Medical Isolation Platforms

Decided to open a discussion on Vibraplane, Halcyonics, Minus-K type tables. What are the merits of active vs passive and industrial vs medical? Is the fuss of setting up compressors and tubing worth the benefits of active and is the only difference with industrial vs medical the mass load? Would a cheap passive platform be an upgrade over say a Symposium or BDR Shelf?
I've tried plenty of shelves, feet, ect... For me the Vibraplane was the best of the bunch followed by the Grand Prix Audio stuff. I think if you are just looking for one platform for say a turntable or CD player the Vibraplane is great. You do have to mess with it every say 2 weeks as they do slowly leak air, but man o man does it ever improve a turntable or CD player immensely. It probably requires about 1 minute of your time every 2 weeks to keep it level and pumped up the right amount. Grand Prix stuff is almost as good and it is totally no fuss. After having a Grand Prix rack and not having one and then having one again, I consider it a pretty important piece of the system if you have a good one.
What accessories do you need to maintain its performance? Is there a specific compressor type? I take it you (Ejlif) use the passive platform type.
Minus-k and Halcyonics are comparable in vertical-isolation performance and both are superior to the Vibraplane. The Minus-k systems are passive and have resonant frequencies (0.5 Hz) that are an order of magnitude lower than pneumatic isolators. Once set up, a Minus-k table needs no maintenance. In contrast, the Halcyonics units are active and require 110 V; they are also much more expensive. The extra $$ buy you somewhat better horizontal isolation compared to Minus-k; however, it's not clear that this offers much benefit in audio applications.

I have Minus-k systems in my laboratory for an atomic-force microscope and a surface-plasmon imaging apparatus. The effectiveness of the isolators can be readily measured with those instruments. What motivated me to buy Minus-k units for the lab was the obvious sonic benefit of mounting my turntable on a Minus-k BM-8 isolator at home. In my view this remains the most cost-effective upgrade I've ever done.
Sdlevene - could you speak to reasons for choosing the particular Minus-k model that you did, versus, say, the BM-6 or BM-10? Thanks in advance.

The BM-8 is their highest-performance isolator for loads in the 100-lb range and has the additional advantage of a low profile (about 4 in. high). I replaced the standard top plate with a 28x20x0.75-in slab of polished granite to support my VPI TNT 'table. The sum of these masses (minus the mass of the original top plate) comes just within the maximum load rating of the BM-8.
silent running audio is very effective isolation
Is resonant frequency an indicator of superior sound quality and why? If the table has a natural resonance (a rarely published spec) and the platform has a resonace that was a fundamental then I can see all modal hell breaking loose. Do these platform manufacturers publish resonance amplitudes? I would think amplitude would have more bearing than frequency. or not?
1. Resonance frequency is the frequency in which a material vibrates the most. Isolation (decoupling) will typically worsen vibrations at and near the resonance frequency, but higher frequencies will improve. That's why you want the resonance to be as low as possible, preferably outside the audible range.

2. All tables (and everything) has a natural frequency; and maybe even more than one, if the table is made of different parts or materials. I've only seen some manufacturers publish this, and it is always dependant on the load or mass on top of it. Every system has an optimal load, and if it's less than that, the resonant frequency will be too high and might make the problem worse. If the spring is overloaded, it will become useless.

3. Don't quote me on this, but I believe amplitude absorption depends on deflection of the spring and the damping factor. Usually audiophile products don't publish these (maybe they don't have the equipment to test). But, for instance, the Minus-K mentioned above pushlishes their transmissibility curve, so do products like Green Glue, and manufacturers of springs, mounts, and dashpots, used in HVAC or auto applications.

The isolator's resonant frequency is a good figure of merit for this type of analysis. All objects have a natural set of resonant frequencies; this mode structure is typically modeled in terms of mass/spring systems. The response of the mass/spring system to a periodic driving force is described by a simple mathematical expression, the Lorentzian function; this is the transmissibility curve that's seen in some manufacturers' technical literature. The Lorentzian has a peak at the resonant frequency, which becomes broader with increasing values of the damping factor (decreasing Q). At a damping factor of 1.0 the system becomes critically damped and no longer responds harmonically to the periodic driving force. With damping factors > 1 displacements of the system from mechanical equilibrium have an exponential response and the return to the equilibrium position becomes progressively slower as damping increases.

The broadening of the resonance peak that's introduced by high damping factors has the net effect of increasing transmissibility at frequencies above the resonance (relative to an undamped system). Therefore, instead of using a critically damped isolation system, it is more effective to have a weakly damped system with a resonant frequency well below that of the system you're trying to isolate.
Sorry for the delay in responding. All you need for the passive version, which is what I have is a bicycle type pump. You attach it, open the valves and give it a few pumps, then let air out of each valve until the table is where you want it. I have never really noticed a huge difference between getting it perfect and it being slightly off. I just tend to it every few weeks and it seems good enough for me. I wouldn't want to have 5 of these though, but for one turntable or digital source it's pretty easy to deal with. One thing to consider, is that it is really heavy and awkward. It probably weighs around 150 lbs, so getting it on the top shelf of a stand can be a 2+ man job.