Disclaimer: I don't now much about music theory.
Anyway, my wife just bought one of those, which I think is called a "tongue drum":
What strikes me is that, as bad as I am at playing music, whatever I randomly do on it, however I play it, it seems to make harmonious music. Or at least, much more harmonious than what I could randomly do on a piano or a guitar. My son, who is 5, plays with it too, and it just works. It seems this thing prevents anyone from playing dissonant music.
I played some other versions of this instument, which I'm pretty sure had a different number of notes, and probably organized differently, and the result was similar.
So, is there a particular method of selecting/organizing notes on an instrument which will make any sequence played with it sound harmonious? Is there a theory behind this?
Edit: So I pushed the investigations further, as the notes still seemed a bit alien, compared to what we usually find on classical instruments.
I used some phone app that measures the frequency of what it gets from the phone mic (typically made for tuning instruments) to get a map of what we had, and here are the results (the raw frequency figures are certainly a bit inaccurate, but I'm pretty sure the resulting notes are correct):
So it seems based on the regular major diatonic scale, but not arranged as the typical CDEFGAB: it has missing notes, a few additional bass and treble notes chosen further away from the main group, and the notes are all over the place.
I don't know what to conclude from this. But it really feels like this organization makes melodies easier on the ear than what you could randomly do with 9 consecutive white keys on a piano. But maybe the clear sound of the instrument itself is also playing a role, here. I don't know.