AK... active capsules are part of the variable miniature microphone system. Together with the KM 100 output stage AK... active capsules form a complete microphone. AK 30 and KM 100, for example, make up the KM 130.
AK 45 is a pressure gradient transducer with cardioid characteristic just like the AK 40. However, it has an acoustic bass roll-off characteristic in the free field and therefore suppresses interfering LF noise (wind, structure-borne noise).
Since proximity effect is a natural feature of pressure gradient microphones, the AK 45 appears to be optimized for a flat frequency response at a recording distance of approximately 15 cm (speech cardioid).