Polk Audio C4 Subwoofer (1992 Car Audio) - Four 6x9 drivers monted in an isobaric push pull configuration, 4th ord… | Car audio, Subwoofer box design, Subwoofer box
Old School Polk Audio C4 Subwoofer - Four 6x9's in Isobaric Teardrop Enclosure — Polk Audio Forum