Amazon.com: Massive Audio TKO104 TKO Series. 10 Inch, 600 Watt, 8mm Top Plate, Dual 4 Ohm Car Subwoofer. Sold Individually. : Electronics
Skar Audio SDR-18 D4 18" 1200 Watt Max Power Dual 4 Ohm Car Subwoofer : Automotive - Amazon.co.jp
Amazon.com: Pyle Car Subwoofer Audio Speaker - 8in Non-Pressed Paper Cone, Black Plastic Basket, Dual Voice Coil 4 Ohm Impedance, 800 Watt Power and Foam Surround for Vehicle Stereo Sound System -