## 4 Results
### Noise Check Test Results  
Regarding the noise check test, when the test was only conducted using a hammer hit, there was no AE source result, while there was a clear waveform change. On the other hand, when the pencil lead break and a hammer hit were applied at the same time, the results had almost no change, with an error of less than \(\pm\) 5% (\(y\) and \(z\) axes and \(d\)), which is presented using pink in Figure 5a. Thus, a hammer hit noise, more than twice the height of the specimen away from the original point, has virtually no influence on this AE source location technique. Even such an enlarged noise, a hammer hit, had no effect on the calculated results. Those smaller noises (walking, speaking, and so on) far from the specimen should also have no effect on this AE source location technique.  
For the inaccurate result of noise check test, the relevant percent errors were a \(y\),error of \(-\)93.4%, z\({}_{-}\)error of \(-\)23.0%, the distance \(d\),error of \(-\)25.0%, and \(t\),error of 1.58%. Thus, it was possibly due to some technique error or human error. For example, when the pencil lead was broken, the source may have been too weak to be traced, by chance (e.g., the quality of pencil lead). However, after the pencil lead was broken, the mouth of the pencil may have touched the surface of the specimen by accident, which would affect the accuracy.  
As mentioned previously, any result with a preced error more than 30% was considered to be inaccurate. According to Figure 5, there was 66.7% accuracy on A point and only 41.7% accuracy on C point, while there was 91.7% accuracy on B point (except in the noise check test). Thus, the calculated results on B point (the central part) had a higher accuracy than those results on A and C points. The calculated results on C point had a lower accuracy of 41.7%. This was possibly due to the direct connection of the metal specimen and the pedestal because it is easy for the PLB wave to be reflected through the connection surface of metal and pedestal. However, the membrane separation (Figure 1) in the upper side can help to reduce such attenuation and reflection of the PLB source wave. Thus, it is believedthat the calculated results on A point are with higher accuracy (66.7%) than those results on C point (41.7%). This suggests that during the triaxial test, the connection of the specimen and pedestal/top cap would have some effect on the final calculation results. It should be noted that the authors just wanted to fix the specimen on the pedestal without considering such a problem in advance.  
In fact, all the PLB sources were applied above the lowest sensors and below the highest sensors, meaning that the generated PLB sources were fully covered by eight sensors. Therefore, those PLB sources could reach the sensors directly, instead of reflections. However, following the results, such inaccurate results appear to be due to the different mounting of the upper part and the bottom part, which suggests that different mounting effects, such as reflections, exist. Moreover, in this real situation, the bottom side was connected to the porous stone and the pedestal and the upper side was connected to the porous stone and the top cap. They are also different connections; thus, they might have some influence on the calculated results. In the future study, a different method of mounting should be considered. So far, it is believed that if both sides have membrane separation, the accuracy of C point may be increased.