I had speakers with cones and down firing subs sitting on a suspended floor in a relatively new home. The floor has a resonant frequency of 34 hz, and I know because at that frequency the amplitude of the vibrations increases so much it shakes the chair and tickles my butt!
To solve it, I cross braced the joists, put a post under the center of the floor, and put a piece of slate between the cones and the carpet (isolation). This combination works very well indeed, and there is no visible movement of the speaker tops.
So, my experience and that of Fiddler are very similar, in that we both found isolation was necessary on a suspended floor. That does not mean coupling should never be used, as these same speakers on a concrete floor shine with just the cones.
To solve it, I cross braced the joists, put a post under the center of the floor, and put a piece of slate between the cones and the carpet (isolation). This combination works very well indeed, and there is no visible movement of the speaker tops.
So, my experience and that of Fiddler are very similar, in that we both found isolation was necessary on a suspended floor. That does not mean coupling should never be used, as these same speakers on a concrete floor shine with just the cones.