Research on Acoustic and Parametric Coupling of Single-Layer Porous Plate–Lightweight Glass Wool Composite Structure Doors for Pure Electric Vehicles

Abstract

Due to the absence of engine noise in new energy vehicles, road noise and wind noise become particularly noticeable. Therefore, studying the noise transmission through car doors is essential to effectively reduce the impact of these noises on the passenger compartment. To address the optimization of the sound absorption performance of single-layer porous plates combined with lightweight glass wool used in the doors of electric vehicles, this study established a microscopic acoustic performance analysis model based on the transfer matrix method and sound transmission loss theory. The effects of medium type, perforation rate, perforation radius, material thickness, and porosity on the sound absorption coefficient, impedance characteristics, and reflection coefficient were systematically investigated. Results indicate that in the high-frequency range (above 1200 Hz), the sound absorption coefficients of both rigid and flexible media can reach up to 0.9. When the perforation rate increases from 0.01 to 0.2, the peak sound absorption coefficient in the high-frequency band (1400–2000 Hz) rises from 0.45 to 0.85. Increasing the perforation radius to 0.03 m improves acoustic impedance matching. This research provides theoretical support and a parameter optimization basis for the design of acoustic packaging materials for electric vehicles, contributing significantly to enhancing the interior acoustic environment.

1. Introduction

Multilayer composite materials, due to their unique structural advantages and designability, offer a highly promising approach to solving acoustic problems. By carefully designing the number of layers of multilayer composite materials, the properties of each layer (such as density, elastic modulus, Poisson’s ratio, etc.) and the thickness of each layer, the propagation, reflection, and absorption behaviors of sound waves within them can be effectively regulated, thereby meeting diverse acoustic requirements [1]. In the field of pure electric vehicles, the impact of in-vehicle noise problems on the driving and riding experience is becoming increasingly prominent. Since pure electric vehicles do not have the noise masking of traditional fuel engines, the sounds of motor operation, tire rolling, wind noise, etc., are more obvious. Therefore, the design of the acoustic package is of vital importance. The acoustic package, as a key component for reducing noise inside the vehicle and enhancing the acoustic comfort of the vehicle, is directly related to the quality of pure electric vehicles. The composite structure of single-layer porous plates and lightweight glass wool, due to its excellent sound absorption characteristics, has become an important research direction for acoustic package materials in pure electric vehicles. Reasonable optimization of the parameters of this composite structure can effectively absorb the medium- and high-frequency noise inside the vehicle and create a quiet riding environment for passengers. It is of great significance to conduct in-depth research on the acoustic properties of multilayer composite materials. Their acoustic wave propagation is complex and involves multi-medium interface interactions, etc. Not only can they improve the acoustic theoretical system, but they also have great application value in fields such as aerospace, automobiles, architecture, and electronic devices, such as optimizing the sound insulation of aircraft, enhancing the quietness of automobiles, and creating high-quality acoustic spaces.

Research on the acoustic properties of multilayer composite materials abroad started relatively early. In the middle of the 20th century, pioneers in the field of acoustics began theoretical exploration of the acoustic problems of multilayer media. For instance, scholars such as Brekhovskikh [2] conducted in-depth research on the propagation of plane waves in multilayer media based on the classical wave equation, and meticulously derived the formulas for the reflection and transmission coefficients of sound waves at the interfaces of different media, laying a solid mathematical foundation for the subsequent acoustic theoretical analysis of multilayer composite materials. These early theoretical works have provided a key basis for understanding the basic propagation mechanism of sound waves in multilayer composites. With the development of science and technology, foreign researchers have made remarkable progress in considering more complex material properties and physical phenomena. In terms of the viscoelasticity of materials, scholars have studied the influence of viscoelasticity on the acoustic properties of multilayer composites by introducing the viscoelastic constitutive relation into the wave equation [3]. Stefano [4] proposed a high-order shell finite element method for analyzing the passive sound insulation performance of composite laminated structures embedded with viscoelastic layers. Kuang [5] conducted research on acoustic ink and acoustic printing technology, demonstrating that ink with phase transition viscoelasticity can resolve the contradiction between sound flow and sound penetration. Çağlar Sivri [6] investigated the most effective medium for sound-absorbing performance among needle-punched nonwovens, meltblown nonwovens, and their mixed configurations, and analyzed their correlations with thermal conductivity. Their results revealed that “pure meltblown” samples exhibited significantly higher sound absorption efficiency compared to most other samples, whereas “pure needle-punched nonwoven” samples demonstrated the lowest sound absorption efficiency across all tested frequencies. Tarkashvand [7] investigated the acoustic scattering and noise reduction performance of a novel polymer-based composite core cylinder. They adopted a stratified viscoelastic model, considered frequency dependence, described the rheological responses of each layer using the Havriliak–Negam model, and analyzed them using the transfer matrix method. Furthermore, for multilayer composites containing microstructures, such as porous media or fiber-reinforced composites, Stefano [8] studied the influence of microstructures on macroscopic acoustic properties through methods such as perturbation theory, thereby establishing a more refined theoretical model. R.Talebitooti et al. [9] explored the influence of boundaries on the sound insulation performance of multilayer aerospace porous elastic composite structures, analyzed the acoustic performance of the composite structure under different boundary conditions, and provided a reference basis for optimizing the acoustic performance and improving the sound insulation effect when applying such materials in the aerospace field. D.v. Parikh et al. [10] studied the acoustic performance of natural fiber composites used in automobiles and found that nonwoven floor coverings made of natural fibers can reduce noise due to their absorbency, and soft cotton padding can enhance their sound absorption performance.

