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

British audio engineer, Gilbert Briggs, who founded Wharfdale in the late 30's wrote a number of interesting books on "loudspeaker" design. He installed speakers into bricked-in corners in a room - must have had a very supportive partner. My takeaway from one of his books was the use of bonded dissimilar materials so that their natural resonances would tend to cancel each other out. Taking his advice, I glued 12" square sheets of mosaic tiles, then grouted them, on the inside surfaces of my cabinets - enjoyed listening to those speakers for 50 years. Probably for the same reason Wharfdale sold loudspeakers with sand-filled voids in their walls in the 50s.