Sound Produced by Simple Musical Instruments

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

How do musical instruments turn plucking and blowing air into music? In this lesson, we will look at simple instruments and explain how they create music as well as how our ear interprets that sound.

Noise vs. Tone

Think about your favorite song, there are probably several instruments involved in creating that song. How do these instruments create music? First, we need to define the difference between noise and tones. Noise is simply all of the wavelengths of sound interfering with each other to make wavelengths of different heights and lengths. While a tone is a group of sound wavelengths that are the exact same, the same distance apart and the same size. Musical instruments are made to force sound waves into the same size and distance. Musical instruments work in various ways to make this phenomena occur.

Wind Instruments

In the simplest sense, wind instruments are simply a tube that you blow air into. When you blow air you are creating waves. It typically doesn't sound like much, because they are just a jumble of wavelengths, each canceling the other out. In order to create the single tone, these wavelengths need to be organized. Tubes are able to reflect these waves back and forth creating a standing wave, or a group of waves that build off of each other to create the waves that are the same distance apart and same size.

When waves are not organized they interfere with each other, if peaks and valleys cancel each other out then we can get silence. If peaks and valleys do not line up then we get noise
Wave interference

Think about shining a light into a tube that is made out of mirrors on the inside. The light will reflect back and forth off of the mirrors, creating a beam of light. Another way to think about this is if you had a mirror outside, you could isolate a single beam from the sun light as it reflects off of the mirror. When the sun is shining light is everywhere, and doesn't create any distinct beam. But a group of the light is reflected off so that it is all in the same angle then we get a bright beam.

Waves are reflected off the sides of the tube to create a single wavelength or tone
Reflect waves

Sound waves work very similar to light waves. Sound waves are also reflected, being reflected off of the sides of the instrument. This takes the sound waves (air that is blown into it) and organizes it into a single tone, just like a mirror organizes the light all around into a single beam. The longest wave that can fit inside the tube is the fundamental wave and is the note that we hear.

But, there are shorter waves that fit in the tube as well. In order for these waves to fit into the tube they still need to cross and reflect at similar times. This means that they still line up with the fundamental wave in such a way that it doesn't interfere with the standing wave. These shorter waves are called overtones.

String Instruments

So, a tube organizes sound waves into specific wavelengths through reflection, but how does a string make music? The string isn't reflecting sound off of the walls of the tube, so how does it organize waves into a single tone? In order for a string instrument to work it needs to have a string tightly strung. This way the string isn't able to move very much, and the string ends up being only able to create a single wavelength as it moves. The movement of the string in one specific way also vibrates the air, creating a sound wave in one specific wavelength.

Only specific wavelengths can fit onto the string
String waves

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