Removing portability opens many options. There's a whole world to explore. Study before you play. Don't be fooled by heavy and hard. Concrete can ring like a bell. Etc. Etc. Etc.
In the metals I would look at magnesium. Similar mass to stiffness as aluminum but higher damping - and much more expensive, of course. I really like the hydrostone / fiber thing I developed and was used on some Hales models. Tension skins on a different & multi) core has lots to recommend it. Remember that the air (acoustic) resonances are only part of the cabinet vibration problem. The drivers must mechanically couple to the shell for rigid launch. They bounce and propagate energy into the shell. Excellent idea is to oppose each driver with an identical one across the cabinet (as in front and back). Bummer is that you then have a bi-pole radiator instead of a point source, which rules out time & phase alignment. So I am opposing the drivers against a rigid vertical spine up the cabinet back. In a new design, that might be quite large. In extant Thiels it will be 1"x 1" and connected to every brace shelf and the cabinet back to damp it. A rod-strut connects each driver magnet to the rod for cooling and mechanical rigidity.
I am exploring an outer shell for extant cabinets. Take a Thiel cabinet, add a few strategic braces if necessary, set the spine, screed non-hardening Permatex type 2 goo, add wood exterior to taste (3/8 x t&g strips). Viola! Inner structure keeps high integrity driver mount x acoustically stiff enclosure volume, and outer shell decouples surface resonances for less sound transmission into the room.
No magic bullet. Plenty of room to play. Let us know your success!
In the metals I would look at magnesium. Similar mass to stiffness as aluminum but higher damping - and much more expensive, of course. I really like the hydrostone / fiber thing I developed and was used on some Hales models. Tension skins on a different & multi) core has lots to recommend it. Remember that the air (acoustic) resonances are only part of the cabinet vibration problem. The drivers must mechanically couple to the shell for rigid launch. They bounce and propagate energy into the shell. Excellent idea is to oppose each driver with an identical one across the cabinet (as in front and back). Bummer is that you then have a bi-pole radiator instead of a point source, which rules out time & phase alignment. So I am opposing the drivers against a rigid vertical spine up the cabinet back. In a new design, that might be quite large. In extant Thiels it will be 1"x 1" and connected to every brace shelf and the cabinet back to damp it. A rod-strut connects each driver magnet to the rod for cooling and mechanical rigidity.
I am exploring an outer shell for extant cabinets. Take a Thiel cabinet, add a few strategic braces if necessary, set the spine, screed non-hardening Permatex type 2 goo, add wood exterior to taste (3/8 x t&g strips). Viola! Inner structure keeps high integrity driver mount x acoustically stiff enclosure volume, and outer shell decouples surface resonances for less sound transmission into the room.
No magic bullet. Plenty of room to play. Let us know your success!