كتاب Engineering Noise Control - Theory and Practice
منتدى هندسة الإنتاج والتصميم الميكانيكى
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 كتاب Engineering Noise Control - Theory and Practice

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تاريخ التسجيل : 01/07/2009
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 Engineering Noise Control - Theory and Practice
Fourth edition
David A. Bies and Colin H. Hansen

كتاب Engineering Noise Control - Theory and Practice  E_n_c_10
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CONTENTS
PREFACE . xviii
ACKNOWLEDGMENTS . xxi
CHAPTER 1 FUNDAMENTALS AND BASIC TERMINOLOGY 1
1.1 INTRODUCTION 1
1.2 NOISE-CONTROL STRATEGIES . 3
1.2.1 Sound Source Modification 5
1.2.2 Control of the Transmission Path 7
1.2.3 Modification of the Receiver . 8
1.2.4 Existing Facilities 8
1.2.5 Facilities in the Design Stage . 9
1.2.6 Airborne versus Structure-borne Noise 11
1.3 ACOUSTIC FIELD VARIABLES . 12
1.3.1 Variables . 12
1.3.2 The Acoustic Field 13
1.3.3 Magnitudes 14
1.3.4 The Speed of Sound . 15
1.3.5 Dispersion 18
1.3.6 Acoustic Potential Function . 19
1.4 WAVE EQUATION 21
1.4.1 Plane and Spherical Waves . 21
1.4.2 Plane Wave Propagation . 21
1.4.3 Spherical Wave Propagation 26
1.4.4 Wave Summation . 29
1.4.5 Plane Standing Waves 30
1.4.6 Spherical Standing Waves 30
1.5 MEAN SQUARE QUANTITIES 31
1.6 ENERGY DENSITY . 32
1.7 SOUND INTENSITY . 33
1.7.1 Definitions 33
1.7.2 Plane Wave and Far Field Intensity . 35
1.7.3 Spherical Wave Intensity . 36
1.8 SOUND POWER 37
1.9 UNITS . 38
1.10 SPECTRA . 41
1.10.1 Frequency Analysis . 43
1.11 COMBINING SOUND PRESSURES . 45
1.11.1 Coherent and Incoherent Sounds 45
1.11.2 Addition of Coherent Sound Pressures 46vi Contents
1.11.3 Beating 47
1.11.4 Addition of Incoherent Sounds (Logarithmic Addition) . 48
1.11.5 Subtraction of Sound Pressure Levels . 50
1.11.6 Combining Level Reductions . 51
1.12 IMPEDANCE 52
1.12.1 Mechanical Impedance, Zm . 52
1.12.2 Specific Acoustic Impedance, Zs . 53
1.12.3 Acoustic Impedance, ZA . 53
1.13 FLOW RESISTANCE . 53
CHAPTER 2 THE HUMAN EAR 56
2.1 BRIEF DESCRIPTION OF THE EAR 56
2.1.1 External Ear . 56
2.1.2 Middle Ear 57
2.1.3 Inner Ear 58
2.1.4 Cochlear Duct or Partition 59
2.1.5 Hair Cells . 62
2.1.6 Neural Encoding 62
2.1.7 Linear Array of Uncoupled Oscillators . 64
2.2 MECHANICAL PROPERTIES OF THE CENTRAL PARTITION . 66
2.2.1 Basilar Membrane Travelling Wave . 66
2.2.2 Energy Transport and Group Speed . 70
2.2.3 Undamping 71
2.2.4 The Half Octave Shift 72
2.2.5 Frequency Response . 76
2.2.6 Critical Frequency Band 76
2.2.7 Frequency Resolution 78
2.3 NOISE INDUCED HEARING LOSS . 79
2.4 SUBJECTIVE RESPONSE TO SOUND PRESSURE LEVEL 81
2.4.1 Masking 81
2.4.2 Loudness 84
2.4.3 Comparative Loudness and the Phon 85
2.4.4 Relative Loudness and the Sone 86
2.4.5 Pitch . 90
CHAPTER 3 INSTRUMENTATION FOR NOISE MEASUREMENT AND
ANALYSIS . 94
3.1 MICROPHONES 94
3.1.1 Condenser Microphone . 95
3.1.2 Piezoelectric Microphone . 98
3.1.3 Pressure Response . 99
3.1.4 Microphone Sensitivity . 99
