Timely: In his latest GR Research YouTube video (posted today, Wednesday 3-23-22), Danny Richie examines the Magnepan Mini send him by a customer. In the video you see not only how Richie evaluates a loudspeaker---and designs a cure for it's ills, if any---but also a tutorial on comb-filtering, a design challenge inherent in all planar loudspeakers.
Finding the video is real easy. Go onto YouTube and do a search for GR Research. The latest video will be first in line. A free education in loudspeaker design!