Considerable progress has been made in the theoretical research on the acoustics of multilayer composite materials in China. In terms of the application and expansion of classical acoustic theory, Chinese researchers closely combine the actual needs of domestic engineering to carry out research. In the field of marine engineering, for the application of acoustic materials in marine environments, considering the fluid characteristics of seawater and the coupling effect between multilayer composite materials and seawater, scholars such as Li [11] established the coupled wave equation and deeply analyzed the propagation characteristics of sound waves in this special multilayer medium. It provides a theoretical basis for the design of acoustic protective materials in marine acoustic detection equipment and marine engineering structures. Zhu [12] focused on ultrafine barium sulfate/butyl rubber composites, involving the preparation methods and the study of their acoustic properties. Jiang [13] studied the acoustic properties of various layered materials with different thicknesses using the NOVA module in VA ONE (2020) software. Combined with the experimental results, they analyzed the influence of the main parameters on the acoustic properties of multilayer composites. Zhou [14] established a three-dimensional cantilever beam model using finite element analysis software to analyze and study the magnetoelectric coefficients of magnetostrictive/piezoelectric/magnetostrictive laminated composites, etc. Wang [15] established a magnetic resonance mechanical model to study the magnetostrictive phenomenon of nickel–zinc and manganese–zinc ferrite rods and the influence of various variables on magnetoacoustic resonance. Wang [16] jointly explored the related issues of sound wave propagation in solid–solid porous media when a single solid is filled in the pores, and analyzed the influence of factors such as pores and filled solids on the propagation characteristics of sound waves, such as the variation laws of sound wave velocity and attenuation, providing a theoretical basis for research and application in related fields. Li [17] collaborated to propose a hollowed-out carved thin plate structure based on a tubular hollow spiral sound insulation unit, which is of great significance for the research in the field of ventilation and sound insulation windows in architectural acoustics. Du [18] designed and developed a new type of laminated composite material sound insulation board. The research shows that this laminated composite material has good sound insulation capacity. Zhang [19] is engaged in the research of the acoustic properties of composite materials, focusing on the exploration and study of acoustic quasi-modes in two-dimensional dispersed random media, providing references for the research of phonon crystals, etc.

Compared with existing studies, this paper presents the following innovation: for the first time, a microscopic acoustic analysis model of a single-layer porous plate combined with a lightweight glass wool composite structure is developed specifically for the door system of pure electric vehicles. This advancement marks a significant departure from the traditional research framework, which has predominantly focused on the acoustic properties of individual materials or conventional multilayer structures in isolation. By integrating the transfer matrix method with sound transmission loss experiments, the study systematically reveals the synergistic effects of key parameters—such as perforation rate, pore size, thickness, and porosity—on high-frequency sound absorption (above 1200 Hz). Notably, the research identifies an enhancement effect (ranging from 0.45 to 0.85) in peak sound absorption within the high-frequency band for rigid/flexible media, where the absorption coefficient reaches up to 0.9, particularly under perforation rates between 0.01 and 0.2. This finding deviates from the conventional single-parameter optimization approach commonly applied in micro-perforated plate structures. Furthermore, the study innovatively integrates lightweight design elements—such as honeycomb perforated plates and ultrafine glass fibers—with acoustic performance optimization. Based on impedance matching theory, a parameter optimization model is established, offering a solution that combines theoretical rigor with engineering applicability for NVH design in electric vehicles. This work effectively addresses a critical research gap in the application of composite structures for onboard high-frequency noise control.

2. Acoustic Optimization of the Doors of Pure Electric Vehicles by the Composite Structure of Porous Plates and Glass Wool

2.1. Acoustic Mechanism of Composite Structures

The acoustic optimization of the single-layer porous plate–lightweight glass wool composite structure is grounded in the theory of multi-interface coupling and energy dissipation, and realizes high-frequency noise suppression through a three-tiered mechanism. Different from the single resonance sound absorption principle of traditional micro-perforated plates, the “transmission–scattering–loss” three-level sound absorption chain proposed in this paper is original: through the matching of aperture and wavelength (for example, a 0.03 m aperture corresponds to a 1200 Hz high-frequency wave), the directional introduction of acoustic energy into the glass wool layer is achieved. This mechanism has not been involved in the existing research on single-layer structures. It was discovered that the flexible medium reduces the interface acoustic impedance difference through elastic deformation (with a 15% reduction in the reflection coefficient compared to the rigid medium), and for the first time, a quantitative relationship between the medium type and the sound absorption frequency band was established, breaking through the research limitations of traditional rigid backings. The acoustic wave regulation of the porous plate is described as follows. The perforated structure forms a “frequency-selective channel”. High-frequency acoustic waves (with wavelengths smaller than the pore size) are transmitted through the pores into the glass wool, while low-frequency acoustic waves are reflected due to diffraction. Meanwhile, the stiffness of the plate body changes the mechanical impedance of the incident sound wave, forcing the high-frequency acoustic energy to be transmitted inward. The glass wool exhibits porous dissipation, and the ultrafine fiber network builds dense pores. Sound waves cause viscous friction between air particles and fibers within the pores, converting sound energy into heat energy (accounting for 60–70% of high-frequency loss). The random fiber structure causes sound waves to scatter and prolong the propagation path, increasing the number of energy dissipations. High porosity further optimizes pore connectivity and enhances viscosity and heat conduction losses. The interface coordination of the interlayer medium, with the rigid medium forming a strong reflection boundary, causes the sound wave to be reflected multiple times within the composite structure, increasing the internal sound pressure level of the glass wool. Flexible media absorb vibration energy through elastic deformation, reduce the interface acoustic impedance difference, and decrease reflection loss. The two types of media, respectively, target high-frequency reflection enhancement and wideband vibration damping to collaboratively optimize the sound absorption frequency band. The perforation rate and porosity determine the efficiency of sound wave transmission. The thickness matching the half wavelength of the sound wave forms resonance loss. The type of medium regulates the reflection characteristics at the interface. Together, the three form an efficient sound absorption chain of “transmission–scattering–loss”, achieving the directional suppression of high-frequency noise (800–2000 Hz) in the doors of pure electric vehicles. The design schematic diagram of the acoustic package for new energy vehicle doors is shown in Figure 1.

2.2. Theoretical Regulation Logic of Core Parameters

Perforation rate, pore diameter, and acoustic energy guidance are dominated by pore connectivity. The perforation rate determines the pore density on the material surface. By increasing the perforation rate, the transmission ability of sound waves into the interior of the glass wool can be enhanced, and surface reflection can be suppressed. The perforation radius affects the size of the pore channel. A larger pore diameter is conducive to the penetration of high-frequency sound waves into the interior of the material and prolongs the interaction path with glass wool. Theoretically, a reasonable match between the perforation rate and the aperture can increase the transmission efficiency of sound energy by 40% to 60% and significantly reduce the reflection coefficient.

Thickness and porosity form the physical basis of acoustic energy loss. The thickness of glass wool directly determines the length of the sound wave propagation path. Increasing the thickness can prolong the round-trip reflection times of sound waves in the pores and enhance the frictional loss. Porosity regulates the proportion of gas and solid phases within the material. High porosity (such as above 0.9) forms a more complex pore network, increasing the contact area between sound waves and fibers and enhancing the efficiency of viscous loss. The combined effect of the two can increase the efficiency of acoustic energy loss in the high-frequency band by more than 50%.

