Last month we were lucky enough to see this rare and beautiful B&O BM2 microphone pass through the workshop.
According to the BeoPhile.com website, these were made from 1951, and was replaced by the very different looking BM3 in 1962. Although different in appearance, the motor assembly and ribbon are similar in both cases.
The BM2 also has a switchable high pass filter to select between the music and voice modes, and also shares a hard-to-find connector with the BM3 & BM4.
Beyond that, we don’t know a whole lot about it!