Diddley Blog

In our STEAM class, LST, we have covered the L (Light) and moved onto the S, Sound. Like light, we have learned about waves in this unit, given the fact that waves are what make each sound unique. We went over sine and cosine waves, wavelength and frequency, and other things that are more exclusive to sound, like asin (bx + c) + d and the anatomy of the ear. For this action project, we were assigned to make a diddley bow. A diddley bow is a one stringed acoustic guitar built upon a plank with an open tin can as a resonator on the opposite side. The sound hole (open side of the tin can) amplifies the vibrations from the string as it is plucked. The images below will give you a better grasp of how the bow is assembled. Diddley bows originated in the South and became a big influence on the blues.

Why were we assigned to make an instrument for the AP of our sound unit in LST? Instruments are great demonstrators of producing varying sounds, with some of them being quite harmonic. The diddley bow is a simple instrument that demonstrates wavelength and frequency on one string.
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Sound is very mechanical. Sound waves are created as mechanical energy from a vibrating source (the string) is transferred to the air around it. The vibration of the string disturbs air molecules next to it and causes them to bump into each other. When those air molecules hit your eardrum, your eardrum moves. The bones in the middle ear amplify the sound vibrations and send them to the fluid-filled cochlea in the inner ear. Hair cells bump and bend as chemicals rush into the cells and create an electrical signal. This signal is sent to the brain by the auditory nerve, which turns it into a sound we hear.

Image by: SN

This is an image of the diddley bow I crafted. The string that is stretched across the wood plank is used to produce sound, and the can at the front amplifies that sound. The can at the front plays the same role as the sound hole of a guitar - it resonates a fuller sound that is pleasing to the ear. Without the sound hole, the sound would be harmonic.

Illustrated by: SN

This is a diagram of my diddley bow. I labeled all of the functioning parts, along with their measurements. The area underneath the string is found by adding the height of the nut with the height of the bridge, dividing it by 2, and multiplying it with the distance between them. This gives you 30 inches.

.5 + 2 = 2.5 / 2 = 1.25 x 24 = 30in

To find the upper angle of the area under the string, you must first subtract the height of the bridge with the height of the nut. Then, you divide the distance between the two with the number you get from subtracting them. Finally, you use the inverse tangent on it to find the upper angle. The upper angle is 86.42 degrees.

2 - .5 = 1.5 --> 24 / 1.5 = 16(tan^-1) = 86.42 degrees

 You find the lower angle by taking 360 degrees and subtracting it with the two 90 degree angles, along with the upper angle we just found. This gives you 93.58 degrees.

360 - 90 - 90 - 86.42 = 93.58 degrees

 In order to get the volume of the sound hole, all you have to do is multiply its height and radius by 2 and pi. This gives you 57.33 inches.

2 x 2 x pi x 4.5625 = 57.33in

 Harmonics are the wavelength and frequency of a sound at a certain point. You might have noticed those black markings on my diddley bow in the first image. Those points mark the halfway, one third, and one fourth points on it. Each of those points have their own harmonic frequency and wavelength. The wavelength and frequency of a wave are the volume and pitch of a sound. When one of the two goes up, the other goes down. Doing a little tone test on my instrument earlier, its first harmonic frequency is 125 hertz and its wavelength is 2.744 inches. To find the frequency of the other points, I just added 125Hz to the number the previous point had to find the number for the next one. I did a similar thing for the wavelength, but divided it by 2 each time.

Illustrated by: SN

This is a diagram of what each harmonic wave looks like. This displays a visual of what is affected when you change each of them. I do believe I made the waves in the second harmonic way too tall, so keep in mind that they actually should be as tall as every other wave shown above.


I may not be much of a musician, but I hope this video gives you a good visualization of the diddley bow in action. I needed to point the resonator towards the recording device in order for the sound to be easily heard. The sound would not have been as clear if the sound hole was pointed in another direction. It is like a water hose where the top of its walls are built to face the same direction at once, so the water can't travel any other way except straight forward. Sound can travel in many ways and through many things, like water and air. Sound is mechanical. It is a tool most of us use to communicate and entertain ourselves when we play or listen to music. The diddley bow is a very basic example of how sound is made and amplified all on one wood plank. Kind of like light, each sound is defined from the length and frequency of its wave, making it unique from any other. I hope you enjoyed!

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