I've seen some 12" 500W RMS subs and even a 15" one at a well known computer store and they are only like £50, think they are called Lanzer or something, I was thinking of getting an amp and that and building a box and wiring my Z5500 sattelites on it too.
When I play a 20Hz test tone the sub has like 1+" excursion, posted it on youtube, and in some parts of the room what I hear is LOUD, it sounds more like 35Hz though and not 20Hz that its trying to play.
Also on some songs I've wacked it up to the point of bottoming out, then turned it down one bar, waited like 5 seconds and wacked it past the point were it was bottoming out and the weird thing was it was no longer bottoming out, but I have to watch how long I play it that loud as the voice coil heats up abit.
I have abit of Hardstyle on here and some chavvy beats lol and wack those up and they shake the room and are very loud, thats the only reason I listin to those sort as the bass or mid range is very loud and thumping. Played this song called H two O or something and the bass or mid range on that really does pound! And its loud were I sit in the corner but when I go to the window its at least twice as louder to my ears, also when I'm sitting at the PC and turn it up my vision shakes about.