Originally Posted by yveletnik
it suppose to compensate for a slight dip in that region in the on axis.
Just fyi, you can`t really "control" off-axis response separately from the on-axis response.... you can only equalize the sound power response as a whole, normally by taking the 0 degree on-axis response as the reference.
What you do there, will affect what happens everywhere else. Of course different drivers and crossover slopes contribute differently to that sound power, so you can play around a little with it, but overall, what you do on one axis, you automatically do to every other axis!
I guess what I mean to say is, that while the on-axis response might be slightly depressed for whatever reason, the goal isn't to "compensate" for it off-axis - the vice versa - to compensate for too much off-axis energy by depressing the forward axis in isolation - isn't necessarily true either.
as for what acoustic phenominon causes more energy off-axis than on, I don't know.