Acoustics: Sound Fields and Transducers

Acoustics: Sound Fields and Transducers

1st Edition - September 20, 2012

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  • Author: Tim Mellow
  • eBook ISBN: 9780123914866
  • Hardcover ISBN: 9780123914217

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Acoustics: Sound Fields and Transducers is a thoroughly updated version of Leo Beranek's classic 1954 book that retains and expands on the original's detailed acoustical fundamentals while adding practical formulas and simulation methods. Serving both as a text for students in engineering departments and as a reference for practicing engineers, this book focuses on electroacoustics, analyzing the behavior of transducers with the aid of electro-mechano-acoustical circuits. Assuming knowledge of electrical circuit theory, it starts by guiding readers through the basics of sound fields, the laws governing sound generation, radiation, and propagation, and general terminology. It then moves on to examine: Microphones (electrostatic and electromagnetic), electrodynamic loudspeakers, earphones, and horns Loudspeaker enclosures, baffles, and waveguides Miniature applications (e.g., MEMS in I-Pods and cellphones) Sound in enclosures of all sizes, such as school rooms, offices, auditoriums, and living rooms Numerical examples and summary charts are given throughout the text to make the material easily applicable to practical design. It is a valuable resource for experimenters, acoustical consultants, and to those who anticipate being engineering designers of audio equipment.

Key Features

  • An update for the digital age of Leo Beranek's classic 1954 book Acoustics
  • Provides detailed acoustic fundamentals, enabling better understanding of complex design parameters, measurement methods, and data
  • Extensive appendices cover frequency-response shapes for loudspeakers, mathematical formulas, and conversion factors


Research scientists and engineers working in acoustics; Mechanical, electrical, audio and architectural engineers; Physicists; Acoustical consultants.