3.1.5 Field Effects and Calibration . 100
3.1.6 Microphone Accuracy . 103
3.2 WEIGHTING NETWORKS 103Contents vii
3.3 SOUND LEVEL METERS 105
3.4 CLASSES OF SOUND LEVEL METER . 107
3.5 SOUND LEVEL METER CALIBRATION . 107
3.5.1 Electrical Calibration . 107
3.5.2 Acoustic Calibration 108
3.5.3 Measurement Accuracy 108
3.6 NOISE MEASUREMENTS USING SOUND LEVEL METERS 109
3.6.1 Microphone Mishandling 109
3.6.2 Sound Level Meter Amplifier Mishandling 109
3.6.3 Microphone and Sound Level Meter Response Characteristics . 109
3.6.4 Background Noise 109
3.6.5 Wind Noise . 110
3.6.6 Temperature 110
3.6.7 Humidity and Dust . 110
3.6.8 Reflections from Nearby Surfaces . 111
3.7 TIME-VARYING SOUND 111
3.8 NOISE LEVEL MEASUREMENT . 111
3.9 DATA LOGGERS 112
3.10 PERSONAL SOUND EXPOSURE METER . 112
3.11 RECORDING OF NOISE 114
3.12 SPECTRUM ANALYSERS 115
3.13 INTENSITY METERS 116
3.13.1 Sound Intensity by the pBu Method . 117
3.13.1.1 Accuracy of the pBu Method 118
3.13.2 Sound Intensity by the pBp Method . 119
3.13.2.1 Accuracy of the pBp Method 121
3.13.3 Frequency Decomposition of the Intensity 123
3.13.3.1 Direct Frequency Decomposition 123
3.13.3.2 Indirect Frequency Decomposition . 124
3.14 ENERGY DENSITY SENSORS 125
3.15 SOUND SOURCE LOCALISATION 126
3.15.1 Nearfield Acoustic Holography (NAH) 127
3.15.1.1 Summary of the Underlying Theory 128
3.15.2 Statistically Optimised Nearfield Acoustic
Holography (SONAH) . 131
3.15.3 Helmholtz Equation Least Squares Method (HELS) 133
3.15.4 Beamforming 133
3.15.4.1 Summary of the Underlying Theory 135
3.15.5 Direct Sound Intensity measurement . 136
CHAPTER 4 CRITERIA 138
4.1 INTRODUCTION 138
4.1.1 Noise Measures 139
4.1.1.1 A-weighted Equivalent Continuous Noise Level, LAeq . 139
4.1.1.2 A-weighted Sound Exposure . 139viii Contents
4.1.1.3 A-weighted Sound Exposure Level, LAE or SEL 140
4.1.1.4 DayBNight Average Sound Level, Ldn or DNL . 141
4.1.1.5 Community Noise Equivalent Level, Lden or CNEL . 141
4.1.1.6 Effective Perceived Noise Level, LPNE . 142
4.1.1.7 Other Descriptors . 143
4.2 HEARING LOSS . 143
4.2.1 Threshold Shift 143
4.2.2 Presbyacusis 144
4.2.3 Hearing Damage . 145
4.3 HEARING DAMAGE RISK 146
4.3.1 Requirements for Speech Recognition 147
4.3.2 Quantifying Hearing Damage Risk . 147
4.3.3 International Standards Organisation Formulation . 149
4.3.4 Alternative Formulations 151
4.3.4.1 Bies and Hansen Formulation 152
4.3.4.2 Dresden Group Formulation . 153
4.3.5 Observed Hearing Loss 154
4.3.6 Some Alternative Interpretations 156
4.4 HEARING DAMAGE RISK CRITERIA . 159
4.4.1 Continuous Noise 159
4.4.2 Impulse Noise . 160
4.4.3 Impact Noise 161
4.5 IMPLEMENTING A HEARING CONSERVATION PROGRAM . 163
4.6 SPEECH INTERFERENCE CRITERIA . 164
4.6.1 Broadband Background Noise 164
4.6.2 Intense Tones . 166
4.7 PSYCHOLOGICAL EFFECTS OF NOISE . 166
4.7.1 Noise as a Cause of Stress 166
4.7.2 Effect on Behaviour and Work Efficiency . 167
4.8 AMBIENT NOISE LEVEL SPECIFICATION 167
4.8.1 Noise Weighting Curves . 168
4.8.1.1 NR Curves 169
4.8.1.2 NC Curves 171
