I'm leaning toward building my own sub. My requirements are that it hits at least 20hz, be comparable to the SVS PB-1000 and HSU VTF-2 MK4 in terms of sound quality and performance. Is this possible for less than $500? Or for that money should I buy one? My room is 14'x13'. I have 2 PA-120s that do a good job now, but I want to take a step up in class and want a lower response.