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.