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This paper focuses on the development of treatments to control airborne noise through the dash panel. For a noise control material supplier, these treatments can be the most challenging to design because of the number of pass-throughs and design constraints. The dash panel development process includes extensive in-truck testing and analysis to identify sound paths (location and magnitude) and establish design criteria, laboratory material testing to aid in the selection of appropriate materials, laboratory component testing to select areas requiring treatment and to design the shape of the treatments, and in-truck testing to verify the performance of the new treatments.

This paper discusses an analytical tool that has been developed to predict what types of interior sound package treatments may be necessary in a truck cab to meet a predetermined target sound level at the driver location. The steps that were taken to develop this tool involved a combination of experimental measurement and analytical based studies. Measurements were conducted to identify the acoustic strengths of the major noise paths through which sound travels from outside to inside the truck. These findings were then used to develop a sound package that reduced the vehicle interior noise to meet the target. Measurements were primarily made on a chassis roll dynamometer with final road verification to substantiate the dynamometer data. Data obtained from these measurements were also used in the analytical model that predicts the impact of various acoustics parts in the vehicle, and has the capability to optimize the sound package treatment in the vehicle.

Once the design of a door sheetmetal and accessories is confirmed, the acoustics of the door system depends on the sound package assembly. This essentially consists of a watershield which acts as a barrier and a porous material which acts as an absorber. The acoustical performance of the watershield and the reverberant sound build-up in the door cavity control the performance. This paper discusses the findings of a design study that was developed based on design of experiments (DOE) concepts to determine which parameters of the door sound package assembly are important to the door acoustics. The study was based on conducting a minimum number of tests on a five factor - two level design that covered over 16 different design configurations. In addition, other measurements were made that aided in developing a SEA model which is also compared with the findings of the results of the design study.

Advances in vehicle noise control are leading the automotive industry to place increasing emphasis on weatherseals to block exterior noise. As a result, properly evaluating the acoustical performance of automotive weatherseals is of increasing importance. There is no current specific standard for this testing. Rather, there has been reliance on adaptations of SAE Standard 51400 “Laboratory Measurement of the Airborne Sound Barrier Performance of Automotive Materials and Assemblies” by testing laboratories. However, the 51400 standard addresses testing of flatstock materials and does not readily lend application to pre-formed parts such as weatherseals. For this reason, adaptation of the standard can vary significantly from facility to facility and manufacturer to manufacturer. These differences can be significant and can render comparisons between test results on competing materials very difficult.

The paper discusses the importance of a well documented standardized laboratory test procedure to evaluate damping material performance for the automotive industry, and to understand the parameters that influence the precision of the test method. The standard outlines a methodology which was developed with the general consensus of automotive engineers, suppliers, and independent test laboratories. The methodology is based on the Oberst bar test method where a damping material is bonded to a specific size steel bar and the system is excited at its various modes of vibration under a cantilevered configuration. The damping performance is expressed in terms of composite loss factor, ηc, within the frequency range of approximately 100 Hz to 1000 Hz, and over the useful range of temperatures for the given application.

The presence of any weak paths or leakage limits the best design and the acoustical performance of a sound package system in a vehicle. Techniques to predict the response at the design level could help in improving the performance of the sound package system. This paper discusses the development, verification, and implementation of an analytical technique for predicting the acoustical performance of a sound package system based on the principles of sound transmission coefficient and the surface area covered by each sub-system. This technique is especially suitable for predicting the acoustical performance of a weak path created by passthroughs or plugs in a sound package system. Initially, a simple system was developed and studied to verify the model. The predicted values were compared with the measured values. Based on the comparison, different parameters were identified and modified such that the model agrees closely with the measured data.