The regulation of medium type, boundary conditions, and impedance matching is discussed next. Rigid media (such as metal back plates) force sound waves to reflect multiple times within the composite structure, enhancing sound absorption. Flexible media (such as damping layers) absorb vibration energy through elastic deformation and reduce low-frequency coupling noise. Selecting rigid or flexible media can specifically optimize the impedance matching of specific frequency bands. For instance, rigid media can increase the sound absorption coefficient to around 0.9 in the high-frequency band (above 1200 Hz), while flexible media can expand the lower limit of the effective sound absorption frequency band. The research flowchart is shown in Figure 2.

The acoustic model, established using the transfer matrix method, enables quantitative analysis of the influence of individual parameters on sound absorption coefficients and impedance characteristics. When applied to automotive doors, by modeling the composite structure as a multilayer system comprising a “porous plate–medium–glass wool” configuration and incorporating the rigid boundary conditions of the door cavity (steel plate backing), the reflection and transmission behaviors of sound waves at each interface can be accurately predicted. Theoretical analysis demonstrates that the optimized composite structure can improve high-frequency noise absorption performance by 30% to 50% compared to conventional materials. Furthermore, through lightweight design strategies—such as employing honeycomb porous plates and ultrafine glass fibers—the balance between acoustic performance and weight constraints is effectively achieved, thereby providing theoretical support for NVH design in electric vehicles.

3. Theoretical Model of Acoustic Performance of Single-Layer Porous Plate–Lightweight Glass Wool Composite Materials

This paper studies the acoustic performance of single-layer porous plate–lightweight glass wool double-layer composite materials. Parameters such as perforation rate, perforation radius, thickness, and porosity need to be set. When conducting experimental predictions, a single variable needs to be changed while keeping others unchanged, so as to carry out theoretical research.

We assumed the multilayer composite material to be a combination of several discrete thin layers and conducted theoretical analysis of sound propagation. A plane wave with a wave number is incident on a composite material at an angle to the axis. After the incident sound wave passes through each thin layer, the following propagation relationship can be obtained [20]:

$$V_1=\left[T_{1n}\right]V_n$$

(1)

In the formula, $V_1$ and $V_n$, respectively, refer to before and after the composite material surface acoustic state vector and the different medium state characteristic parameter vector; $\left[T\right]$ stands for the current multilayer composite total transfer matrix, which depends on the material properties, achieved by coupling each child between discrete thin layer transfer matrices.

3.1. The Influence Mechanism of Discrete Interface Materials on Sound Propagation Characteristics

In multilayer composite acoustic materials, their discrete layers can be classified into four categories: fluid layers, solid layers, porous material layers, and viscoelastic layers. As shown in Figure 3. The state vectors between each medium are, respectively, expressed as

$$V^f(M)={\left[P(M),v_x^f(M)\right]}^{\mathrm{T}}$$

(2)

$$V^s(M)={\left[v_x^s(M),v_y^s(M),{\sigma }_{xx}^s(M),{\sigma }_{xy}^s(M)\right]}^{\mathrm{T}}$$

(3)

$$V^p(M)={\left[v_x^f(M),v_x^s(M),v_y^s(M),{\sigma }_{xx}^f(M),{\sigma }_{xx}^s(M),{\sigma }_{xy}^s(M)\right]}^{\mathrm{T}}$$

(4)

In the formula, the superscripts s, f, and p represent the fluid layer, solid layer, and porous material layer, respectively; P(M) represents the sound pressure value; V_x and V_y are the velocities of the particle along the X-axis and Y-axis, respectively; ${\sigma }_{xx}$ and ${\sigma }_{x\mathrm{y}}$, respectively, are the normal and tangential stresses of the particle.

When sound waves propagate in a fluid medium, the form of their transmission matrix is

$$\left[\begin{array}{c}p(M_1)\\ v(M_1)\end{array}\right]=\left[\begin{array}{cc}\cos (kd\cos \theta )& j{\displaystyle \frac{\rho c\sin (kd\cos \theta )}{\rho c}}\\ j{\displaystyle \frac{\sin (kd\cos \theta )}{\rho c}}\cos \theta & \cos (kd\cos \theta )\end{array}\right]\times \left[\begin{array}{c}p(M_2)\\ v(M_2)\end{array}\right]$$

(5)

In the formula, ρ is the density of the flow field; c represents the speed of sound in the current environment. When sound waves are incident on a solid medium, refracted longitudinal and transverse waves as well as reflected longitudinal and transverse waves will be produced. The corresponding displacement potential functions can be written as

$$\phi =C_1{e}^{j(\omega t-k_{y}y-k_{yx}x)}+C_2{e}^{j(\omega t-k_{y}y+k_{yx}x)}$$

(6)

$$\psi =C_3{e}^{j(\omega t-k_{y}y-k_{xx}x)}+C_4{e}^{j(\omega t-k_{y}y+k_{xx}x)}$$

(7)

In the formula, C₁, C₂, C₃, and C₄ represent the amplitudes of the incident and reflected longitudinal and transverse waves, respectively, k_y is the component of the sound wave in the Y direction, and K_xx and K_yx represent the numbers of waves of the longitudinal and transverse waves in the X direction, respectively.

Based on the fundamental elastic properties of solids, it is assumed that

$$C^s={[(C_1+C_2),(C_1-C_2),(C_3+C_4),(C_3-C_4)]}^{\mathrm{T}}$$

(8)

Then the state variable V^s(M) of the solid layer can be expressed as

$$V^s(M_n)=\Gamma (M_{n-1})C^s$$

(9)

In the formula

$$\Gamma (x)=\left(\begin{array}{cc}\omega k_y\cos (k_{yx}x)& -j\omega k_y\sin (k_{yx}x)\\ -j\omega k_{yx}\sin (k_{yx}x)& \omega k_{yx}\cos (k_{yx}x)\\ -D_1\cos (k_{yx}x)& j{D}_1\sin (k_{yx}x)\\ j{D}_2{k}_{yx}\sin (k_{yx}x)& -D_2{k}_{yx}\cos (k_{yx}x)\\ j\omega k_{xx}\sin (k_{xx}x)& -\omega k_{xx}\cos (k_{xx}x)\\ \omega k_y\cos (k_{xx}x)& -j\omega k_y\sin (k_{xx}x)\\ j{D}_2{k}_{xx}\sin (k_{xx}x)& -D_2{k}_{xx}\cos (k_{xx}x)\\ D_1\cos (k_{xx}x)& -j{D}_1\sin (k_{xx}x)\end{array}\right)$$

(10)

In the formula

$$D_1=\lambda (k_y^2+k_{yx}^2)+2\mu k_{yx}^2$$

(11)

$$D_2=2\mu k_y^2$$

(12)

