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# Sound.ppt

senior lecturer at NILAI INTERNATIONAL UNIVERSITY em NILAI INTERNATIONAL UNIVERSITY
16 de Mar de 2023
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### Sound.ppt

1. Sound
2. Definition of Sound Sound is a wave created by vibrating objects and propagated through a medium from one location to another.
3. If a tree falls in a forest, and there is no one there to hear it, does it make a sound? Based on our definition, there IS sound in the forest, whether a human is there to hear it or not!. Sound is a physical disturbance in a medium. A person to hear it is not required. The medium (air) is required!
4. What type of waves are sound waves?
5.  The sound wave is transported from one location to another by means of particle-to-particle interaction. • If the sound wave is moving through air, then as one air particle is displaced from its equilibrium position, it exerts a push or pull on its nearest neighbors, causing them to be displaced from their equilibrium position. Sound is a mechanical wave
6. Since a sound wave is a disturbance that is transported through a medium via the mechanism of particle-to-particle interaction, a sound wave is characterized as a mechanical wave.
7. A sound wave is different than a light wave in that a sound wave is a. produced by a vibrating object and a light wave is not. b. not capable of traveling through a vacuum. c. not capable of diffracting and a light wave is. d. capable of existing with a variety of frequencies and a light wave has a single frequency. Check your understanding:
8. --When a tuning fork vibrates, it creates areas of high pressure (compressions) and low pressure (rarefactions). --As the tines of the fork vibrate back and forth, they push on neighboring air particles. --The forward motion of a tine pushes air molecules horizontally to the right and the backward retraction of the tine creates a low-pressure area allowing the air particles to move back to the left.
9. Graphing a Sound Wave. Sound as a pressure wave The variation of pressure with distance is a useful way to represent a sound wave graphically. But remember – sound is actually a longitudinal wave.
10. A sound wave is a pressure wave; regions of high pressure (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. These compressions and rarefactions result because sound a. is more dense than air and thus has more inertia. b. waves have a speed that is dependent only upon the properties of the medium. c. can be diffracted around obstacles. d. vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations. Check your understanding
11. --The vibrating object that creates sound could be the vocal cords of a person, the vibrating string of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker. --As a sound wave moves through a medium, each particle of the medium vibrates at the same frequency. This makes sense since each particle vibrates due to the motion of its nearest neighbor. --And of course the frequency at which each particle vibrates is the same as the frequency of the original source of the sound wave. Frequency of Sound
12. A guitar string vibrating at 500 Hz will set the air particles in the room vibrating at the same frequency of 500 Hz, which carries a sound signal to the ear of a listener, which is detected as a 500 Hz sound wave. Frequency of Sound Example
13. • 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. The frequency of sound
14. Frequency of Sound • The human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20 000 Hz. • Any sound with a frequency below the audible range of hearing (i.e., less than 20 Hz) is known as an infrasound. • Any sound with a frequency above the audible range of hearing (i.e., more than 20 000 Hz) is known as an ultrasound.
15. Animation showing Frequency and Pitch
16. Ultrasound?  Ultrasound is a medical imaging technique that uses high frequency sound waves and their echoes.  The technique is similar to the echolocation used by bats, whales and dolphins.
17. How it works: Ultrasound  The ultrasound machine transmits high- frequency (1 to 5 megahertz) sound pulses into your body using a probe.  The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone).  Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected.
18.  The reflected waves are picked up by the probe and relayed to the machine.  The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue and the time of the each echo's return (usually on the order of millionths of a second).  The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.
19. What about animals? Dogs can detect frequencies as low as approximately 50 Hz and as high as 45 000 Hz. Cats can detect frequencies as low as approximately 45 Hz and as high as 85 000 Hz.
20. Frequency and music Certain sound waves when played (and heard) simultaneously will produce a particularly pleasant sensation when heard. Such sound waves form the basis of intervals in music. For example, any two sounds whose frequencies make a 2:1 ratio are said to be separated by an octave and result in a particularly pleasing sensation when heard. That is, two sound waves sound good when played together if one sound has twice the frequency of the other.
21. Loudness
22. Intensity Intensity: the rate at which a wave’s energy flows through an area Sound intensity depends on Amplitude Distance from source Measured in decibels (dB)
23. Loudness is sort of like intensity, but… Loudness is Subjective! (This means it depends on the person who is hearing it.) Loudness is a personal, physical response to the intensity of sound. As intensity increases, so does loudness, but loudness also depends on the listener’s ears and brain.
