A completed subwoofer enclosure I designed for a friend a couple years ago.
He called & gave me dimensions, woofer specs, and what tuning frequency he wanted. I ran the numbers & gave him port specs & chamber sizes.
Each sub sits in 2.3 cubic feet of airspace, and the ports are tuned around 35 hertz. The subs are Phoenix Gold XS and the amp running them is a Phoenix Gold ZPA 0.5.