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An in-vehicle study was conducted to understand how damping treatments on the floor of a vehicle affect the interior sound in the vehicle. Three differently formulated damping treatments were tested on three similar sport utility vehicles for this purpose. Numerous on-road sound and vibration data were collected under different operating conditions, and were reduced to understand the value of the damping treatment in controlling interior noise caused by powertrain and rolling-tire/road interaction. The paper discusses different data analysis procedures that were used in this study to understand whether there is a damping treatment that performs better than others in spite of variances in test vehicles, and still minimize the adverse influence of other variables that are related to the vehicle performance variation itself.

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.

Damping treatments have been used in reducing structure-borne noise in vehicles for many years. Although sheet based heat bondable mastic products (often called melt sheets) are quite common in the industry, sprayable products have several advantages and have been cited in the literature. This paper discusses findings of numerous structure-borne noise studies that were conducted on sprayable materials with different base-chemistries. The analyses show that a waterborne product is the most advantageous damping treatment in an automotive assembly process. The results also reveal that application of this product provides effective damping treatment as well as reduces structurally radiated noise.

Most of NVH related issues start from the vibration of structures where often the vibration near resonance frequencies radiates the energy in terms of sound. This phenomenon is more problematic at lower frequencies by structureborne excitation from powertrain or related components. This paper discusses a laboratory based case study where different visco-elastic materials were evaluated on a bench study and then carried on to a system level evaluation. A body panel with a glazing system was used to study both airborne and structureborne noise radiation. System level studies were carried out using experimental modal analysis to shift and tune the mode shapes of the structure using visco-elastic materials with appropriate damping properties to increase the sound transmission loss. This paper discusses the findings of the study where the mode shapes of the panel were shifted and resulted in an increase in sound transmission loss.

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.

Heat reactive expanding sealer materials are used as acoustical “baffles” to block noise propagation in rails, pillars, posts, and rockers. However, should moisture enter and collect in vertical pillars water damage may occur. Therefore, effort is being made to implement a drainage system for these problem applications. This paper discusses an effective way to prevent water damage by adding an acoustical drain plug to the baffle system with a minimal reduction in acoustical performance. The paper also discusses the performance and the effect of adding this plug to the baffle system. Finally, results of design variations of the plug on the baffle system are reported.

Journal of the Acoustical Society of America Book Review INCE/NCEJ Book Review What is acoustics? What is noise? How is sound measured? How can the vehicle noise be reduced using sound package treatments? Pranab Saha answers these and more in Acoustical Materials. Acoustics is the science of sound, including its generation, propagation, and effect. Although the propulsion sources of internal combustion engine (ICE) vehicles and electric motor-powered vehicles (EV) are different and therefore their propulsion noises are different, both types of vehicles have shared noise concerns: Tire and road noise Wind noise Vehicle noise and vibration issues have been there almost from the inception of vehicle manufacturing. The noise problem in a vehicle is very severe and is difficult to solve only by modifying the sources of noise and vibration. Sound package treatments address the noise and vibration issues along the path to reduce in-cabin noise.

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.

This paper provides an overview of sound and sound package (noise control) materials that are used in heavy trucks and buses. Transportation noise is a longstanding and complex problem. The challenge is to have a thorough understanding of the source-path-receiver relationship with respect to the noise generation and propagation such that one can find feasible solutions and applications of noise control materials. This paper discusses different types of noise control materials and also provides some examples of different noise control material applications.

Automotive noise control involves many aspects of the total vehicle design - the powertrain, body structure, chassis and so forth. Noise control materials in conjunction with intelligent vehicle design can help produce a pleasant, desirable vehicle. Understanding the basic functions and uses of noise control materials is one of the objectives of this paper. In some situation, thermal insulation materials are combined with or used in conjunction with noise control materials, and an understanding of the thermal properties of materials can be useful. Vibration isolators are important devices in controlling the transfer of sound and vibration energy and these are discussed.

The approaches used to develop an NVH package for a vehicle have changed dramatically over the last several years. New noise and vibration control strategies have been introduced, new materials have been developed, advanced testing techniques have been implemented, and sophisticated computer modeling has been applied. These approaches help design NVH solutions that are optimized for cost, performance, and weight. This paper explains the NVH practices available for use in designing vehicles for the new millennium.

The purpose of this paper is to identify various concerns that need to be evaluated prior to the design and construction of a reverberation chamber, such that the chamber can be used for various automotive related acoustical measurements. Some of the concerns involve issues such as room shape and size, the degree of sound and vibration isolation required, the use of conventional building materials versus traditional massive construction, construction cost, and the performance requirements for the test noise generation system. Various uses of a reverberation chamber include random incidence sound absorption measurements, small sample sound transmission loss measurements, vehicle insertion loss tests, dash panel, door, and other “buck” evaluation tests, and sound power level measurements of small automotive components and devices. These uses have differing and in some cases conflicting requirements that compete in the selection of room design parameters.

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.

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.

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.