Thanks, Michael. And yes, they are getting on the heavy side, even without drivers.
The MTM sealed sub-chamber does not get the sonic barrier, but it will have poly fill when completed. Rick could probably comment on the need or lack thereof for the damping material in that area.
I've waffled on the type of finish to use on these because ultimately, they will not be seen behind the acoustically transparent screen wall. Originally, I figured I would just seal the MDF, do some decent priming/ sanding, and use Duratex or a matte black paint and call it a day. Then my anal retentive side steps in and reminds me how nice these drivers look and how I should take more pride in the finished cosmetics. It's the battle between wanting to hear them ASAP and just using patience and effort to do it right. I'm leaning hard toward wait and work!
I'm contemplating using a Benjamin Moore product called Advance. It's target application is for kitchen cabinet refinishing, so it has some good qualities like durability, some degree of hiding ability (MDF seams), and it is supposed to level to a very smooth finish.
I'll keep you posted when I get to that stage because Bondo, primer, sanding, sanding, and sanding for surface prep could take a while.