Sealed really doesn't need that much volume. The "not low" Qts on this driver suggests it's more at home sealed... or at least wants a bigger box if vented. The plus side for that is if you do vent it, she goes nice and low on not-many-watts. I have 4 in 1.3 cuft each right now in front of me and it'll beat the ported 12 nearly across the board. Ported single beats mine at 15hz by just under 3dB, they match around 17Hz, I'm up by 5dB at 20Hz, that grows to a very significant 9+ dB at 30Hz, and it's 10dB+ 40Hz on up. On the other side of that spike mine had more output below 14hz and by 10Hz has 14dB more output. Real world with music/movies that's huge
. Worried about a high-Q alignment? Linkwitz transform that baby. Graph attached is in the same 6.25 cuft box, just 4 drivers and sealed instead of vented. Really the sealed should get a small box volume allowance for no port volume, but for napkin math this suffices. Efficiency wise 30Hz on up the sealed will play louder on the same watts. They will soak it up down low though, for sure.
I picked up a QHD 4 hole pre-made sub enclosure for this application and it cost me about $70 with some careful searching. You can do that with smallish sealed enclosures, you can't do that with larger ported ones. Economy of scale I guess.
4 drivers: $120
$220 all in for 4 sealed, minus amp and DSP, no MDF or plywood to mess with, no extra cost for finishing assuming carpet is ok (for me, ok for behind couch or under desk).
If you needed to put them in 2-3 cuft each I'd agree with you, but you definitely do not need to. That kinda throws your comparison out the window. Nothing against a 6 cuft ported, I like it. If I just had one driver, or maybe two, I'd probably do exactly that. It just starts losing when you shoehorn a bunch of these into a small sealed box and eq the bajezus out of it. At $30 each that's kinda the point, unless you're just super budget minded on the whole thing. I'm pointing out, box volume aside, you're going to end up losing on the money side of things with plywood vs. more drivers and pre-made boxes provided you have the amplifier capacity.
Course I have Crown amps out my wazoo here, some unused ones just waiting for applications, tons of DSP and around 20 extra JBL's at the moment. And by "extra" I mean still in box waiting for next project, not unneeded, no such thing as unneeded.