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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.

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.