No substitute for surface area when it comes to bass. Apart from excursion.

Best REL demos have three top model woofers on top of each other per channel.

A mid range Apogee Duetta is equivalent to 3 12 inch woofers per channel. But excursion is limited.

Bohne a few years ago did one of the best demos I have ever heard. 18 inch JBL subs with 15 inch JBL mains using Apogee like real ribbon mid/treble. Very little volume constraint and massive bass volume way beyond achievable planar magnetic levels.

Huge space required to accommodate such a system. Not as seamless as a full ribbon design and not as articulate as planar magnetic bass, but still absolutely kiss arse fantastic.

Given it's DIY, who actually made them, Martin?