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A flexible rebound-type acoustic metamaterial with high sound transmission loss (STL) at low frequency is proposed, which is composed of a flexible, light-weight membrane material and a sheet material - Ethylene Vinyl Acetate Copolymer (EVA) with uneven distributed circular holes. STL was analyzed by using both computer aided engineering (CAE) calculations and experimental verifications, which depict good results in the consistency between each other. An obvious sound insulation peak exists in the low frequency band, and the STL peak mechanism is the rebound-effect of the membrane surface, which is proved through finite element analysis (FEA) under single frequency excitation. Then the variation of the STL peak is studied by changing the structure parameters and material parameters of the metamaterial, providing a method to design the metamaterial with high sound insulation in a specified frequency range.

Acoustic performance of auto interiors is definitely important to control the NVH (noise, vibration, and harshness) performance inside a vehicle, and it is determined by the material parameters, such as density (ρ), thickness (d), open porosity (OP), airflow resistivity (σ), tortuosity (T), viscous characteristic length (VCL), thermal characteristic length (TCL), young's modulus, poisson's ratio, and damping coefficient. Firstly, by making different felt samples (of different surface density and thickness), the sound absorption performance and related parameters were obtained. Then the correlation between the parameters and the sound absorption coefficient (SAC) was summarized. Through this method, database of acoustic parameters and the corresponding SAC for porous materials can be established and sound package design and adjustment can be easily conducted based on the database.

PE (polyethylene) membranes are widely adopted in sound insulation pads inside vehicle. However, there are few studies on the acoustical effects of these inserted membranes. This study focuses on these effects. Frequently sound insulation is made up of two layers of felt (a pad made of cotton or synthetic fiber), separated by a PE membrane. The normal incidence sound absorption coefficient and sound transmission loss for this type of insulation construction were calculated through the micro perforated membrane theory and the analytical model (NOVA) which is based on Biot theory. Impedance tube measurement was used to derive the poroelastic properties needed to utilize these models. Comparison between the calculated and measured results showed that the absorption coefficient obtained from the micro perforated membrane theory was closer to the measured value above 3 kHz. And that calculated using NOVA was closer to the measured value below 3 kHz.

Several methods have been established to measure the normal incidence transmission loss of noise control materials using the standing wave tube. In the automotive NVH field, multi-layered systems are common-place, for example in the interaction between the traditional mass-decoupler dash insulator and the front dash sheet metal. Most of the sound transmission loss studies utilizing the standing wave tube have so far been focused on single layer systems with only a limited number of studies on multi-layered systems. Therefore there is only some degree of information on the correlation between this said method and the more widely accepted two-room methods of determining sound transmission properties in these systems.

Each time a new vehicle is developed, engineers face the challenge to develop the ideal sound insulation package. The goal is to attenuate powertrain, wind and road/tire noise from entering the vehicle while complying with cost, weight and packaging constraints. The design process is greatly facilitated if the engineer has effective tools to rapidly quantify how various sound insulation components contribute to the overall NVH performance of the vehicle. This paper discusses how an interactive vehicle acoustical design tool can be developed that assists the designer in making rapid decisions as to how to balance the performance of the various sound package components. The acoustical design tool is unique for each vehicle, and must take into account design decisions such as type of powertrain, body style, and numerous other factors in order to correctly predict the performance of the total package.

This paper explores the performance of light weight attenuators, which take a dissipative approach to sound abatement in the motor vehicle. An analytical model is used to predict the sound transmission loss and random incidence sound absorption of attenuators, absorbers and sandwich insulation systems. Then, a mathematical expression is developed which combines the dissipative and sound transmission loss performance to determine the total noise reduction provided in the vehicle. Using this equation, the performance of multi-layered attenuators is shown to be comparable to, or better than that of sandwich insulators. Finally, test results from various studies in vehicles show that significant weight savings can be realized by using these multi-layered attenuators, which take a dissipative approach to vehicle sound insulation, rather than the traditional sandwich insulation system.

Although automotive headliners are primarily designed for their aesthetic qualities, technical experts realize that they play a significant role in affecting the acoustics in the cab of the vehicle. This paper suggests that the roof sheet metal and headliner perform as an assembly system, and explores how the acoustical attributes of that system, including the sound absorption, sound transmission loss and damping, can be assessed in the acoustics laboratory. New test methodologies and devices are introduced, and a wide variety of headliner and roof assembly designs are tested.

This paper discusses an empirical method for predicting the Sound Transmission Loss (STL) performance of Sound Barrier Assembly (SBA) materials that are commonly used in the automotive industry. The prediction method is based on basic STL theories of single and double-wall systems, in conjunction with the double wall resonance and the standing wave resonance between the two walls. In addition, a practical technique for determining the acoustical influence of the decoupler in a double-wall system is proposed. When all these considerations are put together properly, one gets a much clearer picture of the STL characteristics of typical double wall systems, and understands how the barrier and decoupler together affect the STL performance. The validity of the empirical prediction method is substantiated by comparing predictions with measured results of more than 60 samples.