## 2 Materials and Methods  
### Sample Preparation  
The main raw materials used in this study were earth, WHA, and SBA. These materials were chosen since they are readily available and cheap. The earth was obtained locally in Busia County, Mayenje Ward, Kenya. The earth from this region has been praised for its value in making high-quality earth blocks. Following one month of storage at room temperature with a relative humidity of 63% and shaded storage, the collected earth samples were broken down and made suitable for use by passing them through a 0.2 mm sieve in order to remove the large particles. The water hyacinth was taken from Lake Victoria near Kisumu, Kenya. After being collected, the hyacinth sample was cleaned and washed in water in order to remove dirt and other contaminants. The sample was then uniformly divided into 2 cm long pieces, which were subsequently sun-dried for two weeks. After being dried, the sample was baked for 10 h at 230 \({}^{\circ}\)C in order to convert the organic material into an inorganic substance, after which it was milled. The duration and the temperature were ideal for the conversation. The ground sample was then run through an 8 mm sieve in order to obtain a fine powder. Sugarcane bagasse was obtained from a local sugar factory (Kibos Sugar Factory, Kisumu, Kenya). The obtained bagasse was then dried in the open air for one week, after which it was burnt in the air in order to obtain the SBA. Figure 2 shows the prepared raw materials. The choice of the sample mixture was informed by that of a previous study [35], where earth was replaced with cement of up to 15%. The three raw materials (earth, WHA, and SBA) were then weighed using the Mettler Toledo PB303 (Mettler Toledo, Z\(\ddot{\text{u}}\)rich, Switzerland) with an analytical balance of accuracy at 0.001 g and a maximum weighing capacity of 310 g, after which they were mechanically mixed at different ratios (Table 1). Following the addition of water, the mixture continued until the mixture became homogenous. In preparing the sample CEBs, a sample holder was used. The sample holder was a cylindrical metal sheet with an internal diameter of 76.2 mm and a thickness of 20 mm. The choice of the measurement of the internal diameter was guided by the internal diameter of the acoustic waveguide where the CEB samples were placed when making the acoustic transmission measurements. With the help of a nearby welder, the mould was created. The mould is displayed in Figure 3a. By employing a hydraulic press (Hydraform, model number M7/TWIND, South Africa), the CEBs were created. The prepared cylindrical mould was placed inside the cuboid mould of the Hydroform, which is usually used for making standard-sized CEBs. The prepared mixture was then placed into the mould (Figure 3b) and then pressed to a pressure of 25 bars. Although increasing the compaction pressure increases the density and mechanical properties of CEBs, extremely high compaction pressure values are not good for the acoustical properties of the blocks because they reduce porosity, which results in a poor signal-to-noise ratio. Following the compaction, the CEBs were kept at an ambient temperature and relative humidity of 60% for 14 days. The sample identifiers (SG1-SG8) were assigned to the CEB samples. Figure 3d shows some of the prepared CEB samples that had already been removed from the mould, whereas Figure 3c shows the prepared CEB samples still inside the mould. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample ID** & **Soil** & **WHA** & **SBA** & **Water (mL)** \\ \hline SG1 & 100 & 0.0 & 0.0 & 60 \\ \hline SG2 & 95 & 5.0 & 0.0 & 90 \\ \hline SG3 & 90 & 10.0 & 0.0 & 160 \\ \hline SG4 & 85 & 15.0 & 0.0 & 170 \\ \hline SG5 & 85 & 12.0 & 3.0 & 110 \\ \hline SG6 & 85 & 10.0 & 5.0 & 100 \\ \hline SG7 & 85 & 7.0 & 8.0 & 120 \\ \hline SG8 & 85 & 4.0 & 11.0 & 90 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The different percentages by mass (in grams) of earth, water hyacinth ash, sugarcane bagasse ash, and water.