It’s funny that many of the answers in this thread (but not necessarily unique to this thread) are just people posting speakers they like instead of answering the actual question from the poster. In this thread the OP’s question was "most advanced" and "rectangular"/box, as in interesting materials, construction techniques, new driver arrangements, driver types etc., not "most pleasing, most natural, warmest" classic design.
Instead I see people nominating classic speaker which while fantastic and classic and landmark, by definition are not the most advanced standmounts in a square box today. If I asked what’s the most advanced car today that is still gasoline powered, you wouldn’t say a Porsche 959 or McLaren F1 even though they were landmarks at the time and still eminently collectible valued and esteemed.
I think evolutions of driver materials and types (particularly tweeters), bass porting, time alignment/driver arrangement/phase tweaking, cabinet construction and now re-thinking the traditional two wires going into a passive box are genuinely changing what you can expect at every price point. ATC showed what you can do with active speakers a few decades ago (even though it really rubs audio tweakers the wrong way in some aspects) and now the LS50W and Dynaudio Xeo show me we still have a long way to go in that sort of evolution. I would love to see a cost no-object active standmount from the world’s best leading edge designers, so that the trickle down and market awareness can grow.
