I suspect it has something to do with resonance. Resonance occurs when frequencies match approximately. It isn’t just in the fundamental or pitch frequency of t

I suspect it has something to do with resonance. Resonance occurs when frequencies match approximately. It isn’t just in the fundamental or pitch frequency of two notes— resonance can also occur via frequency matching in the shared overtones of two notes. Consonant notes tend to share a lot of overtones. I have heard that the pentatonic scale maximizes internote resonance. This seems relatively straightforward to test empirically. The first known scientific experiment (empirical test of mathematical model) was the attested case of the pythagoreans casting bronze chimes in the same rational proportions of lengths of a string. The experiment demonstrated that small integer ratios produce consonance. Here is the most recent and up-to-date theory of harmony in music (that I know): https://downloads.spj.sciencemag.org/research/2019/2369041.pdf https://downloads.spj.sciencemag.org/research/2019/2369041.p...