> Thomas Edison experimented with cement phonograph cases.  Edison
> worked a great deal on Portland cement and prefab houses at one
> point.  In one of the Edison books are pictures of a very elaborate
> and ornate statue model with an Amberola 30 mechanism inside.

There's also a long tradition of concrete enclosures for loudspeakers.
Years ago, some were made like Grecian urns or abstract sculptures,
but I once saw a rectangular speaker system at a high-end audio store
that was made of concrete with walnut veneer applied to the outside,
presumably to make it look a bit less scary and more expensive.

I think bricks and mortar and such are about as acoustically stiff and
dead as any materials we have, though I had a customer once who'd built
speaker enclosures of heavy plywood, the walls of which were made
hollow and then filled with sand.

Mark Kinsler