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Technical University of Liberec
Sound absorption property of perpendicularly-laid nonwovens were tested by Brüel and Kjær measuring instrument. The effect of manufacturing techniques on sound absorption performance was investigated. The effect of porosity and airflow resistivity on sound absorption ability was studied. It is found that there is no significant influence of two manufacturing techniques on sound absorption performance. The increase of areal density results in improvement of sound absorption ability. The increase of thickness can improve sound absorption coefficient at low-frequency range, but decrease of the coefficient occurred at high-frequency range. A quadratic relationship between porosity and sound absorption ability has been found. The airflow resistivity is a key parameter to predict accurately the acoustical properties of fibrous media. There is a large number of theoretical and empirical models which can be used to predict the airflow resistivity of this type of porous media. However, there is a lack of experimental data on the accuracy of these models in the case of multi-component fibrous media. This study presents a detailed analysis of the accuracy of several existing models to predict airflow resistivity which make use of the porosity, bulk density and mean fiber diameter information. The AFD300 AcoustiFlow device was employed to measure airflow resistivity. It is shown that some existing models largely under- or overestimate the airflow resistivity when compared with the measured values. A novel feature of this work is that it studies the relative performance of airflow resistivity prediction models that are based on the capillary channel theory and drag force theory. These two groups of models are then compared to some purely empirical models. It is found that the mean absolute values of relative error (MAVRE) by some models is unacceptably high (e.g. >20-30%). The results suggest that there are existing models which can predict the airflow resistivity of multi-component fibrous media with 12.8% accuracy. A simple empirical model based on fiber diameter and fabric bulk density has been obtained through power-type model. This model exhibits very small error which is 5.1%.
nonwovens, acoustic properties