Amazon.com: 1PC 4 Inch Hi-Fi 8ohm / 4ohm Subwoofer Speaker Audio Super Bass Woofer Loudspeaker 40W High Power Speakers (Size : 4ohm) : Electronics
Subwoofer Reviews | Stereophile.com
One unit (not pair) |15 Inch Woofer for Bass Compensation of Open Baffle or Cabinet | W-15 - Lii Song (Lii Audio), unique speaker, amplfier, quality and cost-saving parts for HiFi DIY