DEVELOPING STUDY ON EVALUATION METHODS OF SOUND INSULATION CHARACTERISTICS OF PLATES USING SMALL AREA MATERIALS AND TRANSFER FUNCTION ANALYSIS

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A very simple evaluation method of sound insulation characteristics of a palate was proposed. By this method, sound insulation characteristics could be observed from transfer functions of transmitted sound through a test plate with small area or exited vibration on it against incident sound just to the surface of the plate.A new method could be carried out in semi-free field by using the technique receiving only transmitted sound and reducing diffraction sound to the behind.Therefore, it had not necessity of special acoustical test room such as anechoic room or reverberation room. The tests under not only normal incident condition but also oblique incident angle condition could be carried out. From several tests, in a typical room in a building, on such as glass plate, gypsum board and plywood boards with square size of 900mmx900mm and supported at their four corner edges, following results were obtained.At first, sound insulation characteristics similar "transfer functions" could be observed by comparing the analyzed results. Secondly, coincident effects for each material or for each incident angle were shown as the higher peak, meaning strong sound transmission, and lower peak, meaning not so clear effect, in transfer functions at high frequency range. Also frequency changes of the peak caused by coincidence effect could be clearly shown for each sound incident angle condition.As for two leaf plate walls, using small anechoic chamber was also tested to insulate and to reduce direct and diffraction sound pressures on receiving side plate. By this method, resonance transmission effects in low frequency and their frequency changes with setting conditions could be observed. As the conclusion, the new method is useful in design or developing process of dry board walls.