SUB TO MATCH WITH QUAD 22L'S

400-500 doesnt buy a good sub new so maybe try a nht or B&W used in that price range

Well, I'd be interested in seeing what others suggest, but good, musical subs (as opposed to simple, theater appropriate subs) tend to cost more than the price range you have given. I would look for a used Rel, though again, you are going to have to increase your cash outlay for one.

Also, a key question is how big is your room? It is hard for people to offer sub recommendations with out knowing that.

Ok. I have no problem with good used-Audiogon! I have a studio apt approx. 25 x 35. I am basically looking to augment the bass-the quad's are impressive on their own but I've yet to hear a system that didn't benefit from proper sub enhancement. I prefer fast and tight bass as opposed to HT rumble boxes. I can go as high as $750.00 on budget.

REL strata 3, if you can stretch. It's a great sub, and now it's discontinued it appears to be holding its value. I bought one used for $800 4 years ago and they are still selling for $800 now.