To withstand the beating that this driver will go through, the gigantic pulp paper cone is impregnated with carbon fiber and then reinforced with resin and fiberglass. The xmax of 15 mm ensures incredible air displacement for serious low frequency pressure, and the 72 mm of peak to peak excursion keeps the voice coil protected from over excursion and bottoming out during hard hitting transients. With a rugged accordion surround and dual silicone damped spiders the 21SW4000-NDY-2 excursion stays linear to the limits of its excursion. Finally, holding everything together is a rugged cast aluminum frame that provides an additional level of cooling and even includes integrated push button terminals making it easy to connect this driver when using large gauge wire. The 21SW4000-MDY-2 presents a whole new level of high output subwoofer from PRV Audio.