Sound and Music
Sound Waves
Sound is all around us. All sounds have one thing in common; they
are all produced by a vibrating object. Examining musical
instruments is a useful way to show what is vibrating.
String vibrating
Air vibrating
Reed vibrating
Skin vibrating
When a vibration occurs, sound waves are produced. These sound
waves carry energy from the vibrating object to our ears. It is
receiving this energy that allows us to hear the sound.
Sounds can be identified by their frequency. In the same way as
radio waves [Telecommunications Unit] sound wave frequency
means the number of waves produced per second.
In music the word pitch is used to describe sounds. A high pitch is
the same as a high frequency.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
The apparatus shown
speaker
can be used to
oscilloscope
examine the electrical
signal that produces
sound from a
signal
loudspeaker.
generator
The shape of the
pattern produced by the oscilloscope depends on the frequency of
the sound and also on its loudness.
This is the pattern produced when a sound
is played through the loudspeaker.
This is the pattern produced when a louder
sound of the same frequency is played
through the loudspeaker.
The number of waves in the pattern has not
changed.
The height of the waves has increased.
This is the pattern produced when a sound
of the same loudness but increased
frequency is played through the
loudspeaker.
The number of waves in the pattern has
increased
The height of the waves has stayed the
same.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
Louder sounds always have waves that go higher up the
oscilloscope screen.
Higher frequency sounds always have more waves on the
oscilloscope screen.
There is a special way of
describing a frequency that
doubles or halves. Frequencies
are said to be one octave apart if
their frequency changes by a
factor of two. It is called an
octave because eight white keys
separate these frequency
changes on a piano keyboard.
128 Hz
256 Hz
512 Hz
Original frequency 256 Hz
One octave higher: frequency = 256 x 2 = 512 Hz
One octave lower: frequency = 256 ÷ 2 = 128 Hz
The frequency of a vibrating string can be increased in two ways.
One way is to increase the
tightness of the string.
Performers often do this when
they are tuning their
instruments.
Another way is to shorten the
length of the string. Performers
do this when they play stringed
instruments, moving their
fingers along the fretboard.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
Musical instruments that use air as their vibrating material produce
higher notes by decreasing the length of the air column. The
trombone is a good example of
this. Trombone B will produce
a higher note than trombone A
because the vibrating air
column is shorter.
A
B
Speed of Sound
Sound travels through air in the form of waves. These waves take
time to travel from one place to another. Sound travels quickly
through air but light travels even faster. An
example of this is when there is a
thunderstorm. Lightning and thunder are
produced at exactly the same time in the
cloud. You will always see the flash of
lightning before you hear the rumble of
thunder. [If you get both at the same time
you’ve just been struck by lightning!!!]
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
We can measure the speed of sound in air by doing an experiment.
In the experiment we have to measure the distance that the sound
travels. That is distance ‘d’ in the diagram below.
We also have to measure how long it takes for the sound to travel
that distance. The electronic timer measures the time for the sound
to go from one microphone to the other.
screwdriver
bottle
timer
microphone
d
microphone
When we have both of these measurements, the speed can be
calculated using the equation
distance
speed =
time
Example: distance = 1.5 m
time
= 0.0044 s
speed =
distance
time
=
1.5
= 341 m/s
0.0044
Any method used to measure speed of sound must measure both a
distance and a time.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
Using Sound
Sound can travel through solids, liquids and gases.
Sound will travel along
the string in a string
telephone.
Dolphins communicate by
passing sound through
water.
We can hear people
singing because the sound
travels through the air.
Sound cannot travel through a vacuum.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
Range of Hearing
Humans are not able to hear every sound that is produced. If a
sound is produced outside the frequency range 20 – 20 000 Hz then
we will not hear it. Other animals are able to hear sounds outside
this range.
up to 45 000 Hz
up to 30 000 Hz
up to 80 000 Hz
If a sound has a higher frequency than humans can hear [above 20
000 Hz] it is called Ultrasound. Cats, dogs and whales can all hear
some ultrasound.
Ultrasound is used in
medicine to examine
unborn children.
Ultrasound is used in industry to help metals plate better.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
It is important that sound level values are kept to a reasonable
level. If the sound level is too high then it is possible that hearing
could be damaged.
Sound levels are measured in the unit called the decibel (dB).
Some common sounds with their decibel levels are shown below.
 0 dB The softest sound a person can hear with normal
hearing
 10 dB normal breathing
 20 dB whispering at 5 feet
 30 dB soft whisper
 60 dB normal conversation
 80 dB ringing telephone
 110 dB shouting in ear
 120 dB thunder
 150 dB jet engine taking off
If sound levels are above 85 dB
then damage will occur if no
protection is used. Ear defenders
should be used in situations where
the sound level is above 85 dB.
If there is a source of loud noise that causes a
disturbance it is known as noise pollution. Some
examples of this could be airport noise, roadworks,
heavy traffic, and noisy neighbours.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
Amplified Sound
An amplifier can be used to make a sound louder. An amplifier
is used as part of the school tannoy system; it allows the
headteacher to speak to everybody in the school without having
to shout. The amplifier only makes the sound louder; it does not
change its frequency. We know this because we can recognise
the voice that comes through the tannoy.
Amplifiers are also used in music performances, public address
systems [in airports or railway stations]
The system is made up of three parts:
1. Microphone: changes sound energy into
electrical energy
2. Amplifier: gives the electrical signal
more energy
3. Loudspeaker: changes the electrical
signal back into sound.
A measure of how much louder a sound can be made is by
finding out the voltage gain of the amplifier. This is how many
times bigger the voltage is made.
