Welcome back to my blog. This post is for the second Action Project of the STEAM class: Light, Sound, and Time. This unit, sound, was all about how sound is made and what happens for humans or animals to perceive it. Sound travels as a longitudinal wave and is explained as vibrations coming from a source that we perceive to be sound. To start, we examined how the human ear worked and our range of audible frequencies compared to infrasound and ultrasound which humans can’t hear. We then looked at the speed of sound and how it changes based on the medium it travels through. Following the understanding of how sound travels, we investigated traveling faster than the speed of sound or breaking the sound barrier and also the Doppler Effect. Lastly, we looked at stringed instruments like guitars and found how they make sounds. We also had one Field Experience at Guitar Center to look at the guitars and other instruments there. For this Action Project, the task is to create a diddley bow which is a one-stringed guitar. With this instrument, we would not only try playing it but also use it to explore the different science principles learned earlier in the unit. I hope you enjoy reading about my diddley bow.
How a diddley bow produces sound:
When you pluck the string of a diddley bow, it vibrates. The vibrations are sound waves that can be interpreted by our brains. The vibrations from the string travel to the can where it resonates and produces the sound waves that travel through the air. Tightening or loosening the string can affect the pitch of the sound. The pitch can also change with the length and thickness of the string.
Here is an audio clip of me playing my diddley bow:
Demonstration of science principles:
My diddley bow demonstrates many scientific principles that we have covered in this unit. Because the instrument has strings, it can be plucked to create vibrations or sound waves. For the sound to come from the instrument and reach the ear, it vibrates the air molecules and travels in compression or longitudinal waves. The diddley bow has a single string that is fixed on both ends which when moving creates a standing wave. At each end, some points that do not move are called nodes, and points that move the most called antinodes. The pattern a wave moves in is called a wavelength and the frequency determines whether a pitch is low or high. The amplitude of the wave is the displacement of a wave from its resting position and in a sound wave, it determines the volume.
Measurements for the diddley bow:
Length of string: 24.01 inches
Diameter of string: 0.052 inches
Height from wood to battery string: 0.75 inches
Height from wood to can string: 1.5 inches
Width of wood from the battery to can: 24 inches
Radius of can: 1.5 inches
Height of can: 4.5 inches
Math concepts:
Calculations for the resonator were also required so I found the volume of my can. The formula for volume is Volume=𝜋r^2h. The radius or “r” was from the edge of the can to the middle where my string was which equaled 1.5 inches. The height or “h” was how tall my can was which measured to be 4.5 inches. Using the formula I found the volume of my resonator was 31.81 inches cubed.
Harmonics:
Using an online tuner, I found the frequency of the open note of my diddley bow. I did this by plucking the string multiple times because each time is not going to come out as the same note. After a few plucks, I determined the most common frequency of the open note was 57.7 hertz. Using the wavelength formula, wavelength=velocity/frequency, I divided 343 meters per second (our common speed of sound) by 57.7 hertz. This equaled 5.94 meters. My soundboard shows the different harmonics of my diddley bow and I calculated the frequency and wavelength of them. For the second harmonic, the frequency was 115.4 hertz and the wavelength was 2.97 meters. For the third harmonic, the frequency was 173.1 hertz and the wavelength was 1.98 meters. For the fourth harmonic the frequency was 230.8 hertz and the wavelength was 1.485 meters. This pattern from the first to fourth harmonic shows that each time you go up a harmonic, the frequency is increased from the original by 2 times, 3 times, or 4 times. In turn, the wavelength decreased by half, a third, or a fourth of the original.
I hope you enjoyed reading about my diddley bow. I had a lot of fun working on this Action Project. I always like to build things so making the diddley bow was right up my alley. It was interesting to see the other diddley bows my classmates made because all of them are different in their own way and can create higher or lower-pitched notes. If I could do it again, I would maybe try to add more strings on the diddley bow and see how that compares to the original one. I think building diddley bows could be a nice project for younger kids to teach them about sound and also be nice to create an instrument. Maybe I inspired you to make a diddley bow. Again, thank you for reading and I hope to see you in the next blog.
