CIGO Community

CRASH! BANG! Did you hear that sound? It was made by air vibrating. The same is true for sounds made by musical instruments. The difference between NOISE and MUSIC is that musical sounds are organized into patterns that have pitch and rhythm. Noise is just random, disorganized sounds. Sounds are made and travel in the same way whether they are musical sounds or noise.

A musical sound is called a tone, and is produced by air vibrating a certain number of times per second. These vibrations are called waves. These sound waves must be contained in some way so that the performer can control the loudness, quality of the tone, and how long it plays. Most musical instruments have a reed, a string, or some other device that creates sound waves when moved. Sounds are different because of harmonics, which are higher and quieter sounds mixed in. They are not heard separately, but add to the tone of the sound, making an oboe sound different from a trumpet or drum.

The number of times that a sound wave vibrates in a second is called its frequency. Scientists even have a name for how they measure the frequency of sounds. They measure it in cycles and call it hertz. High notes have a higher frequency than lower notes and this changes their shape. Different types of sound waves have different shapes. Look at these images to see what sound waves "look" like.

soundwave2.GIF (12001 bytes)

Notice that even if pitch and volume change, the shape of the sound wave stays the same.

Some instruments produce sound when blown into. For the brass instruments, the vibration of the player’s lips make the column of air vibrate. Most woodwinds have a reed, which vibrates when the player blows on it, making the column of air vibrate. Sound is produced from the flute when the player blows across the mouthpiece, causing vibration of the column. This image shows how the sound waves of different instruments might look.

soundwave3.GIF (6378 bytes)
PROJECT:

Wrap some stiff tissue paper around a comb. Hum on the paper and feel the vibration as it shivers. OR, tape some paper tightly over one end of a cardboard tube. Sing into the tube, gently touching the paper. Can you feel the vibrations? Try making your voice higher or lower, and notice the different types of vibrations.

The string section of the orchestra, such as the cello, violin and harp, produce sound when one or more of their strings vibrate. The vibrating strings then cause part of the instrument to vibrate, putting the surrounding air in motion. The strings of cellos and violins are usually stroked with a bow. With some instruments the strings are plucked, such as the harp or guitar.
PROJECT:

Wrap a rubber band around your fingers. Pluck it a few times. Can you see and feel the vibrations? The harder you pluck the rubber band, the more it will vibrate, creating a louder sound. If you stretch the rubber band, making it longer and thinner, what do you hear? (It will be a higher pitch.)

Other instruments produce sounds when struck, banged, shook or scraped. When the membrane (the stretched part) of a drum is hit, it vibrates and creates a sound. Instruments such as the xylophone or chimes, have a series of tubes or bars. When you strike one of the tubes or bars, a sound is produced.
PROJECT:

Tap an empty metal tin with a spoon. Feel it vibrate as it makes a sound. This is similar to playing a triangle. Fill an empty glass jar with water almost to the top. Take a pencil, and gently tap it near the rim. Fill other jars with different amounts of water in them. Do the jars sound differently? The more water in the jar, the lower the pitch, because the vibrations are slower.