Classification of rock micro-fractures by acoustic emission (AE) parameters is of great significance for rock health monitoring, instability assessment, and precursor warning. But the criteria have not yet been universally formed for the most commonly used method employing rise angle (RA) and average frequency (AF). We conducted expansion rupturing experiment and elastic wave attenuation experiments to investigate the uncertainties of the RA-AF method. Results show the range of the RA-AF distribution extends with the reduction of the AE source scale. The RA-AF moves to the shear-type area in the axis for AE hits with delayed triggering. The RA increase togethering with AF decreasing when the specimen become more compact and smaller in size. It indicates that the fixed micro-fracture reference line is difficult to match potential changes in the RA-AF distribution and the classification criteria is highly dependent on the experimental environment. The uncertainty of the RA-AF method is influenced by the ray path and the source scale. The underlying reason is the uncoordinated distortion between the numerator and denominator in the RA-AF calculation caused by the attenuation and dispersion of elastic wave as well as the measurement error of characteristic parameters. It is concluded that the characteristics of RA-AF are available to understand the comparative relation of different micro-fracture types, but quantify their relations by the absolute proportion requiring consideration of a number of prerequisites. This work not only clarifies the phenomena and reasons for the uncertainty of the RA-AF method but also provides theoretical and experimental guidance for more rational improvement and engineering application.

利用声发射（AE）参数对岩石微裂缝进行分类对于岩石健康监测、不稳定评估和前兆预警具有重要意义。但是对于采用上升角 (RA) 和平均频率 (AF) 的最常用方法，标准尚未普遍形成。我们进行了膨胀破裂实验和弹性波衰减实验来研究RA-AF方法的不确定性。结果显示RA-AF分布的范围随着 AE 源规模的减小而扩展。RA-AF移动到轴上的剪切型区域以进行延迟触发的 AE 命中。RA与AF一起增加当样品变得更紧凑和尺寸更小时减少。这表明固定的微骨折参考线很难匹配RA-AF分布的潜在变化，分类标准高度依赖于实验环境。RA-AF方法的不确定性受射线路径和源尺度的影响。其根本原因是由于弹性波的衰减和色散以及特征参数的测量误差导致RA-AF计算中分子和分母之间的不协调失真。结论是RA-AF的特征可用于了解不同微裂缝类型的比较关系，但通过需要考虑许多先决条件的绝对比例来量化它们的关系。该工作不仅阐明了RA-AF方法存在不确定性的现象和原因，而且为更合理的改进和工程应用提供了理论和实验指导。