Last time I ordered some speaker elements from Germany I ordered some extra Tang Band W8-740C subwoofer elements for a later build. I’ve been oogling this design to go with my home-built?ProAc 2.5 clones. Micke, a friend will make the boxes for me, provided I sent him the drawings. What an exellent excuse to try to learn Solidworks. Amazing program. I have designed my own version of the venerable GainClone amplifier with a beefed up power supply and will use two subwoofers in stereo. Nice to not have to build the boxes. Last time when I built the clones the apartment was filled with MDF dust for months.