In addition to straight versus slant (straight is boomier IMHO too) and speaker selection, good solid wood throughout definitely helps too, so you may want to compare what your current cab is made of and what your target cab is made of. I found this phenomenon out accidentally with my first Boogie 4x12, one of the old half-backs with metal grate, back in the early 90s. I had decided to make a pedalboard the exact size of the top open-half. My logic was I could pop the pedalboard into the back of the 4x12 for transport. So I started making the pedalboard platform with a scrap of old big chip particle board I had lying around in my shed. I noticed it was slightly warped after I cut it and tried to seat it flat in the cab's frame. Since it was going to require more effort and a nicer piece of wood, I went and got some multi-ply birch, like the actual cab was made of. Twice as thick, twice as heavy, flat as a pancake. After I had finished the two boards and before I stuck pedals all over the "good" one, I decided just to bolt them in to see how the cab sounded fully closed, I had never tried that. Neither sounded as good as the half-back to my ear, but the solid birch back definitely threw more boom and authority compared to the shit wood. Similar thing went down about six years ago when I inherited a old 1936 series horizontal Marshall 2x12 from a buddy. I noticed it had a particle board backboard when I was tinkering with it. I soon changed that out for a heavier (and I assume stiffer) multi-ply back and it definitely made the cab sound bigger than it was.
