Study on Acoustic Characteristics of Lined Duct

Lined ducts are widely used to reduce the noise generated from various equipments such as large wind tunnels and exhaust pipes of engines. Especially, noise reduction is required in offices and hospitals accompanying with the spread of air conditioning equipment. The noise reduction of non-lined ducts is usually predicted by using the FEM and the BEM techniques. However, there were a few cases that the analytic value was compared with the actual measurement of the lined duct which the noise absorbing material was used. In this research, the analytic value of BEM was compared with the actual measurement value for the attenuation quantity within a lined duct. Then, a noticeable gap was caused between both results in specific frequency. Thus, the cause was probed with a viewpoint of the specific acoustic impedance ratio used for BEM. As a result, it was found that the prediction of sound attenuation of the duct agrees with the experimental result by applying the impedance measured by the impedance tube with φ100 diameter to the BEM analysis.