Sound

1
Sound

• Properties

2
Sound Properties

• Sound Wave

3
Sound Properties Detection

• Microphone
• Convert kinetic energy to electricity
• Ear
• Measure in decibel (dB)

4
Sound Properties Frequency

• Pitch vs. Frequency
• pitch is relative (a matter of common agreement
  among musicians), while frequency is absolute (a
  precise, unambiguous measurement).

5
Sound Properties Loud

• Amplitude is loudness
• Read decibel article

6
Sound Properties Doppler Effect

• Perceived frequency
• How often the pressure front hits your ear per
  second
• Scenarios
• Sound source stationary, you stationary
• Sound source moving, you stationary
• Sound source stationary, you moving
• Sound source moving, you moving

7
Sound Properties Doppler Effect
8
Doppler effect equations
9
Sound and Music
10
Sources

• Resonators
• Strings
• Sound boards/surfaces
• Emmet Otter

11
Resonators

• Resonance
• Not just reflection
• Increases the amplitude of a vibration by
  repeatedly applying a small external force at the
  same natural frequency.
• Closed Pipe (pg 413, fig 15-11)
• Open Pipe (pg 413, fig 15-11)
• Displacement and Pressure

12
Resonance

• Closed Pipe

13
Resonance

• Open Pipe

14
Resonance

• Strings

L
15
Consonance and Dissonance

• Consonance
• Combination of pitches that is pleasant
• Dissonance
• Combination of pitches that is not pleasant

16
Beat

• Two frequencies are very close, causes
  oscillations in amplitude

17
Binaural Beat Brain Wave
18
Review

• Doppler Effect

19
Doppler Effect

• The source of the sound is moving toward the
  detector
• The detector is moving toward the sound source
• The source is moving away from the detector
• The detector is moving away from the source
• The source and detector are moving toward each
  other
• The source and detector are moving away from each
  other
• Which situations result in an increased frequency
  and which result in a decreased frequency

20
Doppler Effect
21
Decibels

• 3dB increase is double power
• 3dB decrease is half power
• 20dB increase is 10x as much power
• 20dB decrease is 1/10 as much power

22
Pipe resonator

• Closed pipe
• ¼ wavelength at fundamental harmonic
• Open pipe
• ½ wavelength at fundamental harmonic
• Each successive harmonic is ½ wavelength higher
• or
• The distance between any two consecutive
  harmonics is ½ wavelength

23
Assumptions

• Assume that the speed of sound in air is 343 m/s,
  at 20C, unless otherwise noted.
• Assume that the speed of sound in water is 1533
  m/s, at 25C, unless otherwise noted.
• Assume that the speed of sound in water is 1530
  m/s, at 20C, unless otherwise noted.

24
Problems
18.5Hz
25
Problems

• An open-pipe resonator has a length of 2.39m.
  Calculate the frequency of its third harmonic if
  the velocity of sound is 343 m/s.

26
Problems

• You are listening to an outdoor concert on a day
  when the temperature is 0C. The sound of a
  wavelength of 0.490 m is emitted by a flute on
  the stage 125 m from where you are standing.
• a.What is the time elapsed before you hear the
  sound emitted from the stage?
• b.What is the frequency of the sound?

27
Problems

• The pulse-echo technique is used in diagnostic
  medical imaging. A short ultrasound pulse is
  emitted from the device, and echoes are produced
  when the pulse is reflected at a tissue
  interface. The echo signals are received back at
  the device and then analyzed to build up an image
  of the organ. The speed of sound in soft tissue
  is 1540 m/s. If an echo is received 58.2106 s
  after the pulse was emitted, how far is the
  tissue interface from the ultrasound device?

28
Problems

• The engine of a jet plane taking off produces a
  sound level of 140 dB, and the sound wave has a
  pressure amplitude of 200 Pa. A baggage handler
  working next to a jet plane that is taking off is
  wearing specially designed hearing protectors
  that reduce the sound level entering his ear by
  40 dB. What is the pressure amplitude of the
  sound waves entering his ear?

29
Problems

• While fishing from a boat anchored offshore, you
  see another fishing boat between your boat and
  the shore. The other boat sounds a 510-Hz horn as
  it heads toward the shore at a speed of 18 m/s.
• a. If your fishing boat is stationary, what is
  the frequency of the sound waves from the horn
  that reach you?
• b. If your fishing boat now heads out to sea at
  a speed of 15 m/s, what is the frequency of the
  sound waves from the horn that reach you?

30
Problems

• A species of bat navigates by emitting short
  bursts of sound waves that have a frequency range
  that peaks at 58.0 kHz.
• a. If a bat is flying at 4.0 m/s toward a
  stationary object, what is the frequency of the
  sound waves reaching the object?
• b. What is the frequency of the reflected sound
  waves detected by the bat?
• c. What is the difference between the frequency
  of the sound waves emitted by the bat and the
  frequency of the sound waves detected by the bat
  if the bat is flying at 4.0 m/s and the object is
  a moth approaching at 1.0 m/s?

