I would base it on the size of the room and how much space you have for each enclosure. If a small room I would go sealed and if large go ported. Then build as many as fits your needs 1,2,4 etc. I would base it off of one of the commonly used 18" from UM18, SI HT. Each of those designs you listed has its positives and its drawbacks.
The VBSS will need to be used in multiples to be of much use for home theater since it has low Xmax so it does not have as much output down low. Negative is that you have to build that many more enclosures so that much more cost for wood and that much more time building each enclosure. Plus is it is cheap per woofer and lower power requirement because it is an efficient driver. In my opinion, most will need 3-4 of these to get good output in the lower frequencies. It will take 2 VBSS to equal 1 sealed 1 U18 in the lower FR range so 4-6cf enclosure for the UM18 vs 11-12cf for 2 VBSS. It will take 3 VBSS to equal 1 ported UM18 so 18cf+ to 9-11cf for 1 ported UM18.
Tuba HT good is that it is efficient so it can get loud from minimal drivers, less amp power requirement, negative is that it is a larger enclosure, complex to build and less output down low. They drop off fast below 20hz.
Marty- good output all around, negative is a larger size, fast drop off in the output below tune if you want output down in the low teens or single digits.
Sealed good simplest design/build, plays the lowest, smallest enclosure. The drawback is they require a more expensive driver, more power, and more drivers to get equal output to a ported subwoofer around the tune. For example, a single Um18 in a Marty would require approximately 3 sealed UM18 to match the single Um18 around port tune but then below port tune, the sealed pulls away.
That is just a quick generalization and my opinions, other peoples will vary. I have used most of these subs or similar designs in my room and in most cases I would recommend sealed from simplicity unless someone has a large room and/or they are willing to build larger enclosures for the extra output that a ported or horn loaded subwoofer gives.
HTPC, Sony 40es, 120" Silver Ticket, 7702mkii, Sunfire Amp 225w, JBL 590, JBL 520
PSA XS30, Seaton Submersive, 2 Um-18 8cf sealed, Outlaw Ultra x 12, Kappa Pro 18LF, BFM Tuba 60 horn, B&C 18TBW100 6cf 41hz, 34hz, 28hz tune
iNuke 3000 & 6000 DSP's, Crowson Motion Actuator
Last edited by bscool; 08-09-2017 at 12:00 PM.