The science behind harmony. Why do certain notes sound more pleasing when played together than others?
In: Physics
Let’s use a guitar as an example. When you pluck a string, the string vibrates, and this vibration transfers to the air which we interpret as sound.
Now, the way the string moves back and forth is not random: the string is fixed at both ends, so it can only moves using those fixed points as “anchors”. [Let’s use this image as a guide](https://upload.wikimedia.org/wikipedia/commons/thumb/c/c5/Harmonic_partials_on_strings.svg/807px-Harmonic_partials_on_strings.svg.png). The main way the string moves is the uppermost diagram (the one that says “0” and “1”), it goes back and forth from one side to the other. That specific vibration is called the “fundamental frequency” and it makes the biggest contribution to how the string sounds. There are other ways the string vibrates: we call them “harmonics”, the image shows the main ones but you might have realized the pattern. Because those segments are shorter, they also vibrate faster, giving sounds that are higher in pitch.
When you play two strings together, and they have different fundamental frequencies, they might sound good or bad together depending on how both harmonics fit together. For instance, if you play a C and a G, the G matches (well, “matches”) all the harmonics that divide the C string in thirds (1/3, 1/6, 1/9…).
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