I always make it a point to make time for MBL to listen to their unique and impressive systems and talk to their designer, Juergen Reiss. In Munich I was fortunate enough to sit in on Juergen's demo where he explained some of the principles behind the extreme Radialstrahler mbl 101 X-treme speakers and one of the key points he made is best illustrated here:

image from an article in HiFi/Stereo Review December 1960