4.8.1.3 RC Curves . 172
4.8.1.4 NCB Curves . 174
4.8.1.5 RNC Curves . 174
4.8.2 Comparison of Noise Weighting Curves with
dB(A) Specifications 178
4.8.3 Speech Privacy 179
4.9 ENVIRONMENTAL NOISE LEVEL CRITERIA 180
4.9.1 A-weighting Criteria 180
4.10 ENVIRONMENTAL NOISE SURVEYS . 183
4.10.1 Measurement Locations 183
4.10.2 Duration of the Measurement Survey 184
4.10.3 Measurement Parameters . 184
4.10.4 Noise Impact . 185Contents ix
CHAPTER 5 SOUND SOURCES AND OUTDOOR SOUND
PROPAGATION . 187
5.1 INTRODUCTION 187
5.2 SIMPLE SOURCE 188
5.2.1 Pulsating Sphere . 188
5.2.2 Fluid Mechanical Monopole Source 191
5.3 DIPOLE SOURCE 192
5.3.1 Pulsating Doublet or Dipole (Far-field Approximation) . 192
5.3.2 Pulsating Doublet or Dipole (Near-field) 195
5.3.3 Oscillating Sphere 197
5.3.4 Fluid Mechanical Dipole Source . 199
5.4 QUADRUPOLE SOURCE (FAR-FIELD APPROXIMATION) 200
5.4.1 Lateral Quadrupole . 201
5.4.2 Longitudinal Quadrupole 202
5.4.3 Fluid Mechanical Quadrupole Source . 202
5.5 LINE SOURCE . 203
5.5.1 Infinite Line Source 203
5.5.2 Finite Line Source 205
5.6 PISTON IN AN INFINITE BAFFLE 206
5.6.1 Far Field . 207
5.6.2 Near Field On-axis . 210
5.6.3 Radiation Load of the Near Field 212
5.7 INCOHERENT PLANE RADIATOR . 214
5.7.1 Single Wall . 214
5.7.2 Several Walls of a Building or Enclosure 218
5.8 DIRECTIVITY . 219
5.9 REFLECTION EFFECTS . 220
5.9.1 Simple Source Near a Reflecting Surface 220
5.9.2 Observer Near a Reflecting Surface 221
5.9.3 Observer and Source Both Close to a Reflecting Surface 222
5.10 REFLECTION AND TRANSMISSION AT A PLANE / TWO MEDIA
INTERFACE 222
5.10.1 Porous Earth . 223
5.10.2 Plane Wave Reflection and Transmission . 223
5.10.3 Spherical Wave Reflection at a Plane Interface 227
5.10.4 Effects of Turbulence 230
5.11 SOUND PROPAGATION OUTDOORS, GENERAL CONCEPTS . 232
5.11.1 Methodology . 232
5.11.2 Limits to Accuracy of Prediction . 233
5.11.3 Outdoor Sound Propagation Prediction Schemes . 233
5.11.4 Geometrical Spreading, K . 234
5.11.5 Directivity Index, DIM 235
5.11.6 Excess Attenuation Factor, AE 236
5.11.7 Air Absorption, Aa 237
5.11.8 Shielding by Barriers, Houses and Process
Equipment/Industrial Buildings, Abhp 237x Contents
5.11.9 Attenuation due to Forests and Dense Foliage, Af . 241
5.11.10 Ground Effects 243
5.11.10.1 CONCAWE Method . 243
5.11.10.2 Simple Method (Hard or Soft Ground) . 244
5.11.10.3 Plane Wave Method . 244
5.11.10.4 ISO 9613-2 (1996) Method . 245
5.11.10.5 Detailed, Accurate and Complex Method . 246
5.11.11 Image Inversion and Increased Attenuation at Large Distance 248
5.11.12 Meteorological Effects 249
5.11.12.1Attenuation in the Shadow Zone
(Negative Sonic Gradient) . 251
5.11.12.2 Meteorological Attenuation Calculated
according to Tonin (1985) . 253
5.11.12.3 Meteorological Attenuation Calculated
according to CONCAWE . 254
5.11.12.4 Meteorological Attenuation Calculated
according to ISO 9613-2 (1996) 255
5.11.13 Combined Excess Attenuation Model . 259
5.11.14 Accuracy of Outdoor Sound Predictions . 259
CHAPTER 6 SOUND POWER, ITS USE AND MEASUREMENT . 260
