Schematic diagram of the setup for impedance tube experiments. Acoustic measurements are performed using four microphones separated by distances L_1…4). Vibrations are evaluated using a Laser Doppler vibrometer, and two measurement points are defined on the beam. The back cavity of length B can be removed to characterize the blade alone. The inset pictures display the composite sample used for the normal incidence measurements, as well as a zoom on the laser cut slits.