BOSS Audio Systems BE8D Elite Series 8 Inch Car Audio Subwoofer - 600 Watts Max, Dual 4 Ohm Voice Coil, For Truck Boxes and Enclosures, Hook Up To Amplifier - Walmart.com
Monacor SP-8/4SQ Universal Speakers 4 Ohm, New in box, Lot of 2 speakers | eBay
Pyle - PLPW12D - Marine and Waterproof - Vehicle Subwoofers - On the Road - Vehicle Subwoofers
Loudspeaker Impedance 4-Ohm vs 8-Ohm: Which is Better? - YouTube