Below is an earlier picture of the area behind my sofa back when I was planning to build DIY subs instead of going ID. The large cardboard boxes along the back wall on either side of the main LP are placeholders for two of the four JTR Cap 1400's that were on order. Both rear Cap 1400's are now placed sideways with their driver/port facing the center position. Each one is about 4 feet from the LP in the center. The other Cap 1400's are at the front of the room with my main speakers.
The rear sofa table has a opening below that's currently housing my two old Energy ESW 150 subs. This is where I want to build a near field sub for tactile response as I'm on a concrete floor in a huge 10,000 cf room. The 18 x 48 x 16 space under the existing sofa table would accommodate a 6.1 cu ft internal volume enclosure. it could be painted in black and relatively east to build.
I could also replace the existing sofa table with a larger enclosure at 24 x 54 x 18 with 10.3 cu ft internal volume. It would need to be finished in Qtr Teak to match other furniture and would require the use of a woodworker I know to build and finish.
Lastly, the opening in the rear sofa table could also accommodate a Captivator S2 if I cut out the bottom shelf if I didn't want to go DIY. But that would be a lot more money, so I am in the process of getting two UXL-18 drivers for my near field subwoofer.
You're suggesting that ported near field subs have more tactile response than sealed. Which of the SEALED/PORTED options below will give me the best response in combination with the two Cap 1400's that are already there?
I already have two cap 1400's on the rear wall to either side of the main LP, each one is about 4-5 feet away from the center position. Sealed UXL-18's in the rear center wall about 2 ft behind the LP might help bring up the ULF tactile response below the cap's 17 Hz port tune.
I can put the UXL's in two DIY Sound Group Stonehenge enclosures centered 2 ft behind the LP. This might have more tactile response although their higher port tune at 22 Hz might create problems with the Cap's tune at 17 Hz