Worlds of David Darling > Children's
Encyclopedia of Science > Sounds Interesting > Chapter 4 SOUNDS INTERESTING:
The Science of Acoustics
a book in the eXperiment! series by David Darling
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Contents 1. Good Vibrations 2. Sounds Different 3. Hear, Hear! 4. Making Music 5. Through the Sound Barrier 6. Animal Chatter Glossary |
4. Making Music
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Music is a series of sounds arranged so that people – or some people, at least – enjoy them. The basic building blocks of musical sounds are notes. In these, the sound waves vibrate in a regular and repetitive way. A noise, on the other hand, is made up of sound waves that have no regular pattern.
Strums, Hums, and Drums
Music can be made in many different ways. Some instruments, like the guitar, have strings that are plucked. Others have strings that are stroked with a bow. Wind instruments, such as flutes, trumpets, and saxophones, are playing by blowing into them. Others, including xylophones and drums, make musical sounds when they are struck.
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The Sounds of Music
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Blowing into a wind instrument, such as a flute, causes a column of air to vibrate. The length of this column determines the pitch of the note – the longer the column, the deeper the sound. For example, if you cover just the top hole of a recorder, the note is high because the air can vibrate only as far as the next open hole. However, if you cover all the holes, the note is lower because the air can now vibrate throughout the whole length of the instrument. Some wind instruments, in order to produce very low notes, have such long tubes that they must be bent around several times. The coiled brass piping of a tuba, for instance, measures over twelve feet in length.
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A percussion instrument, such as a xylophone or drum, works in the simplest possible way. Its playing surface is struck and caused to vibrate directly.
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You will need:
- A plastic recorder (or penny whistle)
- A jug of water
- Two drinking straws
- Scissors
- Several glass bottles of the same size
- A wooden spoon
- A piano
What to do:
Cover all the holes on the recorder with your fingers. Blow gently into it and listen to the pitch of the sound it makes. Take a deep breath and blow into the recorder while you push it into a jug of water. What happens to the pitch of the note? Take another breath and blow again while you pull the recorder out of the water. Can you explain what you hear?
Flatten the end of one straw and snip off the corners as shown in the diagram. Hold the cut end lightly between your lips and blow gently. What happens? Cut off half the straw. How does the sound change? Prepare the end of another straw in the same way. Take a deep breath and, as you blow into the straw, quickly snip off short sections from the end. With practice you may even be able to play a scale.
Fill the bottles with water to different heights. Tap each bottle gently in turn with a wooden spoon. What do you notice? Try to tune the bottles to some of the notes on a piano. Blow across the open top of the bottles. Compare these sounds with those produced by tapping.
Ask an adult to show you the inside of a piano. What happens when one of the keys is pressed? How is the sound produced? What happens when the various pedals o the instrument are pushed down? How many strings are there for each key on the keyboard? Why should this be? Try holding all but one of the strings while someone presses the corresponding key. How does this affect the sound?
Good Listening
Sounds inside a room travel not just directly to your ears, but also after bouncing off the walls, floor, and ceiling. If these surfaces are hard and bare – as they often are in a church, for example – any sounds you hear may seem harsh and confused. If you ever moved from your house you may have noticed how much the rooms echo when they are empty of furniture, curtains, and carpets.In the case of a concert hall, the quality of sound reaching the audience's ears is all-important. For this reason, great care has to be taken in designing the shape of the room and the materials that cover the walls, ceiling, and floor.
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Synthetic Sound
A synthesizer can produce the sound of a church organ, of breaking glass, of a trumpet, or of weird sounds no human ear has heard before. To synthesize means to put together. So a synthesizer is an instrument that can build complex sounds from simpler ones. It uses a computer to create and store sounds electronically. These sounds can then be called up and played – usually by pressing the keys of a keyboard that is connected to the synthesizer.An extension of the synthesizer is the "sampler." This can record real sounds, such as those of a drum or an electric guitar, and convert them into a series of numbers which are stored by a computer. Samplers are used in recording studios to capture the sounds made by separate instruments and singers. Recordings of a number of performances are made and, from these, the best parts are put together and improved electronically. Strange as it seems, none of today's hit records were ever played as you hear them.
The Human Voice
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When you speak or sing, air from your lungs is forced over the vocal cords causing them to vibrate. In turn, this makes the air in your throat and mouth vibrate at the same rate. Muscles in the throat stretch the vocal cords tighter to make high sounds and relax them to make deeper tones. Women generally have higher voices than men because their vocal cords are shorter.
The basic sound from the vocal cords can be altered a great deal through movements of the mouth, tongue, and lips. In this way, we can produce all of the many variations of found in human languages.
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