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#16
12-31-2012, 12:45 PM
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thank you!
Murray 
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#17
12-31-2012, 01:12 PM
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I had the pleasure of being a student of Al Carruth and his knowledge of properly tuning a top and back in truly mind boggling. He has perfected the method for achieving the best tonal qualities from wood that I know of. The biggest problem I found was finding a variable tone generator that works well enough to be used for this purpose. They aren't cheap. I tried downloading some cheap software that does alright, but nothing like Al's custom signal generator that he had built for him.
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#18
01-01-2013, 01:30 PM
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One problem with tapping a bunch of guitars in a store (aside from the gorilla they send around to evict you for denting things!) is that what you hear is most likely the 'main air' resonance. Usually that's down around G on the low E string, but it can range all the way from F or F# to A or a bit higher. The low tone of the 'air' resonance masks the sound of the top or back. To hear those, you need to plug the soundhole as you tap. Usually the 'top resonance will be something like an octave higher than the 'air'; so somewhere near the open G string pitch. The back can be anywhere from a little lower in pitch than the top to as much as a fifth higher; so, maybe F or F# to D or thereabouts.
The scholars who have looked carefully at this aver that the exact pitches of the lower order modes (the 'air', 'top' and 'back') don't make much difference in the overall sound of the guitar, but do effect the sound of note close to those pitches. I'm not sure I agree; I tend to find guitars with relatively high 'air' pitches sound 'forward' or 'bright' to me, and there are a few other things that seem to change the overall timbre. Still, it's a problem: it's hard to get information on the higher order resonances, but those seem to be the most important in the sound. You have to get a pretty bad guitar to see a 'main air' or 'main top' resonance that is very far from the 'normal' range, but there are guitars that are perfectly 'normal' that sound much better than others. Those main resonances don't predict as much as you'd like.
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