Foundations of Engineering Acoustics (eBook)

Cover 1
Contents 6
Preface 14
Acknowledgements 20
Chapter 1. Sound Engineering 22
1.1 The importance of sound 22
1.2 Acoustics and the engineer 23
1.3 Sound the servant 24
Chapter 2. The Nature of Sound and Some Sound Wave Phenomena 27
2.1 Introduction 27
2.2 What is sound? 27
2.3 Sound and vibration 28
2.4 Sound in solids 30
2.5 A qualitative introduction to wave phenomena 30
2.6 Some more common examples of the behaviour of sound waves 42
Chapter 3. Sound in Fluids 44
3.1 Introduction 44
3.2 The physical characteristics of fluids 44
3.3 Molecules and particles 45
3.4 Fluid pressure 46
3.5 Fluid temperature 46
3.6 Pressure, density and temperature in sound waves in a gas 47
3.7 Particle motion 50
3.8 Sound in liquids 50
3.9 Mathematical models of sound waves 51
Chapter 4. Impedance 69
4.1 Introduction 69
4.2 Some simple examples of the utility of impedance 71
4.3 Mechanical impedance 73
4.4 Forms of acoustic impedance 77
4.5 An application of radiation impedance of a uniformly pulsating sphere 93
4.6 Radiation efficiency 93
Chapter 5. Sound Energy and Intensity 95
5.1 The practical importance of sound energy 95
5.2 Sound energy 96
5.3 Transport of sound energy: sound intensity 97
5.4 Sound intensity in plane wave fields 99
5.5 Intensity and mean square pressure 103
5.6 Examples of ideal sound intensity fields 103
5.7 Sound intensity measurement 109
5.8 Determination of source sound power using sound intensity measurement 112
5.9 Other applications of sound intensity measurement 113
Chapter 6. Sources of Sound 117
6.1 Introduction 117
6.2 Qualitative categorization of sources 118
6.3 The inhomogeneous wave equation 127
6.4 Ideal elementary source models 127
6.5 Sound radiation from vibrating plane surfaces 145
6.6 The vibrating circular piston and the cone loudspeaker 147
6.7 Directivity and sound power of distributed sources 150
6.8 Zones of a sound field radiated by a spatially extended source 155
6.9 Experimental methods for source sound power determination 156
6.10 Source characterization 157
Chapter 7. Sound Absorption and Sound Absorbers 161
7.1 Introduction 161
7.2 The effects of viscosity, thermal diffusion and relaxation processes on sound in gases 162
7.3 Forms of porous sound absorbent material 168
7.4 Macroscopic physical properties of porous sound-absorbing materials 170
7.5 The modified equation for plane wave sound propagation in gases contained within rigid porous materials 174
7.6 Sound absorption by a plane surface of uniform impedance 177
7.7 Sound absorption by thin porous sheets 184
7.8 Sound absorption by thick sheets of rigid porous material 188
7.9 Sound absorption by flexible cellular and fibrous materials 192
7.10 The effect of perforated cover sheets on sound absorption by porous materials 193
7.11 Non-porous sound absorbers 195
7.12 Methods of measurement of boundary impedance and absorption coefficient 199
Chapter 8. Sound in Waveguides 202
8.1 Introduction 202
8.2 Plane wave pulses in a uniform tube 204
8.3 Plane wave modes and natural frequencies of fluid in uniform waveguides 208
8.4 Response to harmonic excitation 215
8.5 A simple case of structure-fluid interaction 220
8.6 Plane waves in ducts that incorporate impedance discontinuities 222
8.7 Transverse modes of uniform acoustic waveguides 232
8.8 Harmonic excitation of waveguide modes 241
8.9 Energy flux in a waveguide of rectangular cross-section with rigid walls 243
8.10 Examples of the sound attenuation characteristics of lined ducts and splitter attenuators 245
8.11 Acoustic horns 248
Chapter 9. Sound in Enclosures 257
9.1 Introduction 257
9.2 Some general features of sound fields in enclosures 260
9.3 Apology for the rectangular enclosure 264
9.4 The impulse response of fluid in a reverberant rectangular enclosure 264
9.5 Acoustic natural frequencies and modes of fluid in a rigid-walled rectangular enclosure 266
9.6 Modal energy 269
9.7 The effects of finite wall impedance on modal energy-time dependence in free vibration 270