Let x in Equation (10) be 0 and t, respectively, and the propagation matrix of sound waves in the solid layer can be obtained:

$$T^s=\Gamma (0){\Gamma }^{-1}(t)$$

(13)

For the porous material layer, it integrates the characteristics of fluid lamination and the solid layer. According to the Biot porous medium sound propagation theory [21], its displacement potential function includes

$${\phi }_1^s=C_1{e}^{j(\omega t-k_{y}y-k_{yx}x)}+C_2{e}^{j(\omega t-k_{y}y+k_{yx}x)}$$

(14)

$${\phi }_2^s=C_3{e}^{j(\omega t-k_{y}y-k_{zx}x)}+C_4{e}^{j(\omega t-k_{y}y+k_{zx}x)}$$

(15)

$${\psi }_2^s=C_5{e}^{j(\omega t-k_{y}y-k_{xx}x)}+C_6{e}^{j(\omega t-k_{y}y+k_{xx}x)}$$

(16)

$${\phi }_i^f={\mu }_i{\phi }_i^s(i=1,2)$$

(17)

$${\psi }_1^f={\mu }_3{\phi }_2^s$$

(18)

In the formula, C_i (_i = 1, 2, … 6) are six amplitudes, and µ_i (_i = 1, 2, 3) are all related to the material parameters of the porous material. Similarly, due to the stress–strain relationship of porous materials, it is given that

$$C^p={\left[\begin{array}{c}(C_1+C_2),(C_1-C_2),(C_3+C_4),\\ (C_3-C_4),(C_5+C_6),(C_5-C_6)\end{array}\right]}^{\mathrm{T}}$$

(19)

Then the state variable (M) of the porous material layer can be expressed as

$$V^p(M_n)=\Gamma (M_{n-1})C^p$$

(20)

After simplification, the transmission matrix of sound waves in the porous material layer with a thickness of t is obtained:

$$T^p=\Gamma (0){\Gamma }^{-1}(t)$$

(21)

3.2. Coupling of Discrete Transfer Matrices

According to the continuity conditions between each discrete layer, the transfer matrices of each medium are assembled to obtain the transfer matrices between multilayer composites:

$$\left[I_{f,1}\right]V_1^f+\left[J_{f,1}\right]V_{M2}^f=0$$

(22)

$$\left[I_{k,k+1}\right]V_{M_{2k}}^k+\left[J_{k,k+1}\right]V_{M_{2(k+1)}}^f=0,(k=1,2,\cdots ,n-1)$$

(23)

Sorted out,

$$D_m{V}_0=0$$

(24)

In the formula

$$D_m=\left[\begin{array}{ccccc}{I}_{f,1}& J_{f,1}{T}^1& 0& 0& 0\\ 0& I_{1,2}& J_{1,2}{T}^2& 0& 0\\ \cdots & \cdots & \cdots & \cdots & \cdots \\ 0& 0& I_{(n-2)(n-1)}& J_{(n-2)}{T}^{n-1}& 0\\ 0& 0& 0& I_{(n-1)n}& J_{(n-1)(n)}\end{array}\right]$$

(25)

By combining the boundary conditions between the incident end and the transmission end of the composite material or the impedance equation of sound pressure and velocity, the total transfer matrix D can be obtained.

According to the definition of the surface impedance of the medium, the surface impedance at both ends of the composite material can be expressed as

$$Z_0=p(M_1)/v_0^f(M_1)$$

(26)

$$Z_s={\displaystyle \frac{D^{\prime }}{D^{″}}}$$

(27)

In the formula, D is the algebraic cofactor of the total transfer matrix D after removing the elements of the first column. D is the algebraic cofactor of the total transfer matrix after removing the elements in the second column.

When the end of the multilayer material is a rigid backing, the reflection coefficient and sound absorption coefficient of the multilayer composite material can be expressed as

$$R={\displaystyle \frac{Z_s\cos \theta -Z_0}{Z_s\cos \theta +Z_0}}$$

(28)

$$\alpha =1-|R{|}^2$$

(29)

When the end of the multilayer material is in the semi-infinite fluid domain, the transmission coefficient and the reflection coefficient have the following relationship:

$${\displaystyle \frac{p(A)}{1+R}}={\displaystyle \frac{p(B)}{T}}$$

(30)

Substituting Equation (30) into the total transfer matrix, the transfer loss can be obtained by the same token:

$$TL=-10\lg \left(\left|T{(\theta )}^2\right|\right)$$

(31)

4. Experimental Study on Acoustic Characteristics of Pure Electric Vehicle Doors Made of Single-Layer Porous Plate–Lightweight Glass Wool

Experimental Methods and Single-Factor Experiments

This experiment took the single-layer porous plate–lightweight glass wool composite material as the research object and conducted research around structural parameters such as perforation rate, perforation radius, thickness, and porosity. In terms of the experimental method, the sound absorption coefficient, impedance coefficient, and reflection coefficient of each group of samples were measured by the sound transmission loss method, and the acoustic data within the frequency range of 20–2000 Hz were obtained. Multiple groups of composite material samples with different parameters were prepared: the perforation rates were set as 0.01, 0.1, and 0.2, the perforation radii as 0.01 m, 0.02 m, and 0.03 m, the thicknesses as 0.01 m, 0.03 m, and 0.05 m, and the porosity as 0.35, 0.65, and 0.95. The influence of each variable on the acoustic performance was explored through the single-factor experimental method to lay a data foundation for in-depth exploration of the influence of parameters on the sound absorption, impedance, and reflection characteristics of composite materials. The sample test photos are shown in Figure 4.

The test conditions for the material were as follows: The sound wave frequency was set at 20–2000 Hz, the application excitation was plane wave excitation, and the rear boundary condition was a rigid wall. The test results of the lightweight glass wool impedance tube method are shown in

Table 1. Parameters of multilayer perforated plate–lightweight glass wool composite acoustic materials.

Material Parameter	Default Test Value
Perforation Ratio of Single-Layer Perforated Plate	0.10
Perforation Radius of Single-Layer Perforated Plate	0.02 m
Thickness of Single-Layer Perforated Plate	0.03 m
Flow Resistance of Lightweight Glass Wool	3000 N·s/m4
Density of Lightweight Glass Wool	1.213 kg/m3
Sound Velocity of Lightweight Glass Wool	342.2 m/s
Porosity of Lightweight Glass Wool	0.65
Tortuosity of Lightweight Glass Wool	1.00
Viscous Resistance Coefficient of Lightweight Glass Wool	0.000192 m
Thermal Conductivity of Lightweight Glass Wool	0.000384 m

.

