Sound-absorption coefficient of a pin-holder structure for sound waves incident in the direction perpendicular to the cylinder's axis

In this study, the sound-absorption coefficients of a pin-holder structure consisting of a group of cylinders were estimated and compared with the experimental values for the case where sound waves are incident in the direction perpendicular to the cylinder's axis. To estimate the sound-absorption coefficient, the gap in the pinholder structure is divided into elements and approximated as being between two parallel planes, taking the exact shape of the divided elements into account. The characteristic impedance and propagation constant of the approximated clearances were calculated and treated as a one-dimensional transfer matrix. The transfer matrices for each element were used to calculate the sound-absorption coefficient. The calculated theoretical values were compared with the experimental ones. In the experiment, the samples were fabricated using a 3D printer, and the sound-absorption coefficient was measured using a two-microphone impedance-measurement tube. Although the experimental and theoretical values differed, they showed similar trends. We also found that the prediction error in the practical sound-absorption coefficient could be reduced by adjusting the diameter of the pins used in the calculation.