(a) Measured fundamental frequency (blue markers) and sound pressure level L_p of the sound emitted 20 cm away from the open end of the duct as functions of the applied fingering, for a feedback gain Γ₀ ≈ 1.5, for both cases of L_cav = 3 cm and L_cav = 2 cm. The predicted onset frequencies of self-oscillations are also reported with red markers, as well as those for a modified model which accounts for a high-pass filtering of the feedback with a cut-off frequency of 8 Hz (green markers). (b) The corresponding acoustic pressures for both cases of L_cav = 3 cm and L_cav = 2 cm and when all side holes are kept closed. p(t) and p_rad(t) stand for the pressure in the cavity, and that 20 cm away from the open end of the duct, respectively.