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:
