B&C 21SW152-4 21-Inch 4 Ohm Neodymium Subwoofer 4000 W continuous program power capacity153 mm (6 in) split winding copper voice coil30 - 1000 Hz response96 dB sensitivity60 mm peak-to-peak excursion before damage Neodymium magnet allows a very high force factor and linear excursion Double silicone spider with optimized compliance Ventilated voice coil gap for reduced power compression Aluminum demodulating ring for very low distortion