It could be 3 ported/1 sealed. The difference between ported isn't much at all (1dB) but the 4th order has a +6db peak at 36-37Hz when tuned to 40 Hz, it is the same as ported before 32 hz and after 45 hz (45 hz @ 0dB), 60 Hz @ -5dB. Would 1 cube sealed be choking it? Is 3 too small? 42.5 hz port tune = 0dB @ 50 hz w/3 & 1 cubes (more preferable if 2.5 & 1.5 is too low).
2.5 & 1.5 have a +4db peak over ported between 35-55 Hz.
I was told that bandpasses are distortion monsters. thats not true if you set it up properly, right? if you set the gains and the filters correctly how could you go wrong? do they not provide good lows down to 20hz or something and move a lot of air up top?