To determine sound absorption coefficients of fine granular materials, the materials must be cased to suppress their flowability. In this study, effects of casing on the sound absorption coefficients of fine granular materials were investigated. The normal incidence sound absorption coefficients of cased hollow glass beads were measured using cylindrical impedance tubes. The measurement results demonstrated that the hollow glass beads present a sound absorption peak, which was attributed to the vibration of a particle frame, in the frequency range of 180 to 700 Hz for sample thickness in the range of 20 to 550 mm. With an increase in the material thickness or diameter of the casing, the first peak of the sound absorption coefficients shifted to a lower frequency. The sound absorption coefficients were calculated using an elastic frame model for porous materials. The effects of friction between the lateral wall of the case and the particle frame were incorporated in the bulk modulus and bulk density of the particle frame in the model. The model predicts correctly the frequency at which the first sound absorption peak occurs with an uncertainty of 10%.

中文翻译：

---

套管对细球形颗粒材料的吸声特性的影响。

为了确定细粒状材料的吸声系数，必须将材料装箱以抑制其流动性。在这项研究中，研究了套管对细颗粒材料的吸声系数的影响。装箱的空心玻璃珠的法向入射吸声系数是使用圆柱形阻抗管测量的。测量结果表明，对于厚度为20至550 mm的样品，中空玻璃珠在180至700 Hz的频率范围内呈现出吸声峰，这是由于颗粒框架的振动所致。随着外壳的材料厚度或直径的增加，吸声系数的第一个峰值移动到较低的频率。使用多孔材料的弹性框架模型计算吸声系数。在模型中，将壳体侧壁与颗粒框架之间的摩擦力影响纳入了颗粒框架的体积模量和体积密度。该模型可以正确预测第一个吸声峰出现的频率，不确定性为10％。