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This four-session course provides a detailed understanding of the source–path-receiver relationship for developing appropriate sound package treatments in vehicles, including automobiles, commercial vehicles, and other transportation devices. The web course provides a detailed overview of absorption, attenuation (barrier), and damping materials and how to evaluate their performances on material, component, and vehicle level applications. A significant part of this course is the case studies that demonstrate how properly designed sound package materials successfully address vehicle noise issues.

Liquid spray applied damping materials have potential advantages over conventional sheet damping materials in automotive body panel vibration applications. In order to understand the acoustical impact, a laboratory based NVH study was conducted to compare the damping and stiffness performance characteristics of various sprayable damping materials versus the production damping treatment. Based on this comparison, a criteria was developed to select potentially viable sprayable damping materials for vehicle testing. In-vehicle tests were also performed and compared to the laboratory findings to understand how well the results correlate. This paper discusses a criteria for selecting sprayable damping materials based on bench-top tests for vehicle applications, and the potential benefits of sprayable materials.

The paper discusses the development of a new SAE standard J2883 for measuring sound absorption performance of absorption materials in a small reverberation room. It discusses the need for such a standard particularly in the automotive industry. It also discusses the need for understanding the parameters such as the room volume, diffusion and cut-off frequency, and the sample size that affect the measurements and how to address these parameters in developing a robust test method. Finally, the paper discusses some of the findings of the round robin tests where measurements were conducted in various size rooms, task force activities, and the proposed repeatability and reproducibility values of the test method.

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.

This paper discusses the thought process that one needs to go through for developing an appropriate sound package treatment for a vehicle. In the development process one needs to put proper emphasis on understanding the source, path, and the receiver system. One needs to have an understanding on how to reduce the noise at the source, path, and/or receiver location. One may need to conduct a feasibility study of the benefits of various noise control options. In terms of sound package treatments one needs to understand the fundamentals of acoustical materials how they work and why one material performs differently than another one, as well as the importance of a well documented specification that every supplier has to meet.

This paper discusses the importance of studying different variabilities (test and product variations) that may affect the noise reduction capabilities of automotive headliners, constructed from different materials. For this purpose, interior noise measurements were made at a position approximating the operator ear level, with different headliner materials under various operating conditions. For better understanding of the effect of different variabilities on acoustical performance, various single number values were computed from the measured data reduced in 1/3 octave band frequencies. Statistical data analyses show that the acoustical performance evaluation of headliners is affected by the product variation from one headliner to another, as well as experimental variation due to vehicle performance and test variation.

This paper discusses the results of an experimental study on sound absorption of a number of automotive carpet materials. The results are compared to each other and to other “acoustical materials”. Initial impedance tube measurements of 18 different materials showed the expected trend of increasing absorption as thickness increased. Twelve materials were then tested in a reverberation room. Test results showed that most materials had significant absorption above 500 Hz with values for the better materials approaching values for fiber glass. Absorption correlated highly (r = 0.92) with thickness and very highly (r = 0.98) with the product of thickness and surface weight, indicating that the absorption of new constructions can be predicted. However, reverberation room results did not correlate well with impedance tube results.

Test standards are essential for evaluating the performance of a product properly and for developing a data base for the product. This paper discusses various standards that are available for determining the acoustical performance of sound package materials. The paper emphasizes various SAE standards that are available in this area, the reasons why these standards are important to the researchers working in the mobility industry, the history behind the development of these standards, and how they are different from standards that are available from other standards organization on similar topics.

Automobile manufacturers recently requested the help of the SAE Acoustical Materials Committee to develop standard data formats that could be used by suppliers to present data on NVH products. An SAE task force with representatives from material suppliers and from OEMs chose formats covering a broad range of acoustical tests commonly conducted in the automotive industry. These formats cover both material and vehicle tests. They include details on samples and test conditions and graphs with preferred axes and data ranges. SAE recommended practice J2629 will be issued that describes the use of these preferred formats for acoustical data. The automobile manufacturers have requested that all suppliers of NVH products use these formats to present results from this point onward.

A study was conducted to understand the acoustic viability of using post consumer rebond seat foam materials in vehicles for floor carpet underlayment applications. These foam materials were obtained from two different sources: 1) polyurethane foam dismantled from seats of end of life vehicles (ELV or scrap vehicles), and 2) polyurethane foam recovered and cleaned from auto shredder residue (ASR) by the Argonne National Laboratories (ANL) using their cleaning method. The study was conducted using three North-American cars, each serving different market segments. Based on both laboratory and on-road tests conducted on each vehicle, the study concluded that the acoustical performance of the floor carpet underlayment part made of post consumer rebond foam is comparable to that of the current production part mostly made of shoddy materials.

This paper discusses the importance of having an industry-wide standardized laboratory test procedure for proper evaluation of vibration damping materials, and for consistency between damping tests conducted by different test facilities. Several different vibration damping test procedures that are presently used in the automotive industry are briefly discussed. However, a test method that has been selected for a new proposed SAE Recommended Practice based on exciting a beam at various modes of vibration and at different temperatures is discussed here. The relative superiority of this test method over other methods, the importance of selecting the most appropriate beam size, and how the damping performance should be measured for consistency and clarity are emphasized. A round-robin test was conducted to determine the variability of the test procedure. Factors considered were type of damping material, bar mounting, and differences between laboratory instrumentation.

