Transcript Chapter 15 Sound  15.1 Properties of Sound  15.2 Sound Waves  15.3 Sound, Perception, and Music.

Chapter 15 Sound
 15.1 Properties of Sound
 15.2 Sound Waves
 15.3 Sound, Perception, and Music
Chapter 15 Objectives

Explain how the pitch, loudness, and speed of sound are
related to properties of waves.

Describe how sound is created and recorded.

Give examples of refraction, diffraction, absorption, and
reflection of sound waves.

Explain the Doppler effect.

Give a practical example of resonance with sound waves.

Explain the relationship between the superposition principle
and Fourier’s theorem.

Describe how the meaning of sound is related to frequency
and time.

Describe the musical scale, consonance, dissonance, and
beats in terms of sound waves.
Chapter 15 Vocabulary Terms
 acoustics
 frequency
 rhythm
 beats
 spectrum
 shock wave
 cochlea
 microphone
 sonogram
 consonance
 musical scale
 speaker
 decibel
 note
 stereo
 dissonance
 octave
 subsonic
 Doppler effect
 pitch
 supersonic
 Fourier’s theorem
 pressure
 reverberation
Inv 15.1 Properties of Sound
Key Question:
What is sound and how do we hear it?
15.1 Properties of Sound
 If you could see atoms,
the difference between
high and low pressure is
not as great.
 The image below is
exaggerated to show
effect.
15.2 The frequency of sound
 We hear frequencies of sound as
having different pitch.
 A low frequency sound has a low
pitch, like the rumble of a big
truck.
 A high-frequency sound has a
high pitch, like a whistle or siren.
 In speech, women have higher
fundamental frequencies than
men.
15.1 Complex sound
Common Sounds and their Loudness
15.1 Loudness
Every increase of 20 dB,
means the pressure
wave is 10 times
greater in amplitude.
Logarithmic
scale
Linear
scale
Decibels (dB)
Amplitude
0
1
20
10
40
100
60
1,000
80
10,000
100
100,000
120
1,000,000
15.1 Sensitivity of the ear
 How we hear the loudness of
sound is affected by the
frequency of the sound as well
as by the amplitude.
 The human ear is most
sensitive to sounds between
300 and 3,000 Hz.
 The ear is less sensitive to
sounds outside this range.
 Most of the frequencies that
make up speech are between
300 and 3,000 Hz.
15.1 How sound is created
 The human voice is a complex
sound that starts in the larynx, a
small structure at the top of your
windpipe.
 The sound that starts in the
larynx is changed by passing
through openings in the throat
and mouth.
 Different sounds are made by
changing both the vibrations in
the larynx and the shape of the
openings.
15.1 How sound is created
 A speaker is a device
that is specially
designed to reproduce
sounds accurately.
 The working parts of a
typical speaker include
a magnet, a coil of wire,
and a cone.
15.1 Recording sound
1. A common way to record
sound starts with a
microphone.
2. The microphone transforms
a sound wave into an
electrical signal with the
same pattern of oscillation.
3. In modern digital recording,
a sensitive circuit converts
analog sounds to digital
values between 0 and
65,536.
15.1 Recording sound
4. Numbers correspond to the amplitude of the signal
and are recorded as data. One second of compactdisk-quality sound is a list of 44,100 numbers.
15.1 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.
15.1 Recording sound
6. The electrical signal is amplified until it is powerful
enough to move the coil in a speaker and reproduce
the sound.
Chapter 15 Sound
 15.1 Properties of Sound
 15.2 Sound Waves
 15.3 Sound, Perception, and Music
Inv 15.2 Sound Waves
Investigation Key
Question:
Does sound behave like
other waves?
15.2 Sound Waves
We know sound is a wave because:
1. Sound has both frequency and wavelength.
2. The speed of sound is frequency times
wavelength.
3. Resonance happens with sound.
4. Sound can be reflected, refracted, and
absorbed and also shows evidence of
interference and diffraction.
15.2 Sound Waves
A sound wave is a wave of alternating highpressure and low-pressure regions of air.
15.2 Amplitude of sound
 The amplitude of a
sound wave is very
small.
 Even a loud 80 dB noise
creates a pressure
variation of only a few
millionths of an
atmosphere.
15.2 The wavelength of sound
15.2 The Doppler effect
 The shift in frequency caused by motion is called the
Doppler effect.
 It occurs when a sound source is moving at speeds
less than the speed of sound.
15.2 The speed of sound
 The speed of sound in air
