A few years a go Rick Turner and Steve Rabe (SWR amps) did a similar experiment where they hooked guitar up to a low frequency transducer. They reported similar effects. Interesting. They patented the proces, or the device, but I don't think it ever went anywhere
http://www.acousticguitar.com/gear/a...ibration.shtml
I always assumed that the changes with age are the result of the wood changing character, not viibrations--in grad school I did a fair amount of remodeling work on old rowhouses in San Francisco--old as in 70 years or so. The wood in those houses was hard to work--it was really hard to drive a nail into it compared to new lumber. It could be because they used "old growth" timber, but I doubt it--those were rowhouses that were built after the SF earthquake, in a hurry. My house was built in 1949, a typical DC area postwar brick cape cod, built in a hurry to standard specs, and the floor joists are similarly harder to nail and drill than new timber, and I just can't believe they were using some kind of old growth lumber in 1949. My guess is that the resins in the wood age and grow harder and more brittle. But who knows? I'm not even convinced that old instruments always sound better. I've played plenty of expensive old guitars that sounded blah. But I've never played a really old bass.