Three bifurcation diagrams of the two quasi-harmonic resonance air column (with Z₁ < Z₂, in practice Z₂/Z₁ = 3/2) with respect to the control parameter γ. From top to bottom: Inh = 0 (a), Inh = 0.015 (b) and Inh = 0.030 (c). Each case is described with two plots. Upper plot (a): Maximum of the absolute value of the periodic solution with respect to γ. The branch in red (respectively in blue, and in green) corresponds to the octave regime (respectively the fundamental regime associated to the standard Helmholtz motion, and the inverted Helmholtz motion fundamental regime). Lower plot (c): Frequency with respect to γ. The frequency branch in red (respectively in blue) corresponds to the fundamental frequency of the octave regime (respectively the fundamental regime). The frequency of the red branch has been divided by 2 for sake of clarity. The reference dashed horizontal lines are the reference frequencies: f_res1 and f_res2/2.