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Acoustic, Sound and Noise Control

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Acoustic, Sound and Noise Control

  1. 1. Acoustics is a branch of physics that study the sound, acoustics concerned with the production, control, transmission, reception, and effects of sound. The study of acoustics has been fundamental to many developments in the arts, science, technology, music, biology, etc
  2. 2. División of acoustics. Aero acoustics Architectural acoustics Bioacoustics Biomedical acoustics Environment noise Psychoacoustics Physiological acoustics Physical acoustics Speech communication Structural acoustics Transduction Musical acoustics Underwater acoustics Nonlinear acoustics
  3. 3. Sound • Sound is reflected, transmitted, or absorbed by the materials it encounters. • Soft surfaces, such as textiles, and bat insulation, tend to absorb sound waves, preventing them from further motion. • Hard surfaces, such as ceramic tile, gypsum board, or wood, tend to reflect sound waves, causing „echo‟. Reverberation is the term used to describe sound waves that are reflected off of surfaces. • Dense, massive, materials, such as concrete or brick, tend to transmit sound waves through the material. • High frequency sound waves (think of a high whistle) are not capable of being transmitted through massive, heavy, material. • Low frequency sound waves (bass) are transmitted through massive materials.
  4. 4. The human ear is capable of hearing sounds within a limited range.
  5. 5. Animals have varied hearing ranges
  6. 6. Hearing range of some animals
  7. 7. Hearing range of some animals • Many animals hear a much wider range of frequencies than human beings do. • For example, dog whistles vibrate at a higher frequency than the human ear can detect, while evidence suggests that dolphins and whales communicate at frequencies beyond human hearing (ultrasound). • Frequency is measured in hertz, or the number of sound waves a vibrating object gives off per second. The more the object vibrates, the higher the frequency and the higher the pitch of the resulting sound.
  8. 8. Decibel levels • 0 The softest sound a person can hear with normal hearing • 10 normal breathing • 20 whispering at 5 feet • 30 soft whisper • 50 rainfall • 60 normal conversation • 110 shouting in ear • 120 thunder
  9. 9. Decibel levels • The human ear's response to sound level is roughly logarithmic (based on powers of 10), and the dB scale reflects that fact. • • An increase of 3dB doubles the sound intensity but a 10dB increase is required before a sound is perceived to be twice as loud. • Therefore a small increase in decibels represents a large increase in intensity. • For example - 10dB is 10 times more intense than 1dB, while 20dB is 100 times more intense than 1dB. • The sound intensity multiplies by 10 with every 10dB increase.
  10. 10. Decibel levels • 130dB - Jack Hammer (at 5ft)
 • 120dB - Rock Concert / Pain threshold
 • 110dB - Riveter or a Heavy Truck at 50ft
 • 90dB - Heavy Traffic (at 5ft)
 • 70dB - Department Store or a Noisy Office
 • 50dB - Light Traffic
 • 30dB - Quiet Auditorium
 • 20dB - Faint Whisper (at 5ft)
 • 10dB - Soundproof room / anechoic chamber
  11. 11. An anechoic chamber is a space in which there are no echoes or reverberations. The surfaces absorb all sound, and reflect none.
  12. 12. Acoustics: sound • Sound is a mechanical wave and therefore requires a medium in which it can travel. • Acoustics is classically divided into sound and vibration. • Sound refers to waveforms traveling through a fluid medium such as air • Vibration describes energy transmitted through denser materials such as wood, steel, stone, dirt, drywall or anything besides a fluid. • It is not heard as much as felt, due to its extremely low frequency, which is below the range of most human hearing.
  13. 13. The speed of sound versus the speed of light • sound travels at 1130 feet per second at normal room temperature. • light travels at 299,792,458 meters per second, which is roughly 974,325,489 feet per second (974 million feet per second!!)
  14. 14. Sound Waves: amplitude & frequency (cycles)
  15. 15. Radio signals: am & fm
  16. 16. Radio signals: am & fm • „am‟ means: amplitude modulation: the height of each wave changes • „fm‟ means: frequency modulation: the length of each wave changes • FM signals have a great advantage over AM signals. • Both signals are susceptible to slight changes in amplitude. • With an AM broadcast, these changes result in static. With an FM broadcast, slight changes in amplitude don't matter -- since the audio signal is conveyed through changes in frequency, the FM receiver can just ignore changes in amplitude. The result: no static at all.
