1.1 该测试方法包括使用阻抗管、两个麦克风位置和数字频率分析系统来确定材料的正入射吸声系数和正常比声阻抗比。 1.2 实验室认证- 认证实验室执行本试验方法的程序见 附件A1 . 1.3 以国际单位制表示的数值应视为标准值。本标准不包括其他计量单位。 1.4 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、健康和环境实践，并确定监管限制的适用性。 1.5 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 该试验方法可用于测量吸收性材料在垂直入射（即0°）下的吸声系数。它还可用于确定比阻抗和导纳比。用该测试方法测量的性能对吸声材料的基础研究和产品开发很有用。 5.2 在某些情况下，当材料放置在靠近声源的小声学腔中时，例如紧密安装的机器外壳中，正入射吸声系数非常有用。 5.3 当无法在混响室中获得用于准确随机入射测量的大样本时，该试验方法允许比较吸声的相对值。可以从局部反应材料的法向阻抗数据中获得随机入射吸收系数的估计值( 2. ). 注2: “局部反应”分类包括具有高内部损耗的纤维材料。已经开发了将吸声特性从正入射转换为随机入射的公式，用于局部和局部两种情况- 反应和散装反应材料( 3. ). 5.4 本试验方法中描述的测量可以高精度进行，但这些测量可能会产生误导。其他来源可能会产生比测量结果更大的不确定性。应注意充分采样不均匀材料（参见 11.1 ).

1.1 This test method covers the use of an impedance tube, two microphone locations, and a digital frequency analysis system for the determination of normal incidence sound absorption coefficients and normal specific acoustic impedance ratios of materials. 1.2 Laboratory Accreditation— A procedure for accrediting a laboratory for performing this test method is given in Annex A1 . 1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 This test method can be applied to measure sound absorption coefficients of absorptive materials at normal incidence, that is, 0°. It also can be used to determine specific impedance and admittance ratios. The properties measured with this test method are useful in basic research and product development of sound absorptive materials. 5.2 Normal incidence sound absorption coefficients can be quite useful in certain situations where the material is placed within a small acoustical cavity close to a sound source, for example a closely-fitted machine enclosure. 5.3 This test method allows one to compare relative values of sound absorption when it is impractical to procure large samples for accurate random-incidence measurements in a reverberation room. Estimates of the random incidence absorption coefficients can be obtained from normal impedance data for locally-reacting materials ( 2 ). Note 2: The classification, “locally-reacting” includes fibrous materials having high internal losses. Formulas have been developed for converting sound absorption properties from normal incidence to random incidence, for both locally-reacting and bulk-reacing materials ( 3 ). 5.4 Measurements described in this test method can be made with high precision, but these measurements may be misleading. Uncertainties of greater magnitude than those from the measurements may occur from other sources. Care should be exercised to sample nonuniform materials adequately (see 11.1 ).