9.8 The response of fluid in a rectangular enclosure to harmonic excitation by a point monopole source 272
9.9 The sound power of a point monopole in a reverberant enclosure 274
9.10 Sound radiation into an enclosure by the vibration of a boundary 275
9.11 Probabilistic wave field models for enclosed sound fields at high frequency 277
9.12 Applications of the diffuse field model 283
9.13 A brief introduction to geometric (ray) acoustics 288
Chapter 10. Structure-borne Sound 291
10.1 The nature and practical importance of structure-borne sound 291
10.2 Emphasis and content of the chapter 295
10.3 The energy approach to modelling structure-borne sound 297
10.4 Quasi-longitudinal waves in uniform rods and plates 299
10.5 The bending wave in uniform homogeneous beams 300
10.6 The bending wave in thin uniform homogeneous plates 306
10.7 Transverse plane waves in flat plates 307
10.8 Dispersion curves, wavenumber vector diagrams and modal density 308
10.9 Structure-borne wave energy and energy flux 311
10.10 Mechanical impedances of infinite, uniform rods, beams and plates 314
10.11 Wave energy transmission through junctions between structural components 318
10.12 Impedance, mobility and vibration isolation 319
10.13 Structure-borne sound generated by impact 322
10.14 Sound radiation by vibrating flat plates 325
Chapter 11. Transmission of Sound through Partitions 336
11.1 Practical aspects of sound transmission through partitions 336
11.2 Transmission of normally incident plane waves through an unbounded partition 336
11.3 Transmission of sound through an unbounded flexible partition 341
11.4 Transmission of diffuse sound through a bounded partition in a baffle 349
11.5 Double-leaf partitions 351
11.6 Transmission of normally incident plane waves through an unbounded double-leaf partition 352
11.7 The effect of cavity absorption 357
11.8 Transmission of obliquely incident plane waves through an unbounded double-leaf partition 359
11.9 Close-fitting enclosures 363
11.10 A simple model of a noise control enclosure 368
11.11 Measurement of sound reduction index (transmission loss) 369
Chapter 12. Reflection, Scattering, Diffraction and Refraction 373
12.1 Introduction 373
12.2 Scattering by a discrete body 375
12.3 Scattering by crowds of rigid bodies 379
12.4 Resonant scattering 380
12.5 Diffraction 383
12.6 Reflection by thin, plane rigid sheets 394
12.7 Refraction 396
Appendix 1. Complex exponential representation of harmonic functions 401
A1.1 Harmonic functions of time 401
A1.2 Harmonic functions of space 403
A1.3 CER of travelling harmonic plane waves 403
A1.4 Operations on harmonically varying quantities represented by CER 404
Appendix 2. Frequency Analysis 405
A2.1 Introduction 405
A2.2 Categories of signal 406
A2.3 Fourier analysis of signals 407
A2.4 Presentation of the results of frequency analysis 413
A2.5 Frequency response functions 413
A2.6 Impulse response 414
Appendix 3. Spatial Fourier Analysis of Space-Dependent Variables 415
A3.1 Wavenumber transform 415
A3.2 Wave dispersion 415
Appendix 4. Coherence and Cross-Correlation 418
A4.1 Background 418
A4.2 Correlation 418
A4.3 Coherence 419
A4.4 The relation between the cross-correlation and coherence functions 420
Appendix 5. The Simple Oscillator 422
A5.1 Free vibration of the undamped mass-spring oscillator 422
A5.2 Impulse response of the undamped oscillator 422
A5.3 The viscously damped oscillator 423
A5.4 Impulse response of the viscously damped oscillator 424
A5.5 Response of a viscously damped oscillator to harmonic excitation 424
Appendix 6. Measures of Sound, Frequency Weighting and Noise Rating Indicators 427
A6.1 Introduction 427
A6.2 Pressure–time history 427
A6.3 Mean square pressure 428
A6.4 Sound pressure level 429
A6.5 Sound intensity level 429
A6.6 Sound power level 429
A6.7 Standard reference curves 430
Appendix 7. Demonstrations and Experiments 432
A7.1 Introduction 432
A7.2 Demonstrations 432
A7.3 Formal laboratory class experiments 436
Answers 442
Bibliography 451
References 453
Index 456