5. Acoustic Characteristic Analysis of Door Structure Parameters of Single-Layer Porous Plate–Lightweight Glass Wool Composite Material

5.1. Analysis of the Influence of Different Media on the Acoustic Performance of Single-Layer Porous Plate–Lightweight Glass Wool Composite Door

Under fixed parameter settings, the medium between the single-layer porous plate and the lightweight glass wool was sequentially replaced with a rigid medium, a flexible medium, and an air medium, followed by experimental testing. The results are presented in Figure 5, Figure 6 and Figure 7.

When the frequency of the rigid medium was 200 Hz, the absorption coefficient was approximately 0.15. When the frequency increased to 1200 Hz, the absorption coefficient reached approximately 0.9. In the high-frequency band of 1200 Hz–2000 Hz, the absorption coefficient remained at around 0.9, showing good high-frequency sound absorption performance. This is because high-frequency sound waves are more likely to interact with the internal structure of rigid media, causing sound energy loss. The absorption coefficient of the flexible medium was approximately 0.1 at 200 Hz and reached about 0.92 at 1200 Hz, slightly higher than that of the rigid medium. In the high-frequency band of 1200 Hz–2000 Hz, the absorption coefficient remained between 0.92 and 0.95, with excellent sound absorption performance. The flexibility of the flexible medium caused more internal friction and deformation under the action of high-frequency sound waves, enhancing the sound absorption effect. The absorption coefficient of the air medium was nearly 0 at 200 Hz, approximately 0.2 at 1200 Hz, and about 0.4 at 2000 Hz. Throughout the entire frequency band, the absorption coefficient was much lower than that of rigid and flexible media, mainly because the intermolecular forces of air are small and its ability to lose sound energy is limited.

For rigid media in the low-frequency band of 200 Hz, the measured value was approximately −20,000, while the theoretical value was approximately −15,000, with a significant difference. In the high-frequency band of 2000 Hz, both the measured value and the theoretical value approached 0, and the difference gradually decreased. At low frequencies, the structural characteristics of the rigid medium made its obstructive effect on sound waves complex, resulting in a large deviation between the measured value and the theoretical value. At high frequencies, the interaction between sound waves and the medium was more in line with the theoretical model. At 200 Hz, the measured value of the flexible medium was approximately −35,000, while the theoretical value was about −25,000, showing a significant difference. At 2000 Hz, both the measured value and the theoretical value were close to −500, and the difference was significantly reduced. Due to the complex response of the flexible structure of the flexible medium at low frequencies, the deviation between the measured value and the theoretical value of the impedance was large. At high frequencies, the structural response tended to be stable and was closer to the theoretical situation. The difference between the measured value and the theoretical value of the air medium in the low-frequency band was relatively small. For example, at 200 Hz, the measured value was approximately −100, and the theoretical value was approximately −80. The high-frequency band was 2000 Hz; both were close to 0, with relatively gentle changes. The characteristics of the air medium were relatively simple, and the obstructive effect on sound waves did not change much in each frequency band.

At 200 Hz, the reflection coefficient of the rigid medium was approximately 0.8. It gradually decreased as the frequency increased. At 1200 Hz, it was about −0.2, and at 2000 Hz, it was about 0.1. At low frequencies, sound waves were reflected in large quantities on the surface of the rigid medium. At high frequencies, the reflection decreased, and part of the sound energy was absorbed or transmitted. The reflection coefficient of flexible media was approximately 0.9 at 200 Hz, −0.3 at 1200 Hz, and 0.15 at 2000 Hz. Similar to rigid media, it had strong low-frequency reflection and weakened high-frequency reflection. Moreover, the reflection of flexible media was slightly higher than that of rigid media at low frequencies because its flexible structure has a stronger reflection effect on sound waves at low frequencies. The reflection coefficient of the air medium was approximately 0.95 at 200 Hz, −0.1 at 1200 Hz, and −0.05 at 2000 Hz. The reflection coefficient of the air medium was high in the low-frequency band and approached 0 in the high-frequency band. Low-frequency sound waves were severely reflected at the air–material interface, and at high frequencies, part of the acoustic energy could enter the interior of the material.

In the single-layer porous plate–lightweight glass wool composite material system, the type of medium (rigid, flexible, or air) exerted a significant influence on its acoustic performance. The absorption coefficients of rigid and flexible media in the high-frequency range (1200 Hz and above) reached approximately 0.9, indicating excellent sound absorption capabilities. In contrast, the absorption coefficient of the air medium in the same frequency range was only around 0.4, reflecting relatively poor sound absorption performance. Regarding impedance characteristics, the measured and theoretical values of the three media exhibited considerable discrepancies at low frequencies, whereas they became more consistent at high frequencies. With respect to reflection behavior, the reflection coefficients of all three media were relatively high at low frequencies (for instance, at 200 Hz, the values were approximately 0.8 for the rigid medium, 0.9 for the flexible medium, and 0.95 for the air medium), while these coefficients decreased significantly at higher frequencies. These findings provide a novel theoretical foundation for the field of acoustic design, clearly demonstrating that rigid and flexible media offer distinct advantages in high-frequency sound absorption. This insight enables engineers and designers to select appropriate medium types with precision and rationality based on specific acoustic frequency requirements, thereby optimizing the design of acoustic products and spaces and advancing the development of acoustic engineering.

5.2. Analysis of the Influence of the Perforation Rate of a Single-Layer Porous Plate–Lightweight Glass Wool Composite Door on Sound Absorption, Impedance, and Reflection Characteristics

Under fixed parameter settings, the perforation rates of the single-layer porous plate were sequentially adjusted to 0.01, 0.1, and 0.2 for experimental testing. The results are presented in Figure 8, Figure 9 and Figure 10.

As can be seen from the sound absorption coefficient diagram, with the increase in the perforation rate, the sound absorption performance of the composite material was significantly improved, especially in the high-frequency band (1600–2000 Hz). The green curve with a perforation rate of 0.2 has the highest sound absorption coefficient, indicating that the greater the perforation rate, the better the high-frequency sound absorption effect. This is because an increase in the perforation rate enhances the internal pore connectivity of the material, which is more conducive to the loss of sound energy.

In the impedance coefficient diagram, the comparison between the theoretical values and the measured values of different perforation rates shows that the impedance variation amplitude in the low-frequency band (20–400 Hz) is relatively large, and the perforation rate affects the impedance matching characteristics of the material. In the high-frequency band, the material properties such as flow resistance and porosity of lightweight glass wool dominate the acoustic response, weakening the influence of perforation rate on impedance, resulting in the coincidence of curves with different perforation rates. Meanwhile, high-frequency sound waves fully interact with the material, resulting in a significant loss of acoustic energy. Eventually, the impedance coefficient approaches zero. This can also indicate that the higher the perforation rate is, the more conducive the material impedance characteristics are to the absorption of sound energy, further supporting the conclusion that the sound absorption performance increases with the perforation rate.

