Development of a small size narrow directivity microphone

We developed a new microphone that has very sharp directivity even in the low-frequency band. In an ordinary environment of sound pick-up, the energy of background noise is distributed mainly in frequencies lower than 1000 Hz. In such frequencies, a typical cardioid microphone has the directivity pattern close to that of omni-cardiod. Consequently, it is difficult to pick up the objective sounds clearly from background noises. To suppress the noises with very small level, the directivity pattern should be also sharpened in the low-frequency band. In this report, we describe a new method to sharpen directivity for the low-frequency band. The method requires three microphone capsules. One capsule is the main microphone with a very short acoustic pipe. The others compose a second-order gradient microphone to cancel the signal that comes from behind the main microphone. A special feature of this microphone is to control a dip frequency of behind sensitivity without changing the frequency response of the front sensitivity.