A Study On The Acoustic Measurement Methods Of Static Flow Resistivity

The acoustic measurement methods of the static flow resistivity of fibrous materials are investigated in this thesis, where the analytical formula for measuring the static flow resistivity is derived and the effect of the parameter configuration on the measurement accuracy of acoustic measurement methods is studied. A new acoustic method is proposed to measure the static flow resistivity and the feasibility of this method is validated by the experiment.The applications of the flow resistivity are introduced firstly and the present measurement methods of the flow resistivity are assorted. The measurement accuracy and robustness of the acoustic measurement methods are investigated based on the finite element modal (FEM). The effect of the test sample’s and the microphones’ position on the measurement accuracy is also studied analytically. The measurement accuracy and the robustness of the Ingard&Dear measurement method and the Mclntosh measurement method are better than other acoustic measurement methods. Changing the microphone position in front of the test sample in the Ren&Jacobsen measurement method reduces the measurement accuracy. When the termination of the impedance tube is non-reflective, the measurement accuracy does not vary with the position of the test sample. When the termination is rigid, the measurement accuracy is better if the distance between the test sample and the termination is an odd number of quarter wavelengths. When the termination is neither non-reflective nor rigid, the measurement accuracy depends on the position of the test sample and the acoustic impedance at the termination.A novel acoustic measurement method is proposed based on the impedance transfer theory in the common impedance tube, which is designed for the sound absorption coefficient measurement using the transfer function method. The measurement accuracy and the robustness of the proposed method are investigated based on the FEM modal. The measurement accuracy of the proposed method is within the allowable range of the International Standard ISO9053. The measurement accuracy of the method does not change with the distance between the test sample and the termination, the thickness of the test sample and the materials changed. However, it should be noted that the measurement frequency should not be too high and the position of the test sample not offset.Finally, the flow resistivity of a randomly chosen material is measured by using the proposed method and the surface impedance is calculated. It is found the results agree with the flow resistivity obtained by using the Ingard&Dear method and the surface impedance obtained by using the transfer function method. The feasibility of the proposed method is validated and the accuracy is discussed based on the experiment data.