Loudspeaker-Floor Interface
Posted by: CharlieP on 15 November 2015
I started this thread because I received a phone message from a forum member asking about the bases under my speakers. Unfortunately, I could not quite make out the correct phone number nor do I know his forum name. Hopefully this may address his questions. Having said that, it would be fine if a discussion ensues.
Here is my current configuration, which is providing me the best music replay I have yet enjoyed. This is not to say that it could not be improved!
There is wool carpet on the oak hardwood, under which is a suspended wood-framed floor, under which is a crawl-space. 16" square by 2" thick concrete slabs (gray) sit on the carpet. The speakers have three pointed cone feet, which I think are brass. The cones sit in Fraim Chips. Under each frame chip are three 3/16" diameter ball bearings. Because of the textured upper surface of the concrete, the balls do not roll.
Until last spring, these speakers sat for many years with their spikes through the carpet into the hardwood, which left small dimples. My system was in storage through summer, and the hardwood floors were refinished. For two months the carpet remained in storage and the speakers sat on the new Fraim Chips, as a necessity to avoid dimples in the newly-finished oak flooring. I cannot comment on the sonic difference contributed by the Chips, compared to no Chips, because several months ensued and my shelving was rebuilt with closer attention to cable dressing. When the carpet was finally returned, two months ago, I faced the challenge of whether to trim the carpet shorter, or do something else? Really, just as an experiment, I procured these concrete slabs. Similar arrangements have been reported as effective by several forum members.
Initially I placed the speaker's cones directly onto the concrete upper surface. Letting this configuration "settle in" a few days, I felt with considerable relief that it sounded better than when the chips sat directly on the oak flooring absent the carpet. The points tended to "dig in" a bit to the concrete, making a bit of grit. (Each speaker weighs about 100 lb). This made me a bit concerned (for the sound, not the concrete), and I had these Chips sitting there, so I tried putting the chips under the points. Again listening for a few days I felt the Chips a worthwhile addition, confirmed when removed. The effect of the Chips was not profound, but the improvement was there. A similar concern led me to try the balls under the chips - in an attempt to further linearize the interface. Again, I felt there was an improvement, if perhaps subtle. I have not yet tried to remove the little ball bearings - they are "swearing nuisance" to fit, with my wife's patient assistance.
My motivation is to have the best possible natural sound. In service of this, I try to minimize within reason the vibration of the speaker itself and the floor. Further, it is essential that what vibration remains (there will always be some, however small) must be highly linear - free of micro-rattle and hysteresis.
I have to say that my music has never sounded so wonderful - due principally to other improvements I have made - which makes me disinclined to experiment further. But I am open to persuasion if there is a better way.
Charlie
If it works - it works! 
I'm impressed by the ball-bearing idea - but I think I will not try it as I foresee doom in my case, even if it may be better.
Slabs usually - when I try tried them - improve everything except that there is then usually a 'lump' in the bass where the slab wants to have its own resonance. With smaller speakers this can be ok, as there is not a lot of low-bass feeding it, but on larger full-range speakers it can become definitely un-tuneful in the bass, as any resonance, however will managed shifts the phase and also stores and releases energy, which kills PRaT.
Also the material of the slab is critical. Some natural stone rings in the audio band and some materials are much better. In fact I use a certain type of stone as damping on my empty Fraim shelves to very good effect on three bearings onto the glass - but then carefully critically damping the slab resonance itself. In your case the carpet is probably critical.
But if your method works and the system holds a tune in the low bass, then well-done!
Slabs can work well in some locations and with some speakers - and they can have problems too. Experiment can be the only way sometimes.
DB.
If it works - it works!
I'm impressed by the ball-bearing idea - but I think I will not try it as I foresee doom in my case, even if it may be better.
Slabs usually - when I try tried them - improve everything except that there is then usually a 'lump' in the bass where the slab wants to have its own resonance. With smaller speakers this can be ok, as there is not a lot of low-bass feeding it, but on larger full-range speakers it can become definitely un-tuneful in the bass, as any resonance, however will managed shifts the phase and also stores and releases energy, which kills PRaT.
Also the material of the slab is critical. Some natural stone rings in the audio band and some materials are much better. In fact I use a certain type of stone as damping on my empty Fraim shelves to very good effect on three bearings onto the glass - but then carefully critically damping the slab resonance itself. In your case the carpet is probably critical.