The reflection coefficient diagram shows that the higher the perforation rate, the lower the reflection coefficient (especially in the high-frequency band). For instance, the purple “Measured value” curve with a perforation rate of 0.2 rapidly decreases in the high-frequency band, approaching −1, indicating that the material’s reflection of sound energy weakens and its sound absorption capacity enhances, which is consistent with the law of the sound absorption coefficient.

Overall, in the single-layer porous plate–lightweight glass wool composite material, the perforation rate is a key factor affecting the sound absorption performance. Not only was the rule that the higher the perforation rate, the greater the high-frequency sound absorption coefficient, the smaller the reflection coefficient, and the better the sound absorption performance of the material discovered, but also the multi-dimensional effects of the perforation rate on the sound energy absorption mechanism and reflection suppression effect of composite materials were analyzed in depth. Previous studies on micro-perforated plates [22] have primarily focused on the coupled effects of perforation rate and aperture size within a single structure, or have relied on multilayer configurations to achieve broadband sound absorption. However, these approaches often encountered challenges such as complex multi-parameter optimization and insufficient high-frequency absorption efficiency, where the sound absorption coefficient above 1600 Hz was generally below 0.6. In this study, by implementing a co-design strategy integrating porous plates and glass wool, the high-frequency sound absorption coefficient was enhanced to 0.9 above 1200 Hz. Furthermore, the individual contributions of key parameters—such as perforation rate (ranging from 0.01 to 0.2, with the high-frequency absorption peak increasing from 0.45 to 0.85) and perforation radius (where optimal impedance matching occurs at 0.03 m)—were quantitatively analyzed and decoupled. This approach effectively avoids the complexity of multi-parameter coupling and provides a more straightforward and practical basis for engineering applications.

5.3. Analysis of the Influence of the Perforation Radius of Single-Layer Porous Plate–Lightweight Glass Wool Composite Door on Sound Absorption, Impedance, and Reflection Characteristics

Under fixed parameter settings, the perforation radii of the single-layer perforated plate were sequentially adjusted to 0.01 m, 0.02 m, and 0.03 m for experimental testing. The results are presented in Figure 11, Figure 12 and Figure 13.

It can be known from the sound absorption coefficient graph that the curves with perforation radii of 0.01 m, 0.02 m, and 0.03 m all increase with the increase in frequency. Among them, the green curve with a perforation radius of 0.03 m has the fastest growth and the highest value in the sound absorption coefficient in the high-frequency band (1800–2000 Hz). This indicates that the larger the perforation radius, the better the high-frequency sound absorption performance of the composite material. The reason lies in that a larger perforation radius increases the size of the pore channel, making the friction and viscous losses between the sound wave and the interior of the material more thorough. Especially in the high-frequency band, the efficiency of sound energy loss is significantly improved.

In the impedance coefficient diagram, the impedance coefficient curves of different perforation radii overlap in the high-frequency band. This is because at high frequencies, the intrinsic acoustic characteristics of lightweight glass wool, such as flow resistance and porosity, dominate, weakening the influence of perforation radii, and these characteristics mask the differences in pore diameters. The impedance coefficient approaches 0 as the frequency increases. This is because the wavelength of high-frequency sound waves is shorter, and they can easily penetrate the porous structure of glass wool. The viscous loss and heat conduction loss inside the material fully consume the sound energy. At the same time, the resistive components (inertial resistance, elastic resistance) in the acoustic impedance are weakened by the frequency, and the resistive components take the lead. Coupled with the better high-frequency sound absorption performance of glass wool, the reflection and obstruction of sound energy are reduced. Finally, this causes the impedance coefficient to tend toward 0.

The reflection coefficient diagram shows that the larger the perforation radius, the lower the reflection coefficient. The purple “Measured value” curve with a perforation radius of 0.03 m rapidly decreases in the high-frequency band (1800–2000 Hz), approaching −1, indicating that the acoustic energy reflection is significantly weakened and more acoustic energy is absorbed by the material. Compared with the orange theoretical value curve with a perforation radius of 0.01 m, the curve with a perforation radius of 0.03 m decreases more significantly, further verifying the law that an increase in the perforation radius can suppress the reflection of sound energy and enhance the sound absorption effect.

This study, based on the single-layer porous plate–lightweight glass wool composite material system, breaks through the traditional coupling parameter research framework, and independently quantifies the influence of the perforation radius on the acoustic performance of the composite material. With the increase in the perforation radius, the high-frequency sound absorption performance of the composite material is significantly improved. In the sound absorption coefficient graph, the curve with a perforation radius of 0.03 m has the highest sound absorption coefficient in high-frequency bands such as 2000 Hz. In the reflection coefficient diagram, a larger perforation radius corresponds to a lower reflection coefficient, resulting in weaker acoustic energy reflection. In the impedance coefficient diagram, at low frequencies, the low-frequency sound absorption performance can be effectively regulated by adjusting the perforation radius. However, at high frequencies, adjusting the perforation radius has a limited effect on optimizing high-frequency sound absorption. Compared with the research of Wang Weichen et al., which focused on a single micro-perforated plate (MPP) [23], this study achieves breakthroughs across four dimensions: system architecture, mechanism analysis, parameter optimization, and application scenarios. By moving beyond the conventional structural framework of “micro-perforated plate + back cavity”, a dual-porous composite system—“perforated plate + lightweight glass wool”—is established, introducing two synergistic acoustic energy dissipation mechanisms that overcome the limitations inherent in single-structure studies. Unlike previous studies that primarily investigated the linear relationship between perforation diameter and sound absorption performance within a single structure, this work systematically analyzes how the perforation radius influences “double porous interface impedance matching, acoustic energy propagation paths, and multi-interface scattering” within the composite system. Furthermore, the synergy threshold between the perforation radius and glass wool thickness is identified—for example, when the radius is 0.03 m, a 40% wider absorption peak is achieved by matching with appropriate glass wool—thus breaking away from the simplistic correlation logic of single-structure parameter design. Rather than focusing solely on optimizing the sound absorption coefficient or bandwidth of a single structure, this study realizes the synergistic integration of high-frequency sound absorption (sound absorption coefficient > 0.9 in the 1200–2000 Hz range) and lightweight design (density < 1.5 kg/m³) through perforation radius control. A multi-parameter adaptive model is developed to resolve the engineering contradiction between high-frequency sound absorption and weight reduction. Targeting the specific requirements of electric vehicle doors—namely, limited installation space and high-frequency noise (without engine masking)—this study verifies that perforation radius optimization enables efficient sound absorption within a 3 cm thick composite material, overcoming the traditional reliance on thick back cavities in micro-perforated plate design. The influence on “modal-acousto-vibration coupling of the car door” is also quantified, thereby addressing the research gap in acousto-vibration coupling scenarios associated with single-structure studies. This work completes the transition from general theoretical understanding to automotive NVH engineering adaptation.

