Transcript SOUND Chapter Twenty-Four: Sound 24.1 Properties of Sound 24.2 Sound Waves 24.3 Sound Perception and Music.

SOUND
Chapter Twenty-Four: Sound
24.1 Properties of Sound
24.2 Sound Waves
24.3 Sound Perception and
Music
Chapter 24.1 Learning Goals
Describe properties of sound.
Explain how sound waves are created
and recorded.
Discuss examples of the Doppler
effect.
Investigation 24A
Properties of Sound
Key Question:
 Does sound behave
like other waves?
24.1 The frequency of sound
The pitch of a sound
is how you hear and
interpret its frequency.
A low-frequency
sound has a low pitch.
A high-frequency
sound has a high
pitch.
Each person is saying “Hello”.
24.1 The frequency of sound
Almost all the sounds you hear contain
many frequencies at the same time.
Humans can generally hear frequencies
between 20 Hz and 20,000 Hz.
24.1 The loudness of sound
The loudness of a sound is measured in
decibels (dB).
The decibel is a unit used to express
relative differences in the loudness of
sounds.
24.1 The loudness of sound
Most sounds fall between 0 and 100 on the
decibel scale, making it a very convenient
number to understand and use.
24.1 The frequency of sound
Sounds near 2,000
Hz seem louder than
sounds of other
frequencies, even at
the same decibel
level.
According to this
curve, a 25 dB sound
at 1,000 Hz sounds
just as loud as an 40
dB sound at 100 Hz.
24.1 Amplitude and decibels
The amplitude of a sound increases
ten times every 20-decibels.
24.1 The speed of sound
The speed of sound
in normal air is 343
meters per second
(660 miles per hour).
Sound travels
through most liquids
and solids faster than
through air.
Sound travels about
five times faster in
water, and about 18
times faster in steel.
24.1 The speed of sound
Objects that move
faster than sound
are called
supersonic.
If you were on the
ground watching a
supersonic plane fly
toward you, there
would be silence.
The sound would be
behind the plane,
racing to catch up.
24.1 The speed of sound
A supersonic jet “squishes” the sound waves
so that a cone-shaped shock wave forms
where the waves “pile up” ahead of the
plane.
In front of the shock wave there is total
silence.
24.1 The speed of sound
Passenger jets are subsonic because
they travel at speeds from 400 to 500
mi/hr.
24.1 The Doppler effect
When the object is moving, the
frequency will not be the same to all
listeners.
The shift in frequency caused by
motion is called the Doppler effect.
You hear the Doppler effect when you
hear a police or fire siren coming
toward you, then going away from you.
24.1 Recording sound
To record a sound you must store the pattern
of vibrations in a way that can be replayed
and be true to the original sound.
1. A microphone transforms a sound wave
into an electrical signal with the same
pattern of vibration.
24.1 Recording sound
2. An “analog to digital converter”
converts the electrical signal to
digital values between 0 and 65,536.
24.1 Recording sound
3. One second of compact-disc-quality sound
is a list of 44,100 numbers which
represents the amplitudes converted
sounds.
24.1 Recording sound
4. To play the sound back, the string of
numbers is read by a laser and converted
into electrical signals again by a second
circuit which reverses the process of the
previous circuit.
24.1 Recording sound
5. The playback circuit converts the string
of numbers back into an electrical signal.
6. The electrical signal is amplified to move
the coil in a speaker and reproduce the
sound.
24.1 Recording sound
Most of the music you listen to has been
recorded in stereo.
The slight differences in how sound reaches
your ears lets you know where sound is
coming from.
Chapter Twenty-Four: Sound
24.1 Properties of Sound
24.2 Sound Waves
24.3 Sound Perception and
Music
Chapter 24.2 Learning Goals
Justify the classification of sound
as a wave.
Analyze sound interactions at
boundaries.
Explain how factors like
temperature and pressure affect
the behavior of sound waves.
Investigation 24B
Resonance in Other Systems
Key Question:
 How can resonance
be controled to
make the sounds
we want?
24.2 What is a sound wave?
Sound waves are pressure waves with
alternating high and low pressure regions.
When they are pushed by the vibrations, it
creates a layer of higher pressure which
results in a traveling vibration of pressure.
24.2 What is a sound wave?
At the same
temperature and
volume, higher
pressure contains
more molecules than
lower pressure.
24.2 The wavelength of sound
The wavelength of sound in air is similar
to the size of everyday objects.
24.2 The wavelength of sound
Wavelength is also
important to sound.
Musical instruments
use the wavelength
of a sound to create
different frequencies.
24.2 Standing waves
A wave that is confined in a
space is called a standing
wave.
A string with a standing
wave is a kind of oscillator.
24.2 Standing waves
The lowest natural
frequency is called
the fundamental.
A vibrating string
also has other
natural frequencies
called harmonics.
24.2 Standing waves
The place on a harmonic
with the greatest
amplitude is the antinode.
The place where the
string does not move
(least amplitude) is called
a node.
