Speaker cabinet materials.

Check out Green Mountain Audio. They use cast marble cabinets that are supposedly extremely rigid. Their bookshelf monitors alone weight in around 50 lbs each! There is supposed to be nearly zero box loss contributing to an incredibly clean and coherent sound.
Djembeplay (Threads | Answers)

Even marble flexes. One of the first mods GMA made to the Diamante was adding aluminum ribs bonded to the inside of the cabinet to reduce flexing.

Green Mountain enclosures are cast using our proprietary Q-Stone (TM). It has a much different formulation than used in our Diamantes from 1993 to 1997. No internal braces are required. It is far more rigid, and with far greater internal damping. And yes, heavy too, which by itself has little effect on the sound.

Best regards,
Roy Johnson
Designer
Green Mountain Audio

Hey Roy,

Nice to see you on here. I'm excited about your new Eos line. I'm scraping my pennies together for a pair of Eos 1's... I'm hoping I can manage it by the end of July :).

Keep up the good work!

Tejay

My comment wasn't made to disparage GMA in any way. I just wanted to point out, that a material that one would not think of as being able to flex/vibrate, can do so much to one's surprise. To GMA's credit, they found a problem and fixed it. I have great respect for their designs.

Bamboo laminate is used by Escalante and Ascend Acoustics. Ascend has a CSD graph of the bamboo cabinet to show how little resonance there is in the v-lam bamboo. Go to the last graph on Ascend Acoustics Sierra graph page to check it out.