On Sound Absorption Properties of the Molded Bark Fiber

Abstract

Sound absorption properties and an estimation method of normal incidence absorption coefficient were investigated for the molded bark fiber in which pulp was mixed as a bonding material. First, the characteristic impedance and the propagation constant of the molded article were obtained as a function of f/σ (a ratio of frequency to airflow resistivity) in conformity with the method of Delany-Bazley. Furthermore, relational expressions between the bulk density and the airflow resistivity of the molded article were obtained for the bark fiber and the pulp which are the components of the molded article. The calculated values gave close agreement with the measured values after estimating normal incidence absorption coefficient from the bulk density and the sample thickness of the molded article by using those expressions. And, sound absorption properties of the molded article were clearly articulate, and the guideline of the compressing condition was obtained from the measured values and the estimated values by varying the bulk density and the sample thickness.