Well, you're over 4000 cubic feet already. Is that room sealed? Or does it have openings to any other space as well?
Regardless, you need some very capable output.
I know I'll get the Epik fans all saying how great Epik's subs are. Lots of people do seem to like them. I'm not a fan. I simply want to give you the other side of the opinion spectrum because I fell into the same hype back when I was looking to upgrade my HSU VTF-3 MK2 (a sub that I still use and enjoy very much in my bedroom, by the way). I fell into the Epik hype and bought a pair of Epik Sentinel subs, sight unheard. They weren't "bad" subs, don't get me wrong. They had the one key feature I was originally looking for, which is that they played lower and output higher SPL in the really low 20-25Hz range than my VTF-3 MK2. But they also gave up the tight transient response and had too much overhang, which made complex bass passages "smear" and turned anything other than very simple bass into a bit of a mess.
I also think the amps that Epik uses are pretty poor. The power cords fit loose, they have an operational buzz that you can pick out if you're seated close enough, they get warm - sometimes hot. And they're just plain cheap. Epik should be using BASH amps at their price point. Instead, they went for something even cheaper to try and hit their price points.
Are they a good deal? It depends. They don't even sell ported subs anymore - only their two twin opposed models. Some folks think they sound better than their old models. Some folks are reporting the same sort of overall compromise that I heard with their old models - good extension, no questions there, but not the greatest transient response. Not bad. Just not the greatest.
So I'm not saying Epik is a "bad" choice. Let's be clear about that. And if you're upgrading from a HTiB sub, I'm certain an Epik sub would blow you away and really impress you, which I think is what happens a lot on various forums where lots of people hype Epik so much.
My whole thing is, just don't fall too hard into the hype trap. If you blindly follow the fans, Epik's subs seem like the best deal on Earth! But if you listen and compare, there IS a reason why the price is so low. Higher quality components DO cost more money. So just take notice that you're looking at two 15" drivers and a high wattage sub in a large box for a very low price. Is there high value in that? Of course. But it's also a very good indication that the drivers and amp are lower priced, lower quality parts. It's a design choice and a marketing choice. It's a perfectly fine choice. But just be aware that you're not magically getting way more than you're paying for. Prices are EXTREMELY competitive in the online subwoofer world and Epik isn't magically undercutting everyone else somehow. They're limiting their costs with the parts that they use, which is fine. It's just not something that lives up to the crazy hype that you find on forums from the Epik fans and you need to have your expectations in the right place is all.
Personally, Epik wouldn't be my choice. It's perfectly ok if you want to ignore me though
On the other end of the spectrum, I'm extremely impressed with the SVSound Ultra subs, but they ARE expensive. Personally, I think they're a tremendous value. Again, you look at the quality of the parts that are used and it's somewhat of the opposite case from Epik where the driver and amp in the SVSound Ultra subs are so high quality that the price is actually crazy low for what you're getting. An Ultra would have no problem at all with your room size and the quality of bass that it produces is second to none. The supreme control of the Ultra driver with the Sledge amp gives superb transient response and ridiculously low distortion. It's also impossible to bottom out, drive into high distortion or damage thanks to the impeccable engineering in those Sledge amps.
To be honest, I'm at the point now in my own listening where I find it somewhat difficult to be happy with anything less than the Ultra's quality. For that reason, if someone can afford an Ultra, I find it difficult to recommend going for anything less. But no lone sub can do what multiple subs can - which is offer the ability to create more even and uniform bass across multiple seats in a theater. A lone sub can be rather easily EQ'd and placed to provide very linear bass to a single "sweet spot" seat. But to get uniform bass across multiple seats takes two or more ideally placed subwoofers - usually with some EQ thrown in on top of that too
Now one very good alternative that would fall within your price range would be a pair of SVSound PC12-Plus cylinder subs or SVSound's Legato package, which is a pair of PC12-Plus passive cylinder subs with a shared external 800 Watt Sledge amp. The SVSound Plus ported subs give up about 3dB across the entire frequency range in max output to the Ultra models. This doesn't seem like a whole lot, but it is twice the power, so it's not insignificant either! The Ultra models also provide slightly lower distortion and the slightest bit more control, but it's really, really close. The Plus models are a tremendous value and might really hold the key to getting what you're looking for at your price point. You should also be aware that you can lay the cylinder subs on their side with no problem. If there's an issue of placement options, it helps to know that the cylinder subs take up very little floor space when they're standing up, but that if you can't stand one up for some reason, you CAN lay it on its side without any danger or loss of performance.
