ASHRAE标准68-78和相关ISO草案标准ISO DIS 5136描述了一种使用位于最佳径向位置的B&K UA 0436采样管测量风机辐射到管道中的声功率的方法，无论有无气流。自ASHRAE标准68-78发布以来，不同的实验室已将该方法与更传统的方法进行了比较，如AMCA 300或使用ISO 3741的混响室测量。这些实验室报告了一些结果之间的不一致，尤其是高于管道截止频率的结果，取样管的结果比其他方法的结果稍低，并且差异随着频率的增加而增加。 为了确认这些趋势，并计算出可能的校正系数，我们将采样管法与最近开发的导管内双麦克风强度技术进行了比较，该技术带有消声终端，以确定不同噪声源的绝对声功率。

ASHRAE Standard 68-78 and the related ISO draft standard ISO DIS 5136 describe a method for measuring the acoustic power radiated by a fan into a duct, with or without flow, using a B & K UA 0436 sampling tube located at an optimum radial position. Since the publication of ASHRAE Standard 68-78, different laboratories have compared this method with more conventional ones, such as the AMCA 300, or reverberation room measurements utilizing ISO 3741. These laboratories have reported some disagreement between results particularly above the cut-off frequency of the duct, the results being somewhat lower with the sampling tube than with other methods, and the difference increasing with frequency.In order to confirm these trends, and to work out possible correction factors, the sampling tube method has been compared with a new, recently developed 2-microphone intensity technique in the duct, with an anechoic termination, to determine the absolute sound power of different noise sources.