Medical Isolation Platforms

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.