Does anyone have a theory as to why an air-everything turntable with vinyl record vacuum hold-down sounds better with a record clamp?
my guess.
part of optimal stylus-groove behavior is controlling resonance without over-damping. records 'like' to be loaded, but 'clamping' removes a degree of 'life'. whether using a screw down clamp, or vacuum hold down there is gripping pressure exerted on the record that has a cost in degrees of energy lost and an element of smearing while also lowering noise to some degree and flattening too. somehow the proper weight seems to get closer to the ideal than clamping/vacuum.....
IMHO, YMMV, and my 2 cents.
combining the weight with vacuum I think reduces the smearing to some small degree.....stops an element of resonance.....without more life-robbing gripping action....for a net gain. not to say it might be a higher net gain without the vacuum.
another way I view it.....is.....imagine a record surface as a passive spring. I think there is an ideal perfect weight, density of that weight, and surface interface with the label surface that together ideally 'load' that spring to give it maximum life and minimal resonance. brute force vacuum or clamping bypasses that ideal.
I do think that platter material does influence how a record weight works. as it's part of the equation of loading.
i'm not a techie and certainly no engineer. these are just SWAG's based on years of observation and hearing the Rockport Sirius III with vacuum hold-down and other turntables with various clamps and weights, and finally observing the development of the Durand Record Weight. I know how my records sound with and without the Durand. and i'm guessing a few other record weights do similar if not even better things.