Amazon.com: Earthquake Sound PRO-X188 18-inch Pro-X Series 8-Ohm Die Cast Subwoofer (Single) : Everything Else
SoundQubed HDX4 Series 6000W Car Audio Subwoofer 18 Inch Dual 2 ohm | eBay
Adire Audio KH2501 18" | 2500w Car Audio Subwoofer
Pa-061 Professional Audio 18 Inch Subwoofer Speaker Unit 100mm 8 Ohm 800w 97db (1PCS) - AliExpress
18-in next generation high performance subwoofer, specifically designed for high SPL very low frequency applications in either a reflex, bandpass or horn loaded configuration - Walmart.com