1.1本试验方法包括使用阻抗管（也称为驻波装置）测量声学材料的阻抗比和正入射吸声系数。 1.2 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管限制的适用性。 1.3以国际单位制表示的数值应视为标准。 ====意义和用途====== 吸声材料的声阻抗特性与其物理特性有关，如气流阻力、孔隙度、弹性和密度。因此，本试验方法中描述的测量值对吸声材料的基础研究和产品开发非常有用。 在某些情况下，正入射吸声系数比随机入射吸声系数更有用。 例如，它们用于预测在小型封闭空间（如机器内部）中放置材料的效果。 材料的随机入射或统计吸收系数的估计值可以从正入射阻抗数据中获得。对于局部反应的材料，即平行于其表面的材料内部没有声音传播的材料，可以使用London推导的表达式从特定的法向声阻抗值估计统计吸收系数 (1) . 5. 局部反应材料包括与表面平行的内部损耗高的材料，如高密度的多孔或纤维材料，或由分隔空腔（如蜂窝芯）支撑的材料。还开发了估算局部和整体反应材料以及有无空气空间的多层系统的随机入射吸声特性的公式 (2) .

1.1 This test method covers the use of an impedance tube, alternatively called a standing wave apparatus, for the measurement of impedance ratios and the normal incidence sound absorption coefficients of acoustical materials. 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 1.3 The values stated in SI units are to be regarded as the standard. ====== Significance And Use ====== The acoustical impedance properties of a sound absorptive material are related to its physical properties, such as airflow resistance, porosity, elasticity, and density. As such, the measurements described in this test method are useful in basic research and product development of sound absorptive materials. Normal incidence sound absorption coefficients are more useful than random incidence coefficients in certain situations. They are used, for example, to predict the effect of placing material in a small enclosed space, such as inside a machine. Estimates of the random incidence or statistical absorption coefficients for materials can be obtained from normal incidence impedance data. For materials that are locally reacting, that is, without sound propagation inside the material parallel to its surface, statistical absorption coefficients can be estimated from specific normal acoustic impedance values using an expression derived by London (1) . 5 Locally reacting materials include those with high internal losses parallel with the surface such as porous or fibrous materials of high density or materials that are backed by partitioned cavities such as a honeycomb core. Formulas for estimating random incidence sound absorption properties for both locally and bulk-reacting materials, as well as for multilayer systems with and without air spaces have also been developed (2) .