Best Buy: JBL CX Series 12" Single-Voice-Coil 4-Ohm Subwoofer Black CX1200
2) JBL JRX212 1000w 12" 2-Way DJ P/A Speakers+(2) 18" 1400w Subwoofers Pro Subs - Walmart.com
Amazon.com: JBL Club WS1200 12" Shallow Mount subwoofer w/SSI (Selectable Smart Impedance) Switch from 2 to 4 ohm Bundled with Alphasonik Earbuds : Electronics