Table of Contents

  • Preface


    Chapter 1. Introduction and terminology

    Part I Introduction

    1.2 What is sound?

    1.3 Propagation of sound through gas

    1.4 Measurable aspects of sound

    Part II: Terminology

    1.5 General

    1.6 Standard International (SI) units

    1.7 Pressure and density

    1.8 Speed and velocity

    1.9 Impedance

    1.10 Intensity, energy density, and levels


    Chapter 2. The wave equation and solutions

    Part III The Wave Equation

    2.2 Derivation of the wave equation

    Part IV Solutions of the Wave Equation in One Dimension

    2.4 Solution of wave equation for air in a tube terminated by an impedance

    2.5 Solution of wave equation for air in a tube filled with absorbent material

    2.6 Freely traveling plane wave

    2.7 Freely traveling cylindrical wave

    2.8 Freely traveling spherical wave

    Part V Solutions of the Helmholtz Wave Equation in three Dimensions

    2.10 Cylindrical coordinates

    2.11 Spherical coordinates


    Chapter 3. Electro-mechano-acoustical circuits

    Part VI Mechanical circuits

    3.2 Physical and mathematical meanings of circuit elements

    3.3 Mechanical elements

    Part VII Acoustical circuits

    Part VIII Transducers

    3.5 Electromechanical transducers

    3.6 Mechano-acoustic transducer

    3.7 Examples of transducer calculations

    Part IX Circuit theorems, energy, and power

    3.8 Conversion from admittance-type analogies to impedance-type analogies

    3.9 Thévenin’s theorem

    3.10 Transducer impedances


    Chapter 4. Acoustic components

    4.1 Introduction

    Part X Acoustic elements

    4.3 Acoustic compliances

    4.4 Acoustic resistances

    4.5 Cavity with holes on opposite sides—mixed mass-compliance element

    4.6 Intermediate-sized tube—mixed mass-resistance element [a (in meters)>0.01/ and a<10/f] [2]

    4.7 Perforated sheet—mixed mass-resistance element[a (in meters)>0.01/ and a<10/f] [2]

    4.8 Acoustic transformers

    Part XI Elementary reflection and radiation of sound

    4.9 Reflection of a plane wave from a plane

    4.10 Radiation from a pulsating sphere

    4.11 Radiation from a monopole point source (simple source)

    4.12 Combination of point sources in phase

    4.13 Steered beam-forming array of point sources

    4.14 Dipole point source (doublet)

    4.15 Radiation from an oscillating sphere

    Part XII Directivity index

    Part XIII Radiation impedances

    4.18 Oscillating sphere

    4.19 Plane circular piston in infinite baffle

    4.20 Plane circular free disk

    4.21 Plane circular piston radiating from one side only in free space

    Part XIV Viscous and thermal losses

    4.23 Wave equation for an infinite lossy tube


    Chapter 5. Microphones

    Part XV General characteristics of microphones

    5.1 Pressure microphones

    5.2 Pressure-gradient microphones

    5.3 Combination pressure and pressure-gradient microphones

    Part XVI Pressure microphones

    5.4 Electromagnetic moving-coil microphone (dynamic microphone)

    5.5 Electrostatic microphone (capacitor microphone)

    Part XVII Pressure-Gradient microphones

    Part XVIII Combination microphones

    5.8. Acoustical combination of pressure and pressure-gradient microphones

    5.9. Dual-diaphragm combination of pressure and pressure-gradient microphones


    Chapter 6. Electrodynamic loudspeakers

    Part XIX Basic theory of electrodynamic loudspeakers

    6.2 Construction [2]

    6.3 Electro-mechano-acoustical circuit

    6.4 Power output

    6.5 Thiele–Small parameters [5]

    6.6 Sound pressure produced at distance r

    6.7 Frequency-response curves

    6.8 Electrical input impedance

    6.9 Efficiency

    6.10 Measurement of Thiele–Small parameters

    6.11 Examples of loudspeaker calculations

    Part XX Design factors affecting direct-radiator loudspeaker performance

    6.12 Magnet size

    6.13 Voice-coil design

    6.14 Diaphragm behavior

    6.15 Directivity characteristics

    6.16 Transfer functions and the Laplace transform

    6.17 Transient response

    6.18 Nonlinearity [14]


    Chapter 7. Loudspeaker systems

    Part XXI Simple enclosures

    7.1 Brief summary of common loudspeaker systems

    7.2 Unbaffled direct-radiator loudspeaker

    7.3 Infinite baffle

    7.4 Finite-sized flat baffle

    7.5 Open-back cabinets

    7.6 Closed-box baffle [1,2]

    7.7 Measurement of baffle constants

    Part XXII Bass-reflex enclosures

    7.9 Acoustical circuit

    7.10 Electro-mechano-acoustical circuit

    7.11 Radiated sound

    7.12 Alignments for predetermined frequency-response shapes

    7.13 Port dimensions

    7.14 Diaphragm displacement

    7.15 Electrical input impedance and evaluation of QL

    7.16 Performance

    7.17 Construction and adjustment notes

    Part XXIII 2-port network for small enclosures

    7.18 2-port network for a bass-reflex enclosure

    Part XXIV Transmission-line enclosures

    Part XXV Multiple drive units

    7.21 Dual concentric drive units


    Chapter 8. Cellphone acoustics

    Part XXVI Acoustical transducers for cellphones

    8.1 Loudspeaker and microphone

    8.2 Circuit diagram for a cellphone loudspeaker

    8.3 Design considerations

    8.4 Head and torso simulator

    8.5 Microphones

    Part XXVII Type approval testing of cellphones

    8.6 Measurements for type approval


    Chapter 9. Horn loudspeakers

    Part XXVIII Horn drive units

