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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.

Recent effort has focused on correlating random incidence absorption coefficients obtained in different sizes of reverberation rooms based on round robin testing of identical samples in a database driven approach. An alternate approach presented here is to correlate random incidence sound absorption coefficients among different reverberation rooms using an apparent linear relationship between sound absorption coefficients and a geometric property of the test samples. Linearity can be judged in relation to the uncertainty of each individual measurement. The study will encompass experimental work on three different sizes of reverberation rooms for both a single layer material and a multi-layered material. By examining the different sound absorption coefficient values from each size of room, as a function of geometric parameters, we illustrate the quantitative correlation that might be established between the different sizes reverberation rooms.

Seat covers made from textiles, leather and vinyl were evaluated for noise absorption. The textiles included woven velours, pile knits and flat wovens. The noise absorption of the covers and the corresponding seat assemblies was tested by the reverberation room method per ASTM C423. The effect of different foams was also tested. For the leather and vinyl covers, the effect of perforation was evaluated. Test results showed distinctive differences between textiles and leather/vinyl with cloth seats having superior noise absorption. Even among the textiles, there are significant differences. Core foam densities affect the characteristics as well. For pile fabrics (woven velours and pile knits), the size of the pile fiber does not affect the acoustic characteristics of the seat. Also, no significant difference was observed between a bonded seat and a conventional (cut and sew) seat.

Road simulators like shaker tables are commonly used in the automotive industry for component level dynamic testing. The purpose of a shaker table is to duplicate measured vehicle accelerations in a lab environment. However, there is no universal measure to describe the accuracy of iterated drive files for road simulators. This paper compares frequency domain methods based on discrete Fourier transforms with various time-frequency techniques to develop an accuracy measure which gives more information than metrics which are now common. Results are presented using road data from two typical vehicles and iterated drive files from a six axis shaker table.

In recent years, the perceived quality of powered seat adjusters based on their sound during operation has become a primary concern for vehicle and seat manufacturers. Historical noise targets based on overall dB(A) at the occupant's ear have consistently proved inadequate as a measure of the sound quality of a seat adjuster. Significant effort has been devoted to develop alternative sound quality metrics that can truly discriminate between “good” and “bad” seat adjusters. These new metrics have been successfully applied for some years by product development engineers in test labs. However, in the assembly plant the sound quality of the seat adjuster is still assessed subjectively by an operator at the end of the assembly line. The main problem with this approach is not only the lack of consistency and repeatability across large samples of seat tracks, but also the fact that the only feedback provided from the end-of-line to the product development team is of subjective nature.

Composite multi-layered systems are of particular interest in the automotive industry since the design of the various components in an efficient sound package requires a good predictive model. The state of the art in this matter shows that the medium and high frequency ranges are well mastered in terms of predictive tools based on infinite models. But this is not the case for the lower frequency range. The paper will start with a discussion of the medium and high frequency range where, for example, the Transfer Matrix Method (TMM) is an efficient framework to predict the acoustical properties of multi-layer materials. Emphasis will be put on correlation data obtained with a variety of multi-layer systems. In the low frequency range the use of infinite models leads to significant discrepancies. In the present paper the authors propose a finite “hybrid type” formulation which combines the advantages of both single layer and multi-layer approaches of stratified composite structures.

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.

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.

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.

Interior noise has become a significant performance attribute in modern passenger vehicles and this is extremely important in the luxury market segment where a quiet interior is the price of entry. With the elimination of early prototype vehicles to reduce development costs, high frequency analytical SEA models are used to design the vehicle sound package to meet targets for interior noise quality. This function is important before representative NVH prototypes are available, and later to support parameter variation investigations that would be cost prohibitive in a hardware test. This paper presents the application of an analytical full vehicle SEA model for the development of the acoustic package of a cross over luxury utility vehicle. The development concerns addressed were airborne powertrain noise and road noise. Power flow analysis was used to identify the major noise paths to the interior of the vehicle.

Unweighted dB, dB(A), and Articulation Index do not always accurately identify the sound quality of vehicle interior noise. This paper attempts to determine the relevance of sound quality in interior automotive acoustics. Traditionally, overall dB(A) levels have been the driving factor, along with cost, in selecting an interior automotive acoustic package. In this paper, we make use of subjective jury evaluations to compare perceptions of various interior acoustic packages and compare these results to objective values. These values include, but are not restricted to, dB, dB(A), and Articulation Index. Considerations are made as to whether differences between packages can be perceived by customers. This paper also attempts to show that subjective evaluations can differ with the standard metrics used to select acoustic packages and describe why such evaluations might be important in acoustic package selection.

