## 4 Discussion
### Correlation Analysis of Impact Sound Reduction Performance According to Bare Slab Thickness
#### 4.1.2 Correlation Analysis between the Bare Slab Thicknesses of 150 mm and 180 mm in Test Bed A  
A correlation analysis was conducted on the SNQs of the impact sound reduction performances evaluated on bare slabs with thicknesses of 150 mm and 180 mm in test bed A. The correlation analysis was conducted on the reduction performance. The results of the correlation analysis are shown in Figure 12. As shown in Figure 12a, the correlation analysis of SNQs with light-weight impact sound reduction performance was high, with a correlation of \(R^{2}=0.67\) (\(y=0.57x-14.52\)) being recorded. The correlation of the data obtained from the two test beds when using the bang machine was \(R^{2}=0.80\) (\(y=2.07x\) \(-\) 0.50), as shown in Figure 12b, and the correlation of the data obtained when using the rubber ball was \(R^{2}=0.89\) (\(y=2.00x-7.90\)), as shown in Figure 12c. Based on the results of the analysis, the evaluated values of light-weight impact sound and heavy-weight impact sound reduction performance in test bed A when bare slab thicknesses of 150 mm and 180 mm were used are reliable in terms of impact sound reduction.  
1.3 Correlation Analysis between Test Bed A (Bare Slab Thickness of 180 mm) and Test Bed C (Bare Slab Thickness of 210 mm)  
A correlation analysis was conducted on the impact sound reduction performance SNQs evaluated on bare slabs with thicknesses of 180 mm and 210 mm. The thickness of the two floor structures differs by about 30 mm, but it is included in the floor thickness range specified in KS F 2865. The results of the correlation analysis of the impact sound reduction performance of the two floor structures are shown in Figure 13. The correlation of the SNQ for light-weight impact sound reduction performance was somewhat lower, with a correlation of \(R^{2}=0.37\) (\(y=0.89x+5.79\)), as shown in Figure 13a. The correlation of the data obtained from the two floor structures when using the bang machine is \(R^{2}=0.61\) (\(y=1.08x+1.65\)), as shown in Figure 13b, and the correlation of the data obtained when using the rubber ball is as high as \(R^{2}=0.83\) (\(y=8.17x-6.33\)), as shown in Figure 13c. Based on the results of the analysis, the correlation between light-weight impact sound and the SNQ of impact sound reduction performance was low. The factors that were analyzed for low correlation were the different structures of the two test beds and the fact that the floor impact sound test bed with a bare slab thickness of 210 mm had a ceiling structure, which had a higher reduction performance in the high frequency band when evaluating light-weight impact sound. In the case of the bang machine, the correlation value of impact sound reduction performance was also somewhat lower than the correlation analysis results according to other floor thicknesses. However, the correlation value of the impact sound reduction performance of the rubber ball is at a level that can be trusted as the amount of impact sound reduction. Looking towards the future, it is necessary to change the conditions, such as the acoustic chamber, in the floor impact test room with a bare slab thickness of 210 mm. In addition, it is necessary to conduct additional floor mat tests in the changed test room to evaluate the impact sound reduction and to correlate the results  
Figure 12: Correlation analysis between slab thicknesses of 150 mm and 180 mm in test bed A. (a) Tapping machine; (b) bang machine; (c) rubber ball dropping at 1 m height.  
with other bare slab thicknesses and conditions. Based on the results, it is judged that it is necessary to consider whether the slab thickness range mentioned in KS F 2865 can be met.