Amazon.com: JINGERL 50W 4Ohm 8Ohm Car Subwoofer 4 Inch Woofers Speaker in Car Bass Speaker Long Stroke Loudspeaker for Automotive Sound Box IPC (Color : 1 pieces-4Ohm) : Electronics
4 Inch 40W-100W Subwoofer Speaker 4Ω 8Ω High Power Long-Stroke 2Way Divider Bass | eBay
4 Inch High-End Shielded Woofer: perfect for replacing/upgrading or building bookshelf, surround, sound bar speakers, or other diy speaker projects.