Worlds of David Darling > Children's
Encyclopedia of Science > Sounds Interesting > Chapter 4
The Science of Acoustics
a book in the eXperiment! series by David Darling
4. Making Music
Jazz, opera, rock, soul – music comes in an amazing variety of forms.
It is played in every country on earth, to relax, to rejoice, to dance,
or to march by. But what is the difference between sounds that are musical
and those that are not?
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
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 played
by blowing into them. Others, including xylophones and drums, make musical
sounds when they are struck.
All instruments have their own special sound by which they can be recognized.
Even when the same note is played on two different instruments – a
clarinet and a trombone, for example – we can tell them apart. The
reason is that each instrument, as well as producing a basic note, also
gives off a wide assortment of other, related notes at the same time. It
is these accompanying sounds which, together with the basic note, create
the unique sound quality, or TIMBRE, of each instrument.
Same Note, Different Sound
You will need:
- A variety of musical instruments and people who can play them
- Several blindfolded volunteers
What to do:
Ask each musician to play (in turn) the same note – for example,
middle C – on his or her instrument. After each note, asked
the first blindfolded volunteer to say which instrument, from a list
of possible choices, has just sounded. Repeat the test with other
volunteers What are the results? Did any instruments prove especially
hard to identify? Why do you think this should be?
Do the experiment again, but this time ask the musicians to sound
the note in pairs. For example, a piano and a flute might play the
same note together, or a clarinet and a guitar. In each case, the
musicians should try to play at the same volume. Ask each volunteer
to say which instruments are playing. How well do the volunteers score?
Which instrument pairs do they have the most difficulty in identifying?
Taking it further:
The best way to study the differences in sound produced by various
musical instruments is with a microphone connected to a device called
an oscilloscope. Perhaps a demonstration using this equipment could
be set up in your school laboratory. An oscilloscope will show the
shape of the sound waves picked up by a microphone. It also allows
you to measure the frequency at which most of the sound is being given
off. How does this differ from one instrument to another? How does
the shape of the sound wave change if the note is played louder or
Use the oscilloscope to look at the pattern of sound waves in your
own voice. Try saying different words or vowel sounds. Compare your
"voice patterns" with those of other people. Can you see any differences?
Compare the appearance of the sound wave of a noise, such as hands
clapping, with that of the note from a tuning fork.
The Sounds of Music
All string instruments have a set of stretched strings or wires. These vibrate
at different rates depending on their length and tightness. The vibration
of a string causes the whole body of the instrument to vibrate. This results
in a much louder sound. A violin and guitar have only a few strings, so
the musician must hold down the strings in various positions to play all
the possible notes of the instrument. A piano or harp, on the other hand,
contains one or more strings for every note.
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.
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.
You will need:
- A plastic recorder (or penny whistle)
- A jug of water
- Two drinking straws
- 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. You can also find
a piano teacher to show you. 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?
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
A Model Concert Hall
You will need:
- An empty, bare room
- Old sheets, rugs, padded chairs, cushions
- A tape recorder and music tape
- A table
What to do:
Place the tape recorder on a table against one wall of the room. Turn
on the recorder so that it plays at a fairly high volume. Stand at
the back of the room and listen to the sound. How would you describe
it? Is it harsh or mellow? Why should this be?
Bring some items such as a rug, a few padded chairs, and some sheets
into the room. Ask an adult to help you hang the sheets against one
or two of the walls. Play the recorded music again. Has the sound
changed? In what way? Experiment with other arrangements of wall and
floor coverings and items about the room. How is the quality of sound
affected? Try to achieve the best possible sound – not too harsh
and not too muffled. Does the sound quality vary from one part of
the room to another?
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
If you touch the front of your neck while you say something, you will be
able to feel your throat vibrating. This is because you have two flaps of
skin inside your throat called vocal cords.
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.
Blow Your Own Horn
Lightly touch your neck while you hum a note. Now hum a higher note,
followed by a lower note. Can you feel any change? If so, can you
explain what may have moved? As you hum, press gently several times
against your neck. Does the sound change? Why should that be? Open
your mouth wide and make a sound without moving your mouth. This is
the basic sound produced by your vocal cords. Now try moving your
mouth, tongue, and lips in different ways. Listen to the variety of
sounds that come out.