You might be thinking about the design change of the CS7.2 vs. the older CS7. The CS7 had concrete but the newer CS7.2 uses a composite material of Mineral + Polyester. Our CS6 speakers feature the composite material as well as shown in the technical literature. btw- the technical brochure also shows a picture of the crossover circuit board. No electrolytic capacitors in this speaker- all rolled film capacitors.
Thiel CS6 Concrete front baffle
Thiel replaced the concrete baffle at some point with another material. Do you know if there was any difference in the sound peformance, between the two versions?