Why does a piccolo sound so high while a tuba sounds so low? It’s all about pitch! Pitch, or frequency in physics terms, is a way of measuring sound, specifically how many sound waves pass a point in a second. Sound is nothing more than a series of compressions of air molecules. Our ears can sense these compressions and the number of compressions per second it senses is what our brain uses to interpret into pitch.
Now here’s the fun part – sound waves, no matter how high or how low they are, travel at a constant speed, depending on air temperature. So, if the speed at which different pitches travel is the same, then the only other way to vary how many pass a point in a second is to vary the length of the wave, or the sound’s wavelength. Let’s illustrate it by creating a straw oboe:
What to Do:
- Flatten one end of a straw, about 1/3″. You can use your fingers or teeth
- Cut on a diagonal the sides of the flattened portion of the straw to create your “reeds” or the part that will vibrate to create the sound
- Place your new oboe in your mouth with the reeds parallel to the top and bottom of your mouth.
- Tighten your lips and blow through the straw. If you don’t hear a sound, adjust your lip tension, slowly loosening and tightening. It takes a little practice to get the hang of it.
- Once you hear a sound, try shortening your straw length by cutting off pieces. What happens to the sound?
- Try other kinds of straws that are wider, longer, etc. What happens to the sound?
What’s Happening?
The straw oboe is a tube instrument, which means its length directly correlates to the wavelength of the sound being made. A longer straw has a longer wavelength. Because sound travels at a constant speed, the longer wavelength causes fewer sound waves to pass a point in a second, so it has a lower pitch. But, short tube has a higher wavelength which therefore produces a higher pitch! You can also stop by the Children’s Museum of Houston’s How Does It Work? gallery and explore pitch with strings with Play That Pitch.