Perforating certain layers of laminated material can improve the sound absorption performance of the material. The hole size, shape, angle, spacing and pattern can be tuned to improve sound absorption in a certain frequency range using a validated acoustical model. The model is based on a numerical calculation of acoustical properties of porous multi-layers using a transfer matrix method in the context of the Biot theory in NOVA software. An additional calculation of airflow resistivity and porosity from the hole size and hole spacing is also conducted. The model predictions agree with the testing data. Based on this model, the acoustical performance of the material can be optimized to meet vehicle acoustical requirements. The vehicle level SEA models are used to examine the effects of the perforation on the vehicle interior acoustics.

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.

At certain key stages in the vehicle development process, prototype vehicles are available for NVH testing. This testing fulfills two functions: primarily it is used to assess the status of the vehicle to the program NVH performance targets, but it also provides an opportunity to validate the vehicle SEA model. These single vehicle test events provide a snapshot of the NVH performance but do not provide any understanding of the variability of the NVH performance, which is due to many factors: components, build or assembly and test setup variability. SEA models can be used to estimate the vehicle level variability, if the variability of the interior components is understood, but there is limited data available to confirm the accuracy of these predictions. In this paper we examine the repeatability and reproducibility through a standard gage R&R study of Engine Noise Reduction (engine NR) and Tire NR testing.

In this paper the application of Statistical Energy Analysis (SEA) to the sound package design for a fuel cell powered sedan is presented. Fuel cell vehicles represent a different challenge to a vehicle with a conventional powertrain. With the replacement of the internal combustion engine (ICE), a principal source of airborne and structure-borne powertrain noise, the expectation is that the cabin noise levels would be significantly reduced as the main noise sources would be road and wind noise. A fuel cell powertrain, however, has a number of mechanical sources on the body structure that will radiate airborne noise and may transmit significant structure-borne noise to the vehicle interior. With this alternative power train, much of the conventional wisdom on vehicle sound package developed from experience with ICE's must be reconsidered.

In order to more accurately simulate the load distributions and histories experienced by automotive seats in field use, more biofidelic motion and loading devices are needed. Lear and KUKA have developed a system capable of controlling the coordinated motions of a pelvis, thighs and torso dummy in order to mimic human motions. The system takes kinematic data collected from human trials and converts them directly to a robot program. Additionally, simultaneous measures of human loading using pressure distribution mats can be obtained, and these measures are used as the basis for teaching the robot to correct the kinematic data using a neural net learning algorithm. The robot has direct and indirect load feedback integration that allows the load to be precisely maintained throughout the duration of a cycle test.

Continuing effort in measuring human vibration response results in a new design of vibration comfort dummy. The difference between this new dummy and other mechanical dummies is that (1) it uses a soft human-tissue like lower torso so it matches compliance better than the previous ones, and (2) it utilizes the spring and damping characteristics of the compliant lower torso. The lower torso is integrated with a spring-mass load simulating the top body of human so that the integrated dummy consists of two parts. This unique design greatly improves the accuracy and stability of transmissibility measurement and provides a direct application tool in seat prototype development. The results measured with dummy are compared with that measured with 3 human subjects in different percentiles and good match is found in the first transmissibility resonance and overall vibration response.

In order to more accurately simulate the load distributions and histories experienced by automotive seats in field use, more biofidelic motion and loading devices are needed. A new test dummy was developed by Lear Corporation and First Technology Safety Systems. This dummy uses exact skeletal geometry encased in a one-piece seamless mold with contours based on ASPECT data. A prototype was constructed and tested to demonstrate the efficacy of the concept. The skeleton and contour molds were created from CAD-generated rapid prototypes. The flesh was carefully formulated to have the mechanical properties of bulk muscular tissue in a state of moderate contraction, using data from the literature. This design allows much greater accuracy in reproducing human loads than was ever possible previously. The design has applications in durability, vibration and comfort testing.

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.

Many studies have been done to objectively measure car seat foam properties and correlate them to comfort performance. Typically, the vibration characteristics (namely transmissibility) of the foam cushion are measured. It has been generally accepted that low natural frequency equates to better comfort. However, no subjective studies have been done to verify that humans can feel the vibration differences that are measured. Also, the measured differences of the foam may not be detectable once the foam is built into a complete seat. Three different foam formulations utilizing MDI (methylene diphenyl diisocyanate) and TDI (toluene diisocyanate) technology were evaluated for vibration characteristics. The foams were then submitted to subjective human testing and objective lab testing after being built into seats. The subjective testing was done using a typical ride and drive evaluation where people were interviewed about the comfort of the seat while driving over various road conditions.