Platter mat insanity

Looked at this critically last night. 
Notes:
1. The LP is not stable at all while perched on the strobe disk. Not that I don't know but as @slaw pointed out, the label recess is absent.
2. I ruled out any VTA issues for certain.
3. I removed all mats (10" EP and strobe disk) and tried 3 tiny 5mm high stone tiles between record and platter. Same result with previously noted improvements. (Music became slightly "harder" as the material suggests)
4. Rooting through the workshop, tried 3  tiny flathead brass bolts with screw heads on platter under the label, thread end up. This was quite stable and gave very good results. I am going to explore this path in more detail.

bdp24

... It was long ago established that an LP groove being traced by a phono cartridge stylus causes the vinyl to vibrate/resonate like crazy, especially if the vinyl is suspended in the air, with no surface below it to absorb and damp that vibration ...

Please tell us who you believe established this effect that you report as fact rather than theory.

David Fletcher, Marcel Riendeau, Peter Moncrieff, George Merrill, Austin Jackson. There are others, but that’s enough to get the sincerely interested started.

The record to platter interface is a critical design element in a turntable.

While it ranks behind bearing & speed accuracy in the hierarchy of things, it does make a difference and system tastes and interactions will definitely affect your preferences.

I liken the "free air" preferences to folks who prefer a little bit of reverb. There’s nothing wrong with it, but I’ve found this to be recording-specific - something I’m always wary of.

Strictly speaking, you’re trying to drain as much stylus chatter (noise) as possible from the LP, into the platter and the right mat help in this regard.

This is where matching the acoustical impedance comes into play. The closer the speed of sound of your platter surface matches that of an LP, the more absorption (and less reflection) you’ll have.

It’s the reason we like our carbon fiber top plates (and graphite before that). It’s also the reason we’re puzzled by preferences for acrylic over PVC in monolithic platter designs, because PVC is better behaved with respect to absorbing noise from the LP. It’s not as pretty as flame polished acrylic, and many folks buy with their eyes instead of their ears, but that’s a story for another day.

Cheers,
Thom @ Galibier Design

My search stopped with graphite. I use a 1" slab of graphite atop the platter, like Nottingham Analogue (Tom Fletcher design).

Does two things - couples to vinyl, and deadens the platter.