A Method of Designing condenser microphones for broadcasting based on the signal-to-noise ratio.

Abstract

Due to the requirements in television broadcasting and other fields, it is necessary to miniaturize the condenser microphone. In this case, however, the designing standard, for the signal-to-noise ratio must be made clear. In this paper some designing method, and the permissible limit of the signal-to-noise ratio using the noise level of a broadcasting studio as reference and based on the condition that and increase of the above level is not detected during reception, are described. The signal sound pressure in the original sound field and the signal sound pressure at the time of reproduction are practically equal. Based on this, the sensation level of the noise ( Fig. 4a ) at the original sound field is obtained and the allowable limit of the signal-to-noise ratio was determined according to the conditions described above. ( Fig. 4b ) On the other hand, when the formula which express the signal-to-noise ratio of the condenser microphone and spectrum of the noise which forms the above are noted, since the noise of the condenser microphone has the same form as the noise formula obtained from the allowable limit, Fig. 5 and Fig. 6 have been obtained as the designing conditions of the microphone. The result of a preliminary calculation as a concrete example is shown in Fig. 7 and Fig. 8. The fair values which can be used in actual practice were obtained. Based on the above concept, three microphones were trial manufactured and each microphone had sufficiently high performance so that it may be used, with satisfaction, in broadcasting. ( Table 1 )