The Diddley Bow Experiment

In the second unit of Light, Sound and Time, we learned about sound and how to create it. We learned about the different waves that sound can create and what they look like. For the action project, we were asked to build an instrument and explain how it works and how it relates to some of the science and math topics we covered in this unit. One thing I struggled with was getting my string around my screws. It is very difficult to bend and wrap a guitar string around a screw so it took me a while to finally get it. I also struggled with creating a good sound. I am proud of how my guitar came out. I think that the pitch of my guitar came out really nice and I think the design I created worked well for me. If I could do this project all over again, I would get a thicker wire and get a thicker board so that the screws wouldn’t go through the board and potentially stab someone.

MF (2016). Diddley Bow. 

I built a diddley bow which is a variation of a guitar. I created this to show that it is nice to get a professionally made guitar but it's equally nice to build one yourself so you can see your work and you can know what it feels like to create something. There is a small town in Paraguay called Cateura and it is built completely on a landfill and the people there have taken it upon themselves to create instruments made out of the garbage that they find around their town. There is a documentary about Cateura called The Landfill Harmonic and they have done amazing work and have toured around the world to show kids and adults how you can make something out of nothing.

My diddley bow demonstrates many of the science principles we talked about in this unit. The pitch of the instrument is based on how much tension your wire has, how long it is, and the material of it. When something plucks the string, it vibrates a creates a tiny wave that reaches the tin can then vibrates that creating a sound. The amplitude differs depending on how hard or soft you pluck the string.

MF (2016). Diddley Bow (Back). 

MF (2016). Diddley Bow (Front). 

My guitar produces sound through the tin can. Plucking the string makes it vibrate against the can causing a sound. In order to create a sound, the string has to be extremely tight so I tied my string around two screws, screwed them all the way into the wood and then placed a battery in between two screws so that it would be even tighter. The tin can’s circular shape amplifies the sound when the string is plucked. When using a slide on my guitar, it can change the note rapidly. Using the slide makes the wave shorter. If I place a finger on the string, I can hear two notes: the original note and a higher/lower note.

To create my guitar, I used a wood board, a thin guitar string, a nine volt battery, screws, and a tin can. I poked a hole in my tin can by hammering a screw into it, then I ran my string through the hole and tied it to the screws placed on opposite sides of the board. For tuning pegs, I used screws, and for a nut I used a nine volt battery. I put a screw on either side of the battery and the tin can to keep them in place. The width of my guitar string is 0.84 mm.

MF (2016). Diagram 

I used a can with a diameter of 7 centimeters, which means the radius is 3.5, and a height of 11 centimeters. This means that the volume is 3.14 x (r^2) x heigh t= 3.14 x (3.5^2) x 11= 423.115 cubic centimeters.

The Doppler Effect is the idea that a sound gets a higher or lower pitch as it moves closer or farther from the observer. If someone were to play my guitar and two people were on either side of the player, the person that the player is going towards would hear a higher frequency, and the person that is farther away would hear a lower frequency.

The part of the string on my guitar that vibrates is 24 centimeters long. My open note is G4 with a frequency of 392 hertz and a wavelength of 88.01 centimeters. Below, you can see the approximate first 4 harmonics of my guitar:

MF (2016). Guitar Harmonics Visual

MF (2016). Harmonic Drawing