Currently, due to temporary living situations, the current mutlisub system:
1) a DIY sub with a ~40L cabinet holding Peerless XLS12 (830500), Peerless XLS12-PR tuned to 17Hz, and a Dayton 240W plate amp, placed in a front corner. (I built this sub maybe 7 years ago.) This sub is basically a quarter of the big Genelec sub. (Same driver, similar tuning but from a PR rather than a port, similar power.)
2) Two KEF HTB2 flying saucers, one close to the front on the opposite side wall from the big sub, and one on the same sidewall as the big sub, but much further down. These little saucers actually aren't bad at all, for tiny "designer" subs tuned to ~40Hz with no level or crossover controls and relatively modest power by modern standards. The drivers are beefy, use shorting rings, and the sub/amp combination are clean to over 200Hz.
Placement/calibration using Dr. Geddes methods. Levels/delay/EQ via miniDSP with their Advanced 4-Way Plugin.
Here's a 5-point spatially-averaged measurement, taken using a Velodyne SMS-1 with their MIC-5 spatial averaging kit. (SMS-1 not in the output chain, used only for measurements.)
Once I finish the boxes, hopefully next week, I'm going to upgrade this system to the following: Aurasound NS12-794-4A in a 65L closed box hidden in a chest/kitten-perch where the XLS12 currently sits, push-pull Peerless XLS-12's in a ~20L closed box placed in a bookshelf near where one of the HTB2's currently sits, and an Aurasound NS10-794-4A in a 15L closed box where the third HTB2 currently sits. The NS12 will be powered by a Dayton SA-1000, and the other two subs will be powered by NHT A1 monoblocs. The miniDSP will still be in use.
Why change, given the measured result obtained above, and honestly sound quality exactly what one would expect from that response profile? First, the cabinets will be fit to this room, so no subwoofers will be visible. Second, closed-box subs can pressurize the room below their nominal cutoff, unlike vented or passive radiator subs. Lastly, I have the parts sitting around, so I may as well use them, right?
Once I find a condo/townhome I like that's walkable to my office, and doesn't have leaky pipes above it, the reference system will come out of storage:
1x M-Design Eleganza Godfather (Aurasound NS15-992-4A and unbranded variant of the Dayton 1kW Class G plate amp in a gigantic 250-odd pount piano-black-and-cherry pie wedge)
2x M-Design Eleganza Bellas (Aurasound NS12-794-4A and a 500W Class G plate amp in an elegantly-shaped cabinet), ports plugged
DIY Aurasound NS10-794-4A in 15L closed box, powered by an NHT A1 monobloc (300W/4?), mounted on a bookshelf above the room centerline.
Also, the Tannoy System 12 DMT II-based mains (new cabinets, closed boxes with giant roundovers for low diffraction) will be run full-range, so they will contribute to ULF, too. (In my old room, they measured -3dB at 40Hz by themselves, or about an octave higher than their modeled anechoic performance. I think that was a fluke of that room, honestly.)