Tim, I saw that post several months ago. The guy is somewhat of an engineer and seems to know a lot more about materials science than I do, but his conclusions don't remotely compare to my personal experience, certainly as regards MDF vs slate. In fact, it could be said that his results are proven wrong per se by anyone who has listened to plinths made of these two materials using the same turntable chassis. MDF sucks for direct-drive, IME. I owned a Jean Nantais Lenco plinth made of alternating layers of MDF and baltic birch which was excellent but not as neutral as my slate Lenco. His work did make me more curious about Panzerholz, however,which fared very well. The relationship of his test results to goodness of a plinth material could be a case of "True, True, Unrelated". Remember that choice from College Board tests?
I argued the issue with the poster. For example, I pointed out to him that the result one gets using his technique might be dependent on the orientation of the slate (parallel vs perpendicular to the layered structure) with respect to the vector direction of the stimulus and the placement of the measuring gear, but he insisted it would make no difference without offering proof. I notice that slate is kind of ring-y if struck with force perpendicular to the layers (I.e., top surface of any of my plinths) but is dead as dead can be when struck by a force parallel to its layering. Then there is the whole question of whether the results of striking any material are relevant at all to how it may perform in this application.