## 4 Discussion
### Comparison of Single-Number Quantities for the Same Impact Sound Sources  
Tables 2-4 show the SNQ results of the eight floor mat samples from the different test-beds for the same impact source. Table 2 shows the results for the tapping machine, Table 3 shows the results for the bang machine, and Table 4 shows the results for the rubber ball. Regardless of the type of floor mat, it was found that the light-weight impact sound blocking performance can be sufficiently reduced due to the consistent results recorded after each floor mat was installed in the apartment houses. In addition, the discriminating power of impact sound reduction performance by type of floor mat samples was analyzed. On the other hand, in the case of the bang machine, even if floor mats were installed, there were conditions where there was no impact sound reduction performance depending on the floor structure. However, an impact sound reduction performance of up to 5 dB could be achieved depending on the type of floor mat. The impact sound reduction performance of the rubber ball was found to be at least 1 dB and up to 10 dB or more. However, the impact sound reduction performance was analyzed to be somewhat different depending on the test facility condition and bare slab thickness. Except for test bed D, with a bare slab thickness of 150 mm and 180 mm, the impact sound reduction performance corresponding to the use of the rubber ball was analyzed to be similar. In addition, in test beds C and D, which were designed similarly to actual apartment houses, the bare slab thicknesses were 210 mm and 150 mm, respectively, and the impact sound reduction performance was analyzed to be somewhat lower than in test beds A and B, which were laboratory test beds.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Test Bed with Bare Slab**} & \multicolumn{8}{c}{**Sample No.**} \\ \cline{2-9}  & **Sample \#1** & **Sample \#2** & **Sample \#3** & **Sample \#4** & **Sample \#5** & **Sample \#6** & **Sample \#7** & **Sample \#8** \\ \hline Test bed A (150 mm) & 44 & 43 & 47 & 45 & 38 & 47 & 47 & 46 \\ \hline Test bed A (180 mm) & 40 & 40 & 41 & 42 & 35 & 40 & 41 & 39 \\ \hline Test bed B (150 mm) & 42 & 42 & 44 & 43 & 38 & 43 & 43 & 44 \\ \hline Test bed C (210 mm) & 39 & 39 & 38 & 38 & 35 & 38 & 38 & 40 \\ \hline Test bed D (150 mm) & 41 & 42 & 45 & 43 & 34 & 41 & 43 & 44 \\ \hline Average & 41.2 & 41.2 & 43 & 42.2 & 36 & 41.8 & 42.4 & 42.6 \\ \hline Standard deviation & 1.9 & 1.6 & 3.5 & 2.6 & 1.9 & 3.4 & 3.3 & 3.0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The SNQs measured for the floor mat samples using a tapping machine in different test-beds. The unit is dB.  
Figure 13: Correlation analysis between test bed A with a slab thickness of 180 mm and test bed C with a bare slab thickness of 210 mm. (**a**) Tapping machine; (**b**) bang machine; (**c**) rubber ball dropping at 1 m height.  
There are several reasons for the differences that appeared in the impact sound reduction performance results even when the same floor mat and same slab thickness were used. These reasons are linked to various factors, such as the floor area, the location of bearing walls (both those above and below), and the presence or absence of a sound-absorbing plenum structure. These laboratory conditions may have influenced the amount of reduction due to the differences in floor vibration during impact and the changes in receiving room modes. However, these results are still considered valid since the test was conducted in accordance with KS F 2865. Therefore, the reduction values should be described with their test-bed conditions.