# Cross-Laminated Timber Floor: Analysis of the Acoustic Properties and Radiation Efficiency
## 5 Conclusions  
This work presents the experimental results of acoustic measurements, carried out on a CLT floor, consisting of five layers of 200 mm thickness, according to the ISO 10140 series standards. 1. Firstly, three different types of sources were used in the laboratory of the Free University of Bolzano: tapping machine, dodecahedron and rubber ball. Furthermore, vibration measurements were carried out for each source. The results make it possible to derive the impact sound pressure level obtained from the tapping machine and the rubber ball, the sound reduction index obtained with the dodecahedron, velocity levels and consequent radiation index for each of the sources. For all three sources, the use of velocity level measurements to derive the acoustic parameters has led to excellent results, in comparison to the experimental data. This is not a predictive method and could not be fully verified in in-situ measurements, due to lateral transmissions, which are not trivial, to be determined., As regards the measurement of the radiation index, it can be noted that at the frequency of 63 Hz, the higher value can be found in correspondence with the resonance frequency of the floor for each type of sound source. The same maximum can be found in the sound pressure measurements. Furthermore, the radiation indices of the two impact sources (tapping machine and rubber ball), at low frequency (50-80 Hz), provided results significantly similar, while after 80 Hz, the values of the tapping machine far exceed not only the radiation index of the rubber ball, but also that of the dodecahedron. 2. Then, it was observed that the predicted sound reduction index, evaluated with the mass law \(R=20\lg(m\!f)-47\), was not suitable for the CLT floor examined, and a new proposed law was introduced for CLT floors. Furthermore, a correlation between the normalized impact pressure level and the impact sound pressure level of the rubber ball was detected. 3. Finally, for all three types of sources, the use of velocity level measurements to derive the acoustic parameters has led to good results, in comparison to the experimental data. This could not be fully verified in in-situ measurements due to lateral transmissions, which are not trivial, to be determined. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{Li_{A,Fmax\_meas}}\) & \(\mathbf{Li_{A,Fmax\_Lv}}\) & \(\mathbf{Li_{A,Fmax\_12354-2}}\) & \(\mathbf{Li_{A,Fmax\_pr}}\) \\ **[dB(A)]** & **[dB(A)]** & **[dB(A)]** & **[dB(A)]** \\ \hline
80 & 78 & 81 & 80 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Weighted sound pressure levels. Figure 19: Measured and predicted energy average maximum impact sound pressure level with rubber ball. As for the impact sound pressure level, good correlations (within 2 dB) can be seen, both with the use of the reference curve, and by using the formula provided by the ISO 12354-2 standard, using, in any case, the measured radiation index and the structural reverberation time. As for the sound reduction index, the standard model leads to an underestimation at medium-low frequencies and to a considerable overestimation at medium-high frequencies. From the results obtained, it was possible to see how traditional analytical models do not provide good approximations of the measurements. Good correlations are obtained using the proposed equations; however, these correlations can be used with floors having characteristics similar to those used in laboratory tests. A future development of this work will concern the study of the CLT floor with coverings consisting of acoustic mats, with a concrete screed and the influence of the physical characteristics of the materials, with respect to the acoustic performance. Conceptualization, N.G. ; software, N.G. ; project administration, N.G. ; validation, N.G. and A.M.; methodology, N.G. and A.M.; formal analysis, N.G. and A.M.; investigation, N.G. and A.M.; data curation, N.G. and A.M.; writing--original draft preparation, N.G. and A.M.; writing--review and editing, N.G.