Acoustic Guitar Construction

Not sure this is the exact place for this discussion but as good as any I guess.

A comment on another forum got me to thinking how the different combo radii on tops and backs may effect sound, and such.

LMI has 2 combinations of sanding braces; 25 top/15 back and 30 top and 12 back. So in this combo as the top flattens the back has more curve.

I was taught to build with 25 top/12 back and feel my guitars come out sounding real nice. What combos do others use and do you use different combos for different sized guitars? Different combos to achieve a desired dome to get the "correct" bridge height? Get the picture?

R.Taylor uses "flat" or 65' for the sound-board and for the back braces 12', but the rim is contoured to 15' -- go figure.

kencierp wrote:R.Taylor uses "flat" or 65' for the sound-board and for the back braces 12', but the rim is contoured to 15' -- go figure.

Top and Back of rim contoured to 15'?

Taylor sands the top edge of the rim flat -- don't forget they get the slope in the Neck heel/finger-board extension by machining it in the big mortise cut out of the body. Sanding the top edge of the rim flat with a slope is the standard convension -- no bevel. Huss and Dalton offers both -- the claim is the bevel adds treble response (I suppose a space alien or dog could hear that difference?) John Greven, Preston Thompson, Wayne Henderson to name a few of the top vintage replicators sand flat with a slope. I have not varified but I understand that Wayne Henderson does not even have a radius dish in his shop.

kencierp wrote:Taylor sands the top edge of the rim flat -- don't forget they get the slope in the Neck heel/finger-board extension by machining it in the big mortise cut out of the body. Sanding the top edge of the rim flat with a slope is the standard convension -- no bevel. Huss and Dalton offers both -- the claim is the bevel adds treble response (I suppose a space alien or dog could hear that difference?) John Greven, Preston Thompson, Wayne Henderson to name a few of the top vintage replicators sand flat with a slope. I have not varified but I understand that Wayne Henderson does not even have a radius dish in his shop.

So, what's to stop us from sanding the tops and backs flat (the top with a slope) and then
just radiusing the X braces and the back braces? Wouldn't that work just as well?

You really do want a contour/bevel on the back edge of the rim --- the back is actually a slice off a 15' (12' or 20') sphere. The braces do the most forming width wise and the rim length wise. Now keep in mind that the dome formed is actually adding strength to the back -- you know, the arching principle. While the arch/dome is the wrong way and does not add strength to the soundboard since the strings are pulling upward it -- it is in the correct orientation to help prevent crushing the back inboard.

Gotcha! Sounds good....