spring loaded platform non-suspended turntable

Since my place is old and I live on the second floor, isolation is a must. I'm certainly getting feedback through the floor, no music above 90db. I bought a stand from a research equiptment re-seller, it's made by Newport, not audio jewelry, but not horribly ugly either. I'm in No-Cal so such business are available in my vicinity. It's built to handle very heavy things. I'm going to go for the Minus K since it's free from the need of a compressor, and is made in the US. We will see.

In MY experience, non suspended turntables need a solid foundation to the center of the earth... Spring aids, ruin the sound.

I put my Rockport Capella II on a pneumatic anti-vibration table, similar to that under the Sirius III, and experienced considerable improvement in term of background blackness with no negative effect that I could hear.

My friend put his Technics SP10 MK2 on a Minus K and got similar improvement in background blackness, but I was not familiar with the system so couldn't tell whether there was any negative effect.

However, the Minus K is not self leveling, so if the CG of your TT is not exactly at the centre of the platform you need to add some weight and move it around the platform to level it.

Let's see, if you have an unsuspended turntable on a solid unsuspended base, the structureborne vibration can get right up into the turntable platter, the tonearm and the cartridge. That being the case, I would probably opt for some kind of vibration isolation system.

I believe a cheap experiment would be to put some sort of inner tube, perhaps from a motorcycle tire, under the table and inflate it till it "floats". That should let you know more for little $. I have a VPI Classic that sits on a very old VPI isolation base. It has a sandwich platform, metal outsides over wood, and four foam wrapped springs in the corner. That sits on a wood rack I made, and on a hardwood floor. I can make the arm skip if I step near too heavily, but there is no acoustic feedback.