6.1 INTRODUCTION 260
6.2 RADIATION IMPEDANCE 261
6.3 RELATION BETWEEN SOUND POWER AND
SOUND PRESSURE . 262
6.4 RADIATION FIELD OF A SOUND SOURCE 264
6.4.1 Free-field Simulation in an Anechoic Room 265
6.4.2 Sound Field Produced in an Enclosure 266
6.5 DETERMINATION OF SOUND POWER USING INTENSITY
MEASUREMENTS . 267
6.6 DETERMINATION OF SOUND POWER USING
CONVENTIONAL PRESSURE MEASUREMENTS 268
6.6.1 Measurement in Free or Semi-free Field . 269
6.6.2 Measurement in a Diffuse Field . 273
6.6.2.1 Substitution Method . 274
6.6.2.2 Absolute Method . 275
6.6.3 Field Measurement . 275
6.6.3.1 Semi-reverberant Field Measurements by Method One 276
6.6.3.2 Semi-reverberant Field Measurements by Method Two 277
6.6.3.3 Semi-reverberant Field Measurements by Method Three . 278
6.6.3.4 Near-field Measurements . 279
6.7 DETERMINATION OF SOUND POWER USING SURFACE
VIBRATION MEASUREMENTS . 283
6.8 SOME USES OF SOUND POWER INFORMATION 285
6.8.1 The Far Free Field 286
6.8.2 The Near Free Field 287Contents xi
CHAPTER 7 SOUND IN ENCLOSED SPACES . 288
7.1 INTRODUCTION 288
7.1.1 Wall-interior Modal Coupling 289
7.1.2 Sabine Rooms . 289
7.1.3 Flat and Long Rooms . 290
7.2 LOW FREQUENCIES . 291
7.2.1 Rectangular rooms . 291
7.2.2 Cylindrical Rooms . 296
7.3 BOUND BETWEEN LOW-FREQUENCY AND
HIGH-FREQUENCY BEHAVIOUR . 296
7.3.1 Modal Density . 297
7.3.2 Modal Damping and Bandwidth . 298
7.3.3 Modal Overlap 299
7.3.4 Cross-over Frequency . 299
7.4 HIGH FREQUENCIES, STATISTICAL ANALYSIS . 300
7.4.1 Effective Intensity in a Diffuse Field . 301
7.4.2 Energy Absorption at Boundaries 302
7.4.3 Air Absorption 303
7.4.4 Steady-state Response . 304
7.5 TRANSIENT RESPONSE 305
7.5.1 Classical Description . 306
7.5.2 Modal Description . 307
7.5.3 Empirical Description . 310
7.5.4 Mean Free Path 311
7.6 MEASUREMENT OF THE ROOM CONSTANT . 312
7.6.1 Reference Sound Source Method 313
7.6.2 Reverberation Time Method 313
7.7 POROUS SOUND ABSORBERS 315
7.7.1 Measurement of Absorption Coefficients 315
7.7.2 Noise Reduction Coefficient (NRC) 318
7.7.3 Porous Liners . 319
7.7.4 Porous Liners with Perforated Panel Facings . 319
7.7.5 Sound Absorption Coefficients of Materials in Combination . 321
7.8 PANEL SOUND ABSORBERS 321
7.8.1 Empirical Method 322
7.8.2 Analytical Method 323
7.9 FLAT AND LONG ROOMS 326
7.9.1 Flat Room with Specularly Reflecting Floor and Ceiling 328
7.9.2 Flat Room with Diffusely Reflecting Floor and Ceiling . 330
7.9.3 Flat Room with Specularly and Diffusely Reflecting Boundaries 335
7.9.4 Long Room with Specularly Reflecting Walls 337
7.9.5 Long Room with Circular Cross-section and Diffusely
Reflecting Wall . 340
7.9.6 Long Room with Rectangular Cross-section 342
7.10 APPLICATIONS OF SOUND ABSORPTION . 343
7.10.1 Relative Importance of the Reverberant Field . 343xii Contents
7.10.2 Reverberation Control 343
7.11 AUDITORIUM DESIGN 344
7.11.1 Reverberation Time . 344
7.11.2 Early Decay Time (EDT) . 346
7.11.3 Clarity (C 80) . 347
7.11.4 Envelopment . 347
7.11.5 Interaural Cross Correlation Coefficient, IACC 347