is 343 meters per second
(660 miles per hour) at one
atmosphere of pressure
and room temperature
(21°C).
 An object is subsonic when
it is moving slower than
sound.
15.2 The speed of sound
 We use the term supersonic to describe motion at
speeds faster than the speed of sound.
 A shock wave forms where the wave fronts pile up.
 The pressure change across the shock wave is what
causes a very loud sound known as a sonic boom.
15.2 The speed of sound
 The speed of a
sound wave in air
depends on how
fast air molecules
are moving.
 The speed of sound
in materials is often
faster than in air.
15.2 Standing waves and resonance
 Spaces enclosed by boundaries can create
resonance with sound waves.
 The closed end of a pipe is a closed boundary.
 An open boundary makes an antinode in the
standing wave.
 Sounds of different frequencies are made by
standing waves.
 A particular sound is selected by designing the
length of a vibrating system to be resonant at the
desired frequency.
15.2 Sound waves and boundaries
 Like other waves,
sound waves can be
reflected by surfaces
and refracted as they
pass from one material
to another.
 Sound waves reflect
from hard surfaces.
 Soft materials can
absorb sound waves.
15.2 Fourier's theorem
 Fourier’s
theorem says any
complex wave
can be made
from a sum of
single frequency
waves.
15.2 Sound spectrum
 A complex wave is really a sum of component
frequencies.
 A frequency spectrum is a graph that shows the
amplitude of each component frequency in a complex
wave.
Chapter 15 Sound
 15.1 Properties of Sound
 15.2 Sound Waves
 15.3 Sound, Perception, and Music
Inv 15.3 Sound, Perception, and Music
Investigation Key Question:
How is musical sound different than other types of
sound?
15.3 Sound, Perception, and Music
 A single frequency by itself does not have much
meaning.
 The meaning comes from patterns in many frequencies
together.
 A sonogram is a special
kind of graph that shows
how loud sound is at
different frequencies.
 Every person’s sonogram
is different, even when
saying the same word.
15.3 Patterns of frequency
 The brighter the sonogram, the louder the
sound is at that frequency.
15.3 Hearing sound
 The eardrum vibrates in
response to sound
waves in the ear canal.
 The three delicate
bones of the inner ear
transmit the vibration of
the eardrum to the side
of the cochlea.
 The fluid in the spiral of
the cochlea vibrates
and creates waves that
travel up the spiral.
15.3 Sound
 The nerves near the
beginning see a
relatively large
channel and respond
to longer wavelength,
low frequency sound.
 The nerves at the small end of the channel respond
to shorter wavelength, higher-frequency sound.
15.3 Music
 The pitch of a sound is how high or low we hear
its frequency. Though pitch and frequency
usually mean the same thing, the way we hear a
pitch can be affected by the sounds we heard
before and after.
 Rhythm is a regular time pattern in a sound.
 Music is a combination of sound and rhythm that
we find pleasant.
 Most of the music you listen to is created from a
pattern of frequencies called a musical scale.
15.3 Consonance, dissonance, and
beats
 Harmony is the study of how sounds work together to
create effects desired by the composer.
 When we hear more than one frequency of sound and the
combination sounds good, we call it consonance.
 When the combination sounds bad or unsettling, we call it
dissonance.
15.3 Consonance, dissonance, and
beats
 Consonance and dissonance are related to beats.
 When frequencies are far enough apart that there
are no beats, we get consonance.
 When frequencies are too close together, we hear
beats that are the cause of dissonance.
 Beats occur when two frequencies are close, but
not exactly the same.
15.3 Harmonics and instruments
 The same note sounds different when played on
different instruments because the sound from an
instrument is not a single pure frequency.
 The variation comes from the harmonics,
multiples of the fundamental note.
Sound from a Guitar
 The sound of an acoustic guitar is
shaped by sound waves bouncing
around inside the guitar, as well as
the vibration of the top.
 Because the shape of the guitar is
irregular, there are many
resonances.
 In general, large-bodied guitars
have stronger long-wavelength,
low-frequency sounds, and are
louder.
 Small-bodied acoustic guitars often
lack low frequencies in their range
of sounds.