Archimago's Musings: MEASUREMENTS: Speaker Impedance - Part 2; sealed, ported, and a few of my speakers...
2 Ohm Vs 4 Ohm Subwoofers - Which Is Better?
Speaker Impedance: What Are Ohms in Speakers?
Crown 300W 12" Karaoke Woofer Speaker with Max 8 Ohms Impedance, 20Hz- – JG Superstore
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,Yellow : Electronics
Epique E180HE-44 7" DVC MMAG Extended Range Subwoofer 4 Ohm per Coil
Pyle Plpw10d 10 Inch 1000 Watts Maximum Car Audio Power Dual Voice Coil 4 Ohm Impedance Subwoofer Sound Speaker System Unit, Black (4-pack) : Target
STLF-1804-4 | 18" 450W Raw Woofer Replacement Speaker, 4" Voice Coil, 4-Ohm – Sound Town
Understanding Speaker Impedance and Why You Should Care | HiFiReport.com