1.1 该测试方法涵盖了现场，或 原位 用双面法测量声功率级。该测试方法旨在最大限度地减少混响条件的影响、所考虑的噪声源的方向性以及同时运行的其他附近设备的环境噪声的影响。 1.2 本标准并不旨在解决与其使用相关的所有安全性问题（如果有）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践并确定法规限制的适用性。 1.3 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》中确立的国际公认的标准化原则制定的。======意义和用途====== 5.1 现场设备的功能和操作通常排除在没有来自同时操作的其他设备的干扰声的情况下测量单个设备的自由场声压级。在大多数情况下，双面法将提供在不利环境中工作的样本的正常声功率级的可靠估计。 5.2 该测试方法旨在在通常被认为是干扰背景噪声的情况下用于现场。该测试方法基于Hubner的工作 5 , 6 还有迪尔， 7 但不同于所有其他当前声功率测量程序，因为它需要在两个共形表面处同时测量，并且通过将两个表面处的时间平均声压级解析为0以内。1分贝。这两个特性，同时记录和0.1 dB分辨率，使得当声源的直接声场实际上低于环境噪声时，可以计算声源声功率。 5.3 预计该测试方法的使用主要用于对来自类似声源的声功率进行相对评估，或者根据另一个工厂中类似声源的测量结果预测工厂中的声级。据信，在适当注意应用并完全符合本规程的规定的情况下，该试验方法能够产生相当好的绝对功率水平估计值。 5.4 只有当两个测量表面可以被物理地选择以产生平均声压级差的正值时，双面法才适用。也就是说，内表面声压级减去外表面声压级必须至少为+0.1 dB。该限制适用于所研究的每个频带和每个组成表面积。只有出现零或负差的频带才被认为是无效的，并且通常相邻的频带将是有效的。实际上，给定倍频程的所有三个三分之一倍频程频带很少会在所有组成区域产生无效数据。因此，当使用三分之一倍频程分析并报告完整倍频程结果时，不完整的结果是允许的。 5.5 当在非常混响的房间中或在体积小于由较大尺寸的机器周围的包络所包围的空间的约20倍的房间中测试一些非常大的机器时，双面法可能不会产生结果。在这种情况下，靠近机器的声压级可能不会随着距机器表面的距离增加而以任何规则的方式降低，使得不可能选择产生声压级正差的两个测量表面。

1.1 This test method covers the field, or in situ measurement of sound power level by the two-surface method. The test method is designed to minimize the effects of reverberant conditions, directivity of the noise source under consideration, and the effects of ambient noise from other nearby equipment operating at the same time. 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.3 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 The function and operation of equipment in the field often preclude the measurement of the free-field sound pressure levels of a single piece of equipment in the absence of interfering sound from other equipment operating at the same time. The two-surface method will provide, in most cases, a reliable estimate of the normal sound power levels of a specimen operating in an adverse environment. 5.2 This test method is intended for use in the field in the presence of what is normally regarded as interfering background noise. This test method is based upon the work of Hubner 5 , 6 and Diehl, 7 but differs from all other current sound power measurement procedures by requiring simultaneous measurement at both conformal surfaces and by resolving time-averaged sound pressure levels at both surfaces to within 0.1 dB. These two features, simultaneous recording and 0.1dB resolution, enable source sound power to be calculated when the direct sound field of the source is actually lower in level than the ambient noise. 5.3 The use of this test method is expected to be primarily for the relative assessment of the sound power from similar sources or for the prediction of sound levels in a plant based upon measurements of similar sources in another plant. This test method is believed to be capable of yielding a reasonably good estimate of absolute power level with proper care of application and full conformance to the provisions of this procedure. 5.4 The two-surface method is applicable only when the two measurement surfaces can be physically selected to produce positive values of the difference in average sound pressure level. That is, the inner surface sound pressure level minus the outer surface sound pressure level must be at least +0.1 dB. This limitation applies to each frequency band and each constituent surface area investigated. Only the frequency band in which a zero or negative difference occurs is it considered invalid and usually adjacent bands will be valid. In practice, only rarely will all three one-third octave bands of a given octave yield invalid data at all constituent areas. Therefore, less than complete results are permissible when one-third octave analysis is used and full octave results are reported. 5.5 The two-surface method may not produce results when testing some very large machines in very reverberant rooms or in rooms having a volume less than about 20 times the space enclosed by an envelope around the larger dimensions of the machine. In such cases, the sound pressure level close to the machine may not decrease in any regular way with increasing distance from a machine surface, making it impossible to select two measurement surfaces producing positive differences of sound pressure level.