My current subwoofer is a Hsu Research Stf-1 150 watt. My room is 17.5x25 9'feet high. I feel that the STF-1 is a little weak and rattles at high volume. I want to use the subwoofer mainly for movies and occasionaly for the ipod. Please reccomend me a Subwoofer for me, thanks and Merry Christmas.

Here is my setup.

Harmon Kardon avr 435 reciever
m3ti fronts (I have the m60 v2 coming soon)
vp100 center
qs4 surrounds
hsu stf-1