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

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'....

I’ll second georgehifi’s suggestion of liquid nail and bricks - with a twist; use 4 bricks. Glue them as close as possible to the centres of the sides and back and the available space near the tweeter on the front. Help strengthen and damp the walls while you reduce volume. I believe most cabinets will benefit substantially from bracing. Let you think about it. Cheers. Pete

Google what is trex made of. All the same crap mdf is made of except trex has the added incredient of shredded plastic and probably more ga -luue as a binder for this compost pile. Tom

toddverrone,  asvjerry, ptss, theaudiotweak,

The speakers are breaking in quite nicely. I am very pleased with the results.
Thank you for your help.

ozzy