http://www.minusk.com
I use the BM-1.
The Minus K vibration isolation platform outperforms air isolation by a factor of 10-100x. Air is fairly "stiff" (which is why it works well as a bearing, like in linear tracking tonearms and some of the high-end turntables). However, stiff is what you don't want your vibration isolator to be.
The Minus K vibration isolation platforms have resonant frequencies as low as 0.5 Hz horizontal AND vertical. Air systems at best will achieve 2-3 Hz resonance, and the big buck active isolation systems are still greater than 1 Hz resonance. This means that the Minus K isolators provide 90% attenuation of vibrations at 2 Hz, and 99% at 5 Hz, and 99.7% at 10 Hz.
Minus K isolators are passive - no air pumps, no electricity required. And they are light. The only way the air-based isolators achieve their 2-3 Hz resonance is by using high mass. So air tables are heavy, no question.
With the Minus K isolator, I can actually put it on my equipment rack and not worry about crushing it or having to reinforce the floor.
The 0.5 Hz resonance frequency has some other benefits. The isolation frequency is so low that it can isolate against low frequency building motions. Minus K is the only isolator I am aware of that will allow you to operate a SEM (Scanning Electron Microscope) or AFM (Atomic Force Microscope) on an upper floor of a building.
I've talked to David Platus, the president of Minus K, and he understands vibration isolation better than anyone I'v met. The Stanford nanotechnology lab has replaced all of their air isolators with Minus K isolators to increase the resolution of their STMs (Scanning Tunnelin Microscopes). I had the good fortune of being invited to see the isolators in action - very impressive.
How does it sound?
Imaging is very focused, and there is a bit more space between instruments. The noise floor seems to have dropped a little (I didn't actually measure this). However, the bass seemed to be a bit softer. A quick call to Minus K, and they suggested I ballast the system. So I added a 75-pound granite surface plate between the isolator and the TT. This indeed did firm up the bass.
The WAF is a bit low. But I understand that Minus K is coming out with some new models with the same performance as my BM-1, but in a lower profile - which should have higher WAF.
Here's the best part - this is an industrial solution which can only be purchased directly from Minus K. What that means to us audiophiles is that we are not paying the 50% mark-up that high-end audio dealers hit us with (mind you, I don't mind paying the mark-up when my dealer earns it through good advice and loaners). So for less money than a Vibraplane, and without the grief of the noise and power, and with more performance, the Minus K solution cannot be beat.
Also, if you have problems with walking across floors and having to tip-toe up to your TT - this is not the case with Minus K. I read in a Minus K customer testimonial that a half-dozen scientists - as their final acid test - decided to jump as hard as they could on the floor around their atomic force microscope to see if the vibrations would be transmitted to the microscope. Jump as they did, the AFM never saw any of the vibrations.
I have visited the Minus K booth at various tradeshows (most recently Semicon, for the semiconductor industry). They have a really nice demonstration where they place the isolator on a shaker table, and on the isolator they place a free-standing quarter on its edge. The table is shaking pretty violently with 0.5" displacements. The quarter does not move, it just sits their balancing on its edge. They have also done this with a glass of water - you don't see any ripple in the water. Minus K products are very popular in physics labs as well, where they need superior vibration isolation for experiments.
Once again, I apologize for a long and perhaps overzealous post. But I am truly convinced that if you want real vibration isolation - just bypass all the audiophile "hobbyist" solutions that can cost as much as $10k, and go straight for the real deal - Minus K.
