Interpreting GD on 4way open baffle

[pjanecke]

My drivers are open baffle 4 way with 4th order LR xovers. I’m using IIR filters in FIR files and the frequency response is nearly flat. Crossover points are 150, 500, 1800. I haven’t done any allpass or linear filters to flatten phase.
Audibly it sounds great but the GD has me baffled (no pun intended). Any thoughts?

 

[sm52]

4th order filters. Or 2nd order. Crossover points. These factors do not affect the lag of one driver relative to another. Therefore, you see that the low-frequency drivers are late relative to the mid-high frequencies.