Acoustics for Engineers (eBook)

Preface 5
Contents 6
1 Introduction 9
1.1 Definition of Three Basic Terms 9
1.2 Specialized Areas within Acoustics 11
1.3 About the History of Acoustics 12
1.4 Relevant Quantities in Acoustics 13
1.5 Some Numerical Examples 14
1.6 Levels and Logarithmic Frequency Intervals 16
1.7 Double-Logarithmic Plots 18
2 Mechanic and Acoustic Oscillations 20
2.1 Basic Elements of Linear, Oscillating, Mechanic Systems 21
2.2 Parallel Mechanic Oscillators 23
2.3 Free Oscillations of Parallel Mechanic Oscillators 24
2.4 Forced Oscillation of Parallel Mechanic Oscillators 26
2.5 Energies and Dissipation Losses 29
2.6 Basic Elements of Linear, Oscillating, Acoustic Systems 31
2.7 The Helmholtz Resonator 32
3 Electromechanic and Electroacoustic Analogies 33
3.1 The Electromechanic Analogies 34
3.2 The Electroacoustic Analogy 35
3.3 Levers and Transformers 35
3.4 Rules for Deriving Analogous Electric Circuits 37
3.5 Synopsis of Electric Analogies of Simple Oscillators 39
3.6 Circuit Fidelity, Impedance Fidelity and Duality 39
3.7 Examples of Mechanic and Acoustic Oscillators 40
4 Electromechanic and Electroacoustic Transduction 42
4.1 Electromechanic Couplers as Two- or Three-Port Elements 43
4.2 The Carbon Microphone – A Controlled Coupler 44
4.3 Fundamental Equations of Electroacoustic Transducers 45
4.4 Reversibility 48
4.5 Coupling of Electroacoustic Transducers to the Sound Field 49
4.6 Pressure and Pressure-Gradient Receivers 51
4.7 Further Directional Characteristics 54
4.8 Absolute Calibration of Transducers 57
5 Magnetic-Field Transducers 59
5.1 The Magnetodynamic Transduction Principle 61
5.2 Magnetodynamic Sound Emitters and Receivers 63
5.3 The Electromagnetic Transduction Principle 69
5.4 Electromagnetic Sound Emitters and Receivers 71
5.5 The Magnetostrictive Transduction Principle 72
5.6 Magnetostrictive Sound Transmitters and Receivers 73
6 Electric-Field Transducers 74
6.1 The Piezoelectric Transduction Principle 74
6.2 Piezoelectric Sound Emitters and Receivers 77
6.3 The Electrostrictive Transduction Principle 81
6.4 Electrostrictive Sound Emitters and Receivers 82
6.5 The Dielectric Transduction Principle 83
6.6 Dielectric Sound Emitters and Receivers 84
6.7 Further Transducer and Coupler Principles 88
7 The Wave Equation in Fluids 90
7.1 Derivation of the One-Dimensional Wave Equation 92
7.2 Three-Dimensional Wave Equation in Cartesian Coordinates 96
7.3 Solutions of the Wave Equation 98
7.4 Field Impedance and Power Transport in Plane Waves 99
7.5 Transmission-Line Equations and Re.ectance 100
7.6 The Acoustic Measuring Tube 102
8 Horns and Stepped Ducts 105
8.1 Webster’s Differential Equation – the Horn Equation 106
8.2 Conical Horns 107
8.3 Exponential Horns 110
8.4 Radiation Impedances and Sound Radiation 112
8.5 Steps in the Area Function 113
8.6 Stepped Ducts 115
9 Spherical Sound Sources and Line Arrays 118
9.1 Spherical Sound Sources of 0th Order 119
9.2 Spherical Sound Sources of 1st Order 123
9.3 Higher-Order Spherical Sound Sources 125
9.4 Line Arrays of Monopoles 126
9.5 Analogy to Fourier Transforms as Used in Signal Theory 128
9.6 Directional Equivalence of Sound Emitters and Receivers 131
10 Piston Membranes, Diffraction and Scattering 133
10.1 The Rayleigh Integral 134
10.2 Fraunhofer’s Approximation 135
10.3 The Far Field of Piston Membranes 136
10.4 The Near Field of Piston Membranes 138
10.5 General Remarks on Diffraction and Scattering 142
11 Dissipation, Re.ection, Refraction, and Absorption 145
11.1 Dissipation During Sound Propagation in Air 147
11.2 Sound Propagation in Porous Media 148
11.3 Reflection and Refraction 151
11.4 Wall Impedance and Degree of Absorption 152
11.5 Porous Absorbers 155
11.6 Resonance Absorbers 158
12 Geometric Acoustics and Diffuse Sound Fields 161
12.1 Mirror Sound Sources and Ray Tracing 162
12.2 Flutter Echoes 165
12.3 Impulse Responses of Rectangular Rooms 167
12.4 Di.use Sound Fields 169
12.5 Reverberation-Time Formulae 172
12.6 Application of Diffuse Sound Fields 173
13 Isolation of Air- and Structure-Borne Sound 177
13.1 Sound in Solids – Structure-Borne Sound 177
13.2 Radiation of Airborne Sound by Bending Waves 179
13.3 Sound-Transmission Loss of Single-Leaf Walls 181
13.4 Sound-Transmission Loss of Double-Leaf Walls 184
13.5 The Weighted Sound-Reduction Index 186
13.6 Isolation of Vibrations 189
13.7 Isolation of Floors with Regard to Impact Sounds 192
14 Noise Control – A Survey 194
14.1 Origins of Noise 195
14.2 Radiation of Noise 195
14.3 Noise Reduction as a System Problem 199
14.4 Noise Reduction at the Source 202
14.5 Noise Reduction Along the Propagation Paths 203
14.6 Noise Reduction at the Receiver’s End 207
15 Appendices 209
15.1 Complex Notation for Sinusoidal Signals 209
15.2 Complex Notation for Power and Intensity 210
15.3 Supplementary Textbooks for Self Study 212
15.4 Letter Symbols, Notations and Units 213
Index 217