A buddy of mine who's professional expertise includes mechanical vibration spectrum analysis and is also an experienced woodworker was asked by a friend to fix his violin. My buddy had absolutely no idea about how to do it, but he likes a challenge.

He downloaded a spectral plot of a Stradivarius from some web site and then compared the response to the violin he'd been given to fix. He then poked and prodded until he found something amiss - he knew he'd found (and fixed) the problem when the two plots were very similar (some glue joint that had come loose, I think.)

Actually, there's not too much old Jim hasn't tried. If you're interested in how he fixed the violin (or how to carve stone, cast gold, design a 3500 HP pump, paint flowers or build a wooden canoe) I'm pretty sure he be delighted to tell you about it.