  17. 17. Bonded acoustical cotton; recycled cotton, class A non flammable Melamine Foam Acoustical Panels: fiber free, Class A fire retardant
  18. 18. Fabric wrapped panels provide good acoustical absorption
  19. 19. Reverberation Time • Reverberation time refers to the amount of time required for the sound field in a space to decay 60dB, or to one millionth of the original power. • In simple terms this refers to the amount of time it takes for sound energy to bounce around a room before being absorbed by the materials and air
  20. 20. Reverberation Time • Reverberation time is important because it can affect how well you understand speech, and it can change the way music sounds. • The effect on speech intelligibility is noticeable in a gymnasium or arena, where you often can't understand someone who is only 10 or 15 feet away from you
  21. 21. Useful Reflections • Reflections are an important part of acoustical design for music performance venues. • For effective musical acoustics, the reflections have to arrive within the correct time window, and from the correct direction.
  22. 22. Useful Reflections • The reflections help to boost the level of acoustic instruments and human voices in the audience area. • They also influence timbre and help define the apparent size or perspective of the instruments. • The critical time interval we're talking about is a very brief 0.3 seconds
  23. 23. Useful Reflections • A properly designed acoustical environment provides a good listening experience for the audience by enhancing the performance or presentation. • Even and natural sound coverage, freedom from intruding noise and a sense of presence from the performer or presenter are all-important aspects of "good acoustics.“ • Acoustics should be considered very early in the design process and the aesthetic concept developed in accordance with those requirements
  24. 24. 'Stradia': a sound simulation program
  25. 25. Concert halls demand very careful acoustical analysis
  26. 26. Acoustical Characteristics 1. Liveness 2. Intimacy 3. Fullness 4. Clarity 5. Warmth 6. Brilliance 7. Texture 8. Blend 9. Ensemble
  27. 27. Liveness Measure of reverberation time
  28. 28. Fullness vs. Clarity Refers to the amount of reflected sound relative to the amount of direct sound
  29. 29. Warmth vs. Brilliance Warmth increases with increasing TR for low frequencies
  30. 30. Texture “Good texture” when at least five reflections arrive within 60ms of direct sound
  31. 31. Blend and Ensemble Ability to hear the entire performing group on the stage (ensemble) and in the audience (blend)
  32. 32. Acoustical Design Problems 1. Focusing of sound 2. Echoes 3. Shadows 4. Resonances 5. External noise 6. Double-valued TR
  33. 33. Focusing of Sound Occurs with use of parabolic surfaces either behind performers or at rear of auditorium
  34. 34. Echoes Highly reflective flat or parabolic wall shapes Flutter echoes from parallel walls Standing waves between parallel walls
  35. 35. Resonances Parallel walls Rectangular practice rooms Singing in the shower
  36. 36. External noise Box within a box construction Practice rooms and concert halls in adjacent areas
  37. 37. Double-valued TR Playback room with reverberation Concert halls with side areas
  38. 38. Architectural acoustics is the science of controlling sound in buildings. Embraces all aspects of acoustical design for all types of architectural spaces, in order to optimize environments for many functions, including business, recreation, learning, worship, communication, broadcasting and entertainment. The first application of architectural acoustics was in the design of : •Opera houses •Concert halls •Auditoriums •Radio and television studios •Classrooms, etc.
  39. 39. Aula Magna (UCV) Sydney Opera House
  40. 40. Aula Magna, in “Universidad Central de Venezuela” it was design by Carlos Raul Villanueva In the 80´s this concert hall was catalogued like one of the 5 rooms with better acoustics of the world.
  41. 41. All the details, materials, forms, elements and the design were choose for create a good acustical in the space. For this, Villanueva asked help from some Acustical consultans: “Bolt, Beranek and Newman Inc”. The selection of types of wood, the model of the armchairs and services were carefully chosen.
  42. 42. Even the fabric of the carpet (casimire) was selected to contribute with the acusticals properties. The tapestry in Aula Magna has absorption capacity, when the room is empty does not distort the sound. The material of the doors, and some elements ubicated in the hall are design to prevent the echo and noise.
