I currently have two SVS 16-46PC+ subs tuned at 12Hz, located about 11' away from my seating position. They are not co-located.
I don't have a concrete floor, I have a crawlspace construction, with wood on top of whatever the floor is really made out of. I've never experienced that walls flexing, floor moving, furniture moving thing people talk about when they measure subs in their closed rooms. The house does groan when I push my subs to the limit, but I've never seen visible flexing. And the furniture doesn't vibrate.
I would assume the pant flap I experienced is due just to air movement, not pressurization.
And the reason I'm asking about <10Hz is because I am trying to put together a sub that would give me noticeable output down to 5Hz. I'm having trouble figuring out the right thing to do because:
1) ported/
PR has huge group delay, which I understand you believe to be okay, and driver excursion remains an issue when the tune is 5Hz instead of ~15Hz.
2) sealed rolls off and I'm not sure I can EQ to a flat response without making things worse; 5Hz at 90dB and 30Hz at 120dB.
3) IB isn't a good option for me because this is the first floor of a two-story house. The only potential IB enclosure is the fireplace, and that would be very hard to create a seal around without re-doing the fireplace.
Right now I'm kind of leaning towards a 6-driver sealed sonotube.