I don't know how concrete enclosures sound. I do know that cinder blocks make decent speaker stands. I used some, back in college, for my large Advents. Cheap, minimal resonance and meets a certain post-industrial chic.
Concrete Audio Speakers...Speaker Enclosures made out of Concrete ?..
Could concrete speaker enclosures give us the most realistic sound ?
https://www.concrete-audio.com//en/#lautsprecher
Not connected with this company in any way
https://www.concrete-audio.com//en/#lautsprecher
Not connected with this company in any way