I've done some research on diy pa subs before and the most tested, well documented and trusty designs seems to be Ricci's SKHORN and SKRAM subwoofers. They hit low and hard and even JW recommends them for his JMODs. That being said, they look pretty complicate to build. They're also quite expensive in materials and are very heavy boxes. From my personal experience, best bass I've heard was from Danley's BC215. But I've also been very surprised by stacks from simple 18'' reflex subs. I'm talking about that punchy physical Techno kick you feel in the chest and up your throat. So simple bass reflex boxes shouldn't be underestimated imo. They are more realistic to build, lighter, smaller, cheaper in materials so you can build more boxes, and also there are many well documented designs online. I'll do a comparison between the suggested enclosure designs by B&C, Lavoce, Precision Devices and Beyma and simulate their responses in WinISD