Isolation vs. Absorbtion

I'll try to address both Dan and Jay's questions here as briefly and simply as possible while touching upon Redkiwi's comments. In terms of the MGD rack, i had originally added large "fender washers" between the locking nuts on both the top and bottom of the shelves. Michael said that this was a big no-no, but the nuts seemed to be digging into the shelving material quite a bit and leaving "uglies". He told me that if this was happening that i had the nuts too tight. Tightening these down quite a bit was the only way that i could keep the rack from swaying or leaning to one side (my floor is not level). I was EXTREMELY meticulous as to having the rack level on all shelves and keeping it rigid made that a LOT easier. I have since taken to "playing" with the tightness of the top clamping nuts on each shelf. This has greatly affected the tonal characteristics of the bass, amount of air and ambience along with the overall "pace" of the system. It has also resulted in a rack that is slightly less stable due to less rigidity. That might be a lesson in itself. As to cones or coupling in general, i DO agree with Redkiwi's comments that cones that are securely mounted to a component and not just resting on top of them is more effective. The cones become an active part of the chassis when this is done. In effect, you no longer have an individual component and cones but a one piece chassis with better transfer characteristics. As to explaining the transfer function vs. surface area and coupling, i am not a mechanical engineer nor do i have any background in such. Most of my "deductions" were arrived at from a "logical" train of thought and experience. Reverse my "logic" in the article that Stereophile published. Instead of thinking about how the "arrows" were driven down into the shelf, see how easy it is to drive a nail into the wall with it pointing the wrong direction. There is OBVIOUSLY a major difference in how efficiently the energy is transferred depending on the shape and amount of contact area between the two mating components. Another KEY factor in this equation was brought up by the "Kiwimeister" in terms of the materials used. Redkiwi's comments about specific devices sounding "peaky" or having common sonic traits has to do with the overall transfer of energy between the entire component / shelf / rack / floor / room synthesis. There are obviously vast differences in densities and ranges of resonance in various woods, polymer's metals, etc... Which material works best where or how all of these will blend together is anybody's guess. After all, while we look at each component as an individual link in the chain, the system IS the WHOLE chain and sums everything as one. For those that have electronics background, think of a circuit with dozens of components in it. Even though each diode, resistor, capacitor, inductor, etc.. has specific characteristics, they can all be summed up as one big "MASTER" complex impedance as described in "Thevenin's theory". In our audio system, we could call it "the MASTER complex resonance". It's just a combination of all of the smaller resonances added and subtracted, etc... How to arrive at what sounds good to us is a pretty complex ordeal, just like the above described circuit. While i know that Redkiwi has spent a sizable amount of time investigating some of these specific areas, he may not have come to any "solid" conclusions. To make any real progress in this area would really require test instruments and extensive notes and documentation for various situations and installations. There are SO many variables involved in terms of different isolation / damping devices and designs along with materials for those AND the shelving that you would literally need a lifetime to document them all. It is hard to imagine that ANYONE knows the answer to ALL of the following questions: 1) Do you isolate component A or dampen it ? 2) Do you know which shape or style of isolater / damper works best ? 3) Do you know which material to use for the isolator / damper ? 4) Do you know the optimum place on the chassis of the component to place the isolation or damping device ? 5) Do you know what material, shape, size and weight to make the shelf that the component will be resting on ? 6) Do you know if the shelf / rack should be rigidly coupled to the floor or if it should be isolated ? Etc... This is the reason that so many tweaks exist. There are NO answers set in stone. It is all a matter of trial and error as to what works best, what works poorly and what doesn't work at all. While keeping a notebook on such things might be considered "anal", it might actually produce some very interesting results. I simply offered some of my thoughts / observations as to what i've encountered so far and Jonathan "ran" with it. Like the rest of you, i'm still guessing, learning and "playing it by ear" too : ) Sean > PS.... To all of the "non-tweakers", hope you had a good laugh : )

To add to the above novel, i hope that Redkiwi (or anyone else) does not think that i was attacking him in any way or take anything personal. I have greatly enjoyed many of the posts that he has made on this subject and tend to agree with many of his findings thus far. I was simply commenting on some of the examples that he had referred to in his post and as such, he became an integral part of the response. No disrespect was meant to him, his views or anybody else that does not share my view on the subject being discussed. I hope that i did not come across the wrong way and that my comments will be seen in the correct light. Sean .

Not at all Sean, instead I am a bit embarrassed at your flattery. The general conclusions I have come to are not detailed enough to answer all of the questions you list - but nevertheless so far I believe: it is OK to use multiple structures sitting on top of each other if they are either firmly bolted together or have a point contact - ie spikes or cones; each structure should be light, rigid and damped; there should be no more than one item in the structure that is compliant (ie. non-rigid), that the best place for this compliance is between shelf and component, and that so far the best I have tried are the elastomer E-A-R feet, which have the most even-handed sound without smeering detail. The biggest problem is to achieve the requirement of light, rigid and damped. I believe that if you achieve this in just one place then the best place is in the shelf. All supporting structures under such a shelf can be just light and rigid. Light is important because it means little energy is stored and passed on through the chain - for this reason I think many heavy and damped shelves sound neutral, but smear detail (due to the slow release of too much energy). Rigid is important so that any energy is released as quickly as possible, and because otherwise you may end up with more than one compliant support, causing resonant nodes. Damped is important because if everything was just light and rigid it would ring (the peakiness I have referred to). But I reckon the idea of light and rigid, to make sure energy stored is minimised and released quickly, is in natural conflict with the concept of damping. By its nature damping tries to absorb energy and not return it later, but that is a difficult ideal to achieve in practise. It is in this trade-off that I feel there is as much art as science - finding the trade-off that does the least damage to the music. The reason why I like the items closest to the component to be damped or even compliant (in the case of the feet) is because the component needs to be both isolated from vibrations by the total structure, but also damped. I suspect I am just finding more ways to say what I have said before, but hope this clarifies. But this time I am explaining things in a way that (I hope) is related to Equa's question (isolation or absorbtion). My preference is for the focus to go heavily on isolation, but with a small amount of absorbtion close to the component. I don't like many of the absorbtion products (eg. sorbothane and bladders) because they release energy back into the structure slowly, thereby causing smearing and lack of focus and pace. Used on their own they may subjectively provide an improvement where isolation has not been dealt with well, but I don't think they are the best way to go.

Red, just to clarify something that i've been wondering, have you ever played with "mass loading" any of the equipment ALONG with the various types of isolation / damping type devices ? By this, i mean applying weight to the top of the component ( i.e. sandbags, VPI bricks, etc...) in conjunction with the other tweaks ? My experience is that "lifting" the component higher up of the shelf via cones and "levitating it in air" in effect makes the entire unit prone to ringing and airborne vibrations. This problem does need to be addressed, as it becomes more apparent as volume level is increased. The key to making this work is to find the right amount of weight to damp the cabinet vibrations without adding TOO much mass. Going too heavy will increase the energy transfer from the rack into the component, minimizing the isolation effect of the cones. In order to do this, one must have the weight properly spread out and not concentrated in any one specific area. Freezer sized "zip-loc" type storage type bags filled loosely with a layer of sand can work wonders. Of course, you must pay special attention to ventilation and sources of heat, as blocking off air flow can result in not only a mess with the melting plastic, but also "meltdown" of the equipment in question. Just wondering what your thoughts and experience are on something like this. Sean >

Sean, just a thanks for your follow-up. Jayson