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Porous materials have been applied increasingly for absorbing noise energy and improving the acoustic performance. Different models have been proposed to predict the performance of these materials, and much progress has been achieved. However, most of the foregoing researches have been conducted on a single layer of porous material. In real application, porous materials are usually combined with other kinds of materials to compose a multilayered noise control treatment. This paper investigates the acoustic performance of such treatments with a combination of porous and non-porous media. Results from numerical simulation are compared to experimental measurements. Transfer matrix method is adopted to simulate the insertion loss and absorption associated with three samples of a noise control treatment product, which has two porous layers bonded by an impervious screen.

Highly effective double-wall systems for automotive applications can often have over a 90 dB span in sound transmission loss values between low frequencies, where they are usually least effective and upper frequencies, where they are typically most effective. Particularly for 16-bit measurement systems, but even for 24-bit systems, this can represent a very difficult scenario for measurements in either the source and/or receiving chamber(s). A methodology to balance the observed dynamic ranges in both source and receiving chambers is presented and discussed in this paper. An improved sound transmission loss measurement system can therefore be implemented which reduces the potential of overload or noise floor contamination occurring in measurements within either chamber. Low frequency SPL requirements for the source chamber speaker system and flanking noise issues with adjacent test chambers can also be typically reduced.

Using advanced, multi-layer poro-elastic acoustical material modeling technologies, an example of acoustical performance optimization of an underhood sound absorber application is presented. In this case, a porous facing in combination with a fibrous sound absorber pad is optimized for maximum efficiency, which allows for dramatic reduction in pad density and weight. Overall sound absorption performance is shown to be equal or improved versus frequency relative to the incumbent design.

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.

The new Acoustic Technology Center (ATC) at E-A-R™ Thermal/Acoustic Systems is a purpose-built facility to serve the commercial vehicle, automotive, aircraft, industrial and electronics markets supplied by this company. The design was driven by test versatility and rigorous facility performance specifications, enabling simultaneous testing of heavy duty vehicles and high performance noise reduction materials and systems in adjacent but uncoupled chambers. The intent of the facility layout is to utilize space efficiently while allowing a wide variety of vehicle, subsystem, component and material tests. Working closely with E-A-R, Acoustical Consulting Services established critical facility parameters to achieve intended functional attributes and Affiliated Construction Services constructed the facility to these specifications.

This paper presents the results of a round robin test series of the SAE J1400 Sound Transmission Loss in which more than a dozen different acoustical laboratories participated. The round robin was sponsored by the SAE Acoustical Materials Committee, which is responsible for the SAE J1400 standard. Based on the results of the round robin, significantly more definition, recommendations, clarifications and check procedures are being added to a new draft of the J1400 standard to assure improved reproducibility, repeatability and absolute measurement accuracy. In addition, there are unique differences between current versions of the ISO 140, ASTM E90 and SAE J1400 sound transmission loss standards. These differences are discussed in this paper and a systemic advantage of the SAE procedure is highlighted.

For many complicated design challenges, including those involving sophisticated computer simulations and modeling, it is vital to have a systematic and efficient method for exploring available design spaces and finding optimal or near-optimal design solutions. A simple method for relatively quick and straight-forward sampling and subsequent evaluation of design spaces is proposed. No special optimization software or expertise in optimization is required.

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 acoustic performance requirements of vehicle interior trim elements and sound package elements have increased significantly in recent years. Additionally, the burden of developing these products has been shifted from the Original Equipment Manufacturers (OEMs) to suppliers. To aid in developing lightweight, low cost, and high performance parts, a flexible acoustic testing facility was designed for use in many different applications. Specific, purpose-built chambers for only one type of measurement are typically not cost effective facilities.