  43. 43. The distinguished element of this famous hall, are their clouds also called flying subjects. This elements were not in the original design, but structure of the hall didn´t For that reason, allow a good acoutic. Villanueva asked help from Alexander Calder who was the designer of this clouds. The clouds moved to adapt to the acoustical requirement, then were fixed in
  44. 44. Building Acoustics: Room for Music “the most visible and interesting spaces in architectural acoustics” -It is here that the science of acoustics and the arts of architecture and music are blended
  45. 45. Building Acoustics: Room for Music - The acoustician can only work indirectly with the room surfaces that reflect, diffuse, or absorb the primal energy
  46. 46. Building Acoustics: Room for Music *Concert halls are rooms designed specifically for music in which the musicians and the audience occupy the same space. *In good concert halls the number of seats ranges from 1700 to 2600, with the best halls averaging around 1850. *Above 2600 seats, the chances of success are much reduced and the preferred capacity is between 1750 and 2200.
  47. 47. Building Acoustics: Room for Music There is no division between the stage and the audience in a concert hall. The orchestra is positioned on a raised platform, sometimes with an organ and choir seating behind it. To attain long reverberation times, the ceilings of concert halls are high, 15m(50 ft) or more, and diffusive, with coffered patterns having deep (15 cm or 6 in) fissures. Side walls are adorned with columns, caryatids, statuary, and convex shapes that help diffuse the reflected energy.
  48. 48. Building Acoustics: Room for Music An opera house is a mix of a legitimate theatre and a concert hall, which constrains the design more than a pure concert hall. In opera, the stage performance rather than the orchestra is the main attraction The orchestra is seated in a pit below the stage to balance the level between the singer and the orchestra. The conductor, who must be visible to both the orchestra and the vocalists, stands with his head just at stage level. Open pits, where the orchestra is open to the audience with minimal stage overhang, give the best results in large rooms
  49. 49. Building Acoustics: Room for Music GENERAL DESIGN PARAMETERS The audience should feel enveloped or surrounded by the sound Sound must have adequate loudness that is evenly distributed throughout the hall. Noise from exterior sources and mechanical equipment must be controlled so that the quietest instrumental sound can be heard
  50. 50. Building Acoustics: Room for Music Hall Shape
  51. 51. Building Acoustics: Room for Music Heavy plaster is the most commonly encountered wall and ceiling material Plaster may also be applied directly onto grouted concrete block or concrete When wood is used it should be heavy, at least 1” (25 mm) thick, and be backed with a solid masonry or concrete. Wood can be glued directly to concrete block or concrete walls or applied on furring strips Floors are constructed of concrete or wood on concrete
  52. 52. Auditorium Design
  53. 53. General Design Considerations 1. Visual 2. Ventilation 3. Acoustical a. seating b. stage c. room shape d. room walls
  54. 54. Control of TR TR = 0.050 V / A Where: TR = reverberation time in second V = room volume in cubic feet A = total room absorption in sabins
  55. 55. TR Calculation A = a1A1 + a2A2 + a3A3 + a4A4 + … An is one section of absorbent area an is absorption coefficient TR = 0.050 V/A
  56. 56. Some Absorption Coefficients Frequency (Hz) Material 125 250 500 1000 2000 4000 Concrete/brick 0.01 0.01 0.02 0.02 0.02 0.03 Glass 0.19 0.08 0.06 0.04 0.03 0.02 Plasterboard 0.20 0.15 0.10 0.08 0.04 0.02 Plywood 0.45 0.25 0.13 0.11 0.10 0.09 Carpet 0.10 0.20 0.30 0.35 0.50 0.60 Curtains 0.05 0.12 0.25 0.35 0.40 0.45 Acoustical board 0.25 0.45 0.80 0.90 0.90 0.90
  57. 57. Absorptions (in sabins) Frequency (Hz) Material 125 250 500 1000 2000 Unupholstered seat 0.15 0.22 0.25 0.28 0.50 Upholstered seat 3.0 3.1 3.1 3.2 3.4 Adult person 2.5 3.5 4.2 4.6 5.0 Adult/upholstered seat 3.0 3.8 4.5 5.0 5.2
  58. 58. Dekelbaum Concert Hall at the U MD Smith Center
  59. 59. Dekelbaum Concert Hall (front)
  60. 60. Dekelbaum Concert Hall (rear)
  61. 61. Microphone configuration in concert hall
  62. 62. Loudspeaker configuration in home listening rooms
  64. 64. The nature of sound Sound, a manifestation of vibration, travels in wave patterns through solids, liquids and gases. The waves, caused by vibration of the molecules, follow sine functions, typified by the amplitude and wavelength (or frequency) Sound waves of equal amplitude with increasing frequency from top to bottom
  65. 65. Sound propagation
  66. 66. Amplitude and wavelength (period)
  67. 67. Bels and decibels
  68. 68. Sound power and intensity