To calculate this value we need to know the voltage going into
the amplifier, called the input voltage. We also need to know the
voltage coming out of the amplifier, called the output voltage.
voltage gain =
output voltage
input volt age
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
Example: A cassette player
amplifier has an input voltage
of 0.02 volts. The voltage
from the amplifier to the
loudspeaker is 3.0 volts.
Calculate the voltage gain.
voltage gain =
3.0
output voltage
=
= 150
0.02
input volt age
Your voice
If you hear a recording of your voice it sounds
different to how you normally hear your voice when
you speak. The reason for this is that normally the
energy from your voice travels through your skull to
your ears and the recorded sound energy is
travelling through air. This is why singers wear
earphones when recording songs so that they can
hear how they actually sound.
CD versus Cassette
CDs have become more popular than cassettes as a way of
listening to music. There are various reasons for this
1. The quality of sound reproduction from a CD is better.
2. CDs do not wear away each time you play them.
3. CDs cannot be damaged by magnets.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
• Sound waves
 All sounds are produced by vibrations
 Sounds travel as waves and carry energy from one point to
another
 The frequency of a sound is the number of waves produced
every second.
 Frequencies are measured in the unit the hertz (Hz)
 High frequency sounds can also be described as being high
pitched
 On oscilloscope screens a wave with a larger amplitude(height)
has a louder sound
 On oscilloscope screens the pattern with a larger number of
waves has a higher frequency
 A difference of an octave between sounds means that the
frequency of one sound is double the other
 For a vibrating string
1. Tighter string higher frequency
2. Shorter string higher frequency
 The longer a vibrating air column the lower the frequency
• Speed of sound
 Sound waves travel slower in air than light waves
 To measure the speed of sound you need to
1. measure the distance the sound travels(d)
2. measure the time it takes the sound to travel that distance(t)
 The speed of sound can be calculated using
speed =
distance
time
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
• Using sound
 Sound is able to pass through solids, liquids and gases
 Sound cannot pass through a vacuum
 Humans can normally hear sounds in the frequency range 20 20 000 Hz
 Sounds that are above the highest frequency that humans can
hear are called ultrasounds
 Ultrasound is used in medicine for
1. Scanning unborn babies in the mother’s womb
2. Speeding up healing of soft tissue injuries
 Ultrasound is used outside medicine for
1. Welding plastics
2. Cleaning objects in waterbaths
 Excessive sound levels can be a problem, this is called sound
pollution
1. Heavy traffic
2. Loud neighbours
 Excessive sound levels can damage hearing.
• Amplified sound
 Amplifiers make the energy of a signal larger but do not change
its frequency
 A speech amplification system [the tannoy] needs three parts
1. microphone to change sound into electrical energy
2. amplifier to increase energy of electrical signal
3. loudspeaker to change electrical back into sound energy
 The number of times bigger the amplifier makes the input
voltage is called the voltage gain of the amplifier
Voltage gain =
output voltage
input volt age
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
 Your own voice sounds different to you because the vibrations
carry through the bones in your skull instead of through the air.
 Compact discs are less prone to interference than cassette tapes
and can store more information
Questions
1.(a)
For the instruments above say what vibrates to produce sound.
(i)Horn (ii)Violin (iii)Drum
(b) The horn produces a sound with a pitch of 280 Hz.
(i) There is another word that can be used instead of pitch.
What is it?
(ii) What does 280 Hz tell you about the vibration of the air in the
horn?
2. A piano key when pressed produces a sound of frequency 300
Hz. A key one octave higher is now pressed.
What is the frequency of this new note?
3.
Trumpet B
Trumpet A
Which of the two trumpets shown above will produce the highest
note? Explain your answer.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
4. . Two sounds are passed into a microphone. The trace produced
on an oscilloscope from each sound is shown below.
Trace P
Trace Q
(a) Which trace represents the quieter sound?
(b) Which trace represents the higher pitched sound?
5. Two students want to measure the speed of
sound. One student sets off a firework at one
end of the playing field. The second student
is at the other end of the playing field. The
second student sees the explosion then later
hears the sound.
(a)Why is there a delay between seeing the
explosion and hearing the sound?
(b)What measuring instruments would the students need to do this
experiment?
(c)The length of the field is 200 metres. The sound takes 0.58
seconds to travel this distance.
Calculate the speed of sound.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
6 . A student uses a sound meter to measure a range of sounds.
When they drew up their table they were very careless. They
mixed up the sound levels and the noises. They also forgot to
put headings into the table.
normal conversation
a quiet room
heavy traffic
jet plane
120
60
30
90
(a)Redraw the table putting in headings, units where needed
and match up the values to the correct noises.
(b) Why is it important that we are not exposed to excessive
noise?
(c) Give two examples of noise pollution.
7.(a) What is the highest frequency normally heard by humans?
(b) What do we call frequencies of sound above this value?
(c) Give one medical and one non-medical use for these
frequencies of sound.
8. A student is investigating the working of an amplifier. They
measure the input voltage and the output voltage.
The measurements are given below
Input voltage = 0.5 volts
Output voltage = 4.5 volts
(a)Calculate the voltage gain of the amplifier.
(b) The frequency of the output signal from the amplifier is 400
hertz.
What is the frequency of the input signal?
9. Explain why your voice sounds different to you when you hear
it played back from a tape.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft
10. Give two advantages of listening to or recording music on a
CD instead of a cassette tape.
Dick Orr 2003 Intermediate 1 Physics Revision Book Draft