7.11.6 Background Noise Level 348
7.11.7 Total Sound Level or Loudness, G 348
7.11.8 Diffusion 348
7.11.9 Speech Intelligibility . 349
7.11.9.1 RASTI . 349
7.11.9.2 Articulation Loss . 349
7.11.9.3 Signal to Noise Ratio . 350
7.11.10 Sound Reinforcement . 350
7.11.10.1 Direction Perception . 351
7.11.10.2 Feedback Control . 351
7.11.11 Estimation of Parameters for Occupied Concert Halls 351
7.11.12 Optimum Volumes for Auditoria 352
CHAPTER 8 PARTITIONS, ENCLOSURES AND BARRIERS 353
8.1 INTRODUCTION 353
8.2 SOUND TRANSMISSION THROUGH PARTITIONS . 354
8.2.1 Bending Waves . 354
8.2.2 Transmission Loss 359
8.2.3 Impact Isolation . 364
8.2.4 Panel Transmission Loss (or Sound Reduction Index) Behaviour 365
8.2.4.1 Sharp’s Prediction Scheme for Isotropic Panels 370
8.2.4.2 Davy’s Prediction Scheme for Isotropic Panels 373
8.2.4.3 Thickness Correction for Isotropic Panels 374
8.2.4.4 Orthotropic Panels 374
8.2.5 Sandwich Panels . 376
8.2.6 Double Wall Transmission Loss . 376
8.2.6.1 Sharp Model for Double Wall TL . 376
8.2.6.2 Davy Model for Double Wall TL . 381
8.2.6.3 Staggered Studs 384
8.2.6.4 Panel Damping . 385
8.2.6.5 Effect of the Flow Resistance of the Sound
Absorbing Material in the Cavity . 386
8.2.7 Multi-leaf and Composite Panels 386
8.2.8 Triple Wall Sound Transmission Loss 387
8.2.9 Common Building Materials 387
8.2.10 Sound-absorptive Linings . 387
8.3 NOISE REDUCTION vs TRANSMISSION LOSS . 394
8.3.1 Composite Transmission Loss 394
8.3.2 Flanking Transmission Loss 397Contents xiii
8.4 ENCLOSURES . 398
8.4.1 Noise Inside Enclosures . 398
8.4.2 Noise Outside Enclosures 398
8.4.3 Personnel Enclosures . 402
8.4.4 Enclosure Windows 405
8.4.5 Enclosure Leakages . 405
8.4.6 Access and Ventilation 407
8.4.7 Enclosure Vibration Isolation . 408
8.4.8 Enclosure Resonances . 408
8.4.9 Close-fitting Enclosures . 410
8.4.10 Partial Enclosures . 410
8.5 BARRIERS 411
8.5.1 Diffraction at the Edge of a Thin Sheet 412
8.5.2 Outdoor Barriers . 415
8.5.2.1 Thick Barriers 419
8.5.2.2 Shielding by Terrain . 423
8.5.2.3 Effects of Wind and Temperature Gradients on Barrier
Attenuation 423
8.5.2.4 ISO 9613-2 Approach to Barrier Insertion
Loss Calculations 425
8.5.3 Indoor Barriers 427
8.6 PIPE LAGGING 429
8.6.1 Porous Material Lagging . 429
8.6.2 Impermeable Jacket and Porous Blanket Lagging . 429
CHAPTER 9 MUFFLING DEVICES 432
9.1 INTRODUCTION 432
9.2 MEASURES OF PERFORMANCE . 432
9.3 DIFFUSERS AS MUFFLING DEVICES . 433
9.4 CLASSIFICATION OF MUFFLING DEVICES . 434
9.5 ACOUSTIC IMPEDANCE 435
9.6 LUMPED ELEMENT DEVICES . 437
9.6.1 Impedance of an Orifice or a Short Narrow Duct 437
9.6.1.1 End Correction . 440
9.6.1.2 Acoustic Resistance . 443
9.6.2 Impedance of a Volume . 445
9.7 REACTIVE DEVICES . 446
9.7.1 Acoustical Analogs of Kirchhoff's Laws . 447
9.7.2 Side Branch Resonator 447
9.7.2.1 End Corrections for a Helmholtz Resonator Neck
and Quarter Wave Tube . 449
9.7.2.2 Quality Factor of a Helmholtz Resonator and
Quarter Wave Tube 450
9.7.2.3 Insertion Loss due to Side Branch 451
9.7.2.4 Transmission Loss due to Side Branch . 453
9.7.3 Resonator Mufflers . 456xiv Contents
9.7.4 Expansion Chamber 457
9.7.4.1 Insertion Loss 457
9.7.4.2 Transmission Loss 462
9.7.5 Small Engine Exhaust . 464
9.7.6 Lowpass Filter . 466
9.7.7 Pressure Drop Calculations for Reactive Muffling Devices 472
9.7.8 Flow-generated Noise . 473
9.8 LINED DUCTS . 478
9.8.1 Locally Reacting and Bulk Reacting Liners 479
9.8.2 Liner Specification . 479
9.8.3 Lined Duct Silencers 482
9.8.3.1 Flow Effects . 487
9.8.3.2 Higher Order Mode Propagation . 490
9.8.4 Cross-sectional Discontinuities 494
9.8.5 Pressure Drop Calculations for Dissipative Mufflers . 496
9.9 DUCT BENDS OR ELBOWS . 496
9.10 UNLINED DUCTS . 497
9.11 EFFECT OF DUCT END REFLECTIONS 498
9.12 DUCT BREAK-OUT NOISE . 499
9.12.1 Break-out Sound Transmission . 499
9.12.2 Break-in Sound Transmission 500
9.13 LINED PLENUM ATTENUATOR 501
9.13.1 Wells’ Method . 501
9.13.2 ASHRAE Method . 502
9.13.3 More Complex Methods (Cummings and Ih) 504
9.14 WATER INJECTION . 505
9.15 DIRECTIVITY OF EXHAUST DUCTS 506
CHAPTER 10 VIBRATION CONTROL . 514
10.1 INTRODUCTION . 514
10.2 VIBRATION ISOLATION 516
10.2.1 Single-degree-of-freedom Systems 517
10.2.1.1 Surging in Coil Springs 524
10.2.2 Four-isolator Systems 525
10.2.3 Two-stage Vibration Isolation 527
10.2.4 Practical Isolator Considerations . 529
10.2.4.1 Lack of Stiffness of Equipment Mounted on Isolators 532
10.2.4.2 Lack of Stiffness of Foundations 532
10.2.4.3 Superimposed Loads on Isolators 533
10.3 TYPES OF ISOLATORS 534
10.3.1 Rubber 534
10.3.2 Metal Springs 535
10.3.3 Cork . 536
10.3.4 Felt 537
10.3.5 Air Springs 538
10.4 VIBRATION ABSORBERS 538Contents xv
10.5 VIBRATION NEUTRALISERS 542
10.6 VIBRATION MEASUREMENT 542
10.6.1 Acceleration Transducers . 543
10.6.1.1 Sources of Measurement Error 545
10.6.1.2 Sources of Error in the Measurement of Transients 545
10.6.1.3 Accelerometer Calibration . 546
10.6.1.4 Accelerometer Mounting 546
10.6.1.5 Piezo-resistive Accelerometers 547
10.6.2 Velocity Transducers 548
10.6.3 Laser Vibrometers . 548
10.6.4 Instrumentation Systems 549
10.6.5 Units of Vibration . 550
10.7 DAMPING OF VIBRATING SURFACES 550
10.7.1 When Damping is Effective and Ineffective . 550
10.7.2 Damping Methods . 552
10.8 MEASUREMENT OF DAMPING . 553
CHAPTER 11 SOUND POWER AND SOUND PRESSURE LEVEL
ESTIMATION PROCEDURES . 556
11.1 INTRODUCTION . 556
11.2 FAN NOISE 557
11.3 AIR COMPRESSORS 561
11.3.1 Small Compressors 561
11.3.2 Large Compressors (Noise Levels within the Inlet and
Exit Piping) . 561
11.3.2.1 Centrifugal Compressors (Interior Noise Levels) 561
11.3.2.2 Rotary or Axial Compressors (Interior Noise Levels) 562
11.3.2.3 Reciprocating Compressors (Interior Noise) . 563
11.3.3 Large Compressors (Exterior Noise Levels) . 564
11.4 COMPRESSORS FOR CHILLERS AND
REFRIGERATION UNITS . 564
11.5 COOLING TOWERS . 565
11.6 PUMPS 567
11.7 JETS 568
11.7.1 General Estimation Procedures . 568
11.7.2 Gas and Steam Vents 574
11.7.3 General Jet Noise Control . 574
11.8 CONTROL VALVES . 575
11.8.1 Internal Sound Power Generation . 575
