According to the yellowing Russian leaflet pictured above, the Oktava MD-66a is a ‘Dynamic coil microphone meant for sound amplification of speech and air traffic/transport controllers/officials communications. One direction microphone.’ (literal translation)
Although the Oktava MD-66a doesn’t look anything like an AKG D58 it is clear from the 2 frequency response graphs above that the design intention of both mics is fairly similar, with a steep cut from the mid-range downwards and a considerable boost to the frequencies which affect the intelligibility of speech. N.B. The dotted line on the AKG graph shows how the low-end frequency response is restored to flat when the sound source is very close to the mic (bass proximity effect). Low frequency sound emanating from further away, however, will be greatly attenuated thereby improving the clarity of the close mic’d sound.
The polar plot also shows a narrowing of the high frequency response on axis. High frequency sound arriving off axis will therefore be considerably reduced.
Although I don’t have any ‘air traffic’ or ‘transport’ to control or ‘officials communications’ to make, it does occur to me that this neat little noise-cancelling dynamic might have many other uses.
P.S. Having taken the MD-66a out on a number of live gigs recently it is currently my favourite mic on snare. It delivers a crisp, fat, punchy sound whilst picking up very little of the bass drum.