But if your method works and the system holds a tune in the low bass, then well-done!
Slabs can work well in some locations and with some speakers - and they can have problems too. Experiment can be the only way sometimes.
DB.
DB,
Thank you for your observations. I have not measured the vibration (yet) but only tried to feel it with my hands. I can feel slight vibration on the speaker cabinet part (the layer plywood sections), but I really can feel nothing perceptible on either the concrete slab or the speaker base (the bottom 6" or so, which contains the crossover). In my limited experience, the bass reproduction is very satisfying.
Admittedly, I have said this before, only to make further improvements and be "blown away." 
Charlie
It is a fascinating write up and echoes some things I have seen in the past with some more exotic attempts. The most extreme of which was concrete blocks loaded down deep into the earth several metres surrounded by another concrete containment filled with water creating a moat. The central concrete bore rising up through a hole cut in the wood floor to be flush with the surrounding floor itself with the speakers resting on that. I cannot imagine anyone going to that extreme (even when building a new home) but someone's done it.
Back down to earth, I found a good compromise between concrete plinths (which I cannot use for a number of reasons) and smaller spike shoes are these items from Kripton:
I have yet to use a better spike shoe.
There is a caveat. The silicone ring on the underside doesn't bear any load but it does make them immobile when the slighted pressure is applied. I find starting with Linn Skeet helps because they slide easily over wood floors without scratching so you can get the position just so. Then swap them out one-by-one for the Kirptons once the positioning is set. They have a range of sizes and masses going from low cost to silly money (starting at about 50 quid for 4 going to around 200 quid).
It is a fascinating write up and echoes some things I have seen in the past with some more exotic attempts. The most extreme of which was concrete blocks loaded down deep into the earth several metres surrounded by another concrete containment filled with water creating a moat. The central concrete bore rising up through a hole cut in the wood floor to be flush with the surrounding floor itself with the speakers resting on that. I cannot imagine anyone going to that extreme (even when building a new home) but someone's done it.
Back down to earth, I found a good compromise between concrete plinths (which I cannot use for a number of reasons) and smaller spike shoes are these items from Kripton:
I have yet to use a better spike shoe.
There is a caveat. The silicone ring on the underside doesn't bear any load but it does make them immobile when the slighted pressure is applied. I find starting with Linn Skeet helps because they slide easily over wood floors without scratching so you can get the position just so. Then swap them out one-by-one for the Kirptons once the positioning is set. They have a range of sizes and masses going from low cost to silly money (starting at about 50 quid for 4 going to around 200 quid).
feeling_zen,
Interesting, that the Kriptons have silicone ring on the bottom to (presumably) prevent movement, and clever that you position things first with the Lynn Skeet. The Naim Chips retail for $35, I think, and seemed expensive (to me) at first. I like them because they are solid, have a fairly large, high conical depression in the topside to keep pointed feet from jumping out when moved a small amount. Plus, there is a several mm diameter center to accept the points. This center is milled out from above and below, and forms a "diaphragm" which is a modestly stiff spring of sorts. My guess is this may be essential for speakers with four point support, to help increase the tolerance for adjustment of the four feet without inducing micro-rattle.
Charlie
It is a fascinating write up and echoes some things I have seen in the past with some more exotic attempts. The most extreme of which was concrete blocks loaded down deep into the earth several metres surrounded by another concrete containment filled with water creating a moat. The central concrete bore rising up through a hole cut in the wood floor to be flush with the surrounding floor itself with the speakers resting on that. I cannot imagine anyone going to that extreme (even when building a new home) but someone's done it.
Back down to earth, I found a good compromise between concrete plinths (which I cannot use for a number of reasons) and smaller spike shoes are these items from Kripton:
I have yet to use a better spike shoe.
There is a caveat. The silicone ring on the underside doesn't bear any load but it does make them immobile when the slighted pressure is applied. I find starting with Linn Skeet helps because they slide easily over wood floors without scratching so you can get the position just so. Then swap them out one-by-one for the Kirptons once the positioning is set. They have a range of sizes and masses going from low cost to silly money (starting at about 50 quid for 4 going to around 200 quid).
feeling_zen, have you compared the Kriptons to Naim Chips?
GraemeH, thanks for the link. Interesting that PMC says one must spend a lot of money to make things work. 