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I'm building my 7th guitar, and decided to put some more science into my building by using frequency content via fft using Strobosoft 2, and a PC tone generator to create the Chaladni patterns. The guitar is an OM made to Scott Antes plan layout, with lighter 1/4" x 5/8" spruce X-brace, a spruce top, and curly Narra back and sides. I can't call myself a guitar player right now, but I'm aiming this one at being a fingerstyle type guitar, with good tone clarity and even voice low to high.

Here's where I stand right now. The top's frequency response curve is shown in pic 1, and pic 2 show's the ring+ mode at 235hz. It doesn't close, but I didn't want to take it down any lower. I expect as I gain more experience (and finish watching Alan's DVD), I'll be able to do a better job of closing the ring at a bit higher frequency.

Pic 1- Top frequency response:



Pic 2- Top Ring+ at 235 hz:



Now I'm working on the back. The frequency response is shown in pic 3. I'm not sure which of the resonances around 300 is the Ring+. I think it's the one at 287hz. Pics 4 & 5 show the 287hz and 300hz resonances. Am I correct that the 287hz one is the ring+?

Second, if I want my back Ring+ mode about a semi-tone above the top Ring+ mode, since the top is at 235hz- A#, then should I tune the back to B, or 247hz, correct?

Pic 3- back frequency response:




Pic 4: back @ 287 hz:



Pic 5: back @ 300 hz:

_________________
Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

The main reason I didn't venture to get into back tuning on the video is that it's so hard to say anything for sure. When I talk about getting the 'main back' resonant mode a semitone higher than the 'main top' mode, thats' on the ASSEMBLED guitar. After you've made a few of a particular shape and sizer with a given back bracing scheme, you get to where you can more or less tell when it's going to end up at the right frequency relative to the top when it's assembled, but any change can throw you off.

Other than that: you've got some decent looking modes there. I often find it difficult to close the ring+ mode on tops with asymmetric bracing, which is one reason I went over the the double X pattern.