Dayton Audio RSS390HO-4 15" Reference Series HO Subwoofer 4 Ohm
DS18 EXL-XXB15.4D 4,000W Max Dual 4-ohm 15" Subwoofer
Amazon.com: Timpano 15" Sub D4 1600 Watts Max Power Dual 4 Ohm, 15 Inch Car Subwoofer 16 mm Xmax, TPT-T1500-15 D4, 2.6 in Voice Coil, Double Stacked Magnet Sub Woofer for Car