Best way to decrease the internal volume of a sealed speaker?

Perhaps a little more info is needed.

This is for my DIY speaker project. I purchased high gloss cabinets that were assembled and sized for a particular woofer, but I have decided to experiment further and change the woofer.
The new woofer specs indicate that it would work better with a smaller sealed cabinet.
So, I would appreciate some creative suggestions to make the internal volume smaller.

ozzy

How about using some Black Hole? It's pretty thick, so you may not have to use it on all surfaces, and it's very beneficial in controlling resonance anyway.

Add bracing---dowels attached to opposing walls. It will not only decrease the enclosure's internal volume, but make it more non-resonant (or at least raise the frequency at which it resonates, thus making the resonance less audible).