Regarding risers and tactile feedback:
Building a riser to flex is the right way to go, but just remember that each riser will have a resonant frequency at which it will vibrate more aggressively. So although it will likely vibrate some at all LFE frequencies (certainly more than concrete) to some extent, it may not be as much as you'd think or to what some experience with suspended floors; especially if its resonant frequency is outside of the LFE range.
The trick is building one where it has its resonant frequency in the LF range, or even better, the ULF range. Unfortunately, I have no clue on how to tune your riser to the frequency you want...
Basshead81's visceral shaking is because he has 1) capable subs, 2) nearfield, 3) his couch has a resonant frequency in the LFE range. Take 1 of the 3 ingredients away, and the effect is much less...
My HT seating's resonant frequency is right at 15hz, as another example.
The people that talk about their couches or suspended floors shaking viscerally, likely have LFE resonant frequencies.
One other note: while risers will certainly help the tactile feedback, they will still not likely have the same effect as suspended floors unless the sub is near the riser. With suspended floors, the sub is essentially nearfield to the floor since it spans the entire space. Because it is nearfield, it will excite the floor right next to it, sending waves everywhere else. If the subs are far away from the riser, it has less ability (PVL) to excite the riser as compared to nearfield, and thus will have less of an effect.
Last edited by dominguez1; 11-27-2014 at 02:53 PM.