That was Bert Doppenberg, a dutch audio designer. I visited him once when he started to use the BMS ND4592, like I did back then. I never heard the bass horn myself, maybe he already removed them at that time (around 2005 iirc). His site is www.BD-design.nl (no affiliation). Also for diy parts. He ultimately dissed the horns below the floor in the crawlspace, probably because of the long time delay (back then, dsp was not yet matured/available).
I heard Bert´s subhorns. It was indeed before DSP. Yet at the time, it did not find the time-alignment an issue. I have experienced turning time-correction on and off on much shorter bass horns and the improvement is not subtle. Yet, this sub-system sounded very tight and neutral already. Inspiring, very inspiring. I remember a hiphop/soul recording I played with a lot of "live band" sound. There are synthetic and sub-harmonic sounds and beats added here and there. Those sounds just came out of nowhere and shook me. Nothing like the rumbling and hooting that more conventional bass systems often produce.
I think Bert had several reasons to stop using it. Not only was the time-alignment an (theoretical) issue, it was obviously a subsystem that most of his customers would never own. So demonstrating his loudspeakers with that system might make his customers wonder if they could achieve a similar level of performance at home. I heard Bert's loudspeakers with their own bass system and without an added sub and did not miss a subwoofer. He wasn't hiding anything, he was clearly and rightly confident in his product. I haven't been there in years and years now. I would love to go back and hear the current state of his development. I heard a prototype version of his Orphean horns, basically his Oris horns with coaxial compression drivers. It was up with the very best I have heard, and he was still tweaking.
I think Bert had several reasons to stop using it. Not only was the time-alignment an (theoretical) issue, it was obviously a subsystem that most of his customers would never own. So demonstrating his loudspeakers with that system might make his customers wonder if they could achieve a similar level of performance at home. I heard Bert's loudspeakers with their own bass system and without an added sub and did not miss a subwoofer. He wasn't hiding anything, he was clearly and rightly confident in his product. I haven't been there in years and years now. I would love to go back and hear the current state of his development. I heard a prototype version of his Orphean horns, basically his Oris horns with coaxial compression drivers. It was up with the very best I have heard, and he was still tweaking.