## 3 Results
### Linear Regression Model Comparison
The resonance effects of multi-layered configurations at the critical frequency areas (mostly seen at the 1.6 kHz frequency band) with relatively decreased insulation are observable for both airborne and impact sound measurement data. Regarding specific materials, the effects of resilient layers and floating floor components are clearly beneficial for enhanced sound insulation. Floors with a single resilient layer of 12 mm (vibration mat) provided moderate improvements of 9-13 dB for airborne sound and 13-21 dB for impact sound; this is in terms of single number quantities (SNQ) compared with the reference CLT. The added floating mass (plasterboard, plywood, wooden parquet) plays a role when comparing floors 1 and 2. Significant effects for blocking impact noise transmission are demonstrated even in those simple floor cases. Double resilient layers work more efficiently and combinations of two different vibration mats provided further improvements of 14-18 dB for airborne sound and 16-24 dB for impact sound descriptors (floors 3-5). However, using two of the same vibration mats yielded 1-2 dB better airborne and impact-related SNQs in the case of floor 6. Floor 7 with a vibration mat on top of glass wool still performs slightly worse than floor 6. However, the combination of a vibration mat above glass wool insulation yielded the best results for the so-called wet floor solutions, those that have a concrete screed layer on top of resilient ones. Such cases with parquet floor as the final covering (floors 8-10) demonstrate the highest insulation values, with SNQ improvements of 19-27 dB for airborne sound and 29-34 dB for impact sound. The contribution of the parquet floor is rather arbitrary for dry floor solutions, adding 0-2 dB to the descriptors \(R_{w}\) or \(L_{n,w}\) in comparison with the same floors 1-7 without the wooden parquet layer (see Table 1). However, for the dry floors 8-10, the parquet covering has radical effects, increasing most SNQs, even up to 7 dB for \(L_{n,w}\) of floor 9. Figure 11 (Appendix A) demonstrates that all cases without a parquet floor show a limited airborne sound reduction index \(R\)(f) below 160 Hz. Furthermore, Figure 12 presents larger deviations for impact sound measurement curves for the test cases without a parquet floor than those presented in Figure 3 with a parquet covering. Moreover, the performance of floor 9 is odd, deviating from the overall trends from 315 Hz and above, showing limited impact sound insulation above 800 Hz. Presumably, the thick concrete floating floor (60 mm) somehow resonates at middle and higher frequencies, which weakens the impact sound performance, especially above 500 Hz. When the parquet floor layer is omitted, the impact sound SNQs of wet floor solutions (floor 8: \(L_{n,w}(C_{I})=60(-1)\) dB, floor 9: \(L_{n,w}(C_{I})=61(-2)\) dB) are similar or worse than the best dry solution cases (floor 6: \(L_{n,w}(C_{I})=62(0)\) dB, floor 7: \(L_{n,w}(C_{I})=59(1)\) dB). Floor 10 is excluded from this comparison as it is an enhanced insulation case. Overall, a parquet floor layer is applied in most Swedish dwellings, thus the results from Figures A1 and A2 are not considered realistic. Floor 9 has a considerably decreased impact sound performance above 500 Hz compared with floor 8 for the instances without parquet floors on top (Figure A2 in Appendix A). For those instances, the SNQ values coincide with \(L_{n,w,100}=59\) dB, but when measured from 50 Hz, floor 9 remains slightly better with \(L_{n,w,50}=60\) dB (while floor 8 has 61 dB). The thick concrete screed of 60 mm (floor 9) seems to induce higher transmission in high frequencies above 1 kHz for impact sound performance, while airborne sound reduction remains large, even without the parquet floor on top. The case of floor 10 is a special configuration, similar to floor 9 with the addition of a suspended ceiling with an airgap and double plasterboard. This significantly improved both airborne and impact sound insulation and all of the SNQs (Table 2).