## 5 Acoustic Package Optimization
### Optimization Scheme and Verification
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sequence Number** & **Scheme** & **Thickness/mm** & **Gram Weight/g/m2** & **Fraction of Coverage/\%** \\ \hline
1 & The top is lined with attracting cotton & 20 & 232 & 70 \\
2 & Side interiors attract cotton & 20 & 232 & 70 \\
3 & The rear enclosure interior attracts cotton & 15 & 672 & 80 \\
4 & Door interior panels attract cotton & 15 & 232 & 60 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Acoustic optimization scheme for the cab. Verification results of airtightness and acoustic package optimization scheme are shown in Figures 18 and 19. The noise test method is adopted to verify the improvement effect of cab acoustic performance under typical full load and no-load conditions. As can be seen from Figure 18, in the full load condition of 70 km/h with uniform speed, the cab noise performance has a significant effect at frequencies above 400 Hz, and the ear noise of both the main driver and the co-driver is significantly reduced. In the frequency range of 400-8000 Hz, the ear noise of the main driver and the co-driver is reduced by 2.56 dB (A) and 2.4 dB (A). As can be seen from Figure 18c,d in the full load condition of 80 km/h with uniform speed, the cab noise performance has a significant effect at frequencies above 400-8000 Hz, and the ear noise of both the principal and co-driver decrease by 2.0 dB (A). With the increase of the vehicle speed, the noise performance level tends to be stable. Figure 19 shows the cab acoustic verification results under the no-load condition of 70 km/h and 80 km/h at constant speed. It can be seen from the figure that, in the range of 400-8000 Hz at a constant speed of 70 km/h, the noise around the ears of the principal and co-drivers decreases by 3.1 dB (A) and 4.6 dB (A) respectively, and that at a constant speed of 80 km/h decreases by 3.6 dB (A) and 4.9 dB (A) respectively. As can be seen from the test results in Figures 18 and 19, within the frequency range of 200-8000 Hz, the RMS value of the driver's ear noise is less than 70 dB after the optimization of the cab acoustic package scheme and the vehicle airtightness, indicating a significant optimization effect, which further verifies the effectiveness of the cab acoustic package optimization and airtightness optimization methods adopted in this paper. Figure 17: The layout of the acoustic package for the cab. (**a**) Acoustical optimization scheme for lining sound-absorbing cotton; (**b**) optimization scheme for surrounding sound-absorbing cotton at the back; (**c**) Acoustical optimization scheme for surrounding interior panel at the side. Figure 18: Optimization of acoustic performance under typical load conditions. (**a**) 70 km/h uniform full load condition, comparison before and after optimization of main drive noise; (**b**) 70 km/h uniform full load condition, comparison before and after optimization of first drive noise; (**c**) 80 km/h uniform full load condition, comparison before and after optimization of first drive noise. of first drive noise; (**d**) 80 km/h uniform full load condition, comparison before and after optimization of first drive noise. Figure 19: Optimization of acoustic performance under typical no-load conditions. **(a)** 70 km/h uniform no-load condition, comparison before and after optimization of main drive noise; **(b)** 70 km/h uniform no-load condition, comparison before and after optimization of first drive noise; **(c)** 80 km/h uniform no-load condition, comparison before and after optimization of first drive noise; **(d)** 80 km/h uniform no-load condition, comparison before and after optimization of first drive noise. After the optimization scheme in Tables 9 and 10, the acoustic package and airtightness performance of the cab are optimized. The acoustic performance of the cab is significantly improved.