Polypropylene as a Turntable Base Material

La45,

Would you recommend bolting the subchassis directly to the PP Base, or suspending it above the base on springs? The motor will be isolated from the base in a separate mount.

As I stated above, I got the info in the second paragraph of the threadhead from the WWW, from the website of someone who uses PP materials to make boats quiet from stucture-borne vibrations. Here's the link:
http://www.nida-core.com/french/nidaprod_honeyinfo_rigid.htm
I agree that this is not proof of anything, but was looking for comments from others who may have experimented with PP in the past. Since one of the functions of a TT base is to isolate the stylus from structure-borne vibrations, I thought that maybe there was some relevance there.
As a Ph.D. scientist myself, I realize that there is a lot of bogus and misleading info on the web, that's why I'm reaching out to others who may have gone before.

I think what I'll do is use the PP as a base without cones, so that it just lays flat on the shelf, with the motor attached to it. Then I'll spike the subchassis (which contains the platter and tonearm) around the platter recess and simply lower it onto the top of the PP base so that the motor pulley is in the correct position relative to the platter, and the spikes are in position to drain away bearing and belt-borne vibrations before they get to the tonearm mounting. In this way, I won't need to worry about the PP warping or flowing (since its glass transition is below room temperature this may be a real issue). The PP should still perform it's function of damping structural vibrations in this layout.

Thom, first of all, thanks. That was one of the most useful responses I've ever gotten on a discussion board.
I don't know why this didn't strike me earlier, but a few years ago I was involved in some research with a major US National Lab centering around using both active and passive acoustic spectroscopy to determine changes in the texture of materials being heated inside a sealed steel pressure vessel. One of our biggest challenges was acoustic impedance matching, since that determined the degree of penetration of the sound waves (and we were exploring everything from audible to ultrasound) through the vessel, into the materials of interest, back through the vessel, and to our sensor unit. There is actually quite a body of research in this area - I'm going to go back through my notes and references now, since the light that just went on in my head is telling me that proper impedance matching is the key to properly draining vibrations from where they shouldn't be.
The sheet of aluminum you suggested is one way of coupling the dissimilar materials - I'm thinking that the use of specific acoustical coupling materials (think about the gels the techs use when giving you an ultrasound exam to couple the metal probe to your skin) may produce a much better effect.
Thanks for the inspiration - this should be fun!

For those who would like to explore acoustic impedance matching in the design of their systems, here are some very useful tables of acoustic properties (Z is the acoustic impedance). Remember, the farther apart the impedances, the more acoustical energy is reflected instead of transmitted at the interface. Have fun!

http://www.ondacorp.com/tecref_acoustictable.html

Thom,
My sanity has long ago been compromised, when I think I'm "on to something" I'm borderline OCD (OK full blown OCD). That's one of the traits that has made me pretty successful in science, to the exclusion of some other things - there's certainly no free lunch.
Anyway, I hold no pretenses that what I'm thinking about has never been done before (a quick USPTO.gov search should confirm that), but I'm having fun thinking about multi-layer designs to drain away what we generate despite our best efforts and block what we don't want intruding from the environment. What makes it interesting is that Z is not just Z, but Z(f), so depending upon what frequencies you are interested in, the answers may be quite different. For example, impedance matching is critical in ultrasound work, but subwoofers don't much care what they shake to bits.
When I settle on something, I'll share, unless something else captures my pathology first...