Harmonics / Natural Frequencies In the previous section, the frequency that was calculated was for the first harmonic of the wave. In other words, we only considered waves for each string that had only two nodes (one at both ends of the guitar) and one anti-node (in the middle of the string) for each string. As you press down on the string at a specific fret, you are essentially changing the length of the string, but you are still only hearing the first harmonic for that specific string with that certain mass, length, tension, etc. Even though this is the fundamental idea behind the frets of a guitar, there is still another way we can change the frequency of each string without changing the length; we can change the wavelength! This may seem puzzling at first, but we can very easily change the wavelength by using the idea of harmonics. In essence, harmonics are the natural frequencies that will naturally vibrate for a given guitar string. There are several different harmonics for each of the 6 strings on a guitar, but essentially, each harmonic is determined by multiplying the wavelength by n/2, where n is an integer value. Below is an image depicting this very simple idea of harmonics. http://www.physicsclassroom.com/class/sound/Lesson-5/Guitar-Strings By placing a node in the middle of an open string and creating a wave, you are producing the 2nd harmonic for that certain string with its specific qualities. This can easily be done by gently placing your finger against the string at certain spots. You do not want to press down on the string, because you will then either mute the wave with your finger, or (if you press all the way down to the fretboard), you will change the length of the string, and create a different frequency all together. When you are playing harmonics on the guitar, you only want to gently rest your finger on the string in the desired position to create a node at that spot on the wave (like shown in the image above). Below is a chart showing multiple positions on each string where a certain harmonic can be produced, and the note that results from it. This chart is based on a guitar with standard tuning (E, A, D, G, B, E), and with the lowest string at the bottom of the image. http://www.all-guitar-chords.com/topic.php?id=5125