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The problem with slides is that they are so short: the frequency of the lowest bar mode would be very high. In some cases the damping factor might vary with frequency (that seems to be true of wood), so we'd want our test to be working in a 'normal' range.
Damping is pretty easy to measure if you have the right equipment. Things with low damping only resonate at the exact 'right' frequency, while things with high damping can be driven almst as easily far off resonance as they can at the 'correct' pitch. That's one reason why the 'tap tone' of a low damping material, like glass or Brazilian rosewood, has a definite pitch, while high damping stuff, like styrofoam just makes a sort of 'thud' that doesn't convey as much of a sense of a particular tone. Things with high damping also don't 'ring' as long as things with low damping, so that gives you another way of measuring it.
The way I do it is to get a little bar of the material in question and stick a tiny piece of iron on to one end to act as an armature. I have a rig twith two threads that can be moved around to support the bar at the stationary points when it's vibrating, which are usually about 1/5 of the way in from the ends. There's a coil that I can plug into my signal generator at one end, with a magnet under it, and this pushes the armature (it's just like an electric guitar pickup only backwards; making a motor out of something that we normally see as a generator). I 'listen' to the strip with a dB meter, tune the singnal generator to find the peak frequency of the vibration, and the points on either side where it's 3 dB down. At these frequencies it has half the energy of vibration for the same drive force. The difference in frequency between these 3 dB down points above and below resonance is the 'half power band width', and the Q value is just the peak resonance frequency over that band width.
There's another way to do this called 'Log decrement', but I've never used it. I'll have to look it up, because it may be even easier to do than the strip tests I've used if all you want is the Q value.
This sounds like an interesting test, but right now I'm falling behind on orders, owing in part to a couple of other 'science fair projects' that I've been working on. These things always look easy until you get started, and then, of course, you're caught. The project I did on string forces 'should' have taken a week: I started on it six months ago and there are still some things to clear up.
This would be a great addition to Tim's article, although I could understand it if he doesn't want to dive back in at this point. If I can help out with advice and such I'd be happy to do so, but I'm reluctant to commit to anything more at this time.
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