@Ltryptophan I just realized the 12-page booklet talks about the creation of the mike, and why it is shaped that way and how the openings affect the sound. I did not read the whole thing before posting it.
I assume modern copies of the mike are different, and the housing is just cosmetic, but the original 1939 model depended very much on the shape.
It’s technical beyond my understanding, but here’s a taste:
Bauer’s Unidyne design was configured so that the microphone had a series of front and rear openings which allow sound waves to reach both sides of the element’s diaphragm. The sound waves reaching the diaphragm from the rear had a longer path and passed through openings which produced a time delay between the sound entering from the rear and sound waves striking the front of the diaphragm. By varying the amounts of acoustical resistance encountered at the rear openings, Bauer was able to achieve cardioid, supercardioid, or hypercardioid patterns using a single element, and the first true unidirectional dynamic microphone became reality.