Quote Wurlitzer:Quote Peter Land:
Now out of this one could come up with the sentence....'we hear in fifths'. But why? It's a bit of a disappointing answer to say.....well it's because of the 2nd, 3rd, and 4th partials in the Harmonic series..
Why is it disappointing? That IS the answer, in a nutshell.
Our whole system of harmony is fundamentally derived from the relationships of the harmonic series. The perfect fifth is the strongest relationship after the octave (since it is lowest in the series). Thus we naturally hear notes a perfect fifth apart as being closely related, with the upper note resolving by natural music gravity to the lower one.
A stretched major 3rd or narrow perfect 5th (let alone the same notes on a badly-tuned piano) is a far wilder frequency ratio than a perfectly tuned major 7th. But on imperfect instruments we still perceive them as conchords, and the whole common-practice harmonic system of tension and resolution still works.