## 5 Acoustic Package Optimization
### Optimization Scheme and Verification  
According to the acoustic noise transfer function of the test result of cab air tightness test and optimization and testing to seal cab, sealed cabin pressure relief valve in two places, to smoke tests are carried out from the co-pilot wind window, in the smoke reaches 125 pa pressure for pressure test and record the cab leak, the test process is shown in Figure 15. According to the leakage point smoke screen need to optimize the structure of the cab, air-tightness optimization results as shown in Table 9, through the airtightness test, a total of 19 screening leak, concentrated leakage hole under the wind window 4, side surrounds discharge hole 4, under the small leakage hole 3, 8 from rat hole under the C column, a total of 56.8 SCFM leak value, according to the different leak point respectively adopt partition, glue, glue sealing cavity optimization method for leak tightness. Figure 14: Test results of the acoustic-acoustic transfer function. (**a**) Acoustic-acoustic transfer function under left front wheel excitation; (**b**) Acoustic-acoustic transfer function under right front wheel excitation; (**c**) Acoustic-acoustic transfer function under engine room excitation; (**d**) Acoustic-acoustic transfer function under left rear wheel excitation. High frequency energy distribution simulation results in the reference bridge panel acoustic package scheme determined, based on the modal superposition method of bridge panel energy simulation results shown in Figure 16a it can be seen from the picture, when in 300-5000 Hz frequency range after all modal superposition bridge side surround most area of the energy concentration, need to optimize acoustic package and in the same way according to the Figure 16b,c, the bridge at the top of the interior trim plate position, after the bridge coaming interior trim panels on both sides of the regional distribution of strain energy is larger, the cab floor front strain energy is relatively concentrated, According to the simulation results of acoustic package optimization scheme as shown in Figure 17, in Figure 17a position in the cab roof lining 1-3 area increased absorption material used to absorb the cab at the top of the energy, in Figure 17b in the areas of circumference interior trim panels of 1 to 5, increase the sound-absorbing cotton material, in Figure 17c, lateral confining interior plate left and right side respectively increase 1 area of sound-absorbing material. The optimization scheme of the acoustic package and acoustic material parameters are shown in Table 10.  
Figure 15: The cab sealing test. (**a**) Seal of cab; (**b**) Seal measuring point; (**c**) Cab bottom measuring point; (**d**) Measuring point of connection. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sequence** & **Let the Cat Out of the Area** &
\begin{tabular}{c} **Leakage** \\ **Rate/SCFM** \\ \end{tabular} & **Let the Cat Out of the Path** & **Optimum Proposal** \\ \hline
1 & Leakage hole under air window \(\times\) 4 & 8.8 & The hole communicates with the cavity & PVC Blue sealing \\
2 & Leakage hole is enclosed on the side \(\times\) 4 & 18 & The hole communicates with the cavity & Optimize the partition position \\
3 & Leakage hole is enclosed in front \(\times\) 3 & 10 & communicates with the cavity & Finger pressure glue sealing \\
4 & Mouse hole under pillar C \(\times\) 8 & 20 & Leakage of sheet metal lap joint & Optimize the gluing quality \\ \hline \hline \end{tabular}
\end{table} 
Table 9: The sealing scheme of the cab. Figure 16: Simulation of an acoustic enclosure covering an area of the cab. (**a**) Simulation of acoustic coverage of cab side; (**b**) Simulation of acoustic coverage of cab rear; (**c**) Simulation of acoustic coverage of cab floor.