Accurate Measurement of Small Absorption Coefficients

2007-01-2224

05/15/2007

Event
SAE 2007 Noise and Vibration Conference and Exhibition
Authors Abstract
Content
In this paper procedures for estimating the sound absorption coefficient when the specimen has inherently low absorption are discussed. Examples of this include the measurement of the absorption coefficient of pavements, closed cell foams and other barrier materials whose absorption coefficient is nevertheless required, and the measurement of sound absorption of muffler components such as perforates. The focus of the paper is on (1) obtaining an accurate phase correction and (2) proper correction for tube attenuation when using impedance tube methods. For the latter it is shown that the equations for tube attenuation correction in the standards underestimate the actual tube attenuation, leading to an overestimate of the measured absorption coefficient. This error could be critical, for example, when one is attempting to qualify a facility for the measurement of pass-by noise. In this paper we propose a remedy - to measure the actual tube attenuation and to use this value, as opposed to the value recommended by the standards, to correct the measured sound absorption. We also recommend an alternative way to determine the microphone phase error.
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Details
DOI
https://doi.org/10.4271/2007-01-2224
Pages
7
Citation
Han, J., Herrin, D., and Seybert, A., "Accurate Measurement of Small Absorption Coefficients," SAE Technical Paper 2007-01-2224, 2007, https://doi.org/10.4271/2007-01-2224.
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Publisher
Published
May 15, 2007
Product Code
2007-01-2224
Content Type
Technical Paper
Language
English