22 建築モデュール数値について
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概要
- 論文の詳細を見る
The sound diffraction by a semi-infinite plane screen with knife-edge was measured by AC pulses; short tones with more than 10 seccesive waves from a source at finite distances. This results shows good agreements with diffraction theory of S.W. Red fearn (phil. Mag. 7th. 1940). From the practical point of view, the anther shows that Kirchhoff's diffraction theory is so valuable as it can express the diffraction effects more simply by one parameter and one curve, and it ts applicable to a source or receiver at any distance and to any diffraction angle within ±2db approximately, taking the Fresnel's zone number N as the parameter. Above theories are calculated for a completely absorbent screen, but the experimental results measured by a screen of naked Hornogen-bord show reasonable agreement with the theoretical values, whereas the results by a screen lined with glass-wool-blanket were heigher than that values. It seems to be the term of screen surface condition does not depend on the reflection from the surface, but on the absorption at glancing incidence by screen surface, and unfortunately the factor of this absorption is never considered by any theory of diffraction. Several measurements about the effects of barrier shape were made. The results by a barrier of right angle wedge snow a curve of same form with a curve of diffraction by knife edged plane screen, but few db lower values. The results of experiments on the effects of edge width of screen on diffraction show that, when the edge width is smaller than one or a half wave length the effects of the width are negligible. But when the edge width is not smaller than wave length the measured valnes are reasonablly large.
- 1961-06-25