I've used B&W 804S speakers with their passive crossovers, then went active with digital xo, then into DIY boxed and eventually open baffle. Of course I do measurements for design work. System has now 2 sealed subs to 80Hz, 18" OB midbasses in H panel, and tweeter and midrange sitting above on a much slimmer panel. My tweeter is Beyma TPL-150H, which is actually the same one Spatial Audio uses on their X3 and X4, and I used to use it in a closed box and now open in the back. In fact, when I first ventured into OB I followed the back-to-front symmetry mantra and used a back waveguide like the one it has on the front and eventually realized it sounded as well without it so the back horn was removed (like Spatial does). The TPL is directly driven from Yamamoto 45-type SET...so much definition yet sweetness. The tweeter and midranges sound better to me in OB than boxed - same drivers - however I can easily compensate for the lower frequency decay in the mids, which is a natural phenomenon from the physics of drivers in OB. With passive XO this is trickier to get good results.
There were comments about wide panels. Of course wide panels are needed to support the lower end. However for midranges the wide panel is an issue: above the dipole peak the response is all over the place, especially noticeable at varying angles from the center. Narrow baffles allow reaching higher without this issue, to the point some people use baffleless (been there and came back). Crossing over before the dipole peak is preferred. Spatial Audio, to keep the example above, doesn't do this. Never heard one, but tend to think this would be audible.
Midbass is where I'm still not sure. OB definitely has more definition. However, even using 18" midbasses the sense of impact is much lighter than sealed. Maybe it's because I'm using a Faital driver that is not designed for OB and has low Qts, or because my room can't accommodate speakers 6 feet away from the front wall. I'm contemplating getting 15" Acoustic Elegance LO15, designed for OB, or a slot-loaded open baffle design that apparently conveys more impact while keeping the definition of OB. TBD.
For subs I experimented a bit, exchanged with Danny Richie at GR Research, who developed OB subs with Rythmik, and concluded my room wasn't suitable for such subs. I'm getting two additional sealed Rythmik kits to have 4 sealed subs.
Erik, I remember you at DIY Audio, so you probably have the skills and have fun building stuff. Would encourage you to do so, learn and listen for yourself. I have learnt some "laws" that are commonly accepted in audio fora that turned out not to be audible to me.
Have fun!
