I installed the Kicker 11HS8 Hideaway Subwoofer under my passenger seat and it makes all the difference in the sound of my stock speakers. I set the sub to hit everything from 150hz down and the door speakers to 150hz and up. Sounds great. I think it sound much better than the 10" you get in the trunk from Subaru and doesn't rattle the hell out of the car. Just thought I would share that in case any of you are looking to get a little more bass.