Sound-Absorbing Materials using of Rice Straws (Oblique Incident Sound-Absorption Coefficient of Oblique Arrangement of Hollow Cylindrical Biomass)

It was reported the use of sound-absorbing materials, specifically sound-absorbing structures of bundled rice straws, that are oblique arranged incident to the sound waves. In addition, we investigated the normal and oblique incident sound-absorption coefficients of sound-absorbing structures made of bundled rice straws in free space. In this study, we placed sound-absorbing structures made of bundled rice straws at an angle against the direction of the thickness in order to elongate the rice-straw element without increasing the apparent thickness. We then experimentally investigated the increase in sound absorption in the low-frequency range. For test samples with rice straws arranged both in the normal direction and in the oblique manner, the sound-absorption peak of the oblique incident sound-absorption coefficient in free space was shifted to the high-frequency side compared with that of the normal incident sound-absorption coefficient and the sound-absorption curve became flat in the high-frequency range. We demonstrated that the use of an oblique arrangement of rice straws inside acoustic tubes and in free space can improve the sound absorption in low-frequency range without increasing the apparent thickness of the material.