## 3 Results
### Impact Sound Insulation Comparison  
The impact sound insulation also increases with the floor case order (Table 2), so the normalized impact sound pressure levels decrease from simple to multi-layered floors, as illustrated in Figure 3. The bare CLT floor shows the highest normalized impact sound pressure levels \(L_{n}\) (worst performance) without any exceptions at frequency bands, as observed for floors 1-4 in the airborne sound reduction at the range of 50-125 Hz. The SNQ for the reference floor is \(L_{n,w,100}\) = 80 dB, while it is \(L_{n,w}\) = 86 dB without correction adaptation terms.  
The first eigenfrequency of the configurations seems to affect most measurements (except floor 8), and thus enhance the impact sound at the 100 Hz band, instead of the 125 Hz band, which was observed previously for airborne sound. Similar, but weakerpeaks are found at 160 Hz, probably due to overtone resonances for floors 1-9. Additionally, the critical frequency effects are visible with small peaks of \(L_{n}(f)\) at around 2 kHz, except floor 10, which exhibits such a peak at 2.5 kHz (Figure 3).  
The simplest case (floor 1 with single vibration mat and a gypsum layer) shows improved impact sound pressure levels ranging from 2.8 dB (100 Hz) to 41 dB (5 kHz) relative to the reference. The improvements in \(\Delta L_{n}\) levels against the bare CLT slab appear in Figure 4.  
Floors 3-6 (with double vibration mat) show increasing impact sound insulation. In contrast to the airborne sound analysis, floor 5 (two gypsum layers and two plywood layers on top of double vibration isolation) performs slightly better than floor 6 in middle  
Figure 4: Improvements provided in terms of normalized impact sound pressure levels \(\Delta L_{n}\) of the test floors relative to the reference CLT floor.  
Figure 3: Normalized impact sound pressure levels \(L_{n}\) of the test floors (laboratory measurements).  
frequencies (only two gypsum layers on top of two vibration mat layers of exactly the same kind). This still defines the final result in terms of SNQ. Floor 5 has a value of \(L_{n,w}(C_{I})=60(0)\) dB and floor 6 has \(L_{n,w}(C_{I})=62(0)\) dB, hence floor 5 provides better impact sound insulation by 2 dB in the weighted index.  
Further, floors 7-10 (vibration mat on top of a glass wool layer) provide the best impact sound performance, as observed for airborne sound. In Table 2, floor 7 stands out as the best case with \(L_{n,w}(C_{I})=59(1)\) dB regarding the dry solutions (floors 1-7, without concrete floating floor on top). Most wet floor solutions, namely floors 8, 9, and 10, show the best performance, but not floors 11 and 12.  
The non-floating floor wet solutions, floors 11 and 12, demonstrate peculiar behavior and have the worst impact sound insulation with \(L_{n,w}(C_{I})\) values of 70(0) dB and 66(0) dB, respectively. The results are even worse for floors 11 and 12 without a parquet floor (Figure A2, Appendix A), underperforming the bare CLT floor values. Those bad ratings change substantially with added correction terms, while they remain the worst acoustically.  
In Figure 4, the difference \(\Delta L_{n}\)_(/)_ in normalized impact sound pressure levels relative to the bare CLT floor is depicted. The limited improvements at 80-100 Hz (floors 1-9) and the curve drop at 2000 Hz due to critical frequency effects are apparent. The highest contribution to insulation levels is recorded for floor 9 with 54.8 dB at 1600 Hz and the lowest one for floor 8 at 0 dB (80 Hz). A significant comparison is visible for floors 9 and 10; the former has higher contributions above 1 kHz, besides the overall higher performance of floor 10, which has additional suspended ceiling layers. Surprisingly, the improvements of floor 10 are mediocre above 2 kHz, suggesting that the impact sound radiation from the ceiling's gypsum boards around the critical frequency at 2500 Hz dominates in that range of 2.5-5 kHz. Similar peculiarities have been observed with analytical models in [8] or high variation in statistical models in [29].