31
Problems

• Hannah places an open, vertical glass tube into a
  container of water so that the lower end of the
  tube is submerged. She holds a vibrating tuning
  fork over the top of the tube while varying the
  water level in the tube. Hannah notices that the
  loudest sound is heard when the distance from the
  water to the top of the tube is 32.7 cm, and
  again when the distance is 98.2 cm. What is the
  frequency of the tuning fork?

32
Problems

• The six strings of a standard guitar are tuned to
  the following frequencies 165, 220, 294, 392,
  494, and 659 Hz.
• a. Find the lengths of the shortest open-ended
  organ pipes that would produce the same
  frequencies.
• b. Sketch the pipes, showing their lengths to
  scale.

33
Problems

• The fundamental tone of an open-pipe resonator
  with a length of 48 cm is the same as the second
  harmonic tone of a closed-pipe resonator. What is
  the length of the closed-pipe resonator?

34
Problems

• You receive a CD with the following note The
  first sound on the CD is the sound of a 238-Hz
  tuning fork and a second tuning fork being struck
  simultaneously. The second sound on the CD is the
  sound of the second tuning fork and a 240.0-Hz
  tuning fork being struck simultaneously. What is
  the frequency of the second tuning fork?
  Listening to the CD, you hear that the first
  sound has a beat frequency of 3.00 Hz and the
  second sound has a beat frequency of 5.00 Hz.
  Answer the question found in the note.

35

• fbeat ½f2 f1½
• (f2 f1) fbeat
• f2 f1 fbeat
• 238.0 Hz 3.00 Hz
• 241 Hz or 235 Hz
• fbeat ½f2 f3½
• (f2 f3) fbeat
• f2 f3 fbeat
• 240.0 Hz 5.00 Hz
• 245 Hz or 235 Hz
• The frequency of the second tuning fork must be
  235 Hz.

36
Problems

• A radio station broadcasts their signal with a
  wavelength of 3.5 µm. Although your radio will
  translate this signal into audible sound, explain
  why you cannot hear the radio signal directly.

NO
The threshold of the human ear is around 20,000
Hz, so the frequency of this radio signal is far
higher than what the ear can detect.
37
Problems

• A baseball fan sits in the outfield seats
  watching his home team play while another fan
  watches the same game at her house on television.
  In his seat at the ballpark, the fan sits 134 m
  from home plate. At her house, the other fan sits
  2.0 m from the television speaker, watching a
  signal broadcast from a camera located 8.0 m
  behind home plate. Assume the temperature
  throughout the city is 30.0C and that there is
  no time delay in the television transmission. The
  TV signal travels at c.
• a. The batter hits a fly ball. Which fan hears
  the crack of the bat first? Why?
• b. A third fan hears the crack of the bat a full
  2.00 s after she sees it. How far away is she?

38

• a. The sound of the crack of the bat travels at a
  speed of
• v 331 m/s 0.6T
• 331 m/s (0.6)(30.0C)
• 349 m/s
• For the fan sitting in the seats at the ballpark,

39

• For the fan sitting at home, the time of video
  transmission of the sound is negligible, as radio
  signals travel at the speed of light, c 3.0108
  m/s. Even if the fan is watching from 1000 km
  away, the time of travel for the video signal is
  only 3.3 ms.
• The fan watching the game on television actually
  hears the crack of the bat before the fan in
  attendance at the ballpark.

d 8.0 m 2.0 m 10.0 m
40

• b.

41
Problems

• An engineer at an underwater military station
  listens for submarines by sending an ultrasound
  sonar ping that has a frequency of 3.75 MHz.
• a. A stationary object is detected when the ping
  returns 3.00 s later. How far away is this
  object? The speed of sound in seawater is 1533
  m/s.
• b. A second ping returns with a frequency of
  3.80 MHz, indicating that the object is now
  moving. What is the objects velocity? In which
  direction is it moving relative to the listening
  station? Hint The direction of sound reverses
  after the sound reflects off the moving object.
• c. Sonar equipment has difficulty detecting
  objects smaller than the wavelength of the ping.
  Old sonar equipment used an audible ping with a
  frequency of 4.00102 Hz. What is the smallest
  object this old sonar could distinguish?
• d. What is the smallest object the ultrasound
  sonar can detect?

42

• a. A stationary object is detected when the ping
  returns 3.00 s later. How far away is this
  object? The speed of sound in seawater is 1533
  m/s.
• The distance for the sound to travel and return
  is twice the distance to the object

43

• b. A second ping returns with a frequency of
  3.80 MHz, indicating that the object is now
  moving. What is the objects velocity? In which
  direction is it moving relative to the listening
  station? Hint The direction of sound reverses
  after the sound reflects off the moving object.
• where fs is the frequency of the sonar ping at
  the source and v is the velocity of sound in
  seawater. For the echo, the source (now the
  submarine) is moving, and the sound wave travels
  in the return direction. The frequency that the
  engineer detects is fd2, and the frequency at the
  source is fd1.

44

• Substitute for fd1, and solve for vsub.

Since the frequency of the sonar ping increased,
the ship must be approaching the engineer.
45

• c.
• d.

46
Problems
47
(No Transcript)
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
(No Transcript)
52
(No Transcript)
53
(No Transcript)
54
(No Transcript)
55
Elements
More abstract animations like these can be found
on the Premium Gold Site. Search Bloodhound for
Strange Mechanical.