In this unit I learned many unbelievable facts about sound! I learned about its nature, how it travels, in what materials it travels faster and why, what “breaking the sound barrier” means, and about echo and the Doppler Effect, among many, many other amazing facts. I am most proud of the fact that I can now have an interesting and productive conversation with anyone about sound, about its properties and beauties.
My instrument produces sounds when I pluck its strings, which makes them vibrate. This creates acoustic sound waves which are later amplified by the cans the strings pass through. The pitch of my strings can be changed by adjusting screws (tuning pegs) which the strings are connected to on the other end (the tighter the screw, the higher the pitch). The pitch may also be adjusted by pressing the “slide” (made of glass; much like a shot glass) against the strings and sliding it (the closer the slide is to the cans, the higher the pitch). The amplitude of the sound waves also depends on how strong I strum or pluck the strings.
This is a sketch I made of my instrument, labeling its parts and their measurements:
The Doppler Effect is when we hear a change in the pitch of a sound because it is moving towards or away from us, even though the pitch never really changes. We hear examples of the Doppler Effect in our everyday lives, such as airplanes when they are flying through the sky, and cars passing by. I can demonstrate the Doppler Effect with my instrument by moving it from side to side while the strings are playing.
This is a recording of me playing my instrument and moving it at the same time to create the Doppler Effect:
The base of my instrument is a 32 x 14 x 2 cm plastic drip tray usually used to put under a flower pot. The cans I use to amplify the sound of the strings have a circumference of 23.56 cm, and the cans themselves have a diameter 7.5 cm and they are 11 cm high.The strings of my instrument are threaded through a hole in each can. I also used two screws as tuning pegs that are attached to the nylon strings, which are 1.5 cm long each. These screws are 18 and 19 cm away from the cans, given that one can is placed further back in the plastic drip tray than the other one. I placed the cans at different distances from the screws because this way I can create two distinct sounds, given that the closer the can is to the screw, the duller, more opaque the sound becomes. The thickness of my strings is 0.071 cm, and they are made of nylon, and they are 20 and 21 cm long from the screws to the cans respectively. The approximate volume of my instruments body is 971.94 cm3.
This is a visualization of my instrument’s first four harmonics (of both strings), considering the fact that the average speed of sound in my instrument is approximately 420 m/s:
