Amazon.com: Alpine R-W12D4 Car Audio Type R Series Sub Dual 4 Ohm 2250W Peak 12" Subwoofer and HA-SWKD Dual Subwoofer Sub Box Install Kit : Electronics
Box build for 2-12" Alpine Type-R subs - YouTube
Custom Ported Sub Box Enclosure for 3 10" Alpine Type R SWR-10D2/D4 Subs (35 Hz) | eBay
Alpine 8" Type R Single Enclosure | P.C. Richard & Son
Building a Ported Box for a 12" Alpine Type R - YouTube