Errors in the measurement of transmission loss in a standing wave tube

The four-microphone method of the standing wave tube can be used to effectively measure the transmission loss (TL) of acoustic materials. However, large errors in the measurement results may be observed at specific frequencies. To investigate the mechanism and lower the error, in this paper, experiments are conducted with a standing wave tube, fabricated for these experiments, using a four-microphone method. Specific factor analysis for the error is carried out. Three structure parameters of the standing wave tube are varied to minimize measurement errors. A finite element method (FEM) is employed to calculate the internal sound field distribution and TL in the standing wave tube. Based on the comparison between the experiments and the calculations, the orthogonal experimental design (OED) is performed to optimize the three structure parameters and improve the measurement accuracy to reduce the error in testing TL. The result of this work can be used as a reference for the measurement of acoustic material, which can benefit the noise control community.