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

toddverrone, cliffkhz, theaudiotweak,

Thank you for the help and the posts.
The woofer I will be using will be located very close to the bottom of the cabinet. Because of this it will be near impossible to place wood at the bottom of the cabinet.

The upper inside top appears to be the best place for any type of cabinet internal volume reduction.
So, at this point, I am first going to try the Styrofoam route. I think I can glue a chunk of it to the inside top. If this rattles or comes loose then the next plan would be to change the front baffle so that the woofer can be raised up and allow the installation of wood or bricks etc. at the bottom.
The front baffle is 1" thick and cutting openings again for the ribbon tweeter and the woofer is not an easy task. 

ozzy

Well I've changed my mind about the Styrofoam.
It looks like I can install some 2x4's pieces inside. I have some 2x4 material made out of Trex that seems to be quite dense an much heavier than a regular 2x4.

ozzy

I just installed the Trex 2x4's.
I installed (2) of them 18" long on each long side placed in the middle of the cabinet.
I figure with that wood my cabinets math out to be .62 cu feet. I already can tell the difference with tighter and deeper bass. The woofers will probably need some time to break in fully, but at this point I am very happy.

I really want to thank you all for the ideas and support. 

ozzy

Good to hear! (See what I did there?)

Synthetic wood was probably a good idea.. denser and not affected by humidity. Well done

Trex....yeah, better than that pesky cellular stuff....good call. *G*

The problem with those " quantum mechanical devices" is, if it 'goes south' (or Whatever 'direction' one wants to call That...) is that parts are just insane to procure....it's not the $, it's the shipping and the 'back order wait state'....