Alpine SWR-1242D Type-R 12" subwoofer with dual 4-ohm voice coils at Crutchfield
Alpine Type-R SWR-12D2 12" 3000w DVC 2-Ohm Car Subwoofer + Single Sealed Sub Box | Audio Savings
Amazon.com: Alpine R-W12D4 Car Audio Type R Series Sub Dual 4 Ohm 2250W Peak 12" Subwoofer and HA-SWKD Dual Subwoofer Sub Box Install Kit : Electronics