Polk Audio AA2521-A MM521 5.25-Inch Coax Speaker Neodymium Magnets a rare earth metal offering exceptional strength to performance ratio Carbon Composite Basket based on the spokes of a wheel is lightweight, will not flex during peaks and looks great! Klippel Optimized Components using a state-of-the-art Klippel Distortion Analyzer Woven Glass Composite Cones feature tremendous stiffness-tomass ratio. Lower mass means faster transients and finer detail. Large-Diameter Voice Coils (30mm) in drivers increase reliability and power handling capacity.