Re: What is it that makes chords on e.g. a piano sound harmonic?

Jonas,

Human perception of sound is very complex. There is debate about why certain sets of notes are perceived as being "harmonic".

There are at least two aspects of this, one is the science of the sound waves and your ear, this area is a branch of acoustics (the science of sound waves). The other is your perception of the sound signals your ears pick up, called psychoacoustics.

So, It is not as simple as the relationship of wavelengths.

If you want to learn more, research the acoustics of beat notes and chords. One reference on the web is: http://hypertextbook.com/physics/waves/music/ ...where the author makes a case that much of music perception is about the frequencies and shared harmonics produced.

There are whole books about psychoacoustics, and even more specialized on music, psychomusicology. As a starting point, take a look at the wikipedia article: http://en.wikipedia.org/wiki/Psychoacoustics

And here is a related paper discussing both aspects and an experiment about this: http://ase.tufts.edu/psychology/music-cognition/pdfs/Tekman_Bharucha1998.pdf

This is a very interesting topic because it is very complex. I hope this helps you get started.

-Barry.