spring loaded platform non-suspended turntable

Consider for a moment that there are various vibration isolation designs. Of the mass on spring type, there can be vertical isolation, a combination of vertical and horizontal isolation and a combination of vertical, horizontal and rotational. There are three rotational directions of isolation - roll, rock and twist. No, I'm not talking about the Peppermint Twist. The definition of isolation in a particular direction is the ease of motion in that direction, thus good isolation in the horizontal direction would be characterized by being able to push the component easily in the horizontal directions. For turntables, which exhibit high rotational forces around the vertical axis, especially when heavy platters are involved, I suspect that isolation in the direction around the vertical axis is not desired, since rotational forces produced by the rotating platter would put the isolating system into oscillation, impacting the accuracy of the speed of the platter rotation. For that reason, I would constrain any isolation device so that only vertical and horizontal directions are addressed, keeping the rotational direction around the V axis stiff. If I'm not mistaken I believe that's exactly what Minus K did - constrain motion around the vertical axis by eliminating the isolation capability in that direction.

Excellent guidance, particularly from Pryso.
My 50 kg non-suspended soapstone plinth TT sits on 4 Audioquest sorbothane Big Feet, these act as shock absorbers.
This very heavy, in some extent suspended TT sits on plywood/aluminium plate that sits on 3 metal spikes to DIY metal rack filled with sand. The total weight of this system with all equipment on rack is more than 150 kg. Can´t be moved nor rocked by hand. This metal/sand stand has 4 spikes to floor.
I´m happy with the situation but I will replace the spiked plate with sandbox. I think this would make further progress. If I´m wrong please enlighten me.

While it's fairly accurate that heavy rigid support structures cannot be "moved or rocked by hand," the problem arises in the way seismic vibrations manifest themselves - by moving the entire building, not only up and down and side to side but also in the rotational directions. Hel-loo! For this reason even very rigid and heavy support systems can be easily moved by the seismic type vibration. As I mentioned earlier the effectiveness of isolation is actually a function of the ease with which the component can be moved in the direction of interest. Counterintuitive, eh?

Hello

I have installed the Minus K, it works just as advertised, no feedback which
has allowed an enormous amount in detail and image solidity to be
retrieved.

The process is a little jarring at first, my turntable is so heavy I needed to
move
it in pieces, then reassemble, it's not weighted evenly so I need to use
ballast to get the weight distribution correctly set-up.

I must admit, it's weird having such a heavy object virtually floating, it
reminds me of the film Gravity, I push it and it just a bit and it moves, then
returns exactly where it was. On start-up, the TT turns as the torque sets it
in motion, and then returns to it's place.

I can jump up and down next to it and it is completely impervious.

I am using a Newport stand made for scientific experiments. The legs frame
are made from extruded aluminum, hollow but extremely rigid due to the
form and how it all attaches. I bought it at a wholesale company which
specializes in medical and scientific equipment re-sale after companies
change gear, kinda like us actually.

Will need to continue the evaluation process but for now, I think it works
very well, haven't found any downsides.

C

Congratulations Crubio. I'm sure you will realize the benefit of isolation. On another forum I saw a photograph of the Rockport Sirius III. Interestingly, it sits on a custom stand designed for Rockport manufactured by Newport or TMC for their scientific lab air isolation stands/platforms. The Rockport turntable has the air isolation pistons on top of the stand just below the turntable plinth as opposed to at the bottom under the stand where the isolation would be further away from the turntable and be required to carry a much heavier load.

This design should deal more effectively with airborne vibrations hitting the stand which are thus isolated from the turntable. If the whole stand were sitting on isolation, airborne vibrations hitting the stand would make their way into the turntable.