Best rack for non-suspension turntable?

I agree with Sdlevene... to a certain point. His comment is 100% true with regards to a spring system... if you use a spring or isolation material that bounces, particularly in few attachment points. If you use layers that are NOT springs and do not inherently contain bounce, then the opposite is true. A sheet of "insert your favorite material here" will have a lower resonance if adhesion covers most of the surface of which the isolating material and second sheet is affixed. This can be seen in thousands of examples of lowering resonance frequencies by attaching more mass. If two thin rigid substrates are held by springs... then both the upper and lower substrate will resonate at different frequencies AND be subject to bounce. However; if you glue the flat sides together covering enough surface area to couple to a different rubberized mass, the combination yields a MUCH lower resonance. A telephone pole has a lower resonance buried in the ground... a cheap plastic emblem glued to a brick wall has a lowered resonance, solidly glue a glass ball to your knee and the resulting resonance is lower :) Any material if affixed to more mass will lower it's resonant frequency. This is why the Symposium reference platforms are so amusing in interesting claims... they "de"couple using foam board which defeats the purpose entirely. They "de"couple the stainless steel layered masses with foam board, which is light and rigid... BUT light and rigid makes it into a great transducer. This gives a lowered resonance at very low frequencies, but actually amplifies high frequencies centered in sonic hearing. As an example NXT has made a mint attaching their products to this same foamboard/ gatorfoam material. Vibrations sent to a lightweight & rigid substrate WILL reproduce all the frequencies that it can given it's overall size and thickness. All transducers work this way. If your speaker cone had heavy mass, then it could not "vibrate" to reproduce the lower sound frequencies. The answer is properly decoupled mass like Audiav or advanced response servos like the Minus K... and the latter causes near field EMI... You don't have to believe me for this one, go buy an EMI/EMF meter to "see" for yourself how an active servo based solution actually induces undesired interference :)

The real answer: Neither is good for your application. Either way, they are both solid-to-solids and will carry vibration from the flooring and from/to other components. You should consider looking at different manufacturers, or possibly an on-shelf solution to actually make a difference.

Audiavreseller, I don't think the Minus K is a active isolator as it doesn't use electricity. I think it too is just springs done in an innovative manner. The Audiav clearly is just a rack. The only active isolator is the Halcyonics which I will attest to as exceptional.

Every material has a set of resonant frequencies (mode spectrum). I believe you may be referring to the boundary conditions that apply to the problem and this is why I qualified my comment with the phrase "All other things being equal, . . . ." The example of a partially buried telephone pole shows how boundary conditions affect resonance - one end of the pole is clamped, which shortens the effective length of the pole and raises the resonant frequency.

Layers of adhesive or semi-adhesive polymers like Sorbothane also have resonant behavior; the natural frequency depends on the size and shape of the layer. The product web site has data and a nice downloadable calculator to compute resonant frequencies for various applications. On looking into this, I was interested to learn that it's pretty difficult to get the material's resonant frequency much below 5 Hz in any real-world application, especially for thin layers covering large areas.

I'd also like to point out that the Minus-k products contain no servos; they are completely passive. The principle behind these products is to use a coupled spring-flexure system in which some of the springs are near their buckling points. This can create a negative-stiffness situation, hence "minus-k."

My misunderstanding with the Minus K... there are so many different racks out there; I may have been confused. I think someone had mentioned them being active as many of the active platforms that we have tested and even on my data sheet has been errantly marked active. I could have sworn the Minus K plugged in, leveled and even displayed when vibration was present. I think I like the Minus K much more since they are not an active servo system... what a nice intro they have with the wine glasses from a passive device! It is very hard to control very low resonant frequencies and will be the FIRST to say that ANY rack cannot dampen 100% of the spectrum especially at higher than miniscule velocities.