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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].

Sound transmission loss and sound absorption measurements are conducted to characterize acoustical performance of noise control materials and components used in vehicles. These measured data are often used to select materials and define acoustical targets. It is imperative to have accurate and repeatable data. Process variability is often monitored using measurement data collected over time. A certain amount of variability due to random causes is always expected. Acoustical measurements have inherent variability from different operators, equipment, test setup, environment etc. When variation in the measurements is due to random causes the measurements are in-control and measured data are considered “good”. However, special cause variations in the measured data such as operator error or setup error must be identified and corrected. Control chart is a popular statistical tool for monitoring process variability and improving quality.

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.

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.

Biot's model of elastic porous materials is widely used to predict the acoustical performance of noise control materials in the automotive industry. Material properties of acoustical materials, often referred to as Biot parameters, such as porosity, airflow resistivity, tortuosity, viscous characteristic length and thermal characteristic length are required inputs in the Biot model. Various test methods have been developed to measure Biot parameters. This paper conducts a comprehensive review of the existing test methods, discusses accuracy and applicability of each test method, and provides recommendations to the SAE Acoustical Materials Committee regarding the need for the development of SAE test methods for Biot parameters.