How severe is port resonance in 4th order bandpass?

[BP1Fanatic]

Where's Glax? He says he doesn't use low or high pass filters, only PEQ.

 

[ImpuPerf]

Is it ‘more’ advantageous to try to create (acoustically) these big areas of cancellation in our subwoofer designs instead of trying to fill them in with messy stuff(horn shape instead of this ‘stepped’ resonator shape ) and then erasing it electronically?

Vituixcad has many types of filters that might be useful to adjust the phase and group delay, e.g. "phase EQ"(FIR), "active Linkwitz transform", various type of "phase linearization"(FIR)