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In the early stages of a vehicle program, sound package design is significantly complicated by numerous competing requirements including cost, weight, acoustical targets and packaging space. The problem is further convoluted due to a limited definition of the vehicle at this time. In this article, a Statistical Energy Analysis (SEA) model of the vehicle is created based on a gross description of the vehicle architecture. A large material database of commonly used sound package configurations is then linked to the SEA model. Genetic Algorithms (GA) are finally applied to optimize the sound package design to satisfy cost, weight, acoustical targets and packaging requirements in the vehicle design.

System Engineering has increasingly been applied in the automotive industry to develop quality vehicles efficiently and effectively. It is particularly important to use System Engineering methods in the early stages of vehicle development when all requirements such as performance, package space, cost and weight are actively defined and balanced, and when decisions are made that have substantial downstream design consequences. To achieve effective balance, decisions have to be data driven to complement engineering experience and judgment. Analytical tools (CAE) have been developed in the industry to evaluate and synthesize designs. However, there are limited examples and discussions in the literature on how the “upfront” CAE can be implemented to integrate cross-functional requirements into the component design. Statistical Energy Analysis (SEA) method is the CAE tool used in sound package development.

Small reverberation rooms are used in common practice for determining random incidence sound absorption properties of flat materials and finished parts. Based on current small reverberation room usage in the automotive industry, there is a need for standardization that would bring about an appropriate level of consistency and repeatability. To respond to this need, a feasibility study is being pursued by an SAE task force, under the direction of the Acoustical Materials Committee, to develop a small volume reverberation room test method for conducting random incidence sound absorption tests. In addition to an accepted test method for small reverberation rooms, a data driven correlation that relates full size reverberation room absorption testing to small size reverberation room testing would be beneficial in understanding the usage of both. A Round Robin study has been underway for more than three years and will be completed in 2005.

Lightweighting of vehicle panels enclosing vehicle cabin causes NVH degradation since engine, road, and wind noise acoustic sources propagate to the vehicle interior through these panels. In order to reduce this NVH degradation, there is a need to develop new NVH sound package materials and designs for use in lightweight vehicle design. Statistical Energy Analysis (SEA) model can be an effective CAE design tool to develop NVH sound packages for use in lightweight vehicle design. Using SEA can help engineers recover the NVH deficiency created due to sheet metal lightweighting actions. Full vehicle SEA model was developed to evaluate the high frequency NVH performance of “Vehicle A” in the frequency range from 200 Hz to 10 kHz. This correlated SEA model was used for the vehicle sound package optimization studies. Full vehicle level NVH laboratory tests for engine and tire patch noise reduction were also conducted to demonstrate the performance of sound package designs on “Vehicle A”.

Biot's model of elastic porous materials is widely used to predict the acoustical performance of noise control materials in the automotive industry. Material properties of acoustical materials, often referred to as Biot parameters, such as porosity, airflow resistivity, tortuosity, viscous characteristic length and thermal characteristic length are required inputs in the Biot model. Various test methods have been developed to measure Biot parameters. This paper conducts a comprehensive review of the existing test methods, discusses accuracy and applicability of each test method, and provides recommendations to the SAE Acoustical Materials Committee regarding the need for the development of SAE test methods for Biot parameters.