Abstract
In designing the miniaturization of a condenser microphone, the most important condition is the adequate miniaturization of the diaphragm which determines the external dimensions. In order to satisfy this condition, it is desirable first to determine the minimum area of the diaphragm satisfying the design target and then to determine the various constants of the microphone elements. This paper describes the design method and conditions for the DC biased directional condenser microphone studied with the above design policy. For the miniaturization of the diaphragm, determination of the adequate electrode spacing is an important condition. Furthermore, it is necessary to restrict the lower frequency limit of the front characteristics in the mechanical system because of the necessity for high equivalent stiffness of the diaphragm. First, the relations between electrode spacing and minimum diaphragm area, sensitivity, bias voltage, and constants of the mechanical system which satisfy the design target, like stability, frequency range, inherent noise, dynamic range and directivity, are analyzed. On the basis of these results, the design conditions for the electrode spacing in order to design a directional condenser microphone with minimum diaphragm is considered. Furthermore, two techniques to correct the decreasing of the front characteristics in the mechanical and electrical system, which occurs in the design of high equivalent stiffness diaphragms, are discussed, and the design conditions are obtained.
