Heyden

Are you adding what's in red so about 1/2 the compression chamber is double (1.5") thick?  Are you doing both compression chambers?  Is the vent size adjustable?  My thought was if you make the cutout in the outer "skin" as big as possible, then make a cutout 3/4" smaller all around through the red you would be able to use a "plug", flush to the outside, that you could adjust to the best sounding vent size - including no vent at all.

I have always preferred the sound of a vented/ported box to a sealed box so I'm thinking you might have a good idea here.

Dan

I'm concerned about the low bass note being lost with a port added to the sealed portion...Ports usually lessen the excursion of a woofer which usually means less low bass notes to me one way or another. Meanwhile a sealed box provides good "spring" for the cone to gain its Xmax to its nominal limits...which is why box volume specs exist for most models...however these specs each have their own cons..which have been calculated generically in this design...so one way or another I would assume such a mod would degrade the designs performance...unless of course you are not trying to get the type of performance its designed for ...in my opinion...(SQ)...at least better SQ than a ported box anyway.