Kicker CompVR 07CVR154 15" subwoofer with dual 4-ohm voice coils at Crutchfield
Amazon.com: KICKER 44CWCD154 CompC 15 Inch 4 Ohm 600 Watt RMS Power and 1200 Watts Peak Power Dual Voice Coil Car Vehicle Audio Subwoofer, Black : Electronics
KICKER CompR 15" Dual-Voice-Coil 2-Ohm Subwoofer Black 48CWR152 - Best Buy