ON CONTROL OF A PRESSING FORCE APPLIED TO ACOUSTIC LINER SAMPLE IN A NORMAL INCIDENCE IMPEDANCE TUBE

The study considers the influence of control of the pressing force applied to an acoustic liner sample in a normal incidence impedance tube on the spread of acoustic characteristics of the tested sample. The design of a normal incidence impedance tube with a control system of a sample pressing force is presented. This system is implemented as a piston in a pneumatic cylinder with a pressure control unit. The measurements were taken on days when the characteristics of the environment were different from each other. This made it possible to better track the influence of the pressing force on reducing the spread of acoustic characteristics. In total, 10 measurements of the acoustic liner sample were carried out on a normal incidence impedance tube with and without control of the pressing force. The measurements were carried out for six months. As a result, the study has shown that the control of the pressing force applied to the acoustic liner sample provides a smaller spread of the obtained acoustic characteristics.