Amazon.com: 5 CORE Car Subwoofer Audio Speaker - 8 inch 4 Ohm, 100 Watt Power,1” Voice Coil and Foam Surround for Vehicle Stereo Sound System 110mm Magnet Loudspeaker Woofer Replacement WF 8110G : Electronics
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Amazon.com: Gikfun 2" 4Ohm 3W Full Range Audio Speaker Stereo Woofer Loudspeaker for Arduino (Pack of 2pcs) EK1725 : Electronics
Amazon.com: Rockville RVW1800P4 1800w Raw DJ Subwoofer 4 Ohm Sub Woofer 107OZ Magnet, 18" : Electronics
Amazon.com: Pyle 6.5 Inch Mid Bass Woofer Sound Speaker System - Pro Loud Range Audio 300 Watt Peak Power w/ 4 Ohm Impedance and 60-20KHz Frequency Response for Car Component Stereo PLG64 : Electronics
Amazon.com: Granvela 20W 3-inch All Frequency Range 4-Ohm Speakers Pair of Flax-Fiber Cone for DIY Multi-Media Speakers | Computer Speakers : Electronics
Amazon.com: Audiopipe 6" Woofer 150W Max 4 Ohm DVC Sold Each : Electronics
Amazon.com: Pair of E-12 V.3 D4 - Sundown Audio 12" 500W RMS Dual 4-Ohm EV.3 Series Subwoofers : Electronics