Sub build, which driver?

What is your current sub that you'll be comparing it to?

Is there a box size limitation? As an option, there are many 15 inch (and even an 18 inch Mach5Audio IXL18.2.2) that would do pretty well with that amp and a reasonable enclosure size for the same or less money than the Shiva-X2. The X2 is a great driver, though, as was the previous Shiva 12 inch.

I have a Shiva-X2 in a 3.25cft sealed enclosure with a 500w O-Audio amp. It will definitely be a huge upgrade in output and extension over the Aperion sub. You could get more output by increasing the box size but it's not like it adds a tremendous amount extra. Mine is basically a 21" cube but it's about 19.5" cubed internally...alittle less. I'm assuming your 500w amp has an EQ because you'll need it for a sealed sub.

I did add bracing and some fibreglas fill lined along the walls. I also made it with 3/4" mdf and an additional 1/2" layer of mdf on top of that. If I had to change anything I would probably just use the 3/4" mdf with bracing and not make it thicker. This sub is soooo heavy and it has absolutely no vibration whatsoever (which is good) but I think I could have easily gotten that with just the 3/4" material and kept the weight down abit. You could probably just not even brace a sealed sub that is so small, I don't think you'd notice much/any difference.

I am very happy with the sub. You can see my build thread HERE. Friends and family are pretty amazed at how it sounds. I have a second enclosure already built but the outside isn't finished and I haven't ordered parts yet. I really have no need for a second one but I'm going to add one anyway and really give this room what it deserves

The Shiva-X2 really does have some serious performance for a lil 12" driver. I feel like 2 of these subs in my room/setup will give me amazing performance. They might not be the loudest driver in a sealed sub but the sound quality is amazing. It digs down alittle under 20hz and has really good output to 20hz and then drops off in my room. I've used test tones down to 17hz but that was pushing it's limits.

At this point in my 'evolutionary chain' of upgrading I really see these lasting quite awhile and even with one I am very satisfied. I'm really looking forward to getting 2 going and pumping out some tunes. The SQ for music is amazing. For $500 I have nothing at all to complain about.

The best thing to do is to figure out what size enclosure you're willing to go with. Usually, the bigger the better. Then use WinISD Alpha to figure out which subwoofer models best in that enclosure size. Then tweak enclosure size/vent to match as best as possible.