MODEL D215s Subwoofer: Dynamic, Accurate, Solid. The audiophile's choice. Where sound quality and Transients free of overhang are paramount. Simply no better expression of bass performance then our push-pull subs. Ground up drivers developed by our team of engineers. Carbon fiber composite diaphragms, multiple aluminum shorting rings, massive magnets, multi-layer Nomex spiders and lightweight aluminum voice coil wire are the key ingredients - Proprietary nonlinear modeling techniques allow us to simulate all these components and then optimize for real world driver performance - free air and in box. Further refinement is done with the aid of Klippel laser measurements to dial things in.