Dayton Audio PSS545HE-4 Vortex 21" Professional Subwoofer with 5" Voice Coil 4 Ohm
TXX-BDC4-15 Subwoofer - Quad Stack
Amazon.com: Pyle 10" Car Audio Speaker Subwoofer - 1000 Watt High Power Bass Surround Sound Stereo Subwoofer Speaker System - Non Press Paper Cone, 90 dB, 4 Ohm, 50 oz Magnet, 2