The KMR 81 i Shotgun Microphone from Neumann uses a combination of a pressure gradient transducer and an interference tube. If the wavelength of the frequency is longer than the tube length, the microphone works as a pressure gradient transducer. At higher frequencies, it operates as an interference transducer for lateral sound. Off axis sound sources are picked up with reduced level, but without coloration. Therefore, the microphone is well suited to record individual instruments of an orchestra. The pickup areas of several shotgun microphones may even overlap as, for example, during recordings on a large stage, without causing any problem.
Interference tube microphones with shotgun directional characteristic