Acoustic Guitar Construction

Elsewhere I've seen mention of someone making his top 'x' thick if it's 'forward braced' and 'y' thick if it's 'rear braced'. I dunno what that means and it seems to be important to the builders who speak of it. I'd love for someone to try to explain this to me. Thanks very much.

I have heard of forward shifted and standard. These refer to Martin guitar specs. At some point in time Martin pushed their braces back from the sound hole. I suppose to make the guitar stronger. So forward shifted braces follow the earlier spec and move the X Brace closer to the sound hole. Some like the sound better. I make all of my Martin braced guitars forward shifted. I like that sound. But all of my guitars have light strings on them.

Changing the thickness of the top based on braces seems weird to me. The stiffness of the wood used for the top should play more of a factor in plate thickness than the location of the X brace.

Generally speaking something that is fairly common within our craft – we read stuff like “I make my “X” lower leg lower bout braces thicker than the upper bout ends” one should take that with a grain of salt, if that statement is not followed by “because that does such and such” you can pretty much bet it’s a bunch of BS.

As John mentioned the placement of the “X” intersection in relationship to the saddle is thought to have an affect on volume and tone. Moving that intersection closer to the sound hole weakens the sound-board since the tension of the strings is now farther away from the lower legs of the “X” – this allows the bridge to rock forward with less resistance thus making the top more sensitive. The down side is that the area between the bridge plate and the “X” intersection will have a tendency to collapse over time, especially if the humidity is not controlled properly. So it seems Martin and others (do to warranty issues?) moved the intersection back toward the bridge in a stronger position to help prevent the concave belly situation.

Now to the idea presented (thicker lb legs) – my thought is that this design was/is an effort to have the best of both worlds by making the lower “X” legs heftier perhaps the hope is that long term effects of bridge roll can be prevented – I doubt that would work since the weakened area (between the “X” and bridge) is still getting the same amount of support.

Folks, thanks for the explanations and comments.