THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

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368 14. Machinery Noise ControlTable 14.4. Different Type of Plumbing Noises. Their Means of Generation, andAnnoyance Potentials (from Harries, 1991, Ch. 44).Plumbing SystemComponent/Equipment Generation Mechanism Potential AnnoyancePiping runsCouplings Turbulence MinimalElbows Turbulence MinimalTees Turbulence MinimalFixturesBar sink Cavitation/turbulence/splash/waste flow MinimalBath tub Cavitation/turbulence/splash/waste flow Very significantBidet Cavitation/turbulence/splash/waste flow NominalFlushometer Cavitation/turbulence SignificantHose pipe valves Cavitation/turbulence NominalLaundry tubs Cavitation/turbulence/splash/waste flow NominalPressure regulator Cavitation/turbulence NominalShower Cavitation/turbulence/splash/waste flow Very significantSink Cavitation/turbulence/waste flow SignificantValves Cavitation/turbulence SignificantWater closet, tank stool Cavitation/turbulence/splash/waste flow Very significantUrinal Cavitation/turbulence/splash/waste flow NominalAppliancesDishwasher Vibration/cavitation/spray/water hammer Very significantDrinking fountain Cavitation/turbulence MinimalWashing machine Vibration/cavitation/impact/motor/ Very significantwater hammerWaste disposal Vibration/waste flow Very significantWater heater Cavitation/turbulence MinimalSupply and waste pumpsBooster Rotational flow/cavitation/motor SignificantRecirculation Rotational flow/cavitation/motor NormalSewage Rotational flow/cavitation/motor SignificantSump Rotational flow/cavitation/motor Significantand fixtures of the plumbing system. A potentially great cause of noise is cavitation,which is the formation and subsequent collapse of cavities (bubbles) within theflow of water through and past a restriction in the flow. For cavitation to occur,a localized restriction or a projection must exist within the piping system, whichensues in localized high velocities and low pressures. The formation and suddencollapse of these bubbles result in extreme local pressure fluctuations, which canbe detected as noise. Other water noises occur from splashing (i.e., impact of liquidstriking a surface) and waste water flow (i.e., flow into drainpipes).Much more serious is the sharp intense noise known as water hammer. It occurswhen a steady flow in a liquid flow system is suddenly interrupted, for example, bya quick-action valve. When the fluid is in motion throughout a piping system, evenat relatively low velocities, the momentum from this sudden interruption can bequite large. The sudden interruption of the flow creates an extremely sharp pressure
14.6 Pumps and Plumbing Systems 369rise that propagates as a shock wave upstream from the interrupting valve. Thesteep wavefront can be reflected numerous times back and forth throughout thevarious parts of the piping system until the energy is finally dissipated.Noise control factors which must be dealt with in order to effect noise controlinclude (a) water flow and piping characteristics, (b) radiation of sound to thebuilding structure, (c) selection and mounting of fixtures, (d) isolation of pumpsystems, and (e) water hammer noise control.Water pressure in a plumbing system influences the flow noise caused by piperuns and water supply valves. According to typical building codes, water pressureshould be maintained at least at 100 kPa (15 psi) but not more than 500 kPa (80 psi).For acceptable system performance, the supply pressure should be somewherebetween 230 and 370 kPa (35 and 55 psi), with a preference toward the lowerrange in order to minimize noise. Flow noise radiation from pipes can be lessenedby minimizing the number of pipe transitions (elbows, tees, y-connections, andthe like). This reduces the opportunity for the onset of turbulence and cavitation.Larger pipes are used in building design when noise control is given a higherpriority. In the U.S. 1 / 2 -inch diameter piping is generally used in domestic plumbingsystems but can be as high as 3 / 4 -inch diameter to cut down on noise by as muchas 3–5 dB.Noise resulting from water flow in pipes may be transmitted to the rooms throughwhich they pass, particularly if they are in direct contact with large radiation surfacessuch as walls, ceilings, and floors. Isolation of these pipes from the buildingstructure provides significant noise reduction. If the pipes are mounted with foamisolators, instead of being rigidly attached to the building structure, a considerablenoise reduction of 10–12 dB may be obtained. Whenever piping passes through astructure (block, stud, joist, or plate) or is in contact with a wall or masonry, resilientmaterials such as neoprene or fiberglass should be used to provide isolation.It is vital to seal with a resilient caulking around the perimeter of all pipes, faucets,and spouts that penetrate through floors, walls, and shower stalls.The impact of water hammer can rupture piping; thus, it will spring leaks, causeweakening of connections and produce damage to valves. Water-hammer pulsingassociated with the use of washing machines and dishwashers can be partiallydamped by connecting these machines to the water supply with extra-long flexiblehose. Figure 14.6 shows a schematic of a capped pipe that incorporates an airchamber for water-hammer suppression. The length of the pipe ranges from 30 to60 cm and may be of the same or larger diameter than the line it serves. The volumeof the air chamber, which serves as an air cushion, depends on the nominal pipediameter, the branch line length, and the supply pressure. But if the air chamberbecomes filled with water, it becomes ineffective. A petcock is provided alongwith a shut-off valve, so that the chamber may be drained of water and vented,thereby reactivating the unit.There are commercial devices, called water-hammer arresters, which are notsubject to the limitation of capped pipes, because a metal diaphragm separatesthe water from the air. These devices are best placed near quick-acting valves andshould also be installed at the termini of long pipe runs.
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THE SCIENCE ANDAPPLICATIONS OFACOUS
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xPrefaceReferencesBacon, Sir Franci
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xiiContents16. Ultrasonics 44317. C
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2 1. A Capsule History of Acoustics
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1. A Capsule History of Acoustics 5
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12 1. A Capsule History of Acoustic
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14 2. Fundamentals of AcousticsFigu
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16 2. Fundamentals of Acoustics2.2
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18 2. Fundamentals of Acousticsof t
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20 2. Fundamentals of AcousticsQ z+
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22 2. Fundamentals of Acousticsin t
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24 2. Fundamentals of AcousticsWe c
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26 2. Fundamentals of Acoustics(2)
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28 2. Fundamentals of AcousticsEqua
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30 2. Fundamentals of Acoustics11.
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32 3. Sound Wave Propagation and Ch
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3.14 Performance Indices for Enviro
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3.14 Performance Indices for Enviro
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or in terms of complex exponential
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3.17 Sound Intensity 61Here the sur
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3.18 The Monopole Source 63The thre
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3.21 Energy Density 653.20 The Hemi
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References 67medium. The time avera
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Problems for Chapter 3 69(a) the wa
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4Vibrating Strings4.1 IntroductionI
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4.4 General Solution of the Wave Eq
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4.6 Simple Harmonic Solutions of th
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4.7 Standing Waves 77Figure 4.3. Di
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4.8 The Effect of Initial Condition
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4.10 Forced Vibrations in an Infini
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4.11 Strings of Finite Lengths: For
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References 854.12 Real Strings: Fre
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Problems for Chapter 4 878. A devic
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90 5. Vibrating BarsFigure 5.1. A b
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92 5. Vibrating BarsSettingc 2 = E/
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94 5. Vibrating BarsThe allowable f
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96 5. Vibrating Barsthe acceleratio
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98 5. Vibrating BarsFigure 5.5. Loc
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100 5. Vibrating Barsmore difficult
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102 5. Vibrating BarsFigure 5.7. An
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104 5. Vibrating Barsthe light beam
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106 5. Vibrating BarsFigure 5.8. Tr
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108 5. Vibrating BarsFigure 5.10. T
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110 5. Vibrating Barsof 0.005 m dia
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112 6. Membrane and PlatesFigure 6.
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114 6. Membrane and PlatesBecause t
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116 6. Membrane and PlatesThe left-
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118 6. Membrane and PlatesTable 6.1
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120 6. Membrane and PlatesIn real a
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122 6. Membrane and PlatesTable 6.2
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124 6. Membrane and PlatesAt low fr
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126 6. Membrane and PlatesThe elast
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128 6. Membrane and PlatesFor the f
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130 6. Membrane and Plates(b) Deter
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132 7. Pipes, Waveguides, and Reson
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152 8. Acoustic Analogs, Ducts, and
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9Sound-Measuring Instrumentation9.1
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9.3 Microphones 175Figure 9.1. A cu
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SolutionEquation (9.3) is applied t
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9.5 Selection and Positioning of Mi
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9.6 Vector Sound Intensity Probes 1
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9.8 Proper Procedures for Using the
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9.8 Proper Procedures for Using the
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Example Problem 39.10 Dosimeters 18
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9.11 Noise Measurement in Selected
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9.11 Noise Measurement in Selected
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9.12 Real Time Analysis 193analyzer
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9.13 Fast Fourier Transform Analysi
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9.14 Data Windows and Selection of
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9.16 Measurement Error 199whereβ =
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9.18 Measurement of Sound in a Free
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9.20 Sound Power Measurement in a D
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9.20 Sound Power Measurement in a D
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9.23 The Addition Method for Measur
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References 209acoustical output and
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Problems for Chapter 9 2112. Determ
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214 10. Physiology of Hearing and P
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11Acoustics of Enclosed Spaces:Arch
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11.2 Sound Fields 245Figure 11.1. P
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11.4 Sound Intensity Growth in a Li
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11.5 Sound Absorption Coefficients
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11.6 Growth of Sound with Absorbent
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11.7 Decay of Sound 253Following Sa
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11.8 Decay of Sound in Dead Rooms 2
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11.9 Reverberation as Affected by S
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11.13 Sound Levels due to Direct an
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11.15 Concert Halls and Opera House
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Figure 11.9. A view of the Boston S
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11.16 Band Shells and Outdoor Audit
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11.16 Band Shells and Outdoor Audit
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11.17 Subjective Preferences in Sou
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References 277preferred subsequent
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Problems for Chapter 11 279Siebein,
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12Walls, Enclosures, and Barriers12
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12.3 Mass Control Case 283Figure 12
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12.5 Effect of Frequencies on Sound
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12.6 Coincidence Effect and Critica
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12.7 The Double-Panel Partition 289
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an ideal gas) varies in the followi
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12.8 Measuring Transmission Loss 29
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12.10 Combined Sound Transmission C
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12.11 Noise Insulation Ratings 297F
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12.11 Noise Insulation Ratings 299s
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12.12 Noise Reduction of a Wall 301
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12.12 Noise Reduction of a Wall 303
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12.14 Enclosures 305to the extent t
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12.14 Enclosures 307and similarly f
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12.15 Small Enclosures 309walls. Ac
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12.16 Acoustic Barriers 311Figure 1
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12.16 Acoustic Barriers 313In the c
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Equation (12.67) becomes(11D = λ+
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Page 325 and 326: 13Criteria and Regulations forNoise
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Page 359 and 360: References 353Computer Program, HIC
Page 361 and 362: Problems for Chapter 13 355Problems
Page 363 and 364: 14Machinery Noise Control14.1 Intro
Page 365 and 366: 14.4 Fan or Blower Noise 359Table 1
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Page 381 and 382: 14.8 Gears 375Figure 14.8. Gear tra
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Page 415 and 416: 15Underwater Acoustics15.1 Sound Pr
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15.6 Parametric Variation of Absorp
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15.8 Underwater Refraction 421Figur
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15.9 Mixed Layer 423When G is const
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15.11 Sonar Transducers and Their P
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Example Problem 115.12 The Sonar Eq
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Active and Passive Equations15.12 T
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15.13 Noise, Echo, and Reverberatio
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15.13 Noise, Echo, and Reverberatio
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15.14 Transient Form of Sonar Equat
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Example Problem 315.16 Shortcomings
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15.17 Theoretical Target Strength o
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Problems for Chapter 15 441Wilson,
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444 16. Ultrasonicscatching small i
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446 16. UltrasonicsPlanck constant
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448 16. UltrasonicsEquation (16.5)
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450 16. UltrasonicsFigure 16.1. Sou
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452 16. Ultrasonicsthe positive hal
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454 16. Ultrasonicson each and ever
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456 16. Ultrasonicscomplete as a li
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458 16. Ultrasonicsinitial of their
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460 16. Ultrasonicsoptic axis, deno
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462 16. Ultrasonicstransducer, it h
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464 16. UltrasonicsTable 16.1. Valu
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466 16. Ultrasonicsthe mechanical r
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468 16. UltrasonicsThe Physics of M
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470 16. UltrasonicsFigure 16.7. The
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472 16. Ultrasonicscurvilinear arra
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474 16. Ultrasonics(a)amplitudeinpu
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476 16. Ultrasonicsslow to allow th
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478 16. Ultrasonics5. In the cases
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480 17. Commercial and Medical Ultr
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510 18. Music and Musical Instrumen
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Figure 18.7. The frequencies of the
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Figure 18.20. The violin octet deve
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570 19. Sound ReproductionAlbert, a
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572 19. Sound ReproductionD. Magnet
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574 19. Sound Reproductionon, machi
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576 19. Sound ReproductionIt is fai
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578 19. Sound ReproductionINNER SUS
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580 19. Sound Reproductiontuned ape
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582 19. Sound Reproductionuse of MP
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584 19. Sound ReproductionDickason,
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586 20. Vibration and Vibration Con
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618 21. Nonlinear Acousticsby∇ 2
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620 21. Nonlinear Acousticsmay be i
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622 21. Nonlinear Acousticswhereδ
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624 21. Nonlinear AcousticsThe shoc
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626 21. Nonlinear AcousticsBut the
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Appendix APhysical Properties of Ma
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Appendix A. Physical Properties of
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Appendix BBessel FunctionsB.1 The B
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B.8 Tables of Bessel Functions, Zer
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Appendix CUsing Laplace Transforms
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C.3 Solving Differential Equations
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C.4 Equations with Multiple-Order R
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SolutionC.5 Equations with Complex
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C.5 Equations with Complex Roots 64
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SolutionC.5 Equations with Complex
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650 IndexAuditoriums, design of, 26
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652 IndexElectrostatic speakers, 58
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654 IndexKey notation, 518Kinetic e
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656 IndexPascal (unit), 48Percent i
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658 IndexSound intensity growth in
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660 IndexWater-hammer arresters, 37
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