just found something that in speakers Bessel should be avoided, Butterworth for uneven and Linkwitz for even orders. This may be more for passive filters. But the simulation for Bessel had the biggest dent at the corner frequency from memory. Luckily in an active filter its easier to change elements. Maybe should wire in potentiometers first and once its sortes, get the proper velues. Otherwise eventually the paths in the PCB bord come unstuck.
Building digital filters from scratch, hm, maybe can score one on ebay. Changing frequencies would be way easier then. Maybe I have to go for 4th order, 3rd gets 270deg, does not sound like a good plan. The original plan used 24 db filters that can be set via dip switches or so. But I tought 4th order is not that good at the corner frequencies. Some wavieness. Have to find that article and post a scan. Sidetracked with that rebuilding of a house.