There are various threads saying to stuff the sub with synthetic pillow stuffing for better sound. I did my Boxster sub and Cayman footwell sub. My ear isn't refined enough to know if it made a difference but it's a fun w/e project and something to do with an old pillow.
The kind that doesn't contain feathers. When opened, you can grab a handfull of the polyfill stuffing out of the pillow and stuff it into the cavities of the subwoofer.
__________________
GPRPCA Chief Driving Instructor
2008 Boxster S Limited Edition #005
2008 Cayman S Sport - Signal Green
1989 928 S4 5 spd - black