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Concepts for dual density materials for usage as absorbers and decouplers are based on well-established layered media principles and have been applied for many years in non-automotive applications. Balancing the mass, air flow resistance, and thickness allows for improved noise attenuation in the low to mid frequency range which is of particular interest for automotive NVH management. Using these principles, products were tuned via mass and airflow resistance to reduce noise levels while also significantly reducing mass. Validation in various vehicles confirmed that up to a 55% reduction of a sound package's mass is possible. The considerable weight reductions of dash insulators and carpet systems are possible at the same times as the sound level in the vehicle interior is at least maintained and frequently improved.

For the assessment of vehicle acoustics in the early design stages of a vehicle program, the use of full vehicle SEA models is becoming the standard analysis method in the US automotive industry. One benefit is that OEM's and Tier 1 suppliers are able to cascade lower level acoustic performance targets for NVH systems and components. Detailed SEA system level models can be used to assess the performance of systems such as dash panels, floors and doors, however, the results will be questionable until test data Is available. Correlation can be accomplished with buck testing, which is a common practice in the automotive industry for assessing the STL (sound transmission loss) of vehicle level components. The opportunity to conduct buck testing can be limited by the availability of representative bodies to be cut into bucks and the availability of a transmission loss suite with a suitably large opening.

As customer awareness of product sound grows, the need exists to ensure that product sound quality is maintained in the manufacturing process. To this end in-process controls that employ a variety of traditional acoustical and alternate sound quality metrics are utilized, usually partly or wholly housed in a test enclosure. Often times these test cells are required to attenuate the background noise in the manufacturing facility so that the device under test can be accurately assessed. While design guidelines exist the mere size and cost of such booths make an iterative build and test approach costly in terms of materials as well as engineering and testing time. In order to expedite the design process and minimize the number of confirmation prototypes, SEA can be utilized to predict the transmission loss based upon material selection and booth construction techniques.

The area in the neighborhood of the package tray can be a significant path for road noise and exhaust noise. Air extraction routes and loudspeakers add to the difficulty of effective system design. A variety of designs were prototyped and their transmission loss measured in a standard SAE J1400 sound transmission loss suite. The performance of the various designs was compared to an untrimmed piece of sheet metal with embedded air extraction holes. The addition of trim added from 1 dB to 14 dB to the transmission loss. Statistical energy analysis (SEA) models of a variety of package tray systems will also be shown. Both of these techniques can provide design guidance at an early stage of vehicle program development.

In many cases, the results from a sound transmission loss (STL) test can differ from facility to facility. Despite the presence of standardized test specifications such as SAE J1400 [1], many issues can create variations in the data unique to that particular setup. These situations have presented themselves in recent tasks in which a reverberation room was relocated into a smaller area than was previously available. Current test projects in the relocated test facility have shown a need to better understand the details influencing the quality of the test data. Issues such as the sample orientation, the volume of the reverberation room, the quality of the sealing between the reverberation and anechoic rooms and even the material itself or the operator's style of positioning the sample all had to be reconsidered. It was determined that an investigation into causes of these differences needed to be launched to improve the setup of the STL test and provide more reliable data.

In Statistical Energy Analysis and Energy Flow Analysis models of connected beam systems, it is necessary to determine the power reflection and transmission coefficients of the structural joints. The use of a spectral element formulation to estimate the joint coefficients for any number of rigidly connected beams oriented at any angle in all three dimensions is presented. The longitudinal, transverse, and torsional wave types are modeled and assembled into beam elements. A force is applied to the system and the magnitudes of the transmitted and reflected waves are identified and used to calculate the joint's power reflection and transmission coefficients. Examples are presented to illustrate the procedure.