The paper discusses the process of developing an SAE damping measurement test method that is suitable for testing bars that are not made of steel or are difficult to measure with the traditional Oberst bar method. The method is based on measuring mechanical impedance (force over velocity) of a vibrating bar. The bar is excited at the center using a shaker and hence it is also called a CenterPoint method. The paper discusses the round robin tests that have been conducted so far and discusses the test results that will help develop the standard. The paper discusses the variability of the round robin test results within a laboratory, between laboratories, as well as the coefficient of variation for these measurements. The paper also discusses various parameters that should be carefully monitored in this study, that otherwise could affect the precision of the test procedure.

Random incidence sound absorption measurements of automotive components such as floor carpets, seats, headliners and hoodliners are important during the design and development of noise control treatments in a vehicle. Small volume reverberation rooms [1]1 have been widely used in practice to determine the absorption properties of those components. The SAE Acoustical Materials Committee has organized a task force to develop a standard procedure for measuring random incidence sound absorption properties of flat samples, as well as automotive components in small reverberation rooms. Statistical analysis and correlation study between large reverberation rooms and small reverberation rooms of flat samples using data acquired from a recent round robin study were reported in SAE Paper 2005-01-2284 [2, 3].

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.

The typical goal of most sound absorbing materials is to maximize the sound absorption for a given thickness, weight and cost. In this study, tests were conducted on an example polyester fiber sound absorber pad to establish baseline acoustical performance and to extract poro-elastic material properties, which were then used to computer model the acoustical performance of this material. Good agreement was obtained for the measured and predicted sound absorption for the base fiber material. Opportunities to improve the performance of this material were then investigated using computer models of various acoustically-tuned facings in combination with the base pad. The results show how overall sound absorption can be improved and how the frequency dependent performance can be tuned to meet specific requirements.

Traditionally, the damping performance of a visco-elastic material is measured using the Oberst bar damping test, where a steel bar is excited using a non-contacting transducer. However, in an effort to reduce the weight of the vehicles, serious effort is put in to change the body panels from steel to aluminum and composite panels in many cases. These panels cannot be excited using a non-contacting transducer, although, in some cases, a very thin steel panel (shim) is glued to the vibrating bar to introduce ferrous properties to the bar so it can be excited. In the off highway vehicles, although the panels are made of steel, they are very thick and are difficult to excite using the Oberst bar test method. This paper discusses a measurement methodology based on mechanical impedance measurements and has the potential to be a viable/alternate test method to the Oberst bar testing. In the impedance method, the test bar is mounted to a shaker at the center (Center Point method).

Sealant materials are used in todays automobiles for many applications such as, sealing of body seams, sealing access holes and the filling of hollow cavities. The primary reasons for these applications are to prevent corrosion, prevent water intrusion, and to reduce the noise level in the passenger compartment. However, the noise control capabilities of sealant materials have not been explored until recently. This paper discusses the requirements that a noise control material must possess, and reviews how a sealant material can fulfil these requirements. Properly designed sealant materials can possess sound transmission loss (barrier) properties, vibration damping properties over a given frequency and temperature range of interest, and often sound absorption properties with proper formulation. This paper provides case studies to substantiate the acoustical capabilities of sealant materials.

Laminated steel body panels are used in different applications in vehicles, such as dash panels and wheel wells. A part made out of laminated steel has the potential to provide structure-borne noise reduction and also improve the airborne noise reduction of the part compared to a monolithic part. The use of laminated steel has been more critical when there are deep draws on the part as the deep draws cause localized resonances which degrade the acoustic performance significantly. However, due to lightweighting demands, hybrid laminated panels, commonly known as acoustic patch laminates have become very attractive. This paper discusses the damping and sound transmission loss performances of a dash panel part with monolithic, laminated, and acoustic patch panels.

In the automotive industry, random incidence sound absorption tests are conducted on flat material samples as well as on finished components such as headliners, seats, and floor carpet systems. This paper discusses a feasibility study that 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. This method has the potential to be suitable for flat material and component testing. A round-robin test program is being conducted to determine variability due to test procedures, room size differences and laboratory differences. The paper discusses the selection of test samples and provides an update on the findings of the round-robin test study.

The use of sealant materials to improve interior acoustics has increased significantly in todays automobiles. One such application is to use expandable sealant materials in rails, pillars, and cavities to reduce noise propagation. However, there is no standardized method for evaluating the acoustical performance of these materials. This paper reviews the basics of noise control engineering and discusses a proposed laboratory based test methodology that has been developed for properly evaluating the acoustical performance or expandable sealant materials. The test method is intended to simulate actual applications so that different materials can be evaluated to achieve optimum acoustical performance within a channel representing the rails or pillars in automobiles.