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Micromachined directional microphones (sound source localization sensor) mimicking an auditory organ of Ormia Ochracea have been intensively studied based on center-supported, marginally free 1-D or 2-D diaphragm structures. Based on an exact mathematical formulation, a Gaussian weight function on the diaphragm is shown to be inevitable in the transduction of 1st and 2nd moments. An analysis was performed to obtain the weight distribution assuming an arbitrary thickness distribution of a shell-structured diaphragm. The best result was a marginally-supported face-to-face cantilever structure. We fabricated this structure using SOI wafer and RIE. The experimental results show a strong dependence of the vibration pattern on both zenith and azimuth angles, and a greatly enhanced sensitivity to inclined sound pressure.