Diddley Bows and STEAM

This is the second AP of our Light, Sound, and Time class, and we are in unit 2, which is Sound. In this unit, we focused on the components of Sound and we learned in-depth about what it is. We learned about sound waves, the anatomy of the ear and how sound travels to our brains, the Doppler effect, UltraSound and Infrasound, and stringed instruments. For this AP, we made our own stringed instruments, called Diddley Bows (kind of like a single string guitar), and had the opportunity to go in person, again, to build them. We made them because we were talking about stringed instruments, and this is our visual representation of Sound. I am most proud of my Diddley Bow because it was a little difficult to make, but I think it turned out well. Below, you will see my finished product, an explanation of the instrument, a recording of what it sounds like, and calculations, measuring the instrument and its frequency/wavelengths. Enjoy!

The Diddley Bow produces sound by you plucking the string, and the sound waves vibrate from the battery (applying pressure on the string) to the tin can. Then, it moves inside the hole, and echoes throughout the can, coming out the open side of the can, and further being amplified by it. The device demonstrates pitch/frequency because of how you can apply a certain pressure on the string to increase or decrease the pitch. This means that you can change the pitch based on how hard you press or how tight/loose the string is. My Diddley Bow is very low pitch because the string is 54 gauge (.054inches). Its frequency is about D5 603.9Hz. Below, you will see my Diddley Bow, as well as the 4 harmonics.  

2021. Harmonics. MEM

2021. Diddley Bow. MEM

Below, you will see all the calculations for my Diddley Bow, and a sketch of it from the side, demonstrating its most important parts, and showing most of its measurements. 

Calculations: 

String length - 24 inches 

H - Vibrating string Length - 20 inches 

Thickness - .054in thick (54 gauge) 

Wood length - 27 inches 

B1 - Wood to battery height - 1in 

B2 - Wood to string at can height - 2in 

Height of can - 4.5in 

Radius of can - 1.5in 

2021. Diddley Bow Sketch. MEM

Trapezoid- 

Area - ½ (b1+b2)h 

Area - ½ (1+2)*20 

Area - 30 in^2 

Triangle- 

tan(u) = opp/adj = h/(b2-b1) 

Inverse tangent of (length of wood under vibrating string/difference in heights by can and battery) in degrees 

Inverse tangent of (27/1) in degrees = 87.878 degrees 

360 - 90 - 90 - angle U = angle L 

360 - 90 - 90 - 87.878 

Angle L = 92.122 

Cylinder- 

Volume = πr^2h 

Volume = π1.5^2x4.5 

Volume = 31.8 in^3

Here, you will see the Frequency and Wavelength of each Harmonic, as well as a visual representation of each Harmonic, and a recording of what the Diddley Bow sounds like. 

2021. Harmonics. MEM

Frequency - D5 603.9Hz 

Wavelength (w = speed of sound / f) 343/603.9 = 0.5 meters 

2nd harmonic frequency - 603.9x2= 1,207.8Hz 

2nd harmonic wavelength - 0.58/2 = 0.29 meters 

3rd harmonic frequency - 603.9x3= 1,811.7Hz 

3rd harmonic wavelength - 0.58/3 = 0.193 meters 

4th harmonic frequency - 603.9x4= 2,415.6Hz 

4th harmonic wavelength - 0.58/4 = 0.145 meters 

2021. The Diddley Bow. MEM

In conclusion, I really enjoyed this unit and making our instruments. If I could do it all over again, the only thing I would do differently is choose a thinner string. I would do that so it would be easier to tighten, and so I could hear what a thinner string sounded like. This unit, I struggled with the equations and graphing waves but in the end, I think I had a better understanding. I hope you enjoyed my project!