Concrete Audio Speakers...Speaker Enclosures made out of Concrete ?..

Patented array-technique of the Fraunhofer IDMT – 41 electrodynamic mini-speakers act like one large membrane, allowing for a total depth of only 32 millimetres and giving a convincing performance.

But do they sound Tektonical?

I don't know, I am sure someone said pre 1939, "don't underestimate the skill of a German's engineering" - maybe?

There are marble speakers also.
Find a statue of Cicero or Demosthenes.  

I've heard a round (actually grout) underground vault. It had 4 18" pipe intersections. It was bell shaped. Two were blocked, top was a manhole cover. No bottom, just sat in the sand. This was not concrete, no rock, just fiberglass strands about 4-6" long and an epoxy/grout mix.

2 pro 15" drivers. It had an interior of 20 CF and 1500 pounds or so. It rang so bad, I had to spray the interior with expanding foam.  It bassed  up the whole 2 acre yard. 

A column of Corian at 5/8 thick 18" x 20 x 72" with little bracing will hit a 1/2 ton.. pretty quick. Just a front baffle of @Corian and sides of MDF 550-600 lbs

I'm dealing with 410 lb each, NOW.. With HDF/MDF 

Concrete is the heaviest because of the BIG rock, a lot of weight. Also tough to pump. Light grout mixes that are made with accelerators, can fluff to about HALF concretes weight. Fiberglass, Stainless all kinds of stuff go in the mixes.

Regards

Huh???