5.4. Analysis of the Influence of the Thickness of Single-Layer Porous Plate–Lightweight Glass Wool Composite Door on Sound Absorption, Impedance, and Reflection Characteristics

Under fixed parameter settings, the thickness values of the single-layer porous plate were sequentially adjusted to 0.01 m, 0.03 m, and 0.05 m for experimental testing. The results are presented in Figure 14, Figure 15 and Figure 16.

It can be seen from the sound absorption coefficient graph that the green curve with a thickness of 0.05 m shows a significant peak in the high-frequency band (1400–1800 Hz), and the sound absorption coefficient is much higher than that of the curves with thicknesses of 0.01 m and 0.03 m. This indicates that with the increase in material thickness, the high-frequency sound absorption performance is significantly optimized. The reason lies in the fact that a greater thickness provides a longer propagation path for sound waves, enhancing the friction and viscous loss between the internal fibers of the glass wool and the air. Especially in the high-frequency band, the absorption efficiency of sound energy is higher.

The impedance coefficient diagram shows that there are differences in impedance variations among materials of different thicknesses. The impedance variation amplitude in the low-frequency band (20–400 Hz) is relatively large. The increase in thickness alters the internal acoustic structure of the material, affecting the acoustic impedance matching. Materials with greater thickness are more likely to achieve impedance matching with incident sound waves, promoting the entry of sound waves into the material and their absorption. This explains the mechanism of improved sound absorption performance from the perspective of impedance.

In the reflection coefficient graph, the purple “Measured value” curve with a thickness of 0.05 m shows a more obvious downward trend in the high-frequency band (1400–2000 Hz), approaching −1, indicating that the acoustic energy reflection is significantly weakened and the sound absorption effect is better. Compared with the blue curve with a thickness of 0.01 m, the increase in thickness leads to a more significant decrease in the reflection coefficient, verifying the rule that the increase in thickness can effectively suppress the reflection of sound energy and enhance the sound absorption performance.

Comprehensive analysis shows that the thickness has a decisive influence on the sound absorption performance of single-layer porous plate–lightweight glass wool composites by changing the sound wave propagation path, acoustic impedance matching, and acoustic energy reflection characteristics. This study deeply reveals the multi-dimensional influence mechanism of thickness: Firstly, it alters the propagation path of sound waves. An increase in thickness prolongs the propagation distance of sound waves within the composite material, intensifies friction and viscous losses, and directly enhances the high-frequency sound absorption coefficient. Secondly, the acoustic impedance matching is optimized. The internal acoustic structure of the material is adjusted by changing the thickness to promote the adaptation of the acoustic impedance to the incident sound wave. Thirdly, to suppress acoustic energy reflection, increasing the thickness reduces the reflection coefficient and weakens the acoustic energy reflection. The changes in the sound absorption coefficient, reflection coefficient, and impedance coefficient all verify the rule that “the greater the thickness, the higher the high-frequency sound absorption coefficient, the lower the reflection coefficient, and the better the overall sound absorption performance of the material.” This study achieves a systematic breakthrough compared with previous research on the sound absorbers based on Jiejunxing micro-perforated plates [24]. Theoretically, this work reveals that increasing thickness enhances sound absorption performance by extending the acoustic path and intensifying fiber-induced viscous dissipation, thereby optimizing acoustic impedance matching and reducing the reflection coefficient. This leads to the formation of a “path–loss–impedance” synergistic mechanism. In contrast, earlier studies only observed a rightward shift in resonance frequency induced by thickness variation, without exploring the underlying mechanisms of energy dissipation and impedance matching at the material level. From a performance perspective, when the thickness reaches 0.05 m, the sound absorption coefficient in the 1400–1800 Hz frequency band increases by more than 40%—as shown in Figure 14—and the reflection coefficient approaches −1, as illustrated in Figure 16. These results demonstrate efficient broadband absorption above 1200 Hz. Compared with the literature findings, where thickness adjustments merely shifted the peak absorption frequency without enhancing its magnitude, the effective bandwidth remained limited to 390 Hz. In terms of engineering value, this study clearly identifies a thickness threshold of 0.05 m and establishes multi-parameter coordination involving porosity (>0.9) and perforation rate (>0.1). For example, high-porosity glass wool with a thickness of 0.05 m achieves a sound absorption coefficient of 0.95 in the 1800–2000 Hz range, resulting in a measured noise reduction improvement of 30–50%. In contrast, thickness optimization in the prior literature lacked integration with material co-design and real-world application scenarios, failing to establish any applicable parameter benchmarks. In summary, this study overcomes the limitations of traditional resonant cavity theory and, for the first time, establishes a three-dimensional optimization model—“acoustic path–impedance–multi-parameter”—providing a thickness design paradigm that combines mechanistic insight with engineering precision for high-frequency noise control in electric vehicles.

5.5. Analysis of the Influence of the Porosity of Single-Layer Porous Plate–Glass Wool Composite Door on Sound Absorption, Impedance, and Reflection Characteristics

Under fixed parameter settings, the porosity of the lightweight glass wool was sequentially adjusted to 0.35, 0.65, and 0.95 for experimental testing. The results are presented in Figure 17, Figure 18 and Figure 19.

It can be known from the sound absorption coefficient graph that the green curve with a porosity of 0.95 has the fastest growth and the highest value in the sound absorption coefficient in the high-frequency band (1800–2000 Hz), which is significantly better than the curves with porosities of 0.35 (blue) and 0.65 (orange). This indicates that the higher the porosity, the better the high-frequency sound absorption performance of the composite material. The high porosity makes the internal pore structure of glass wool more abundant, and the frictional and viscous losses during sound wave propagation with the pore walls are greater. Especially in the high-frequency band, the efficiency of sound energy absorption is significantly improved.

In the impedance coefficient diagram, the impedance changes of materials with different porosities vary. The impedance variation amplitude in the low-frequency band (20–400 Hz) is relatively large. The increase in porosity alters the acoustic structure within the material and optimizes the acoustic impedance matching. Materials with high porosity are more likely to achieve impedance matching with incident sound waves, promoting the loss of sound waves as they enter the material’s interior. This explains the mechanism of improved sound absorption performance from the perspective of acoustic impedance.

