High Grade Strontium Ferrite Magnets. Alpine S-W12D4BX 12" Car Subwoofer Fits 14-18 GMC Sierra Crew Cab w/ HA-A800.1 Compatible with 2014 - UP GMC Sierra Crew Cab Alpine Type S S-W12D4 Single 12 Sub Box Enclosure with Harmony HA-A800.1 Amplifier & 4GA Amp Kit.
eBay