視覚構造壁の透過および反射特性とそれらを用いた室の残響時間の計算法

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Acoustically transparent visual structure walls such as slat- and grid-walls have been widely used in the ceilings of large studios and halls, but few quantitative data for the acoustical designing of visual walls have been available as yet and the method of calculating, reverberation time in the room provided with visual walls has not been established yet. In order to make these points clear, reflection and transmission characteristics of slat- and grid-walls were studied by means of scale models. Data obtained from this study were used for discussing the method of designing the room provided with visual structure walls. A finite square plate with an area of 20×20cm^2 was selected as a test-piece in this study. A square aperture of the same area as the test-piece was made in a partition in an anechoic room to receive the test-piece in it. The transmitted or reflected sound pressure was measured as functions of the angle of transmission, that of reflection and frequency. Characteristics of the test-piece of the infinite area were examined on the basis of the diffraction theory, from the results of which characteristics of walls of an infinite area were derived. Acoustic transmission through and acoustic reflection on slat-walls relate to the ratio of the slat period L to the wavelength λ of an incident sound. When the ratio L/λ is smaller than 0. 8, the greater part of an incident sound transmits through slat walls. On the contrary, when the ratio is larger than 1. 6, an incident sound reflects in proportion to the surface ratio of the slat. The reflection on grid walls mainly relates to the depth of the grid, while the reflection coefficient of grid walls more than 10cm in grid width and less than 40cm in grid depth is 0. 1 at most in the frequency range below 4 kHz. From the results of study made by means of a model room of the method of calculating reverberation time in the room provided with visal structure, it has been concluded that (1) in the frequency range in which the reflection coefficient of structure walls is small, reverberation time should be calculated with respect to the whole space of the room including the rear part of the structure with the absorptivity of the visual walls shown in Fig. 12 considered to be additional absorptivity, and (2) in the frequency range in which the reflection coefficient is large, reverberation time should be calculated with the space inside the visual walls considered to be the room capacity on which an acoustic design should be based and with due regard paid to the effective absorptivity of the visual walls.
1969-09-15

視覚構造壁の透過および反射特性とそれらを用いた室の残響時間の計算法

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