Amazon.com: H YANKA 12 Inch Subwoofer - 12 Inch Paper Cone Subwoofer Car Audio, Black Steel Basket, Dual Voice Coil 4 Ohm Impedance 12 subwoofer, 1600W MAX Power 12 inch Competition Subwoofer : Electronics
Subwoofer wiring diagrams
Dayton Audio PSS545HE-4 Vortex 21" Professional Subwoofer with 5" Voice Coil 4 Ohm