Steve Courtwright asked:
"Alan, how about the chamber size of the instrument itself. "
Generally speaking a smaller box will tend to make a more 'treble balanced' guitar. There are a lot of reasons for this. For one thing, the lowest resonance that can actually produce much sound is the 'Helmholtz' air mode, and that will be higher on a smaller box unless the soundhole is really small. Making the soundhole smaller, of course, gives less power in that resonance, so either way you tend to lose it with a small box. Small plates are stiffer and higher pitched, all else equal. There's a lot that gets into it.
Wade S. asked:
"Say you have a back material that is not vary responsive and seems thud-like by its self, so you would say it has a high damping factor. SO, to help make this back a bit more responsive or have less damping factor, would you arch the braces a little more or maybe use an ex bracing system for this back as apposed to the conventional bracing? "
That's an interesting question, and I'm not sure of the answer. The difference in arch height between the usual sprung braced plate and a carved one is considerable. I don't think small differences in radius on low-arched plates will have much effect, but then, I've been wrong before.
gburghardt asked:
"Would sitka come after redwood and englemann for damping? "
Sitka seems to have a 'funny' damping characteristic. The folks who have done the most measurement, particularly Haines, say that most spruces have low damping at low frequencies, and that it rises as you go up. There is normally a 'dogleg' in the graph at about 2000 Hz, and it rises much faster at higher frequencies. Sitka seems to have _high_ damping at very low frequencies, and it actually falls off until you get to that 2 kHz point, where it's like other spruces, and rises after that in the same way. This is odd, and I've never seen a convincing explanation, so take this with a grain or two of salt.
K.O.
"Sorta makes me me contemplate carved back flattops. "
Yup. One of my students made one with a Sitka top and maple back that sounded great. It was based on an old Epi 'Recording' model 3, iirc, but bigger than the original.
Serge Poirier:
"Great idea on arching maple plates but what about sanding the interior of the box to finer grits, 600-800 for instance, would this help the box be more responsive and have less damping?"
Well, it might lower the damping of the air modes, but I've never seen real data on that. Then you have to think about how the air and wood work together. It gets complicated.
gburghardt again:
"One thing, that should also be taken into consideration is the length of string."
Lots more there than you might think. For one thing, longer strings with higher tension have higher impedance. They also tend to have more energy in the higher partials, and those partials tend to be closer to being harmonic. All of this tends to give them a 'brighter' or 'richer' sound.
It's enough to give you a headache, isn't it? ;)
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