:dunno:

No box necessary? Speakers generally work best in boxes. Do a search for "subwoofer".

free air subwoofers are horrible most of the time. just throw a box in the back that's easy to remove if it's that much of a concern.

Didn't see ur original post & now it's edited but I responded to ur PM. Go with the second powered box I used (sounds way more dynamic now that I adjusted the headunit & fooled around with the box controls) http://www.xoutpost.com/bmw-sav-foru...recovered.html or check out this unit I found & u won't have2 build anything http://www.xoutpost.com/bmw-sav-foru...fer-boxes.html

Good luck