## 3 Results and Discussion
### Inversion of the Transmission Coefficient Data Using the EFM Interaction Model  
Figure 7 shows the minima of the cost function with porosity for all eight CEB samples. From the minima, the values of the porosity were determined, which are presented in Table 2. In order to evaluate the performance of the model and the pertinence of the recovered parameters, a reconstructed transmission coefficient was used with the interaction model and the experimental data (Figure 6). The porosity consistently increased as the WHA increased (samples SG1 to SG4), which is in accordance with the finding by [PERSON] et al. [36]. This could be explained by the fact that an increase in the WHA content causes the CEBs to become void-filled, which lowers their resistance to the airflow through CEBs. This study's results on porosity indicate that manufactured CEBs are generally porous, particularly at high WHA concentrations. Therefore, they are appropriate for building porous walls. The SBA, on the other hand, was found to lower the porosity, which is in line with its effect in lowering the transmission coefficient, since a more porous material can transmit more sound and vice versa. However, not much information is available in the literature on the acoustics of CEBs when bound using SBA. This study thus forms a basis for future reference.  
Table 2 shows that the porosities of the CEB samples manufactured in this study were sensitive to the concentration of the binders, with the CEBs bound using WHA (SG1 to SG4) demonstrating higher values of the porosity compared to those bound using SBA (SG5 to SG8). This finding is very consistent with the finding for the transmission coefficients (Figure 6a-d).  
The variation in the airflow resistivity with the WHA and SBA concentration can be observed in Figure 8. As the concentration of WHA (SG1 to SG4) increased, it was found that the airflow resistivity reduced continuously, which is pretty compatible with the rise in porosity, given that the two were inversely connected. The airflow resistivity was observed to rise steadily as the concentration of SBA (SG5 to SG8) increased, which was also consistent with the decline in the porosity. Because WHA increased the number of voids in the CEB samples, it lessened the proximity of the particles, which is why the airflow resistivity decreased as the WHA concentration increased. This increased the samples' resistance to sound passing through them. By contrast, the closeness of the particles  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sample** & **SG1** & **SG2** & **SG3** & **SG4** & **SG5** & **SG6** & **SG7** & **SG8** \\ \hline \(\Phi\) & 0.40 & 0.51 & 0.64 & 0.70 & 0.42 & 0.37 & 0.34 & 0.29 \\ \hline \(\sigma\) (\(\times 10^{3}\) p\(\cdot\)s\(\cdot\)m\({}^{-2}\)) & 11.8 & 9.2 & 7.5 & 6.0 & 11.0 & 13.8 & 17.8 & 22.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The calculated porosity and airflow resistivity for all the eight compressed earth block samples.  
Figure 7: Cost function against porosity for all the eight compressed earth block samples.  
increased by more strongly binding them together as the concentration of SBA increased, which lowers the voids in the CEB samples. This increased the samples' resistance to sound passing through it. Table 2 displays the computed values for the airflow resistivity.