I need to purchase a sub for my HT. The room is 19 x 12 open on one side. I'm using JBL Northridge speakers for the 7.1 surround. I'm looking to spend under $250 if possible, but I could go a little higher. Right now I'm using a old Dual 10" Cerwin Vega center/sub combo. It pretty bad. Only goes down to 38hrz or so. I'd like a sub that can get in the low 20's. Recomendations?