If its just for computer use I don't think you really need a giant badass sub. I moved my sub from my home theater system it was a 12in Definitive (I forgot the model) and it was just way overkill. First it was too big it took up all the extra space I had next to my desk. And it was also too powerful to be used at such a small distance; I had it at the lowest possible settings and it was still causing earthquakes (room/floor wasn't treated). I ended up moving it back to my living room and getting one of these
They go on sale pretty often on amazon.com for $199 which is what I paid for it. Although it is small it is plenty powerful and not loose or boomy.
EDIT:whoops didnt notice you said for computer speakers, I was running a receiver so I could use a sub like the one in my link. Post what speakers you are using becase it may only allow proprietary subs.
Edited by alv4426 - 7/24/12 at 10:43am