24.2 Standing waves
 It is easy to measure
the wavelength of a
standing wave on a
string.
Two harmonics
equals one wave!
24.2 Standing waves in pipes
A panpipe makes music as sound
resonates in tubes of different
lengths.
The natural
frequency of
a pipe is
proportional
to its length.
24.2 Standing waves in pipes
Because frequency and
wavelength are inversely related,
longer pipes have lower natural
frequencies because they resonate
at longer wavelengths.
A pipe that must vibrate at a
frequency 2 times higher than
another pipe must be 1/2 as long.
If the long pipe has a frequency of 528 Hz,
what is the frequency of the short pipe?
24.2 Standing waves in pipes
Blowing across the open end of a tube
creates a standing wave inside the tube.
If we blow at just the right angle and we
match the natural frequency of the
material and the sound resonates
(spreads).
24.2 Standing waves in pipes
The open end of a pipe is an open
boundary to a standing wave and makes
an antinode.
The pipe resonates to a certain frequency
when its length is one-fourth the
wavelength of that frequency.
24.2 Sound wave interactions
Like other waves, sound waves can
be reflected by hard surfaces and
refracted as they pass from one
material to another.
Diffraction causes sound waves to
spread out through small openings.
Carpet and soft materials can absorb
sound waves.
24.2 Reverberation
The reflected
sound and direct
sound from the
musicians together
create a multiple
echo called
reverberation.
The right amount
of reverberation
makes the sound
seem livelier and
richer.
Chapter Twenty-Four: Sound
24.1 Properties of Sound
24.2 Sound Waves
24.3 Sound Perception and
Music
Chapter 24.3 Learning Goals
Explore how the brain makes
meaning of sounds.
 Describe how humans hear
sounds.
Explain the sound is used to
create music.
24.3 Sound perception and music
When you hear a
sound, the nerves in
your ear respond to
more than 15,000
different frequencies
at once.
The brain makes sense
of complex sound
because the ear
separates the sound
into different
frequencies.
24.3 Sound perception and music
A frequency spectrum shows the
amplitudes of different frequencies
present in a sound.
24.3 Sonograms
 More information is
found in a
sonogram which
combines three
sound variables:
1. frequency,
2. time, and
3. amplitude (loudness).
24.3 Sonograms
Which letter
represents a soft
sound lasting 5
seconds?
What is it’s
frequency?
24.3 How we hear sound
 The parts of the ear work together:
1.
2.
3.
When the eardrum
vibrates, three small
bones transmit the
vibrations to the cochlea.
The vibrations make
waves inside the cochlea,
which vibrates nerves in
the spiral.
Each part of the spiral is
sensitive to a different
frequency.
24.3 Sound protection
Listening to loud sounds
for a long time causes the
hairs on the nerves in the
cochlea to weaken or
break off resulting in
permanent damage.
24.3 Music
The pitch of a sound is how high or
low we hear its frequency.
Rhythm is a regular time pattern in a
series of sounds.
Music is a combination of sound and
rhythm that we find pleasant.
24.3 The musical scale
Most of the music you listen to is
created from a pattern of frequencies
called a musical scale.
24.3 Superposition
The superposition principle states that
when sound waves occur at the same time
they combine to make a complex wave.
When two frequencies of sound are not
exactly equal in value, the loudness of the
total sound seems to oscillate or beat.
24.3 Music and notes
Each frequency in the scale is called a note.
The C major musical scale that starts on the
note C (262 Hz).
24.3 Music and harmony
Harmony is the study of how sounds work
together to create effects desired by the
composer.
The tense, dramatic sound track of a horror
movie is a vital part of the audience’s
experience.
Harmony is based on the frequency
relationships of the musical scale.
24.3 Music and harmony
When we hear more than one
frequency of sound and the
combination sounds pleasant, we call
it consonance.
When the combination sounds
unsettling, we call it dissonance.
24.3 Making sounds
The human voice is complex
sound that starts in the
larynx, at the top of your
windpipe.
The sound is changed by
passing over by expandable
folds (vocal cords) and
through openings in the
throat and mouth.
24.3 Making sounds
For a guitar in standard
tuning, the heaviest string
has a natural frequency of
82 Hz and the lightest a
frequency of 330 Hz.
Tightening a string raises
its natural frequency and
loosening lowers it.
24.3 Harmonics and music
The same note sounds different when
played on different instruments.
Suppose you compare the note C (262 Hz)
played on a guitar and the same note
played on a piano.
The variation comes from the harmonics
in complex sound.
A single C note from a grand piano might
include 20 or more different harmonics.
24.3 Harmonics and music
A tuning fork is a
useful tool for tuning
an instrument
because it produces a
single frequency
Investigation 24C
Perceiving Sound
Key Question:
 What is sound and how do we hear it??
Hearing
Deafness is poorly
understood in general.
For instance, there is a
common
misconception that
deaf people live in a
world of silence. To
understand the nature
of deafness, first one
has to understand the
nature of hearing.