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The SAE International standard for testing Oberst bars has been used in the industry for many years with predictable results. Growing interest in testing wider samples to incorporate more of the variability in liquid applied sprayable dampers has led to increased use of a center point damping test method based on a Japanese standard JIS G 0602. This method is similar to that of the ISO 16940 standard for testing laminated glass. Theory shows us that an Oberst test with a free length equal to the half length of a bar used for center point testing will provide the same resonances. This paper intends to show a relationship between the resonances of bars tested with the Oberst and center point test methods. A correlation between the composite loss factor for samples tested with each of the methods will be illustrated.

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.

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.

Body cavity fillers are used to inhibit noise propagation/amplification through body cavities such as sills, pillars, and posts' to improve vehicle NVH performance. Cavity fillers should be optimized by matching their performance with the global NVH objectives of the vehicle. A standard test method must be defined to acquire acoustical profiles and facilitate in the proper selection of materials based on performance. This paper discusses test results of 38 cavity filler samples which represent all currently used materials by the “Big Three” automotive OEMs. The samples were grouped into 4 categories based on their weight and fill configurations. Data was obtained utilizing an established, laboratory based, acoustical test method for fillers (SAE paper 930336). The laboratory results were analyzed to generalize the performance of cavity filler materials and to set acoustical goals for vehicle applications.

The performance of damping materials is generally evaluated by experimental methods. However most damping materials used in the transportation industry cannot be excited by itself. Therefore, the measurements are generally made by exciting a damped system, where the damped system extends from a bar to a panel. The paper reviews various damped systems and excitation methodologies and discusses some of the limitations of a bar to study the damping performance for different applications. It discusses a methodology where a damped panel is mounted on a fixture and the fixture is excited with a shaker. The paper discusses data acquisition and data reduction procedures to obtain the damping performance of laminated steel acoustic patch products on a third octave band frequency basis.

This paper provides an overview of a custom software developed to obtain measurement data in a self-contained acoustic test facility system used for conducting random incidence sound absorption tests and sound transmission loss tests on small samples in accordance with SAE J2883 and J1400 standards, respectively. Special features have been incorporated in the software for the user to identify anomalies due to extraneous noise intrusion and thereby to obtain good data. The paper discusses the thoughts behind developing user-friendly algorithms and graphical user interfaces (GUI) for the sound generation, control, data acquisition, signal processing, and identifying anomalies.

This paper discusses the development of a small sample test facility for properly evaluating the low frequency noise control performances of various automotive acoustical materials. Based on several tests conducted with 0.61 m (24 in) diameter samples, this facility is designed to operate in the frequency range of 35 Hz to 355 Hz. Near-field root-mean-square acoustic pressure and acoustic velocity were measured for this purpose, using a dual microphone probe. This methodology allows one to test acoustical materials without elaborate test facilities and without the need for any special acoustic test environment.

Standards organizations develop standards depending on the need in the market place. With the change in vehicle design, lightweighting structures, and body panels made out of aluminum and composites, SAE’s Acoustical Materials Committee is developing a new damping standard. This standard is also very suitable in determining the damping performance of materials used in the off-highway applications, where the thickness of the steel body panel is much greater than in the automotive application. The general methodology of this standard is based on the mechanical impedance measurement method and has been developed with the general consensus of automotive engineers, suppliers, and independent test laboratories. This method is essentially based on the fact that a bar is excited at the center by a shaker. The force exerted by the shaker and the corresponding vibration is measured at that point to determine the frequency response function of the mechanical impedance signal.

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.

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.

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.

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).

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.

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.

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.

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 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.