抄録
A new method of designing a miniature condenser microphone for broadcasting is described. In order to make a superior T. V. broadcasting microphone, the sound quality and visual quality must be designed compatibly. In this paper, a designing method considering not only the sound quality but also the visual quality is described. At first, the outer diameter of microphone is determined from the visual quality. The result indicates that the diameter of lapel or tie microphone is desirable to be less than 8mm. For the purpose to realizing this requirement, some problems are discussed. The principal problem is to reduce the damping resistance so as to match the mechanical impedance level of a small and light diaphragm without decreasing the electrostatic capacitance that has its minimum value required from the condition of electrical circuit, especially the ratio of signal to noise(Fig. 2). In this paper, a new structure of back electrode that is composed of a porous material is proposed. From some experiments about the electrical and acoustical characteristics, the porous metal which has the crevices of 40μm mean diameter is suitable. Using this material, a miniature condenser microphone(Fig. 23)is manufactured trially. The sensitivity is -47dB(re 1V/μbar)and the frequency characteristics is shown in Fig. 22.
