I was wondering do you need a 90 degree calibration file. I did with my Superlux ECM999 multiple measurments in Mathaudio Room EQ with no 90 degree calibration file. Simpy there is no such file for the ECM999. So to find out the necesaty for such file i did a horizontal an verticale measurments the graphicly measurd differnces could be hardly seen. When listening in a blind test i would not know which is on.