# Cross-Laminated Timber Floor: Analysis of the Acoustic Properties and Radiation Efficiency
## 3 Results and Discussion  
### Experimental Results: Sound Pressure Level-Derived Parameters  
The normalized impact sound pressure level obtained using the tapping machine, the sound reduction index retrieved using a dodecahedron and the maximum sound pressure levels measured impinging the rubber ball on the 200 mm CLT floor are shown in Figure 7.  
Figure 6: Comparison of \(L_{\text{F}\_\text{max}}\) (1/3 oct), \(L_{\text{F}}\) (1/1 octave), \(L_{\text{F}}\) (1/3 octave), \(L_{\text{F}\_\text{max}}\)-\(L_{\text{F}}\) (1/3 oct). Figure 7: Normalized impact sound pressure level (**a**), sound reduction index (**b**), rubber ball impact sound pressure level (**c**) for the 200 mm CLT floor. For normalized impact sound pressure level, a resonant frequency of 63 Hz is clearly highlighted. Above 800 Hz, the impact of the sound pressure level decreases, as the surface dampens the impact of the hammers by attenuating the impact force. This is due to the fact that the wooden surface of the floor is much less rigid than, for example, a concrete floor, for which this phenomenon is much less noticeable [66] (Figure 8). Due to this important aspect, it is not possible, for example, to use the attenuation data of the impact sound pressure level, obtained on a normalized concrete floor, on wooden floors. The \(\Delta L_{\rm n}\) at high frequency, obtained on the normalized concrete floor of a lining, is greater than the same lining applied on a wooden floor, because floating floors are effective above high frequencies, where the wooden floor has a good impact acoustic behavior, with respect to mass. When looking at the sound reduction index, \(R\), (Figure 7b) a resonant frequency at 63 Hz is also determined. It can be noted that a mass-law-like trend, starting from 315 Hz, is present. From the comparison of the impact sound pressure level produced by the standard tapping machine (Figure 7c), and the sound reduction index (Figure 7b), it is clear that the peak of \(R\), at 80 Hz, corresponds to the minimum impact sound pressure level, as expected [67; 68]. Then, in the case of the impact sound pressure level and the rubber ball trends, the resonance frequency is also at 63 Hz. The weighted index values are depicted in Table 3.  
The weighted impact sound pressure level and weighted sound reduction index are consistent with the literature [12], confirming the possibility of extending the results obtained in this research to other CLT floors. In Figure 9, the standard deviations associated to the sound pressure levels and measured for the three sources in the receiving room are compared. Due to the greater variability in the positioning of the source, the rubber ball results are characterized by higher values of standard deviation  
Figure 8: Normalized impact sound pressure level for CLT floor (200 mm) and for concrete floor (140 mm). \begin{table}
\begin{tabular}{c c c} \hline \(\mathbf{L_{\rm n,w}}\) **[dB]** & \(\mathbf{R_{\rm w}}\) **[dB]** & \(\mathbf{L_{\rm IA,Fmax}}\) **[dB(A)]** \\ \hline
88 & 35 & 80 \\ \hline \end{tabular}
\end{table} 
Table 3: Weighted normalized impact sound pressure level, \(L_{\rm n,w}\), weighted sound reduction index, \(R_{\rm w}\), and A-weighted energy average maximum impact sound pressure level measured with rubber ball according to the standard, \(L_{\rm IA,Fmax}\). In the case of the impact measurements, it can be noted that due to the non-homogeneous contact surface, the standard deviation is greater than with the airborne measurements. In the literature, the difference is less evident, probably due to the analysis of homogeneous heavy weight floors [69]. Then, by comparing the measured sound reduction index with the ones derived from the mass law \(R=20\lg(m\!f)-47\)[70], a new correlation was retrieved experimentally, starting from 315 Hz, according also to the range frequency of the mass law. The proposed mass law for the 200 mm CLT timber floor analyzed here is expressed in Equation (10).