Three bifurcation diagrams of the two quasi-harmonic resonance air column (with Z₁ > Z₂, in practice Z₁/Z₂ = 3/2; parameters values in Tab. 1) with respect to the control parameter γ. From top to bottom: Inh = 0 (a), Inh = 0.02 (b) and Inh = 0.04 (c). Each case is described with two plots. Upper plot: Maximum of the absolute value of the periodic solution with respect to γ. The branch in green (respectively in red, and in blue) corresponds to the fundamental regime, the standard Helmholtz motion (respectively the octave regime, and the inverted Helmholtz motion fundamental regime). Note that a black curve corresponding to a direct Hopf bifurcation is branched at γ = γ_thr1. This fundamental regime corresponds to an air column having only one resonance at the frequency f_res1. Lower plot: Frequency with respect to γ. The frequency branch in green (respectively in red) corresponds to the fundamental frequency of the fundamental regime (respectively the octave regime, frequency divided by 2). The reference dashed horizontal lines are the reference frequencies: f_res1 and f_res2/2.