Normally, small differences in day-to-day and laboratory-to-laboratory sound absorption measurements do not have large consequences because most noise control applications are not highly sensitive to small changes in sound absorption. However, in the automotive industry, materials are not purchased unless they meet strict sound absorption targets. As a result, decisions worth millions of U.S. dollars are made based on acoustic measurements. As material sound absorption moves closer to target values, the consequences of small measurement variations, such as those which might be caused by changes in ambient temperature and humidity during the course of a test, become more critical. The purpose of the work presented in this paper is to investigate which materials used for vehicle sound absorption are sensitive to temperature and humidity. Measurements are made using an impedance tube. It is discovered that typical materials used as absorbers in automotive applications are not sensitive to small temperature changes, and only a few materials are sensitive to changes in humidity.

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