Shotgun microphone physics

[Johnno]

CPC's PULSE NPCD664 Shotgun mic has diametrically opposite cutouts running the length of its body that do not go all round the body. Does the way they face make any difference to the orientation of the sensitivity pattern of the mic? In other words, do the side lobes rotate with rotation of the mic given that the cutouts do not go all round the body, or are the lobes essentially 360-degree phenomena?

[Simon Lewis]

They are essentialy 360 degree phenomena. The long tube with the slots gives increasing interference (cancellation) of sound the further the sound goes off axis. The frequency that this works down to is dependent upon the length of the tube, longer tube = more lower frequency directionality). The slot at the very back is there to allow sound to reach the rear of the capsule and to allow pressure gradient operation (i.e. cardioid response). This helps provide some directionality at lower frequencies (but not the sames as the interference tube).