Comparative study on in-situ measurement techniques of surface acoustic properties: experimental investigations of three techniques

摘要

To predict acoustic environment in a realistic situation, it is desirable to measure acoustic properties of absorbing material surfaces and ground surfaces in-situ. Brandao et al. have published a comprehensive review of a number of in-situ measurement techniques of surface acoustic properties [Acta Acust. United Acust. 101, 443-463, 2015]. However, the review is hypothetical in that the techniques are compared on paper and not backed by actual measurements. In this study, three in-situ techniques are chosen from the review and comparative investigations through actual measurements are carried out. The measurement techniques chosen are those proposed in [J. Acoust. Soc. Am. 75, 382-389, 1984] (the Cramond technique), [J. Acoust. Soc. Am. 77, 1617-1618, 1985] (the Allard technique) and [Appl. Acoust. 66, 845-865, 2005] (the environmental anonymous (EA) technique). The Cramond and Allard techniques are chosen because they are considered as two of the origins of more modern techniques. The EA technique is chosen because the authors have been using for ground surface measurements. Measurements of surface impedance and absorption coefficient are carried out for sheets of polyester nonwoven, grass and compacted soil. Measurements of ground surface with low absorption are found to be difficult by the Cramond technique and the frequency interval of obtained results is difficult to make narrower than a few hundred Hz. The Allard technique is found to be unsuitable for indoor measurements but barely suitable for outdoor measurements where no reflected waves from walls or ceilings are present. The EA technique is found to produce reasonable results for both indoor and outdoor measurements.