Isolation vs. Absorbtion

equa: i was hoping rekiwi would respond first to your thread query. he's shared with us in erudite posts his experiences testing "footers/shelf material." i recommend you review the thread of that name. i just wanted to comment on your observation that this hobby is informed with "subjectivity and contradictuions." you are right, of course, but these characteristics are what give it life and, indeed, form the basis for sites like this one. as redkiwi attests: there are no "simple answers" to the paradoxes you'll encounter if you get deeper into the hifi world. don't let this bother you or you'll go a little nuts. sit back, ponder and then enjoy the music as your journey lengthens. good hunting. -kelly

Redkiwi makes some very valid "points" : ) My experience is that i have noticed EXTREME differences when changing racks and isolation devices. I had a "home-brew" all wood rack that i had everything dialed in on very nicely, but i added more components and needed a bigger rack. The way that i had built this rack did not lend itself to "adding on" any further shelving. I went to a Michael Green Designs Deluxe Just-A-Rack and it COMPLETELY changed the way that system sounds. It was SO obvious that i had to put a different amp into that system to "re-balance" it. Upon further consultation with Michael, it turns out that i had tightened the nuts down too tight on the shelves and this was causing the massive (read as "less than good") changes that i had noticed. I am currently in the process of "fine tuning" the characteristics of the rack and it is making a VERY noticeable difference in bass output and tonality, timbre of instruments, attack and decay characteristics, etc... Quite honestly, i would have never believed that something like this could have made SUCH a noticeable difference in a system. As others here have mentioned, this is more of a "black art" involving a LOT of trial and error. While some of this stuff can be understood logically, as to what works best and where at in the system is strictly guesswork and experimentation. Not to toot my own horn, but i covered some of the logistics of why cones couple / uncouple in the February issue of Stereophile in Jonathan Skull's "Fine Tune's" column. He thought that i had hit on something with my original post on that subject and thought it might be worthwhile to share it with others that might not have been able to see it on the web. As such, some of it was slightly altered for publication but the "guts" of the post remained intact. The bottom line is that one MUST be VERY familiar with the system in the first place before subtle changes can be easily detected. Until you have achieved a very good foundation that your basically happy with, doing small "tweaks" to fine tune it might end up taking you in the wrong direction. Hope this helps. Sean >

Not to get off topic, but Sean what tweaks did you make to your Justa-Rack. I have two of these and I found your comments very interesting. - Dan

Sean, since you mention that your explanation of how cones do what they do was quoted at length by J Scull in Stereophile, can I ask for more explanation? No disrespect intended – for you are a sane poster whose views on AudiogoN I tend to pay attention to – but I did not find the S’phile quotation very enlightening. The diode metaphor of how cones pass vibrations one way has an obvious appeal to it, simply because cones look like arrows, but I’ve often wondered if there was a scientific explanation behind it. Your chain of thought about how cones work to drain vibrations in one direction and block vibrations in the other is quite logical and, as you say in your explanation, “it’s all quite simple.” However, in the end it all rests on the familiar proposition that cones pass vibrations one way – which, in my mind, you basically reasserted, rather than explained. ---------- Ideally, the contact area between a flat surface and the point of a cone that meets it is just that, a point. What difference does it make to vibrations on which “side” of the point there is flatness and on which side there is cone-ness? Again, the diode metaphor appeals in a visual way – vibrations get funneled through the cone in one direction but cannot squeeze into the point from a flat surface in the other direction; lower frequency (floor-borne) vibrations have more trouble than higher frequency (equipment) vibrations fitting through a small point – but I don’t assume that necessarily has any correlation to science. Is there any further explanation you can add for this proposition? ---------- BTW, this is a matter of intellectual curiousity, and I am not implying that I need to hear a scientific explanation before I believe that cones have an effect. Right now, I am comparing Mapleshade brass cones against the cones I currently have under my turntable, and there are differences to my ear. But, speaking of Mapleshade, that company sells higher-priced brass cones (Triplepoints) that have three “micro”-cones sticking up from the flat side of the cone. The cone is used point down, and the equipment rests on the points of the micro-cones rather than directly on the flat surface of the cone. The designer Pierre Sprey says that minimizing the contact between the equipment and the big brass cone improves the transfer of vibrations from equipment into the feet. Not that he gives a scientific explanation for this (though he might have one if I asked) ...just another example of differing points of view (no pun intended). -- Jayson

I don't buy the mechanical diode idea as anything more than an analogy (and all analogies are inaccurate), and tend to agree with Mapleshade that for a cone to do its thing it would ideally have a point on both ends - hence the Mapleshade idea of three points on one end and one on the other. Conventional cones sound the best when the flat side is up against the surface that is vibrating least (the equipment), since the flat side does the worse job. Hence also why cones can sound better if they are bolted firmly to the bottom of the equipment. I reckon cones between component and shelf do their job because they release energy very quickly at the pointed end. This reduces smeering, but creates peakiness. The sonic differences between cones depend on hardness (speeds the release of energy), resonance/damping (determines the peakiness) and mass (slows the release of energy), but are also profoundly influenced by the shelf material that the pointed end rests on. The more the shelf material is like the cone material, the more you will hear the peakiness of the cone. In my opinion, cones are only good as an antidote to a shelf that has too little rigidity and too much mass (such as MDF). This is just my theory developed from my experience, no more than that, and I respect the fact that other theories presented here may be more accurate.