Interesting. A few months ago I asked Pindac to define "damping factor" as he applies it to materials used for plinth construction, especially slate, which he dislikes for reasons obvious in the above 2022 post. In the recent exchange he declined to provide the information that he did provide above. Perhaps he did not recall quoting that paragraph describing experiments done by an engineer. I have a dog in the fight, because I own three turntables housed in slate or slate and hardwood plinths. First, I would not argue that panzerholz and the like materials may be superior to slate; I have no way to argue that point, because I do not own a Panzerholz plinth. Albert Porter does or did own an SP10 MK3, like mine, in Panzerholz, and he at least used to sell plinths to others for SP10 Mk2 and Mk3. I have high regard for Albert, so I don’t doubt that P’holz is good.
My thoughts on the experimental results described above are that this may be a classic example of over-interpreting data. Like you said, Noromance, we don’t know much about the slate tile that was used in the experiment. And both of us (apparently) are using very thick (50mm for Lenco and Denon DP80 and 65mm for SP10 Mk3) and very heavy pieces of slate. The engineer says his version of "damping factor" is independent of dimension, but he needs to do an additional experiment to prove that point; I find it hard to believe at face value. In addition, "slate" from different sources is different in density and hardness; Pensylvania slate used by OMA and us is different from slate sourced on the Euro continent; I don't know where the engineer did his work. Another point is that slate is a layered form of stone, so its "damping factor" is likely to be quite different if measured in the plane parallel to the layers vs a plane perpendicular to the layers; this factor is not investigated. In a typical plinth, the layers of a piece of slate are likely oriented in the plane of the TT bearing, where the capacity to absorb vibrational energy is maximal. And finally, who goes around striking a plinth while an LP is in play? I will add one observation: This is completely subjective, but I felt that the SQ from my SP10 Mk3 was slightly enhanced, when I added a base to the slate, composed of solid cherrywood and firmly bolted up into the slate itself, to provide some constrained layer damping. Also, I use the idea I got from Albert, damping the Mk3 bearing housing from below by a heavy metal block. Meantime, my Lenco and DP80 sound wonderful in just plain old slate, the Lenco mounted in the PTP top plate I bought from Peter Reinders.
