Bass is, fundamentally, a function of compressing air. The space inside a speaker enclosure has a finite amount of it, and so the key to creating more bass is to fool the driver into thinking there is more air inside the cabinet than there really is. As the pressure builds inside a speaker cabinet from a moving driver, the air inside heats up, forming a tighter air spring that works against the woofer. Adding polyester filling into a speaker cabinet effectively dissipates much of this heat, resulting in increased bass.
Remove the woofer from the cabinet using the appropriate screwdriver. Lay the woofer aside so that the cabinet opening is easily accessed.
Stuff the polyester batting into the cabinet. Do not pack the stuffing too tightly, as the fibers need to move relatively free when under pressure. The ratio is approximately one pound of stuffing per cubic foot of airspace within the enclosure.
Re-install the woofer, tightening the screws in a crisscross pattern.