The Subwoofer DIY Page v1.1
Sealed Systems: Design Notes
last updated:09 August 2015
You can decrease the volume required for a particular sealed alignment by using a stuffing material such as fiberglass, wool, or polyfill in the cabinet. Reductions of up to 30% in volume requirements are possible. Make sure that you add the volume displaced by the driver and bracing to arrive at a final enclosure volume.

If you plan to stuff the enclosure, use 0.75*Vb as the net volume for the enclosure. When you add stuffing to the enclosure, the resonance frequency should decrease. Continue adding stuffing until the resonance frequency stops

General design notes for all systems - read!