There are four general categories of musical instruments: guitars and pianos are examples of vibrational strings, trombones and flutes are examples of the open-and air column instruments, organ pipes are examples of the closed-end air instruments, and drums are examples of vibrational mechanical instruments.
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All of these instruments work based on the resonance principle. When you strike a drum, pluck a string, blow into the reed, or somehow set the natural frequency in motion for the instrument, it starts vibrating a standing wave pattern. Harmonics refer to the natural frequency of the instrument.
Here’s what you need:
- two tongue depressors
- three rubber bands, one at least 1/4″ wide
- paper
- tape
In the video above, the rubber band acts like a reed to vibrate the air surrounding it. In a woodwind instrument, the vibrating reed resonates the air inside the tube at one of its natural frequencies so you hear a sound. The holes in a tube change the length of the air column, like with a clarinet.
The rubber band vibrates as you blow across the rubber band and you get a great sound. You can change the pitch by sliding the cuffs (this does take practice).
Troubleshooting: This project is really a variation on the Buzzing Hornets, but instead of using wind to vibrate the string, you use your breath. The rubber band still vibrates, and you can change the vibration (pitch) by moving the cuffs closer together or further apart. If the cuffs don’t slide easily, just loosen the rubber bands on the ends. You can also make additional harmonicas with different sizes of rubber bands, or even stack three harmonicas on top of each other to get unusual sounds.
If you can’t get a sound, you may have clamped down too hard on the ends. Release some of the pressure by untwisting the rubber bands on the ends and try again. Also – this one doesn’t work well if you spit too much – wet surfaces keep the rubber band from vibrating.
Exercises
- What is sound?
- What is energy?
- What is moving to make sound energy?
Click here to go to next lesson on Guitar Strings.
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