My question is so close to yours that I have posted it in your thread. Hope you dont mind. We may get combined answers that will help us both.
I have 3 way open baffles with 15" bass drivers, 8" midrangers and 4" tweeters. Playing just the mid and tweeter together, sounds perfect but lack much below 100Hz as expected.
The mid is an exceptional driver (SEAS Exotic W8) which I run full range without filters, and the bass driver is good but not great (Eminence Alpha). If asked to work at just very low frequencies it is perfectly acceptable, having a high Qts which is perfect for OBs.
Unfortunately the 'lower quality' 15" driver with passive low pass filter has a long 'tail' into the higher frequencies and this is muddying the sound of the midrange. My aim is to low pass the bass at 100Hz with a fairly steep slope and perhaps add a bit of amplification.
Throughout the process I am using REW to confirm what I am hearing.
So, does the following sound logical.
Divert the 'high level' signal from the bass driver into a plate amp with high level input. There I can adjust high pass, phase, slope and volume and from then back to the bass driver.