Acoustic Guitar Construction

Hans - early on you posted something, and I wonder if you (or others here) still use the method:
Quote:
"PROCESS 2 -- Again following the suggestions of Gore/Gilet, I tap the bridge area of the open-back box and record the results with a microphone connected to a laptop running Audacity. I use the results to look for the frequency of the top resonance and then carve the fan braces and the lower X-braces and thin the top, particularly around the lower bout, to get the top resonance below 190 - 200 hz. "

Why try the broken X?

I do not tune with an open back as the back has a large effect on the tops resonance frequency. But I could see that it could be a valuable method. I would just have to work out how much the back when properly tuned would drop the tops resonance. With an Xbraced guitar I will work the braces until the tap sound is good for me and then tune the resonance after the box is strung up and I really know where the resonances are.

" I wonder if you (or others here) still use the method." I can't, of course, speak for others, but, for myself, no. I don't. I built up a new guitar shop in early 2018 and didn't duplicate jigs or continue processes that I didn't feel were contributing much to earlier results, no matter how rational they seemed. Testing/refining the open back box and using Edwinson bracing both failed to make the cut.

I've now built five guitars in the new shop -- and have not used instrumented tuning or Edwinson bracing (though one of them does have fan bracing inside the X of the lower bout). Four of the five, all with significantly different bracing patterns from one another, sound remarkably similar to one another and, as best I recall, similar to those that I built in the old shop using the now abandoned techniques. The fifth, built with lattice bracing, did not sound similar. (It's now been retopped.)

Thoughts regarding instrumented, open-back testing: putting the back on changes everything -- and then gluing on the bridge changes more. Adding the back changes the effective stiffness of the sides and neck and, as I use a live back, its coupling to the top moves the main resonance (and, likely, others) in ways that I'm not able to predict. I now tune the top thickness and the top bracing before attaching the sides, again before closing the box, and yet again after adding the bridge, by tapping on the bridge (or bridge area) and listening for what I consider a musical resonance. Not very scientific, but, I feel, more functional.

Thoughts on bracing patterns: within a wide range of X-braced alternatives, I'm not convinced that it makes a significant difference what pattern is used. Alan Carruth has written a number of papers and posts on the topic based on his observations including a number of instruments he's built with various brace patterns. My interpretation of his results suggests that, as long as the braced top is not too stiff and not too loose, the guitar will sound fine. That's consistent with my much-more-limited experience.

FWIW, this all suggests that a "thin" red cedar top should make a fine guitar -- with bracing that's sized compatible with the stiffness of the top.

"My interpretation of his results suggests that, as long as the braced top is not too stiff and not too loose, the guitar will sound fine."

I've come to believe that is totally true.

I think a 2.5 mm top can sound OK as a steel string if it is braced so that it has a nice tap. I do not think it needs any special or unique bracing scheme.

It would be just about right for a classical guitar, so maybe make a nylon string crossover. That is a no compromise situation.

I try different bracing schemes just because I can , though of course the X is safe, but imo a little boring, guitar after guitar. I will say that ladder-bracing is my go-to most of the time and I'm glad I tried it.
Not sure how I'm going to brace this one but it will be a variation on the X.
Thanks for the input.