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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.

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.

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.