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6 Pitch

Pitch is a property of sound. Pitch describes the highness or lowness of a sound. The frequency of sound waves determines the pitch heard. Remember, sound is how pressure waves entering your ears are perceived by your brain. Not everyone perceives a specific sound the same. But all can agree that the lower the frequency, the lower the pitch, and the higher the frequency, the higher the pitch. Pitch has nothing to do with the loudness or softness of a sound.

A flute made from a drinking straw is a simple homemade instrument that, like all wind instruments, vibrates at a specific frequency. The source of the pressure wave that starts the air vibrating is the reed at one open end. The reed is made to vibrate by blowing on it. A straw flute is made with a double reed, consisting of two parts that vibrate, which sends a pressure wave into the straw causing an air column in the open tube to vibrate. The longer the straw, the longer the air column inside and the lower the frequency. This means a longer straw will produce a lower pitch. Conversely, decrease the length of the straw and there is an increase in both the frequency and pitch.

See for Yourself

Materials

 bendy drinking straw

 scissors

 ruler

 marking pen

 helper

What to Do

1 With your fingers, flatten the short end above the accordion folds in the straw.

2 Figure 1 has marks indicating where to cut the straw to form the reed part of the straw flute. Once the two cuts have been made, cut the sharp point off to blunt the end.FIG 1

3 Moisten your lips, then place the reed in your mouth past your teeth and blow. If the flute is not producing sound, try drawing in the lips around the teeth rather than puckering them. Slightly lifting or lowering the straw flute can also help. Don't be too quick to give up. It might take a few tries to reach the goal of making a sound.FIG 2

4 Once you have mastered playing the straw flute, ask your helper to cut small sections off the end of the straw as you continue testing the straw flute.

What Happened?

The length of the straw component of the flute affects the sound frequency. A shorter straw will have a higher frequency. The higher the frequency, the higher the pitch of the sound produced. Thus, as the straw was shortened, it produced a sound with a higher pitch.