Diddley Bow Side, GS, 2022
Diddley Bow Top, GS, 2022
How to build a diddley bow:
To make this diddley bow I used a piece of wood, a tin can, a battery, a guitar string, and some screws. To assemble the diddley bow I made a hole in the can with a nail and put the guitar string through the hole to create the resonator. The hole in the can is the bridge of the guitar. One screw is used as a tuning peg on the opposite end of the wood or soundboard and the battery is used as the nut for the string. The other screws were used for keeping the can and battery in place. As shown in the top view picture, I have marked where the harmonics are on my diddley bow's neck or bridge.
Diddley Bow Sketch, GS, 2022
How a diddley bow produces sound:
When you pluck the string of a diddley bow, it vibrates. The vibrations are sound waves that can be interpreted by our brains. The vibrations from the string travel to the can where it resonates and produces the sound waves that travel through the air. Tightening or loosening the string can affect the pitch of the sound. The pitch can also change with the length and thickness of the string.
Here is an audio clip of me playing my diddley bow:
Demonstration of science principles:
My diddley bow demonstrates many scientific principles that we have covered in this unit. Because the instrument has strings, it can be plucked to create vibrations or sound waves. For the sound to come from the instrument and reach the ear, it vibrates the air molecules and travels in compression or longitudinal waves. The diddley bow has a single string that is fixed on both ends which when moving creates a standing wave. At each end, some points that do not move are called nodes, and points that move the most called antinodes. The pattern a wave moves in is called a wavelength and the frequency determines whether a pitch is low or high. The amplitude of the wave is the displacement of a wave from its resting position and in a sound wave, it determines the volume.
Measurements for the diddley bow:
Length of string: 24.01 inches
Diameter of string: 0.052 inches
Height from wood to battery string: 0.75 inches
Height from wood to can string: 1.5 inches
Width of wood from the battery to can: 24 inches
Radius of can: 1.5 inches
Height of can: 4.5 inches
Diddley Bow Math, GS, 2022
To sketch out my diddley bow, I drew it as a trapezoid which is shown in the image above. To get the area of this trapezoid I used the formula: Area=1/2(b1+b2)h. For these variables: b1,=0.75 inches, b2=1.5 inches, and h=24 inches. After solving this, the area of my trapezoid was 27 inches squared. I also looked for the angles of the sides in my trapezoid. First, I used the Pythagorean Theorem to find the length of my string from the battery to the can which is 24.01 inches. Then I used the inverse tangent to find the “upper angle” of the trapezoid which equaled 88.21 degrees. Using this number I then found the “lower angle” by subtracting it from 90 and that equaled 1.79 degrees. To get the whole angle of the trapezoid I added 90 and 1.79 which equaled 91.79 degrees and that gives me 360 degrees after adding up all of the angles.
Calculations for the resonator were also required so I found the volume of my can. The formula for volume is Volume=𝜋r^2h. The radius or “r” was from the edge of the can to the middle where my string was which equaled 1.5 inches. The height or “h” was how tall my can was which measured to be 4.5 inches. Using the formula I found the volume of my resonator was 31.81 inches cubed.
Diddley Bow Harmonics, GS, 2022
Harmonic Markings, GS, 2022
Using an online tuner, I found the frequency of the open note of my diddley bow. I did this by plucking the string multiple times because each time is not going to come out as the same note. After a few plucks, I determined the most common frequency of the open note was 57.7 hertz. Using the wavelength formula, wavelength=velocity/frequency, I divided 343 meters per second (our common speed of sound) by 57.7 hertz. This equaled 5.94 meters. My soundboard shows the different harmonics of my diddley bow and I calculated the frequency and wavelength of them. For the second harmonic, the frequency was 115.4 hertz and the wavelength was 2.97 meters. For the third harmonic, the frequency was 173.1 hertz and the wavelength was 1.98 meters. For the fourth harmonic the frequency was 230.8 hertz and the wavelength was 1.485 meters. This pattern from the first to fourth harmonic shows that each time you go up a harmonic, the frequency is increased from the original by 2 times, 3 times, or 4 times. In turn, the wavelength decreased by half, a third, or a fourth of the original.
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