?! Considering the ~accuracy of your horn math models, I'm flabbergasted that you could think this. If true, then a horn could only produce discordant sounds. What changes is the harmonic structure's fundamental (F0) and number of harmonics since horns are 1/2 WL resonators, ergo below this frequency their resonance structure is non-harmonic as a function of its flare rate ('M', aka 'T' factor) and frequency (Fc).

GM