.
The original Martin 12-fret designs were all forward-X. AFAIK, all 12-fret Martins made since then have been that way.
The original 12-fret dreadnought designs and the older smaller bodies had 19-fret fingerboards, which means that the soundhole is further from the bridge. In that case, forward-X means the X-crossing is more than 1" from the soundhole. As Greg pointed out, the important thing is the relationship between the bridge and the X-braces.

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John

Interesting. I have a different thread going because I mistakenly place my x brace for 24.75" scale length on a guitar which I meant to use 25.34". This resulted in what you are describing as a forward-shifted X, which should be fine. Except this Sitka top is not very stiff, and I had to make it a bit more thin than I might have because of some deeper scratches that had to be sanded out. As I read this thread, it looks like you're saying that a less stiff top would benefit from NOT being forward shifted. Though it isn't too much difference and would still likely be mostly forward..or at best, standard….maybe I should just make this one a 24.75" to compensate a little.
Does anyone have much of a feel for how much of a tonal effect forward shifting might have on a less stiff top? Also, I did beef up the height of the braces by about 1-2 mm at the X and transverse brace. Thanks, Beth

Hi Beth,
If you follow the link Ken posted, you will notice that the diagram shows the tone bars below the bridge to be closer to perpendicular to the centerline. This helps stiffen the soundboard.
Some folks will add a tone bar directly below the bridge plate running parallel to the bridge if they feel the finished guitar top is too weak in that area. This also helps keep the top from deforming and bridges from lifting.

Also bear in mind that, for Martins, the difference in bridge locations between 12- and 14-fret guitars is minimal in most cases, and somewhat mythical, since the upper bout is flattened on the 14-fret bodies, with the exception of the Norman Blake models. On Gibsons, it's not so clear-cut. This cobbled together image, using grabs from the old Martin web site, shows it pretty well, I think.



Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

In my experience with 12 fretters, this composite photo of Pat's says it all. The box is chopped at the top and the lost area added at the bottom.