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Research on the Effect of Imprecise Size Foam Samples on Acoustic Measurements in Impedance Tube

Polymer foam materials are very commonly used acoustic materials for absorbing sound energy in noise control engineering, because of their higher porosity and light in weight. The acoustic characterization of these materials namely; absorption coefficient and transmission loss are measured using impedance tube, reverberation room method and intensity methods. Among these three impedance tube is the most popular method in laboratory condition. Here the sample size plays a main role in the accurate characterization acoustic materials by using the impedance tube. The present paper discusses effect of variation in the sample size on their acoustic measurements. The foam sample are prepared using Resistance wire foam cutter(RWFC). Their absorption coefficient and transmission loss for large and small samples with variations in sample dimensions are measured and compare with ideal dimension results. A detailed measured data and analysis are done to understand the effect of undersized and oversized foam samples on absorption coefficient and transmission loss results as a function of frequency. The results show that the variations in sample size has immense effect of measured results. The results presented in this study becomes a guideline for characterizing acoustic materials using impedance tube.