the special feature is that the concrete corpuses are completely made of one piece, which could only be realized with lost inside shapes .
The only openings are those of the terminal and the cassis.

In addition they are relatively light because the wall thickness is less than 10mm and at the bass reflex channel even only 6mm.

All threads for spikes and chassis are cast directly in the concrete
produced by casting with dykerhoff flowstone and powerd by high end componets from visaton

2013