This is the custom enclosure that came with my subwoofer. I believe it was in a Chevy Tahoe or Suburban. I measured this enclosure in and out, then plugged the figures into WiNiSd. (free box design program) The program said that this enclosure is tuned at 48 Hz. My testing revealed otherwise. What I think happened is that the program cannot properly predict what the W7 driver will do. The previous owner had a JL Audio VXi1000 on this so the sub never really was thermally maxed out. Maybe only mechanically limited, due to such a large air volume. I wasn't going to sleep until I knew what the tuning was!