My inspiration for this project is: http://dennishavlena.com/tamboura.htm
The tamboura (tambura, tampura, tanpuras) is an Indian fretless drone lute. The strings have a thread tied on to them to dampen the primary tone but allow the harmonic overtones to ring. Tambouras are tuned in unison with some strings as a 5th above the root note.
Step 1: Make a Cigarbox Guitar.
Mine has tuning pegs from a first-act guitar I found in an alley, the nut was another found scrap, the cigarbox was recycled from another project.
The next part is the super simple buzzing bridge.
Step 2: Buzzing Bridge
The size isn't crucial but the shape needs to be different than a regular bridge. A buzzing bridge will be longer than tall, be slightly sloped and have a rounded edge pointed towards the neck. To allow for fine adjustment the bridge is held by the tension of the strings. You can see in the picture that I put a folded business card under one side of mine to act as a shiv when I was fine tuning it.
After the bridge is in place tie some thread on the string and slide them over the bridge. The thread both leverages the string into making a better angle for the buzzing but dampen the string to let the complex overtones in the sustain ring louder.
Step 3: Tune and Play
The rest is experimenting with bridge position, thread location and angles to find the best sound. After you get the string buzzing, move the string slowly up or down until you find a spot that makes it louder, richer, longer sustain or finds some other quality you like.
Patience is the key, it took me 3 times longer to tune and refine the tambora than to make it. Most of the fun and the work is the exploration of sound and it's relations in every small adjustment.
I found when tuned up the best sounds come from just barely exciting the string by running my finger over it or giving it the lightest of plucks. When playing, a clawhammer style thumb and finger pluck works well.
If you watch the video, you will see that my cat likes it. for reference my cats also like to sit in my lap when I play tuba and wanted to sniff the work while I was using the hand drill on it.