This article is a brief description of an easy trick you can use for an interesting and unusual tone quality in string instruments.
The idea is to insert a soft damper, such as a piece of lightweight foam rubber, under the strings at a nodal point for one of the harmonics. If the damper is light enough, then when you pluck the string the fundamental will sound, but it will be quieter than usual and will die out quickly due to the damping. At the same time the harmonic will sustain and sound clearly, since the nodal damper will have minimal effect on the vibration of the harmonic. The result is a tone of clear pitch but a quirky and appealing timbre. The most promising damper position would be the string’s midpoint to bring out the second harmonic at the octave. The 1/3 or 2/3 point for the third harmonic at the twelfth may also work.
It’s crucial that the foam be the lightest, softest variety you can find. Cut a strip of it to a shape that is triangular in cross section. It should be just tall enough that it fits under the strings just barely touching them when you insert it beneath resting on the fingerboard or soundboard below. With the narrow apex of the triangle minimally contacting the strings, you get the needed damping of the fundamental, but the effect is suitably minimal.
This works well with zither-like instruments – those having unfretted strings. It’s also good with guitars or other fretted instruments, but this calls for a little more explanation. On a guitar, the node for the octave harmonic for the open strings is located at the 12th fret. But fretting alters the active string length and the location for the octave harmonic moves accordingly. For instance, when you play the third fret, the nodal point for the octave harmonic moves to the 15th fret. Where, then, do you place the damper for playing a guitar you’ll be fretting? It turns out that the situation is not so terribly exacting: if the damper is positioned not precisely at the midpoint but reasonably close, you still get the desired effect in which the fundamental damps out quickly but the harmonic rings longer. How far from the ideal location can the damper be without undermining the effect too much? Well, if you place the damper somewhere between the 14th and 15th frets on a guitar, you’ll find that the effect still works nicely as long as you don’t fret above the fourth or fifth fret. So there’s my recommendation: place the damper between the 14th and 15th frets and restrict your playing to the first five frets.
This is one of the many ideas discussed in the book of guitar preparations I wrote in 2012 with co-author Yuri Landman. That book is now out of print, although you can sometimes find copies in the used book marketplace.