I will simply say that I was EXTREMELY impressed with the new SVSound PB13-Ultra DSP when I heard it a few weeks ago. If it were my money, and I could only fit a single sub into that size room, there is zero question in my mind that I would opt for either the PB13-Ultra DSP or the cylinder version - the PC13-Ultra DSP if I needed the smaller footprint and didn't mind the much taller size and black cylinder look.
I've been underwhelmed by Axiom's subs. Their EP500 is easily their best, but it doesn't have nearly the output capabilities, nor the option to extend well below 20Hz of the SVSound Ultra subs. The EP600 and EP800 have poorly braced cabinets that lead to some audible cabinet resonance. It's by no means the end of the world and only really nit-picky people like myself would likely notice. But it's there. And it's disappointing for the price. The SVSound Ultra subs basically kick their arse in terms of distortion and lack of cabinet coloration.
I've little doubt that the JL Audio Fathom F113 would be awesome. But it's also a sealed design. And even with its massive amplifier and incredible excursion, I have a tough time believing it's going to match the sheer output capabilities of the SVSound Ultra.
So that is my recommendation
The other thing I will mention is that you still have plenty of room left in your budget to do things right and make sure that your SVSound PB or PC13-Ultra DSP is decoupled from the floor using an Auralex Great GRAMMA (in the case of the PB13-Ultra DSP) or an Auralex SubDude (in the case of the much smaller footprint PC13-Ultra DSP). After spending a good amount of cash on such an excellent subwoofer, it would be a shame to leave any performance "on the table" due to a lack of decoupling that only costs $50-$80!
If you're at all unfamiliar with decoupling, the basics are this:
The subwoofer produces physical vibrations. When the subwoofer is sitting directly on the floor, the floor shakes also - due to those vibrations. When the floor shakes, the walls shake; and when the walls shake, the ceiling shakes. This is called "structure-borne sound transmission" and it is the reason why you can hear bass thumping away in other rooms of the house, even if you cannot hear the higher frequencies at the same volume level.
Decoupling is simply placing a "shock absorber" inbetween the subwoofer and the floor so that the vibrations of the subwoofer never reach the floor and thus, the floor never shakes! The benefits are very noticeable and they are two-fold:
Outside of your theater (ie. other rooms of the house, or neighbors apartments, etc.), that thumping, bothersome bass is greatly reduced! This is probably the biggest benefit of decoupling because you get happier, less annoyed neighbors and significant others. That, in turn, means that you get to play your bass at reasonable levels, which - I'm sure I don't have to tell you - means a happier you!
Second, inside your theater, you eliminate a key source of distortion. With the floor, walls and ceiling no longer moving in sympathy with your subwoofer, they no longer produce sound of their own. That means fewer soundwave interactions and fewer delayed soundwaves reaching your ears. The result is "tighter" sounding bass and a reduction in things like rattles or other sources of unwanted vibrations making noise in your theater.
You don't have to use the Auralex products, but I just happen to recommend them because they are inexpensive, the right size, and they work! $50-$80 is a drop in the bucket for your price range, so there's really zero reason to NOT have a decoupling device under your new sub!
Hope that helps!