24. Intensity is caused by the Amplitude of the vibration Example: A vibrating guitar string forces surrounding air molecules to be compressed and expanded. The energy that is carried by the wave is imparted to the medium by the vibrating string. The amount of energy that is transferred to the medium is dependent on the amplitude of vibrations of the guitar string. If more energy is put into the plucking of the string, then the string vibrates with a greater amplitude. The greater amplitude of vibration of the guitar string thus imparts more energy to the medium, causing air particles to be displaced a greater distance from their rest position.
25. The Decibel Scale: The decibel (abbreviated dB) is the unit used to measure the intensity of a sound. The decibel scale is a little odd because the human ear is incredibly sensitive.
26. Your ears can hear everything from your fingertip brushing lightly over your skin to a loud jet engine . In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smallest audible sound. That's a big difference!
27. On the decibel scale, the smallest audible sound (the threshold of hearing) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB A sound 1,000 times more powerful than near total silence is 30 dB.
28. Intensity (Loudness) is measured in decibels: Source Intensity Level # of Times Greater Than TOH Threshold of Hearing 0 dB 100 Rustling Leaves 10 dB 101 Whisper 20 dB 102 Normal Conversation 60 dB 106 Busy Street Traffic 70 dB 107 Vacuum Cleaner 80 dB 108 Large Orchestra 98 dB 109.8 Walkman at Maximum Level 100 dB 1010 Front Rows of Rock Concert 110 dB 1011 Threshold of Pain 130 dB 1013 Military Jet Takeoff 140 dB 1014 Instant Perforation of Eardrum 160 dB 1016
29. Check your understanding A mosquito's buzz is often rated with a decibel rating of 40 dB. Normal conversation is often rated at 60 dB. How many times more intense is normal conversation compared to a mosquito's buzz?
30. The speed of sound depends only on the properties of the medium it’s travelling through. The Speed of Sound
31. In general, sound travels fastest through solids. This is because molecules in a solid medium are much closer together than those in a liquid or gas, allowing sound waves to travel more quickly through it. In fact, sound waves travel over 17 times faster through steel than through air. Speed of Sound
32. Sound also travels faster in liquids than in gases because molecules are still more tightly packed. In fresh water, sound waves travel 4 times faster than in air! Speed of Sound
33. 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). The speed of sound
34. The speed of sound through a gas depends on the temperature.
35. When we look at the properties of a gas, we see that only when molecules collide with each other can the compressions and rarefactions of a sound wave be passed along. So, it makes sense that the speed of sound depends on how often the particles collide. At higher temperatures, molecules collide more often, giving the sound wave more chances to move forward rapidly. Speed of Sound
36. What characteristic of a sound wave determines the pitch of the sound? Review Question:
37. The frequency or frequencies at which an object tends to vibrate with when hit, struck, plucked, strummed or somehow disturbed is known as the natural frequency of the object. Natural Frequency
38. Some objects tend to vibrate at a single frequency and they are often said to produce a pure tone. A flute tends to vibrate at a single frequency, producing a very pure tone. Other objects vibrate and produce more complex waves with a set of frequencies that have a whole number mathematical relationship between them; these are said to produce a rich sound. A tuba tends to vibrate at a set of frequencies that are mathematically related by whole number ratios; it produces a rich tone. Natural Frequency
39. Other objects will vibrate at a set of multiple frequencies that have no simple mathematical relationship between them. These objects are not musical at all and the sounds that they create could be described as noise. Natural Frequency
40. Natural Frequency
41. The same note from different instruments has different qualities because the sounds from instruments are rarely pure notes, i.e. of one frequency. Rather they consist of one main note which is predominant and other smaller notes called overtones. Harmonics
42. Compare the same note played on a flute and a violin Harmonics
43. The main note or fundamental note is also referred to as the first harmonic and if it has a frequency f, the overtone with frequency 2f is called the second harmonic and the overtone with frequency 3f is called the third harmonic and so on. The sum of all the harmonics is the waveform and determines the quality of the sound. Harmonics
44. The same note sounds different when played on different instruments because the sound from an instrument is usually not a single pure frequency. The variation comes from the harmonics, multiples of the fundamental note. A C note played on a piano and played on a guitar: Harmonics and instruments
45. Standing Waves  Caused by the interference of two identical waves (or a wave and its reflected wave) travelling in opposite directions in a medium.  Wave pattern of alternating nodes and antinodes.  Nodes - areas of no displacement of the medium caused by destructive interference  Antinodes - areas of maximum displacement of the medium caused by constructive interference. node Antinode Note: One wavelength (shown in the diagram) is equal to twice the distance between nodes.