Now, given your room size and the fact that movie performance is still a large consideration for you, I would personally lean strongly towards a ported sub. You're not going to get enough room gain with your room's size to even out a sealed sub that starts to roll off at 40Hz with a 2nd order slope as most do. A ported sub with a 20Hz or lower tuning will give you the extension that you'll want for movies. And you don't have to give up tight transient response and good control with a ported sub. You simply have to get a ported sub with a good enough driver and amp that control over the driver's movement isn't a problem!
Rythmik's ported FV15 and FV15HP are right up there with SVSound's Plus ported subs, IMO. You have to consider that SVSound includes shipping in their prices though. So once you throw in shipping, the price difference doesn't favor Rythmik anymore. It's splitting hairs between a PB12-Plus SVSound box and a Rythmik FV15HP really. Truly cannot go "wrong" with either!
I'm about to get in trouble with HSU VTF-15H fans too
It's not my favorite. In fact, it's about the only HSU sub that I'm not really a fan of. I don't think HSU got the VTF-15H quite "right". Again, don't get me wrong, it's not a "bad" sub - not by any stretch! But it's just not quite what I would have hoped for from a big, 15" HSU ported sub. In MY listening, I heard a bit of a "hump" in the 40Hz-ish range. The Audioholics measurements don't really back me up on that, so it's possible I was off the mark with the particular setup that I was listening to. But then again, some VTF-15H owners report hearing something similar, so maybe I'm not crazy either
Where my listening and Audioholics' measurement line up perfectly is in hearing the deep 20-25Hz stuff roll-off at higher output levels. I just personally found it a little disappointing since I thought the big 15" driver might deliver more down there. It seems as though HSU stuck with a similar sort of extension as most of their other subs, which play really nicely down to 25Hz or so, but sort of drop off after that, especially when you crank up the volume and their somewhat lower Wattage BASH amps start to limit the output. I think that a lower tuning on the box and a more powerful amp would have really allowed the VTF-15H to perform to a higher level with that 15" driver they're using. It likely would have up'd the cost, but I personally think it would have been worth it.
So for me, I prefer the VTF-3 MK4. Full disclosure, I'm basing that on having heard the MK3 version, not the newest MK4. But there's nothing to indicate that the MK4 would have taken a step back in any way
I just personally prefer the overall balance and extension in the sound of the VTF-3 MK3/4. But that's when I'm considering its low price as well. I personally think the VTF-3 MK3/4 does really well when compared up against something like the SVSound PB12-NSD. They're at a similar price point and the SVSound NSD subs have just a tiny hint of overhang that lets other subs compete! But I wouldn't put a VTF-3 MK3/4 up against an SVSound Plus sub, and the price difference reflects that!
Just my opinion, but I think that for your room size, your taste in music and movies, your desire for multiple subs and your indicated budget, the SVSound ported Plus PB12-Plus, PC12-Plus cylinder or Legato system or the Rythmik FV15HP are your best choices. They hit the right balance, IMO, across the board for your situation.
Hope that helps! And I hope I don't tick off the Epik and VTF-15H fans too much because I DO think they're good subs. I just think they have some issues that I don't personally like and that I think make them not the very best choices when they go up against the competition. I don't "hate" them. They're just not what I would personally pick is all. And I just want to offer the "other side of the coin" as it were since they so often gut such high praise that I don't quite agree with is all
