https://www.gr-research.com/diy-subwooofer-kits.html
His DIY forum is here. You can build your own H-Frames (the schematics and wiring diagrams are provided), have someone else build them for you (e.g. local carpenter or cabinet shop to save on shipping) or buy some CNC flat packs from some of the guys on his forum, glue them up and paint them.
https://www.audiocircle.com/index.php?board=16.0
You can buy the drivers and use your own amps if you don't want to go servo immediately to save money. You will have to provide your own XO's and DSP.
People make them in duals, triples, quads and 6 driver towers. Singles are far and few in between.
HTH
