## 4 Model Recognition in Volume Source Mode  
In the cab model verification, the volume sound source is used as the excitation source. The volume sound source is arranged in the left front wheel excitation, the right front wheel excitation, and the engine compartment excitation just below the floor of the cab, respectively. The excitation method is white noise sweep excitation. Acoustic microphones were uniformly arranged on the surface of the inner and outer sound cavities of the hybrid FE-SEA model in the cab to receive the sound from the excitation source. The internal and external sound fields of the cab and the whole vehicle are shown in Figure 11. The internal sound field separates the seat sound field from the cab sound field. The external sound field is shown in Figure 11b,c which represents the sound pressure distribution of the external sound field at different sound velocities. According to the subsystem modeling method of the hybrid model, 8-12 microphones are uniformly arranged on the surface of each internal sound field. The distance between the microphone and the surface of the internal sound cavity is 100-150 mm. The sound pressure value at the surface position of each internal sound cavity is taken as the input sound load of the hybrid FE-SEA model of the cab. In the test process, the sound pressure level of the background noise is required to be 20 dB lower than the sound pressure level of the test condition. In the vehicle test area, except for the engine compartment, the acoustic characteristics of the left and right sides of the vehicle are considered to be symmetrical. During the test, only one side of the vehicle is measured, and the arrangement of measuring points is shown in Figure 12.  
Figure 11: Internal and external sound fields. (**a**) The internal sound chamber of the cab; (**b**) External sound fields at different velocities (70 km/h); (**c**) External sound fields at different velocities (80 km/h). The cab hybrid FE-SEA model validation results are shown in Tables 4-8. Figure 13a,b shows the left front wheel for acoustic excitation, where sound transmission loss within 0-2000 Hz frequency has high precision, there is a simulation value and test value maximum error smaller than 2.66 dB, and an increase of frequency at 2000-7000 Hz frequency range. When the model simulation value and test value of error increases gradually, the individual frequency point error value is bigger. This is mainly due to the errors caused by the relatively dense structural modal density of the finite element subsystem in the hybrid FE-SEA model at medium and high frequencies, as well as the test errors caused by noise signals and external interference signals in the test of the statistical energy parameters of the SEA board, such as input power and energy parameters of each subsystem. At the same time, when building the complex model of vehicle hybrid FE-SEA, the complex structure is properly simplified without considering the influence of partial leakage and holes, and the coverage rate of the interior accessories of the cab is properly simplified, which will also affect the prediction error in the high-frequency band. Figure 13c,d shows the distribution curve of acoustic transmission loss and error of the main driving when the right front wheel is excited. It can be seen from the figure that the error trend is the same as that of the left front wheel excitation, and the intermediate frequency accuracy is high. When the frequency increases, the front end model of the cab can be modified by the test method under the condition of front-wheel excitation, which can be used for the simplification of the subsystem and the errors in the high-frequency band caused by the dense mode density. Figure 13 e-j shows the engine compartment, left rear wheel incentives, and right rear wheel under the incentive of the rear seat sound transmission loss in the 0-7000 Hz of the whole band simulation value. The test value is relatively close  
Figure 12: Observation points in the cab and engine compartment.