Best Buy: Pioneer Champion Series 10" 1000W Dual-Voice-Coil 4-Ohm Subwoofer TS-W257D4
Pioneer TS-W310D4 Champion Series 12" subwoofer with dual 4-ohm voice coils at Crutchfield
Pioneer TS-A301D4 12" Champion Series Component Subwoofer with Power Dual 4 Ohm Voice Coil 1600 Watt Max : Electronics - Amazon.com
Pioneer TS-A300D4 12 Inch 1500 Watts Max Power Dual 4-Ohm Voice Coil A Series Car Audio Stereo Subwoofer Loudspeakers / Free Alphasonik Earbuds : Electronics