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法向入射吸声系数和法向比声阻抗比。 1.2 实验室认证-- 中给出了认证实验室执行该测试方法的程序 附件A1 . 1.3 以国际单位制表示的数值应视为标准。本标准不包括其他计量单位。 1.4 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者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》中确立的国际公认的标准化原则制定的。 ====意义和用途====== 5.1 该试验方法可用于测量吸声材料在正入射即0°时的吸声系数。它还可以用于确定特定的阻抗和导纳比。用该测试方法测量的性能在吸声材料的基础研究和产品开发中是有用的。 5.2 法向入射吸声系数在某些情况下是非常有用的，其中材料被放置在靠近声源的小声学腔中，例如紧密配合的机器外壳。 5.3 当在混响室中无法获得用于精确随机入射测量的大样本时，该测试方法允许比较吸声的相对值。随机入射吸收系数的估计可以从局部的正常阻抗数据中获得- 反应材料( 2. ). 注2: “局部反应”的分类包括具有高内部损耗的纤维材料。已经开发了将局部反应材料和整体反应材料的吸声特性从正入射转换为随机入射的公式( 3. ). 5.4 本测试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。其他来源的不确定性可能比测量结果的不确定性更大。应注意对不均匀材料进行充分取样（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 ).