European Vibraplane?

Sorry that I was less than clear in my post. I am referring to the CM225 low
profile isolators with built in leveling valves. They need a compressor and can
support 60 lbs each for 240 lbs total. If the turntable is 100 lbs, then a steel
slab is another 130 or so and that could be very effective isolation.

I find that if you are isolating a turntable which needs to be absolutely level, then
the self leveling feature is a must. Manually adjusting the height every day or
two is not worth the cost savings for the more basic isolators, IMO. I also found
that with my passive Vibraplane, I had to fill it up slightly every three days, and
that was not fun because of the need to relevel the system. The active units with
a compressor and self leveling are MUCH more convenient, if slightly more
expensive and complex.

This is probably what is inside their benchtop platforms...at 1/2 the price. The full Newport catalogue is available in EU so shipping (apart from the Newport crazy intra EU flat rates) and esp. customs should not be a problem.
The other EU option--ThrowLabs, seems completely unprofessional: they have removed all the specs of their platforms from the web (good that there is a link at the beginning of this thread) and on my question to the tech support about f_res vs load they said they don't know and asked ME where I took f_res<3.5Hz from HAHAHAHA! Probably they make their platforms as an unimportant acessory which must be in the line and don't give a s...t about it.

Mechanical springs have some interesting advantages over air bladder and air spring systems. It is much easier to maintain mechanical spring iso systems since there are no porous rubber bladders, no air fittings that can leak and no air pumps to buy. Mechanical spring systems are inherently self leveling and since hardened steel springs don't change their spring rate over time like porous fabric of the air springs/bladders they remain level.

Mechanical spring systems are not over-damped, whereas air bladder and air spring systems, due to the nature of many stiff rubber bladders/springs, can be over damped. Mechanical spring systems are much easier to tailor to load requirements - the only thing the user needs to decide is what type of material he wishes to use for the heavy mass, if any. Smaller size mechanical springs do not require pre-loading with heavy mass if the component weighs enough - another advantage. Smaller springs, by virtue of their low profile, are very stiff laterally so they can support loads with relatively high center of gravity such as turntables with high-mounted heavy platters.

Finally, mechanical spring-based systems are inherently inexpensive since the springs themselves are inexpensive and heavy masses can comprise almost any stiff, massive material like granite, flagstone, bluestone, marble, even stacks of ceramic or marble tiles, many if which are inexpensive and easily obtained. Plus no air pump is required, and no air fittings. Resonant frequencies of simple mechanical spring based iso systems can be obtained on the order of 2-3 Hz without much difficulty.

Geoffkait, thanks for your very interesting and informative post. Are you describing a commercially available unit or is this more of a DIY type of project? You describe many advantages over air suspension, so I would think there would be many products meeting this need, but I am only aware of the Minus K brand platforms which are quite expensive and do have the center balance issue from what I read.

I agree that the life span and maintenance of an air based system long term may become an issue. My three new Vibraplanes do give great isolation performance and have really helped the sonics of my system at a fairly reasonable cost.

Peterayer, it's more of a DIY project, I am pretty sure there are no commercially available units like the ones I have in mind. I designed the first Sub-Hertz Platform for the audio market, the Nimbus Unipivot, a 6 degree of freedom, single airspring design, about 15 years ago. I developed a mechanical spring based platform, the Promethean, about 10 years ago, the primary advantage of which was that it was modular and could support almost any load, unlike Nimbus...and it was a 2 Hz stand. Some of my Promethean customers had really big turntables like Raven, VPI and Verdier, also amps like JC-1 and the big 200 lb Classe amp. My current DIY project is based on small hardened steel springs and heavy mass. Because the springs are only one inch high compressed they can be placed directly under the component in many cases.