My basement room is 7-1/2'H x 9'W x 14'D.
Relative to the projector location at the "rear", the 14-foot-long wall to the right is solid concrete; the opposite (left) wall is 2x6 stud (for the six feet in front of the display screen) and the remaining six feet (closer to the PJ and couch) is a passway open to the kitchen.
The A/T screen is 115" diagonal (wall-to-wall). It is suspended from the ceiling joists/furring, one foot in front of the plywood shearwall behind it. Speakers behind the screen, subwoofer under it.
Throw distance to the screen is eleven feet. Viewing distance to the couch underneath the PJ is ten feet.
The wall behind the screen (9'W x 7-1/2'H) is a stud-plywood shearwall. The ceiling is 2x6 joists with 5/8" sheetrock (mounted on rubberized furring strips 24" O/C), covered by 2' x 4' acoustic tiles painted black for the first six feet in front of the PJ.
Acoustics: "Softwalls." The concrete wall to the right is planed and furred out two inches with shimmed 2x4 studs, stuffed with R-13 fiberglass and covered with plastic lattice that supports and is covered with dark green indoor/outdoor carpet. The opposite wall is similar but uses R-19 in the 2x6 stud plenum space. Both left and right walls have effects speakers mounted in the walls, and there are "rear" effects speakers to the left and right of the PJ in the ceiling corners to complete the 7.1 audio setup.
The wall behind the screen has 1/2" soundboard covering the plywood sheathing, and is finished with black indoor/outdoor carpet.
Finished acoustics are somewhat "dry" in stereo mode (which is good for clear dialogue articulation), but fill out nicely with the effects speakers. The bass peaks and dips aren't too bad, probably due to the presence of the open passway.
The main compromises with this cozy setup are (1) the location of the rear surround speakers, which would be more effective in a larger (deeper) room, and (2) projector fan noise, as the PJ is above the viewing couch. I can live with (1); I am exploring the possibility of shooting the PJ through an existing window behind the couch, which would eliminate the noise.