2x12 Boxy Blues. Help!

So I've had my vertical recto 2x12 cab for almost a year now. I've gone through the origional V30 speakers (cab is 6 years old so they were broken in) G12t-75's, G12h-30's, and have settled on the G12t-100's as the best sounding to me. Through all this the cab has retained this annoying "cardboard box" quality to the sound that I cant seem to shake with speaker changes. Is there another speaker (Eminence perhaps or EVM) or a modification that I can make like insulation or porting that will make my cab less boxy or is this just the nature of a 2x12? I love the easy handling of a smaller cab but tone trumps all.

I just went through 5 different pairs of speakers in my vert. 2x12 and finally broke down and put my 2 EVs in that I've had sittin around for years. I had the same problem with the vert. as you, sounded like the amp was buried inside the cab and no matter what I did I couldn't get it to come out! I put some memory foam that was 2" thick on the inside to ke the cab resonance down and stuck the EVs in there and I'm a happy camper! I hated the C90s in that cab and my old well broken in V30s were too bright and lacked bass. The best combo was the Celestion G12t75 and an Eminence Private Jack together. But with all those speakers I still had this hollow cardboard sound that you describe and was about to go back to the 4x12. The EVs are the best speaker for my MkV by far! Eminence makes a n EV copy for a lot less, its called the Delta Pro 12A or something like that. Love Eminence stuff btw.

Thanks man. Maybe I'll try one more speaker swap.

Acoustic insulation always helps if a cab sounds too boxy. Not necessarily a speaker change.