Chapter 19: Sound
For those who have ears!
19.1
Properties of Sound
19.1 Objectives
Demonstrate knowledge of the nature of
sound waves and the properties sound shares
with other waves.
Solve problems relating the frequency,
wavelength, and velocity of sound.
Define the Doppler shift and identify some of
the applications.
What is Sound?
What is sound? Sound is a form of energy, just like
electricity and light. Sound is made when air molecules
vibrate longitudinally and move in a pattern called
waves, or sound waves. They are also referred to as
compression or pressure waves.
Think of when you clap your hands, or when you slam
the car door shut. That action produces sound waves,
which travel to your ears and then to your brain, which
says, "I recognize that sound.” For humans, sound most
commonly travels through the air. But it can travel
through other mediums like water.
What does it look like?
Sound is invisible for the most part. It is heard not seen.
There are fun toys that make big air bursts that you can
feel But what does sound “look like”?
Since sound needs a
medium like air, it cannot
travel in a vacuum.
Visualizing Sound
The Speed of Sound
Since sound travels in the medium of air, its speed is
fixed. It does however, vary with the temperature of air.
At 0 C, the speed of sound is 331.451 m/s.
At 20 C, the speed of sound is 343.371 m/s.
At 40 C, the speed of sound is 354.891 m/s.
As a rule of thumb, the speed of sound changes by about
12 m/s for every 20 C of temperature change. The most
common value used is 343 m/s.
Sound Measurement
Sound amplitude is measured in decibels (dB). The
decibel scale is a logarithmic scale. The sound
amplitude is also called sound level or loudness.
Table of sound levels
Jet aircraft, 50 m away
Threshold of pain
Threshold of discomfort
Chainsaw, 1m distance
Disco, 1 m from speaker
Diesel truck, 10 m away
Kerbside of busy road, 5 m
Vacuum cleaner, distance 1 m
Conversational speech, 1m
Average home
Quiet library
Quiet bedroom at night
Background in TV studio
Rustling leaf
Threshold of hearing
dB
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Spinal Tap: This one goes to 11…
Sound Frequency Ranges
Humans can hear from 20 hz to 20,000 Hz. Other
animals have larger ranges.
Species
human
dog
cat
cow
horse
sheep
rabbit
rat
mouse
gerbil
guinea pig
hedgehog
raccoon
ferret
opossum
Approximate Range (Hz)
64-23,000
67-45,000
45-64,000
23-35,000
55-33,500
100-30,000
360-42,000
200-76,000
1,000-91,000
100-60,000
54-50,000
250-45,000
100-40,000
16-44,000
500-64,000
Species
Approximate Range (Hz)
chinchilla
90-22,800
bat
2,000-110,000
beluga whale
1,000-123,000
elephant
16-12,000
porpoise
75-150,000
goldfish
20-3,000
catfish
50-4,000
tuna
50-1,100
bullfrog
100-3,000
tree frog
50-4,000
canary
250-8,000
parakeet
200-8,500
cockatiel
250-8,000
owl
200-12,000
chicken
125-2,000
Sound Speed
Sound Speed - The distance a sound travels in
a given time. It is given as the frequency times
the wavelength. If the frequency increases then
the wavelength must decrease since the speed
is constant.
d 
m

  f    343
t T
sec

1
1
f  frequency  ; T  period 
T
f
  wavelength
Speed of Sound in Other Media
The speed of sound depends on the media the sound
wave travels through.
m
m
 vacuum  0
;  air  343
;
sec
sec
m
m
 water  1,484
;  iron  5,120
sec
sec
 ground   air
Echoes
Reflected waves are called echoes and can be used to
measure the distance from source to the object. This is
how bats, who have poor eyesight and travel at night,
navigate.
d
m

 343
t
sec
Sound can also be diffracted. It
can bend around barriers.

Sonar
Sonar is reflected sound waves (echoes) that travel
through a water media rather than an air media.
d
m
 water 
1,248
t
sec
Doppler Effect
Doppler Shift
Doppler shift: If the sound source is coming towards you
at a significant velocity, the sound pitch will get higher. If
the sound source is moving away from you then the
sound pitch is lowered.
doppler motions
Doppler Shift
Doppler shift: If the sound source is coming towards you
at a significant velocity, the sound pitch will get higher. If
the sound source is moving away from you then the
sound pitch is lowered.
fD 
v  vD 

fS
v  v S 
v  343 m/s; D sound detector; S  sound source

Doppler Demo
19.2
The Physics of
Music
19.2 Objectives
Describe the origin of sound.
Demonstate an understanding of resonance,
especially as applied to air columns.
Explain why there is a variation among
instruments and among voices using the
terms timbre, resonance, fundamental,
harmonic.
Determine why beats occur.
Concept Development Map
Sound Vocabulary
Resonance
Definitions
Re-sonance (again-sound).
The act of resounding,
being resonant
Sound vibrations are
transferred to another object
with the same natural frequency
of vibration. The two agree.
Dissonance
Sonance
Dis-sonance (mismatchedsound).
Sound vibrations that “fight”
With each other.
Discord, disharmony.
Consonance
Latin: sonus (sound) &
sonans (to make a
noise); a sound; a tune
Related words:
Sonic, sonar, sonant,
sonata, sonation
Quality or state of being sonant;
sonancy
Con-sonance (with-sound).
The act of sounding together;
Harmony (different frequency).
Resonance
Resonance - The tendency of a system to oscillate
at maximum amplitude at certain frequencies, known
as the system's resonance frequencies (or resonant
frequencies). At these frequencies, even small
periodic driving forces can produce large amplitude
vibrations, because the system stores vibrational
energy.
Closed Tube
Open Tube
82 Resonance Demo
83 “Break Step” and Bridges
Pitch and Timbre
Pitch - The musician’s word for frequency of the
sound.
Timbre - The tone quality or color of the sound wave
generated by the instrument. The extra distortions of
the pure sine wave accounts for the unique sound of
the human voice, and different instruments.
Beat - An oscillation of wave amplitude caused by
the sounding of two nearly identical frequencies. The
superposition of the waves makes a slower moving
wave.
Timbre
Consonance and Dissonance
Consonance - A pleasant combination of pitches.
Dissonance - A unpleasant combination of pitches.
Can be described as “jarring”.
Harmonics and Octaves
Harmonics - Any higher frequency that is a multiple
of the original frequency ( f ).
e.g. 2 f , 3 f
,4 f ,5 f ,...
Octave - Two frequencies in a 1:2 ratio.

e.g. 440Hz & 880Hz, 220Hz & 440Hz,...
Mr. Mosher’s Band
Trombone - A slide trombone lengthens the
instrument’s tube by tube within a tube action.
Guitar - Various frequencies, Harmonics, and Beats
can all be demonstrated on the guitar.
Throat - Please don’t ask Mr. Mosher to play his
throat!