How was the sound?
it was nice, not the best, possibly because system was too complicated. Lots of potential and minor corrections required, though lot of experiments will have to be done to find out what those changes are. Could be the filter, could be the Onken. Imo he should first just go back to simple 2/3 way Altec instead of a 4 way mix of drivers. Then try without the filter if that does not work.
but all the ingredients of bass, tone, are there, it is getting a bit more coherence, balance and EE in.
For me it was a good lesson in how such big horns did in a 5m wide room. The room is long but the seating position is standard 4m from the speakers, and speakers are in a corner. I think the room fit works fine, and I also checked sound from behind the piano.