  69. 69. Sound pressure level
  70. 70. Sound pressure for known sounds
  71. 71. How sound is measured •Pressure, P, usually Pascals •Frequency, f, usually Hertz P = 1/f •Intensity, I, usually W/m2 I = W/A •Bels, L’, derived from logarithmic ratio L’ = log (Q/Qo) •Decibels, L, derived from bels L = 10*log (Q/Qo) E.g. Implications of the decibel scale: doubling sound level would mean that the sound will increase by 10*log2 = +3dB Ten times the sound level = 10*log10 = +10dB
  72. 72. Exposure to high sound levels
  73. 73. Reflecting on noise  “Noise" derived from "nausea," meaning seasickness  Noise is among the most pervasive pollutants today  Noise is unavoidable for many machines  We experience noise in a number of ways environmental cause and victim generated by others “second-hand”  Noise negatively affects human health and well-being  The air into which second-hand noise is emitted and on which it travels is a "commons“, a public good
  74. 74. Noise regulation Noise regulation includes statutes or guidelines relating to sound transmission established by national, state or provincial and municipal levels of government. After a watershed passage of the U.S. Noise Control Act of 1972[1], the program was abandoned at the federal level, under President Ronald Reagan, in 1981 and the issue was left to local and state governments. Although the UK and Japan enacted national laws in 1960 and 1967 respectively, these laws were not at all comprehensive or fully enforceable as to address (a) generally rising ambient noise (b) enforceable numerical source limits on aircraft and motor vehicles or (c) comprehensive directives to local government.
  75. 75. Local noise regulation  Dr. Paul Herman wrote the first comprehensive noise codes in 1975 for Portland, Oregon with funding from the EPA (Environmental Protection Agency) and HUD (Housing and Urban Development). The Portland Noise Code became the basis for most other ordinances for major U.S. and Canadian metropolitan regions.[18]  Most city ordinances prohibit sound above a threshold intensity from trespassing over property line at night, typically between 10 p.m. and 6 a.m., and during the day restricts it to a higher sound level; however, enforcement is uneven. Many municipalities do not follow up on complaints. Even where a municipality has an enforcement office, it may only be willing to issue warnings, since taking offenders to court is expensive.  The notable exception to this rule is the City of Portland Oregon which has instituted an aggressive protection for its citizens with fines reaching as high at $5000 per infraction, with the ability to cite a responsible noise violator multiple times in a single day.  Many conflicts over noise pollution are handled by negotiation between the emitter and the receiver. Escalation procedures vary by country, and may include action in conjunction with local authorities, in particular the police. Noise pollution often persists because only five to ten percent of people affected by noise will lodge a formal complaint. Many people are not aware of their legal right to quiet and do not know how to register a complaint
  76. 76. Aircraft noise FA-18 Hornet breaking sound barrier
  77. 77.  Adding noise sources and subtracting background noise 10 log 2 = 3 dB
  78. 78. Chart method – adding decibels
  79. 79. Chart method – subtracting background noise
  80. 80. Power ratio and dB http://www.phys.unsw.edu. au/jw/dB.html
  81. 81. Sound and human hearing People generally hear sounds between the “threshold of hearing” and the “threshold of pain” In terms of pressure, this is 20 μPa – 100 Pa The decibel scale was developed from this fact and makes numbers more manageable The decibel scale generally ranges from approximately 0 to 130
  82. 82. How Sound is Heard
  83. 83. Human hearing and Frequency 0 16 Hz 20 kHz 5 MHz
  84. 84. Sound and human hearing – Frequency Humans are less sensitive to low frequency sound and more sensitive to high frequency sound. Therefore, sometimes the dB scale is adjusted to take this into account: A-weighting (db(A)): adjusts overall scale so it better matches what the human ear would hear C-weighting (dB(C)): adjusts scale for loud or low frequency sounds B-weighting (dB(B)): adjusts by factors that are “in between” the A-weighted factors and C- weighted factors (rarely used)
  85. 85. The filters used for dBA and dBC The most widely used sound level filter is the A scale, which roughly corresponds to the inverse of the 40 dB (at 1 kHz) equal-loudness curve. The sound level meter is thus less sensitive to very high and very low frequencies. Measurements made on this scale are expressed as dBA. The C scale (in dBC) is practically linear over several octaves and is thus suitable for subjective measurements only for very high sound levels.
