| 概要 |
しゃ音は多くの因子に影響されるが,材料によらない外部的な因子を特定の条件に整えた場合の実験によって,材料のしゃ音に対する性質を明らかにすることができる.本研究では,小型試験片による透過損失の諸特性に基づき,合板の限界コインシデンス周波数とその透過損失値の比較法について検討した.しゃ音は新たに設計した音波透過測定装置で測定した.この装置は,音源室になる残響室と受音室になる無響室から構成されている.測...定周波数範囲は,両室の音場の拡散性に関する検討結果によったが,試験片の寸法をも考慮して決められた.その結果では,本装置は小型の装置であるが,1830Hz以上の周波数領域で, しゃ音は十分に精度よい測定値が得られた.限界コインシデンス周披数は異方性材料の直交合板を対象に検討した.異方性材料の透過損失では,コインシデンス効果が明確に判断できないので,合板に入射した音波の伝わる方向を制限することによって,コインシデンス効果を確認した.限界コインシデンス周波数は曲げ波が板を伝わる速度から計算でき,最も速い速度が下限値をあたえることが明らかになった.この結果から, コインシデンス効果に関するCreamerの理論が異方性材料にも適用できる.コインシデンス周波数領域の透過損失は,周波数を限界コインシデンス周波数に対する比(f/f_c) で表わし, 透過損失を質量法測の値と実測値の差{R_f(f)-R(f)}で表わすことができる.この表示では,限界コインシデンス周波数が異なる材料の透過損失を相互に比較できる.合板では,容積密度が等しい場合に, 透過損失の差{R_f(f)-R(f)}と合板の厚さの関係は指数関数で表わされる. コインシデンス効果は,厚さが厚い合板でより顕著に認められる結果を得た.
Sound transmission through a partition was influenced by many factors such as physical properties of elements, boundary condition of a partition, etc. But sound transmission of a partition under given condition reveales the relation between sound transmission and physical properties of an element. In this paper, it is presnted the critical coincidence frequency of ply-wood and a comparison method of the transmission loss at coincidence frequency range. Sound transmission is measured with the measuring apparatus for transmission loss (Fig. 1), which is designed for this investigation. This apparatus consists of a reverberant chamber for a sound source room and an anechoic chamber for a sound recieving room. Measuring frequency range of the apparatus is determined with diffusivity of sound field at each chamber and the dimension of a partition. Sound transmission is measured with a small partition (300X300 mm) and sound transmission is measured with accuracy at frequency above 1830Hz. It is examined the critical coincidece frequency with cross laminated ply-wood as one of anisotropic material. By traveling sound wave to the restricted direction of ply-wood, it become apparent that the critical coincidence frequency of ply-wood is determined from the velocity of bending wave traveling a ply-wood plate. As mensioned above, it is clear that Cremer's theory is applied to anisotropic material. Transmission loss in critical coincidence frequency range is expressed in term of the ratio of measured frequency to the critical coincidence frequency (f/f_c) and the differnce of transmission loss at same frequency between the value of the random incidence mass law and measured value (R_f(f)-R). By this expression, it makes possible to compare the transmission loss at the critical coincidence frequency of one partition with that of other partition. In the case of ply-wood with same density, the relation between (R_f(f)-R(f)) at the critical coincidence frequency and thickness is represented by exponential function. Consequently, the effect of coincidence of thick plywood is more remarkable than that of thin ply-wood.続きを見る
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Mendeley出力