The reflection coefficient graph shows that the purple “Measured value” curve with a porosity of 0.95 shows a more obvious downward trend in the high-frequency band (1800–2000 Hz), approaching −1, indicating that the acoustic energy reflection is significantly weakened and the sound absorption effect is better. Compared with the blue curve with a porosity of 0.35, the reflection coefficient of materials with high porosity is lower, verifying the rule that an increase in porosity can effectively suppress the reflection of sound energy and enhance the sound absorption performance.

In the research on the sound absorption performance of single-layer porous plate–lightweight glass wool composite materials, the mechanism of porosity demonstrates a unique value. This study anchors the single-layer porous plate–lightweight glass wool composite system, breaks through the gradient and layered design framework, takes the single porosity as the core, and deeply explores its “trinity” mechanism of action through reshaping the pore structure, optimizing the acoustic impedance matching, and suppressing the acoustic energy reflection. It confirms the correlation that “the higher the porosity—the higher the high-frequency sound absorption coefficient—the lower the reflection coefficient”. And it has been verified in multi-dimensional data such as sound absorption, reflection, and impedance. This research achieves three significant breakthroughs compared with Ma Wenting’s work on gradient porosity acoustic materials [25]. Mechanistically, it is the first to reveal that high porosity (0.95) in a monolayer composite can directionally enhance high-frequency sound absorption through a triple-coupling mechanism: reshaping the pore structure to increase the sound–fiber contact surface, optimizing impedance matching to improve acoustic energy transmission efficiency, and suppressing acoustic energy reflection (with the reflection coefficient approaching −1), as demonstrated in Figure 17, Figure 18 and Figure 19. In contrast, previous studies merely identified porosity as a sensitive parameter via global sensitivity analysis, without establishing any quantitative relationship between porosity and either impedance or reflection behavior. From a performance standpoint, at a porosity of 0.95, the peak sound absorption coefficient in the 1800–2000 Hz frequency band increases by more than 40%, while reflected energy loss is reduced by over 50%. Compared with the literature results, where gradient design improved the RMS value of the sound absorption coefficient by 26.66%, the optimization objectives were scattered across absorption and insulation performance, with insufficient enhancement in the high-frequency range. In engineering applications, this study adopts a single-layer structure combined with a clear porosity threshold (>0.9), which simplifies manufacturing processes and maintains compatibility with lightweight requirements. In contrast, literature approaches relying on a three-layer ABA composite structure still resulted in a 7.1% mass increase after NSGA-II multi-objective optimization, with additional interfacial layers increasing the risk of impedance mismatch. In conclusion, this study overcomes the complexity associated with traditional gradient designs by establishing a precise regulatory framework for porosity and high-frequency sound absorption within a single-layer system, offering a more efficient and practically viable solution for high-frequency noise reduction in electric vehicle doors.

6. Conclusions

This study focuses specifically on the sound absorption performance of the single-layer porous plate combined with lightweight glass wool used in the doors of pure electric vehicles. Compared with traditional electric vehicle door materials such as solid steel plates, the single-layer perforated plate–lightweight glass wool composite structure offers significant advantages. Traditional materials exhibit poor sound absorption performance, particularly in the high-frequency range of 1200–2000 Hz, where their sound absorption coefficients are consistently low. Additionally, the substantial weight of steel plates negatively impacts vehicle energy efficiency and driving range. In contrast, the composite structure achieves a sound absorption coefficient of up to 0.9 within this frequency range, significantly reduces weight, and allows for targeted noise reduction between 800 and 2000 Hz through parameter optimization. Furthermore, it effectively integrates high-frequency sound absorption, lightweight design, and structural stability, thereby providing superior overall adaptability that aligns more closely with the multifaceted requirements of electric vehicles. By analyzing the experimental data of the sound absorption coefficient, impedance coefficient, and reflection coefficient under varying conditions—including medium type, perforation rate, perforation radius, thickness, and porosity—the influence of each parameter on the material’s sound absorption mechanism is systematically investigated. The main conclusions drawn from this research are as follows:

(1) The type of medium significantly influences the acoustic performance of new energy vehicle doors. Both rigid and flexible media demonstrate excellent sound absorption in the high-frequency range (above 1200 Hz), achieving absorption coefficients close to 0.9. In contrast, the air medium exhibits a much lower absorption coefficient of approximately 0.4 in the same frequency range, indicating poor sound absorption performance. These findings provide a theoretical basis for the design of road noise and wind noise isolation in new energy vehicle doors.

(2) The perforation rate of the inner panel has a substantial impact on the sound absorption performance of new energy vehicle door materials. As the perforation rate increases from 0.01 to 0.2, the peak sound absorption coefficient in the high-frequency band (1600–2000 Hz) rises from 0.45 to 0.85. Higher perforation rates correspond to lower reflection coefficients, particularly in the high-frequency range. Additionally, the perforation rate affects the material’s impedance matching characteristics. Due to the properties of glass wool, its influence is more pronounced in the low-frequency band and relatively weaker in the high-frequency band.

(3) The perforation radius and thickness of the inner door panel are critical parameters affecting the acoustic performance of composite materials. When the perforation radius reaches 0.03 m, the sound absorption coefficient increases most rapidly, peaking between 1800 and 2000 Hz. In the 1400–1800 Hz range, the sound absorption coefficient of materials with a thickness of 0.05 m is significantly higher than that of thinner materials. Increasing both the perforation radius and thickness reduces the reflection coefficient, while increased thickness also improves acoustic impedance matching, thereby enhancing sound wave absorption.

(4) The porosity of the inner panel material significantly affects the high-frequency sound absorption performance of the composite structure. When the porosity reaches 0.95, the sound absorption coefficient increases most rapidly, reaching its maximum between 1800 and 2000 Hz. High porosity enhances acoustic impedance matching. In the low-frequency band (20–400 Hz), impedance varies significantly, while the reflection coefficient decreases, leading to improved sound absorption performance.

Future research can be deepened in three aspects: First, explore the multi-parameter collaborative optimization of perforation rate and porosity, and construct a composite design model of high-frequency sound absorption and lightweight construction. Second, introduce the dynamic working condition test of real vehicles to analyze the influence mechanism of door vibration on sound transmission loss. The third recommendation is to develop an integrated structure of gradient porosity glass wool and an intelligent damping layer to expand the noise control capability in the low-frequency band (<400 Hz). These studies will promote the precise application of composite structures in the NVH engineering of pure electric vehicles.