  86. 86. Loudness in phons The phon is related to dB by the psychophysically measured frequency response. Phons = dB at 1 kHz. For other frequencies, the phon scale is determined by loudness experience by humans.
  87. 87. Loudness in sones The sone is derived from psychophysical tests where humans judge sounds to be twice as loud. This relates perceived loudness to phons. A sone is 40 phons. A 10 dB increase in sound level corresponds to a perceived doubling of loudness. So that approximation is used in the definition of the phon: 0.5 sone = 30 phon, 1 sone = 40 phon, 2 sone = 50 phon, 4 sone = 60 phon, etc.
  88. 88. Other descriptors of sound Equivalent sound level – the level of sound that has the same acoustical energy as does a time-varying sound over a stated time period. Percentile sound level – the sound level exceeded “n” percent of the observation time interval. Day-night average sound level – the equivalent sound level for a 24-h period that incorporates a decibel penalty during night hours.
  89. 89. Typical suburban sound and their levels
  90. 90. Major transportation sources of noise pollution: rail, road, and air
  91. 91. Rail Noise: A Case Study The city of Ames, Iowa, began operation of three automated horn warning systems (AHS) in September of 1998. These systems were installed after nearby residents repeatedly expressed concerns over the disturbance created by the loud train horns. The automated horn system provides a similar audible warning to motorists and pedestrians by using two stationary horns mounted at the crossing. Each horn directs its sound toward the approaching roadway. The horn system is activated using the same track signal circuitry as the gate arms and bells located at the crossing.
  92. 92. Train Horn Noise Reduction Sound Level Train Horn AHS Horn Reduction (dBA) Area (acres) Area (acres) > 70 265 37 86% > 80 171 5 97% > 90 31 <1 98%
  93. 93. Intersection of 70 dBA railroad with North Dakota Avenue: A graphical depiction 80 dBA of the reduction 90 dBA Before 70 dBA 80 dBA 90 dBA After
  94. 94. Ames Train Horn Noise Survey
  95. 95. Roadway Noise • An example of a “line source” of noise pollution (as opposed to a “point source”) • Level of noise is a function of volume, type of vehicle, and speed
  96. 96. Roadway Noise - Solutions • Regulations limit the amount of noise some vehicles can produce • Some regulations require vehicles to be properly operated and maintained • Despite regulations, the noise levels are usually only reduced by 5 to 10 dBA
  97. 97. Roadway Noise - Solutions Barriers •Buffer zones •Earth berms/wooden fences/concrete walls •Vegetation (if dense enough)
  98. 98. Aesthetic noise barrier: Highway in Melbourne, Australia
  99. 99. Roadway Noise - Solutions Pavement type Certain asphalts, such as those containing rubber or stone, can be less noisy than other pavements. However, some studies have shown the reduction in noise is only a few decibels, not enough to be significant. More research is needed before pavement type can be an effective noise-reducing technique
  100. 100. Airport Noise Noise contours around an airport calculated using INM (Integrated Noise Modeling) based on previous noise measurements 55 - 60 dB = Light blue 60 - 70 dB = Dark blue 70 - 75 dB = Red 75 - 80 dB = Green 80 - 85 dB = Yellow > 85 dB = Pink
  101. 101. Airport Noise
  102. 102. Other sources of noise pollution that need to be addressed • Boat noise, especially jet skis • Construction noise • Snow mobiles • Industry