are you talking about the Schroederfrequency?
mine is around 203Hz acordig to https://amcoustics.com/tools/amroc?l=408&w=293&h=243&r60=0.3
anyways
is around 800-1000Hz afaik
you're crossing your subwoofers way too high, I feel like I'm repeating myself for the tenth time but i will go ahead and repeat for the 11th.
above shroeder's sound becomes stochastic/chaotic and a measurement at one point in time/space is no longer representative of what you actually hear. if you move 1 cm up the phase will be different and the response will be different. same thing with time, every measurement becomes distinct and different from each other.
we use 'smoothing' to estimate the overall sound energy but that's not really reflective of the actual listening experience.
you have to integrate your subwoofer in the region where sound is 1+1=2. not in the region where watermelon juice is a sexy spaghetti meatballs.