A Study on the Critical Coincidence Frequency and Transmission Loss of Ply-Wood

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Other Title
  • 合板の限界コインシデンス周波数と透過損失に関する研究
  • ゴウハン ノ ゲンカイ コインシデンス シュウハスウ ト トウカ ソンシツ ニ

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Description

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.

Journal

  • 九州大学農学部演習林報告

    九州大学農学部演習林報告 54 137-172, 1984-03-26

    Research Institution of University Forests, Faculty of Agriculture, Kyushu University

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