High End Isolation - HRS, SRA, Active platforms

Prospective buyers of vibration control products should know the basic definitions of, and the distinctions between ISOLATION and DAMPING to enable them to make informed purchases.

ISOLATION refers to the process of preventing (minimizing) externally generated vibratory energy from reaching a structure or component. Although this includes acoustic or air-borne vibration that is difficult to manage in exposed audio/video equipment, we are primarily concerned with the transfer of mechanical vibration. And, it is essential to understand that there is no significant mechanical isolation possible unless there is relative movement between the component and its supporting structure to prevent sympathetic movement with the supporting structure. Therefore, only a device or material that can compress like a spring or deform like an air-bag or a viscoelastic part, or “roll” like a bearing, can be an isolator. Exceptions to these “passive” examples include “active” systems that have electromechanical “self-leveling” capabilities. Obviously, hard “spikes” and (bare) "platforms" or "shelves" are not isolators.

DAMPING is the dissipation of energy in a vibrating structure or component. It refers to the process of removing (minimizing) internally generated vibration that is inherent in a component AND any external vibration that, for lack of adequate isolation, may enter the component, by converting the mechanical vibratory energy of solids into heat energy - a process called hysteresis. Damping is generally accomplished by the bonding of viscoelastic materials to the (vibrating) internal surfaces, mechanisms and parts of a component and by external coupling to viscoelastic materials or damping devices.

In consideration of the foregoing, it is obvious that no isolation platform or device, regardless of its sophistication, can provide effective damping. In other words, while the isolator may essentially "hold the supported component still", the component will nevertheless
be awash in self-generated and acoustically transferred vibratory energy that remains undamped.

In short, to achieve isolation AND damping there must be BOTH isolation and damping mechanisms and/or materials applied to the component!

In my opinion, both isolation and damping are essential to achieve the very best component performance. Therefore, the best solution is not a "cost no object" isolator but rather, a well engineered product that provides both isolation and damping.

Disclaimer: I manufacture vibration control devices.

Our Nimbus and Promethean isolation stands incorporate "selective frequency damping" and viscoelastic damping to "quiet" the top plate and other critical parts.

Our damping techniques address airborne and component generated vibration as well as residual structureborne vibration.

Nimbus is a 6 degree of freedom design with resonant freq. as low as 0.5 Hz.

NB - We design isolation and resonance control products.

I have no doubt on the ability of cones/spikes, elastic interfaces, and shelves of varying density to affect oscillations and change the sound for the better. I have tried some varieties of all of these things.

However, it seems the passive approach is limited by (1) the efficiency of bringing the object to rest, and (2) the selection of frequencies which are a function of the material being used.

I would think that an active system would isolate a component by damping the oscillations. Just as a swinging pendulum is brought to a stop by using your finger as a counter-force, so will an active system bring an oscillating platform to a rest by applying appropriate counter-forces. An active system would also have an advantage of operating over a wide frequency range.

It seems that the other problem with a passive approach, is that they could potentially induce their own oscillations. Placing a component on a displacable material will enhance it's ability to move at certain frequencies. Also, footers are a 2-way street, are not truly fixed, and probably resonate at their own frequencies.

Of course, nothing is perfect. I am also thinking that the only way to truly shield a component from air-borne vibrations is to literally place it in an insulated box.

It is too bad that manufacturers of racks do not routinely provide real data to aid in their design and help consumers make informed choices. Also, our rooms have very individualized frequencies being transmitted through the building structure. Hence, I agree with Jeff above that there is no one-size-fits-all. What may work well in one person's room may not work in someone else's room.

Finally, the huge advantage of passive isolation is obviously cost. Therefore, it remains a useful approach as we are all seeking to obtain the best value for our sound.

I disagree that a rack is designed only to isolate components from vibration coming from the floor. Most rack/shelves are also designed to dissipate vibration coming from the component itself (e.g., the vibration of power transformers). Couplers are used to transfer the vibration to the shelf and the shelves are designed to convert the vibrational energy into heat. Tap the case of a component coupled properly to a well designed shelf and one just sitting on rubber feet on an ordinary rack and you can hear a big difference in how quickly the vibrations are deadened with a good shelf/rack.

Any passive design will have a resonant frequency, below which it will not isolate. In fact, around resonance it will amplify the vibration. Although some passive systems are designed to be tuned to the specific weight they will support, many designs are not and hence, their properties will vary with the supported mass.

Therein lies the beauty of active isolation.