Estimation of sound absorption of three-dimensional treatments based on impedance tube measurements

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Acoustic cones are often the primary absorption treatment choice in the construction of anechoic chambers. The estimation of sound absorption coefficient of three-dimensional treatments, such as cones, is usually accomplished by the reverberation time method. This method requires isolated, large, heavily constructed reverberation chambers which may not be available due to space and cost constraints. Impedance tubes are an alternative to reverberation chamber measurements for estimating sound absorption coefficients. However, due to the two-dimensional nature of samples used in the impedance tubes, sound absorption of three-dimensional objects is difficult to estimate. Absorption coefficient of the material is a function of not only surface area but also material thickness. This paper proposes a technique to estimate the sound absorption of a three-dimensional treatment using the absorption coefficient data from impedance tube tests. This extrapolation of impedance-tube-measured absorption coefficient to actual sound absorption of cones can be used to evaluate the effectiveness of absorptive acoustic room treatments without the need of testing the actual treatment prototypes. © 2007 Institute of Noise Control Engineering.

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Noise Control Engineering Journal