I think we're confusing the heck out of this poor guy! He's looking for a good quality < $600 (delivered) sub for his dad. With 50:50 music/movie usage in a 2800cuft room
that's open to the house. An $800 12" Rythmik won't cut it in a room that size even if it were in budget which it's not. I know that because I had a discussion with the owner when I was looking for a sub for my 3000cuft bedroom.
The problem with a sealed sub (I own 2) is that they don't have the 20hz impact of a ported sub and the bang for the buck isn't there to stay within the OP's budget. It takes a big honking amp to get close to the same level of output and low frequencies tend to start sounding compressed at high volumes and it often takes twice as many subs to reach the same 20hz output. Sealed sound great for music but so do a lot of ported subs. Full disclosure I've heard Hsu subs but not their Outlaw equivalents, however Hsu builds a fine subwoofer. And Rythmik makes great subs if you have twice the money for the same level of output from their sealed subs. I happen to like both styles of sub but for dual use I prefer a ported sub.
Good quality subs that fit the budget and room are the Outlaw LFM-1 Plus or Ex; Hsu's VTF-2 ($13 over budget); Elemental Designs' A3-300. Take your pick but for the money I'd get the EX. Since it's going to sit on a tile floor I'd place whatever you buy on an isolation pad. The down-firing EX is huge and will need an
Auralex Great Gramma, the smaller down-firing LFM-1 Plus or HSU VTF-2 can probably get away with a slightly smaller
Gamma, and I'd just use some anti-vibration pads like
4 of these with the front-firing eD.
BTW the LFM-1EX can be be tuned to 16hz or 22hz, the eD has a native 18hz tuning, and the VTF-2 can be turned to 18 or 25hz. LFM-1 EX specs below: