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

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362 14. Machinery Noise ControlFigure 14.4. Three types of axial flow fans. (Harris, 1991, p. 41.3.)sound level, the data on sound power levels of the fan models under considerationshould be provided by the manufacturer. However, the manufacturer has no controlover the system design for the room, nor that of the acoustical nature of the roomand so cannot be responsible for the resultant noise level. If lower sound pressurelevels are required than that generated by even properly designed fans, then it maybe necessary to provide acoustic attenuators installed as an integral part of thefan assembly. Figure 14.5 shows a centrifugal fan with sound attenuators on boththe inlet and the outlet, which is used in the supply system of a central stationventilating system. A sound attenuator is fitted at the outlet to lessen the flow ofacoustic energy from the discharge of the air to the supply air ductwork.Specific Sound Power LevelSpecific sound power level is defined as the sound power level generated by aparticular fan operating at an air flow rate of 1 m 3 /s (2120 cfm) and at a pressure of
14.4 Fan or Blower Noise 363Table 14.2. Relative Sound Power Generated by Different Types of Fans.Octave-Band Center Frequency, HzFan Type Wheel Size 63 125 250 500 1000 2000 4000 8000 BFI aCentrifugal fansAirfoil or backward-curved Over 0.75 m 85 85 84 79 75 68 64 62 3or backward-inclined Under 0.75 m 90 90 88 84 79 73 69 64 3Radial fans:Low pressure (4–10 in. Over 1 m 101 92 88 84 82 77 74 71 7static pressure) Under 1 m 112 104 98 88 87 84 79 76 7Mediam pressure (10–20 in. Over 1 m 103 99 90 87 83 78 74 71 8static pressure) Under 1 m 113 108 96 93 91 86 82 79 8Highpressure (20–60 in. Over 1 m 106 103 98 93 91 89 86 83 8static pressure) Under 1 m 116 112 104 99 99 97 94 91 8Forward-curved All 98 98 88 81 81 76 71 66 2Axial fansVaneaxialHub ratio 0.3–0.4 All 94 88 88 93 92 90 83 79 6Hub ratio 0.4–0.6 All 94 88 91 88 86 81 75 73 6Hub ratio 0.6–0.8 All 98 97 96 96 94 92 88 85 6Tubeaxial Over 1 m 96 91 92 94 92 91 84 82 7Under 1 m 93 92 94 98 97 96 88 85 7Propeller All 93 96 103 101 100 97 91 87 5a BFI = blade frequency increment.Note: The data listed here are given in terms of specific sound power in dB re 1 (10) −12 W based on avolume flow of 1 m 3 /s and a total pressure of 1 kPa. Equation (14.3) must be used to adjust for actualpressures and volume flow rates. To convert these values into English units, subtract 45 dB in all bands.The base for the English units is a total presure of 1 in. water gauge and a volume flow rate of 1 ft 3 /min.These values are those for total sound power radiated from the fan. To obtain the power levels at eitherthe inlet or the outlet, subtract 3 dB from all bands. No change in BFI is to be made. In performingthe calculations for the sound power levels from this table, do not use a total pressure less than 0.125kPa. From applications where the total pressure is lower than 0.125 kPa, simply use the value of0.125 kPa.Figure 14.5. Centrifugal fan with sound attenuators at inlet and outlet. (Harris, 1991.P. 41.13).
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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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Page 323 and 324: Problems for Chapter 12 3173. A 0.7
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Page 359 and 360: References 353Computer Program, HIC
Page 361 and 362: Problems for Chapter 13 355Problems
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Page 377 and 378: 14.8 Gears 371fromwheref BRC = N r
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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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15.4 Velocity Profiles in the Sea 4
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15.4 Velocity Profiles in the Sea 4
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15.5 Underwater Transmission Loss 4
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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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