Key concepts
Physics
Sound waves
Membrane
Acoustics
Harmonics
Introduction
With summer here you might find yourself at a parade, party or fair sometime soon. While you're there you will probably be surrounded by sounds of all kinds: fireworks, music and, of course, the famous (or infamous) sound of kazoos! Whether you like them or not, these little noisemakers are a great way to learn about the physics of sound. In this activity you'll be investigating how kazoos work by building our own!
Background
A kazoo is a very simple musical instrument, made up of a hollow pipe with a hole in it. The hole is covered by a membrane that vibrates, resulting in a buzzing sound when people sing, speak or hum into the pipe. People have been making and playing kazoos for years. The first kazoos were made from hollowed out bones, with spider egg sacs used for the vibrating membrane!
Although a kazoo looks and feels more like a flute or clarinet, it's actually most closely related to a drum. As the player sings, speaks or hums into the open end, their vocal cords create sound waves that travel through the instrument. As they travel through the tube, some of the sound waves bounce off the walls of the instrument. This change in direction can add harmonics to the sound of the player's voice (depending on the material of the tube); however, most of the sound waves strike the membrane, causing it to vibrate. This vibration adds resonance or harmonics to the sound and creates the characteristic buzzing that we associate with the kazoo.
In this activity you will experiment with sound using a kazoo you can make yourself from materials around your house.
Materials
- Empty cardboard tube, such as an empty paper towel or toilet paper tube
- Plastic grocery bag
- Aluminum foil (a square sheet, approximately four-by-four inches)
- Paper towel sheet (a square sheet, approximately four-by-four inches)
- Rubber band
- Sharpened pencil
- Scissors
- An adult to help
Preparation
- Use the scissors to cut a four-by-four-inch square from the plastic grocery bag.
Procedure
- Try saying a few words out loud. Draw out the sounds and listen to your voice. Say “KAAA-ZOOO!” Pay attention to how your voice sounds.
- Put one end of the cardboard tube to your mouth so that it is touching the skin around your mouth but not touching your lips.
- With the tube to your mouth try speaking again. Draw out your words and make a lot of sounds. Say “KAAA-ZOOO!” Pay attention to the sound of your voice as it travels through the tube. Does your voice sound different as it travels through the tube? What is different about it? Can you feel the tube vibrating as you speak?
- Place the four-by-four-inch square you cut from the grocery bag over one end of the tube. Use the rubber band to secure it firmly in place.
- Put the uncovered end of the tube to your mouth and try speaking again. Make the same sounds you did before. Say “KAAA-ZOOO!” Does your voice sound different with the plastic on the tube? What is different about it?
- Have an adult help you use the sharpened pencil to poke a hole on one side of the cardboard tube, halfway between the two ends.
- Put the uncovered end of the tube to your mouth and try speaking again. Make the same sounds you did before. Say “KAAA-ZOOO!” Does your voice sound different than it did before you cut the hole? What is different about it? Try covering and uncovering the hole with your finger as you continue to speak.
- While you're speaking through the tube gently touch the plastic bag covering the end of the tube. Can you feel the plastic moving? What happens if you try to press the plastic harder to prevent it from moving while you're talking? Does it change how your voice sounds?
- Remove the plastic bag from the end of the tube and replace it with the piece of aluminum foil. Use the rubber band to secure it in place.
- Put the uncovered end of the tube to your mouth and try speaking again. Make the same sounds you did before. Say “KAAA-ZOOO!” Does your voice sound different than it did with the plastic bag covering the end of the tube? If so, what is different about it?
- Like you did with the plastic bag, while you're speaking through the tube gently touch the aluminum foil covering the end of the tube. Can you feel the foil moving? What happens if you try to press the foil harder to prevent it from moving while you're talking? Does it change how your voice sounds?
- Repeat the activity using the paper towel to cover the end of the tube. Notice how the sound of your voice changes with the different covering.
- Extra: Try different-size cardboard tubes. Notice how the sound of your voice changes with different-size tubes.
- Extra: Try poking additional holes in the cardboard tube. Does this change the sound of your voice when you speak into the tube?
Observations and results
At each step of this activity, you changed the structure of the tube. You probably noticed that with each change the sound of your voice changed as well.
In the first step, when you spoke through the tube you may have noticed that your voice sounded deeper or more resonant. This is because when you speak, sing or hum into the tube, some of the sound waves bounce off the walls of the tube, changing the direction from which and timing at which they reach your ears. This adds harmonics to the sound, and the effect is dependent on the material of the tube. (Softer material will absorb the sound waves, making them quieter.)
After you placed the plastic bag over the end of the tube you may have noticed that your voice sounded muffled compared with the tube with no plastic on the end. This is because the plastic created a barrier for the sound waves to pass through before reaching your ears, resulting in them losing energy along the way.
When you cut the hole in the tube, you may have noticed that it was easier to hear the sound of your voice. It also probably sounded amplified and more resonant. This is because the plastic at the end acts as a membrane, vibrating in response to your voice. The hole in the tube relieves the pressure inside the tube, allowing air (and sound) to escape and reach your ears.
When you repeated this activity with the aluminum foil and paper towel you may have noticed that your voice didn’t have the same vibrating quality as it did with the plastic bag. This is because neither the aluminum foil nor the paper towel is quite as effective as a membrane. The aluminum foil is less flexible than the plastic bag, so it did not vibrate as much as the bag did in response to your voice. As a result, sound may have bounced off the foil but it did not amplify in the same way. In contrast, the paper towel was a less-effective membrane because it is too porous. Air—and thus sound waves—could pass directly through it without causing it to vibrate.
More to explore
Take a Musical Step Back in Time: Make Your Own Phonograph from Everyday Items, from Science Buddies
Building Banjos, from Science Buddies
Making Sound Waves, from Scientific American
Talk through a String Telephone, from Scientific American
This activity brought to you in partnership with Science Buddies
