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Technical Paper

Hybrid Laminated Panels Addressing Acoustic Issues in Vehicles

2021-08-31
2021-01-1086
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.
Technical Paper

Development Work for a New Damping Standard SAE J3130

2021-08-31
2021-01-1122
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.
Book

Acoustical Materials: Solving the Challenge of Vehicle Noise

2021-08-11
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.
Technical Paper

Developing a Custom Data Acquisition Software Package for a Self-contained Acoustic Test Facility

2019-06-05
2019-01-1501
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.
Technical Paper

Mechanical Impedance Based Vibration Damping Test

2017-06-05
2017-01-1879
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).
Technical Paper

Some Thoughts on Dissipative Sound Package Systems

2017-06-05
2017-01-1815
This paper discusses the importance of a dissipative sound package system in the automotive industry and how it works. Although this is not a new technique at this stage, it is still a challenge to meet the subsystem target levels that were originally developed for parts based on the barrier decoupler concept. This paper reviews the typical construction of a dissipative system and then emphasizes the importance of different layers of materials that are used in the construction, including what they can do and cannot do. The paper also discusses the importance of the proper manufacturing of a part.
Technical Paper

A Modal Study of Damping Treatments to Improve Low Frequency Sound Transmission Loss of a Structure

2017-06-05
2017-01-1852
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.
Technical Paper

SAE and Other Standards for Determining Acoustical Properties of Sound Package Materials

2015-06-15
2015-01-2207
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.
Journal Article

A Design of Experiments Analysis to Determine the Importance of Relevant Factors on the STL of an Acoustic Part

2013-05-13
2013-01-2009
This paper discusses a design of experiments (DOE) analysis that was performed to understand relevant factors that influence the acoustic performance of a sound package part used in the commercial vehicle industry for the floor mat application. The acoustic performance of the sound package part which is a double wall system and constructed of a barrier and cellular decoupler material is expressed in terms of sound transmission loss (STL). An experiment was designed using the Taguchi DOE technique with three factors and three levels to acquire the STL data and is discussed in the paper. The results of the DOE analysis and the confidence in the model are discussed as well as the benefits of predicting expected STL performances are mentioned in the paper.
Technical Paper

Damping Performance Using a Panel Structure

2013-05-13
2013-01-1938
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.
Technical Paper

The Thought Process for Developing Sound Package Treatments for a Vehicle

2011-05-17
2011-01-1679
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.
Technical Paper

A Correlation between Oberst Bar and Center Point Damping Results

2009-05-19
2009-01-2134
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.
Technical Paper

Thoughts behind Developing SAE Standard J2883 - Random Incidence Sound Absorption Tests Using a Small Reverberation Room

2009-05-19
2009-01-2141
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.
Technical Paper

Random Incidence Sound Absorption Measurement of Automotive Seats in Small Size Reverberation Rooms

2007-05-15
2007-01-2194
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].
Technical Paper

Development of a Small Size Reverberation Room Standardized Test Procedure for Random Incidence Sound Absorption Testing

2005-05-16
2005-01-2284
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.
Technical Paper

A Development Procedure to Improve the Acoustical Performance of a Dash System

2005-05-16
2005-01-2515
This paper discusses a development procedure that was used to evaluate the acoustical performance of one type of dashpanel construction over another type for a given application. Two very different constructions of dashpanels, one made out of plain steel and one made out of laminated steel, were studied under a series of different test conditions to understand which one performs better, and then to evaluate how to improve the overall performance of the inferior dashpanel for a given application. The poorly performing dashpanel was extensively tested with dashmat and different passthroughs to understand the acoustic strength of different passthroughs, to understand how passthroughs affect the overall performance of the dash system, and subsequently to understand how the performance can be improved by improving one of the passthroughs.
Technical Paper

Predicting the Acoustical Performance of Weak Paths in a Sound Package System

2005-05-16
2005-01-2520
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.
Technical Paper

A Data Analysis Approach to Understand the Value of a Damping Treatment for Vehicle Interior Sound

2003-05-05
2003-01-1409
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.
Technical Paper

A Graduated Assessment of a Sprayable Waterborne Damping Material as a Viable Acoustical Treatment

2003-05-05
2003-01-1588
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.
Technical Paper

Automotive Noise and Vibration Control Practices in the New Millennium

2003-05-05
2003-01-1589
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.
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