[. . . ] ENCLOSURE INFORMATION Phoenix Gold subwoofers are over engineered and overbuilt in virtually every way conceivable. [. . . ] Be sure that the enclosure's panels are airtight at all joining seams. lining the walls with a polyester matting 1 to 3 inches thick is sufficient. Your PG dealer has extensive knowledge, tools and the experience needed for the design and construction necessary for your subwoofer application. We also recommend you consult with your dealer for specific technical assistance related to your installation. The charts provided should be used as a reference when building an enclosure for your subwoofer. The Sound Quality enclosure provides deeper, tighter, and more musical output to truly reproduce the original source material. [. . . ] The SPL enclosure fits the "basshead's" need for maximum output while sacrificing some sound quality. [. . . ]