46. Harmonics and Overtones 1st harmonic = fundamental frequency 2nd harmonic = 1st overtone 3rd harmonic = 2nd overtone 4th harmonic = 3rd overtone and so on...
47. Sound Interference – Interference of sound waves produce BEATS Sound Interference – Interference of sound waves produce BEATS
48. The Doppler effect is a phenomenon observed whenever the source of waves is moving with respect to an observer. The Doppler effect is an apparent upward shift in frequency for the observer when the source is approaching, and an apparent downward shift in frequency when the source is receding. The Doppler Effect
49. Let's listen.... One more... The Doppler Effect
50. The Doppler Effect on The Big Bang Theory The Doppler Effect
51. As a car approached with its siren blasting, the pitch of the siren sound (a measure of the siren's frequency) was high; and then suddenly after the car passed by, the pitch of the siren sound was low. That was the Doppler effect - a shift in the apparent frequency for a sound wave produced by a moving source.
52. The source of sound always emits the same frequency. Therefore, for the same period of time, the same number of waves must fit between the source and the observer. If the distance is large, then the waves can be spread apart; but if the distance is small, the waves must be compressed into the smaller distance. For these reasons, if the source is moving towards the observer, the observer perceives sound waves reaching him or her at a more frequent rate (high pitch). And if the source is moving away from the observer, the observer perceives sound waves reaching him or her at a less frequent rate (low pitch). It is important to note that the effect does not result because of an actual change in the frequency of the source. The Doppler Effect
53. For the Doppler Effect to occur, the source may be moving, the listener may be moving, or both may be moving. Important Note
54. Sound wave Behavior: Reflection
55. Sound wave Behavior: Reflection An echo is a reflected sound wave.
56. Builders of auditoriums and concert halls avoid the use of hard, smooth materials in the construction of their halls. With a hard material such as concrete, most of the sound wave is reflected by the walls and little is absorbed. Walls and ceilings of concert halls are made softer materials such as fiberglass and acoustic tiles. These materials have a greater ability to absorb sound. This gives the room more pleasing acoustic properties. Reflection of Sound
57. You’re standing at the bottom of a canyon, and wondering how far away the other side is. To figure out the distance across the canyon, you could yell, and clock the time until you heard your echo. Let's say this took exactly 3.0 seconds. Since you took physics, you know that sound travels at about 0.2 miles per second. How far away is the other wall of the canyon? Reflection can also cause test questions:
58. What is sonar?  A system that uses reflected waves to determine the distance & location of objects.  Uses the d=v/t formula  d = distance  V= wave speed  t = time it takes for wave to reflected off object
59. SONAR High- frequency ultrasonic waves that are use in a system called Sound Navigation And Ranging Ships send sound waves into water that travels in a straight line until it hits an object, the wave is then reflected back to the ship, the time it takes to travel back and forth is measured and used to calculate the distance traveled.
60. A ship on the surface of the water sends a SONAR signal, and it bounces off a submarine in the water. Calculate the distance of the submarine from the ship if the signal is returned in 4.0 seconds. (The speed of sound in water is 1450 meters/sec). Reflection
61. Sound Wave Behavior: Diffraction Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.
62. Diffraction: Light vs Sound Imagine going to a baseball game, and you discover that your seat is directly behind a wide post. You cannot see the game, of course, because the light waves from the field are blocked. But you have little trouble hearing the game, since sound waves simply diffract around the post.
63. Sound Wave Behavior: Diffraction The reason for the difference—that is, why sound diffraction is more pronounced than light diffraction—is that sound waves are much, much larger than light waves. The amount of diffraction increases with increasing wavelength and decreases with decreasing wavelength.
64. Why do sound waves diffract more than light waves? Future test question:
65. If you were to take a guitar string and stretch it to a given length and a given tightness and have a friend pluck it, you would hear a noise; but the noise would not even be close in comparison to the loudness produced by an actual guitar. If the string is attached to the sound box of the guitar, the vibrating string is capable of forcing the sound box into vibrating at that same natural frequency. Forced Vibration
66. The sound box in turn forces air particles inside the box into vibrational motion at the same natural frequency as the string. The entire system (string, guitar, and enclosed air) begins vibrating and forces surrounding air particles into vibrational motion. The tendency of one object to force another adjoining object into vibrational motion is referred to as a forced vibration. This causes an increase in the amplitude and thus loudness of the sound.
67. • Be careful though! • Forced vibration is not the same thing as resonance. • Resonance occurs when something starts vibrating because of another vibrating object that isn’t touching it! Resonance
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