    9.2 Electro-mechano-acoustical circuit [1]

    9.3 Reference efficiency

    9.4 Frequency response

    9.5 Examples of horn calculations

    Part XXIX Horns

    9.7 Possible profiles [2]

    9.8 Mouth size

    9.9 Infinite parabolic horn [11]

    9.10 Infinite conical horn

    9.11 Infinite exponential horn

    9.12 Infinite hyperbolic horn (hypex) [12]

    9.13 Finite horns

    9.14 Bends in horns

    9.15 Cross-sectional shapes

    9.16 Materials


    Chapter 10. Sound in enclosures

    Part XXX Sound Fields in Small, Regularly Shaped Enclosures

    10.2 Stationary and standing waves

    10.3 Normal modes and normal frequencies

    10.4 Steady-state and transient sound pressures

    10.5 Examples of rectangular enclosures

    Part XXXI Sound in Large Enclosures

    10.7 The reverberation equations

    10.8 Air absorption

    10.9 Total steady sound-pressure level

    10.10 Optimum reverberation time

    10.11 Sound Strength G

    10.12 Early and reverberant sound in concert halls

    10.13 Distance for equality of direct and reverberant sound fields

    10.14 Sound levels for speech and music


    Chapter 11. Room design for loudspeaker listening

    Part XXXII Home room design

    11.2 Listening room acoustics


    Chapter 12. Radiation and scattering of sound by the boundary value method

    Part XXXIII Radiation in cylindrical coordinates

    12.2 Radiation from an infinite line source

    Part XXXIV Radiation and scattering in spherical coordinates

    12.4 Scattering from a rigid sphere by a point source

    12.5 Radiation from a point source on a sphere

    12.6 Radiation from a spherical cap in a sphere

    12.7 Radiation from a rectangular cap in a sphere

    12.8 Radiation from a piston in a sphere

    12.9 Radiation from an oscillating convex dome in an infinite baffle

    12.10 Radiation from an oscillating concave dome in an infinite baffle


    Chapter 13. Radiation and scattering of sound by the boundary integral method

    Part XXXV Boundary integrals and the Green’s function

    13.2 The Rayleigh integrals and Green’s function

    13.3 The Kirchhoff–Helmholtz boundary integral

    13.4 The Green’s function in different coordinate systems

    13.5 Boundary integral method case study: Radially pulsating cap in a rigid sphere

    13.6 Reflection of a point source from a plane

    Part XXXVI Radiation and scattering in cylindrical-spherical coordinates

    13.8 Radiation from a resilient circular disk without a baffle [16]

    13.9 Radiation from a resilient disk in an infinite baffle [19]

    13.10 Radiation from a rigid circular piston in a finite circular open baffle [23, 24]

    13.11 Radiation from a rigid circular piston in a finite circular closed baffle [30] (one-sided radiator)

    13.12 The Babinet–Bouwkamp principle

    Part XXXVII Radiation theorems, radiation in rectangular-spherical coordinates, mutual impedance

    13.14 Radiation from an infinitely long oscillating strip in an infinite baffle [36,37]

    13.15 The far-field pressure distribution as a spatial frequency spectrum of the source velocity distribution

    13.16 The bridge product theorem

    13.17 Radiation from a rigid rectangular piston in an infinite baffle [38,39]

    13.18 Mutual radiation impedance between rigid circular pistons in an infinite baffle [40]

    13.19 Near-field acoustical holography [41]

    13.20 Time-reversal


    Chapter 14. State variable analysis of circuits

    14.1 A brief history

    14.2 What is state variable analysis?

    14.3 Why use state variable analysis?

    14.4 What are the restrictions?

    14.5 Some basic circuit theory

    14.6 Graph theory

    14.7 Worked example No. 1: Loudspeaker in an enclosure with a bass-reflex port

    14.8 Solution of the worked example using the Faddeev–Leverrier algorithm [10]

    14.9 Far-field on-axis pressure

    14.10 Worked example No. 2: Loudspeaker in an enclosure with a bass-reflex port using the Norton equivalent source

    14.11 Worked example No. 3: Loudspeaker in an enclosure with a bass-reflex port using a transformer and gyrator

    14.12 Worked example No. 4: Loudspeaker in an enclosure with a bass-reflex port using controlled sources

    14.13 Gyrator comprising two current-controlled voltage sources


    Appendix I. Frequency-response shapes for loudspeakers [1]

    Appendix II. Mathematical formulas [1,2]

    Appendix III. Conversion factors


Product details

  • No. of pages: 720
  • Language: English
  • Copyright: © Academic Press 2012
  • Published: September 20, 2012
  • Imprint: Academic Press
  • eBook ISBN: 9780123914866
  • Hardcover ISBN: 9780123914217

About the Author

Tim Mellow

Tim Mellow
Tim Mellow was educated at Boundary Oak School and Lancing College before obtaining a B.Sc. in Electrical Engineering and Electronics from the University of Dundee, Scotland, in 1985. A career as a Design engineer at BICC, Marconi, Thorn EMI, Racal, VTech, and Nokia followed. In 2011, he co-founded Mellow Acoustics Ltd with Philip Trevelyan to both provide an acoustical consultancy service and to develop high-end audio products. Tim takes a keen interest in music and plays the piano in his spare time. He has published many articles on audio and acoustics over the years, including 11 papers in the Journal of the Acoustical Society of America, mainly with Leo Kärkkäinen as co-author.

Affiliations and Expertise

Director, Mellow Acoustics Ltd., Farnham, UK

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