You would not need to spend a lot of money on a new subwoofer especially for that size of room. An entry level (8 or 10 inch) sub from Axiom, HSU, SVS, Elemental Designs etc would do the trick.

If you are happy with your current sub by all means keep it. I just wanted to point out that there are some budget alternatives.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne