Zargon,
I think you are on the right track to isolate your speakers from the floor. You might find better results with a platform which is more massive that MDF - granite, marble, or custom poured concrete (decorated with something of course). Your speakers should sit on this platform on three pointed feet. If you wish to get adventurous, do what I have done: use bicycle tires to float the platform (isolate) above the carpeted floor. I can give you details if you are interested.
Here are the issues, in order of importance as I see them:
1) You do not want your floors and walls vibrating. If they do, they will radiate sound which is very bad. You cannot avoid exciting floor/wall vibration from acoustic excitation, but you can reduce speaker mechanical vibration from exciting your floor. Please note we are not talking concrete slab floors here, we are talking about wood floor over joists.
2) You do want the mechanical connection, between speaker and floor (or for that matter, all the rest of your system) to be linear. Rattles must be avoided as they destroy music and generate unwanted noise. Also you do not want the mechanical connection to be modulated by the music (or associated speaker vibration). If the connection is through a squishy or rubbery material, this is also less than optimum because the material is not linear, and music loses its pace and timing.
3) You do not want the speaker box to vibrate - only the driver diaphram(s). This of course is a distinguishing feature of loudspeaker designs, the degree to which cabinets vibrate and radiate sound, or excite the floor beneath them.
If you have a concrete floor, anchoring the speakers to the floor addresses item 3. If your floor can vibrate, then item 1 is likely of much greater importance.
Using cone or points under the speakers can actually help all three of these. Transfer to the floor (1) is reduced because the interface points of contact are limited to corners and edges of the cabinet where box modal vibration is minimized. The linearity (2) of the interface is improved. And this usually reduces at least the lowest frequency motion of the box (3)to greater or lesser degree.
In my experience, while using cones under my speakers provided a huge improvement in sound quality (over speakers on bare floor), there was still significant floor and wall vibration which I could hear and also feel with my hands and ear (against the floor). The sound improved even further when I isolated the speakers from the floor. I tried sorbothane, rubber feet, stainless steel sash springs, and finally bicycle tire "air springs."
In your case, you could get some of the best of both worlds ("coupling" vs "isolation") if your speakers sit on cones on (coupled to) a massive platform. The platform (isolated from the floor) sits on soft linear springs.
If you have children or pets, or concern over the 5As being "tipsy", then maybe the air springs are not for you. In my case, after hearing the difference, I am more than willing to explain to visitors why my speakers are "floating" like a turntable and bounce or rock at a few Hertz when you bump them.
Please report your experiences so we all can learn from them.
Cheers,
Charlie