11.8.2 Internal Sound Pressure Level . 582
11.8.3 External Sound Pressure Level . 585
11.8.4 High Exit Velocities . 588
11.8.5 Control Valve Noise Reduction 588
11.8.6 Control Valves for Liquids 589
11.8.7 Control Valves for Steam . 590
11.9 PIPE FLOW 591xvi Contents
11.10 BOILERS . 592
11.11 TURBINES 592
11.12 DIESEL AND GAS-DRIVEN ENGINES 594
11.12.1 Exhaust Noise . 594
11.12.2 Casing Noise 596
11.12.3 Inlet Noise 596
11.13 FURNACE NOISE 598
11.14 ELECTRIC MOTORS . 599
11.14.1 Small Electric Motors (below 300 kW) . 599
11.14.2 Large Electric Motors (above 300 kW) . 599
11.15 GENERATORS 600
11.16 TRANSFORMERS 600
11.17 GEARS . 602
11.18 TRANSPORTATION NOISE . 603
11.18.1 Road Traffic Noise . 603
11.18.1.1 UK DoT model (CoRTN) . 603
11.18.1.2 United States FHWA Traffic Noise Model (TNM) . 608
11.18.1.3 Other Models 609
11.18.2 Rail Traffic Noise 610
11.18.3 Aircraft Noise . 615
CHAPTER 12 PRACTICAL NUMERICAL ACOUSTICS
by Carl Howard . 617
12.1 INTRODUCTION . 617
12.2 LOW-FREQUENCY REGION . 618
12.2.1 Helmholtz Method 620
12.2.2 Boundary Element Method (BEM) 620
12.2.2.1 Direct Method . 621
12.2.2.2 Indirect Method . 623
12.2.2.3 Meshing . 624
12.2.2.4 Problem Formulation . 624
12.2.3 Rayleigh Integral Method . 632
12.2.4 Finite Element Analysis (FEA) . 633
12.2.4.1 Pressure Formulated Acoustic Elements . 635
12.2.4.2 Displacement Formulated Acoustic Elements . 636
12.2.4.3 Practical Aspects of Modelling Acoustic
Systems with FEA 638
12.2.5 Numerical Modal Analysis 640
12.2.6 Modal Coupling using MATLAB 641
12.2.6.1 Acoustic Potential Energy 648
12.3 HIGH-FREQUENCY REGION: STATISTICAL ENERGY
ANALYSIS 649
12.3.1 Coupling Loss Factors . 651
12.3.2 Amplitude Responses 654Contents xvii
APPENDIX A WAVE EQUATION DERIVATION . 658
A.1 CONSERVATION OF MASS . 658
A.2 EULER'S EQUATION 659
A.3 EQUATION OF STATE . 660
A.4 WAVE EQUATION (LINEARISED) . 661
APPENDIX B PROPERTIES OF MATERIALS . 665
APPENDIX C ACOUSTICAL PROPERTIES OF
POROUS MATERIALS 669
C.l FLOW RESISTANCE AND RESISTIVITY 669
C.2 SOUND PROPAGATION IN POROUS MEDIA . 673
C.3 SOUND REDUCTION DUE TO PROPAGATION THROUGH A
POROUS MATERIAL 675
C.4 MEASUREMENT AND CALCULATION OF ABSORPTION
COEFFICIENTS . 677
C.4.1 Porous Materials with a Backing Cavity 683
C.4.2 Multiple Layers of Porous Liner backed by an ImpedanceZL 685
C.4.3 Porous Liner Covered with a Limp Impervious Layer 685
C.4.4 Porous Liner Covered with a Perforated Sheet . 686
C.4.5 Porous Liner Covered with a Limp Impervious Layer and a
Perforated Sheet 686
APPENDIX D FREQUENCY ANALYSIS . 687
D.1 DIGITAL FILTERING 687
D.2 DISCRETE FOURIER ANALYSIS 688
D.2.1 Power Spectrum . 693
D.2.2 Sampling Frequency and Aliasing . 696
D.2.3 Uncertainty Principle . 697
D.2.4 Real-time Frequency . 697
D.2.5 Weighting Functions . 697
D.2.6 Zoom Analysis 700
D.3 IMPORTANT FUNCTIONS 701
D.3.1 Cross-spectrum . 701
D.3.2 Coherence . 702
D.3.3 Frequency Response (or Transfer) Function . 703
REFERENCES . 704
LIST OF ACOUSTICAL STANDARDS 726
INDEX .


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