Study on the Acoustic Performance of a Novel Light Glass Wool-glass fiber mat Composite Material for Cabin Interior Acoustic Packaging of Electric Vehicles’ Cockpits

Abstract

This study employs the transfer matrix method combined with numerical simulations based on the transfer matrix model and an impedance tube testing system to explore the correlation mechanism of acoustic parameters in Light Glass Wool-glass fiber mat composite materials. Through experimental testing, key parameters such as resistivity, tortuosity and porosity were regulated to quantitatively analyze their influence laws on the acoustic characteristics of the composite structure. This study discusses the data analysis process, formula derivation process and basic assumptions of the research. The research results show: First, regarding the tortuosity of glass fibers: At high frequencies (1850 Hz) in the sound absorption coefficient, when the tortuosity increases to 2.8, the sound absorption coefficient increases by 0.86 %. The main reason is that a higher tortuosity makes the spatial structure of glass fibers more complex. When high-frequency sound waves enter, more reflection and refraction occur on the fiber surface, prolonging the propagation path of sound waves inside the material and increasing the contact opportunity with fibers, thus absorbing more sound energy. Second, regarding the porosity of glass fibers: At low frequencies (50 Hz), when the porosity increases to 0.94, the sound absorption coefficient increases by 40.5 %, and the reflection coefficient decreases by 1.6 %. The main reasons are:Reducing "rigid reflection" of materials: Materials with high porosity are more "porous". When low-frequency sound waves hit the material surface, more energy enters the pores instead of being directly reflected. The 1.6 % decrease in the reflection coefficient is precisely because the rigid reflection of sound waves on the material surface is reduced, and more sound waves are guided into the interior to participate in the absorption process. Optimizing "viscous loss" conditions: Low-frequency sound waves vibrate more slowly and require sufficient pore space for air molecules to friction with the fiber walls. The increase in porosity makes the air flow between fibers freer, increasing viscous resistance. Sound wave energy is more dissipated through friction between air and fibers, further enhancing the sound absorption coefficient (40.5 % increase). Third, regarding the air interlayer: As the thickness of the air interlayer increases, the action mechanism of the interlayer space on medium-high frequency sound waves changes. A thicker air interlayer provides more sufficient propagation paths and space for medium-high frequency sound waves. During the multiple reflections, refractions, and dissipations of sound waves in the interlayer, more medium-high frequency sound energy is absorbed and dissipated. Therefore, the medium-high frequency sound transmission loss significantly increases, resulting in a substantial reduction in the medium-high frequency sound energy that penetrates the interlayer and continues to propagate. Finally: This study theoretically provides an optimized design idea for wide-band sound-absorbing composite materials, offering key reference for solving automotive noise problems.