Medical Isolation Platforms

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