Millercarbon concrete and extruded polystyrene are sometimes mixed together, so you could end up somewhere in the middle sound wise.
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