Medical Isolation Platforms

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.
 

Jtimothya,

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.

Ducatirider,

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.

Hi there, thank you for your interest in this topic. I can certainly help you with the first question about merits of active vs passive and industrial vs medical. The benefits of active compression tables is that they have a more gentle compression and are better for patients who need to get up and move around while they're on the table. Industrial tables are stronger than medical tables, but the difference is that they don't have any other features beyond their compressive strength, so it's not worth the fuss.

@sdlevene 1+ 

MinusK platforms are the best available for reasons sdlevene mentioned. Putting any turntable that does not have built in isolation on a MinusK platform will make a significant improvement in performance. This is no idle "tweak."  It is also not cheap costing over $5000. It can be tricky to set up/balance and you have to get use to handling a turntable that can bounce around. They are also not exactly attractive although they do have a relatively new "slim" model. I would recess it into the cabinet. 

If you have an expensive turntable that you really like for whatever reason but, it is not isolated, the MinusK  platform is IMHO mandatory. 

I have a Minus K platform that I use with my turntable.  It does a fantastic job of isolating and is better than most granite/wood/ platforms like HRS/SRA IMO.  It is a bit fidgety initially, but you get used to it just like anything else.  For example, you have to be more careful when you brush the record while it’s rotating on the table or when measuring vtf as the change in weight will bottom out the platform. However, I have not had to adjust the platform due to the different vinyl weights (180/200 gm etc). I did notice and the mfr recommends that optimal results occur when loaded near the rated capacity. I bought the 100 lb rated platform and I think with the additional marble base, the total weight comes close to, but less than 100 lbs.  I think you can go over a few pounds (5 lbs?), but once it exceeds that, it'll no longer work. I also considered a Vibraplane, but having to put in air regularly turned me off. The Stacore had good reviews on WBF, but very expensive. Overall, I'm very happy w my Minus K platform – best bang for the buck. The BM-8 model that I got retails around $3k – the newer low profile platforms are close to $5k. Info at –

https://www.minusk.com/products/bm8-vibration-isolation-platforms-bench-tops-isolators.html

https://www.minusk.com/products/ct2-ultra-thin-low-height-vibration-isolation-platform.html