Kicker 42PSC654 6-1/2" 2-way speakers (4-ohm) for use in motorcycles, boats, and off-road vehicles at Crutchfield
Connecting 4-ohm Speakers to an 8-ohm Receiver | Audioholics
Amazon.com: Facmogu 2PCS 6.5 Inch Audiophile Full Range Speakers, RMS 30W MAX 50W 4 Ohm, HiFi Full Range Car Audio Speaker Drivers, Wideband Stereo Audio Loudspeaker Replacement - Yellow : Electronics
Boss Audio Systems R63 Riot 6.5 Inch 300 Watt 3-way 4 Ohm Full Range Car Audio Coaxial Stereo Speakers With Tweeter And Poly Injection Cone, Pair : Target
Speaker Impedance, Power Handling, and Wiring | Jensen Loudspeakers