Polypropylene as a Turntable Base Material

You shouldn't have any problem with noise transfer through the polypro, but it will change shape and size with changes in temperature and relative humidity. It also has a tendency to warp. It is also difficult to cut or mill accurately because of this.

You can minimize the warp with additional curing. Check with manufacturer or extruder. This material will kick butt in the midrange-bass area with a huge soundstage.

Acrylic is a joke compared to it. Turntable manufacturers can't be bothered with the time/expense in machining the material plus the stability under temperature is its main weakness.

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.

PP seems like an intriguing possibility for a TT base material. But I have some questions/comments about a few of the statements in your threadhead. Maybe you don't know the answers any more than I do and are only repeating what this boat maker says, but...

What is a "natural harmonic", as inherent to a particular material? Maybe I'm ignorant, but this sounds like more of a metaphysical than scientific concept to me. Two objects made from the same material can have very different fundamental resonance frequencies, depending on their form and size.

Also, who defined the "problem hearing range" -- what does that mean, and why? The human ear is sensitive in the 1-3KHz range, but it's also very sensitive in the range occupied by the human speaking voice, which is lower.

And I don't understand the relevence of the point about lower frequencies "requiring" more energy to sound equally loud as higher frequencies. Concerning resonance, if playing a record produces energy at frequencies at which the TT resonates, then it seems to me that's what will happen, as dictated by the amplitude of the exciting frequency and the Q vs. damping of the resonant system. I guess that ideally nothing about the turntable would resonate within the audioband, but that isn't achievable, and for something the size and rigidity of a TT base, I don't think a fundamental resonance as low as 50Hz is possible. If you could do it, the main advantage it seems to me would be that the RIAA curve demphasizes lower frequencies cut on the record (and boosts higher ones), but I don't know how the curve actually intersects with the realistic range of resonances present in TT's.

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.