Loudspeaker Handbook

Loudspeaker Handbook

John M. Eargle

Springer-Science+Business Media, B.Y.

Electronic Services <http://www.wkap.nl>

Library of Congress Cataloging-in-Publication

Eargle, John. Loudspeaker handbook I John M. Eargle.

p. cm. Includes bibliographical references and index.

1. Loudspeakers--Handbooks, manuals, etc. 1. Title. TK5983.E27 1996 621.382'84--dc 20

ISBN 978-1-4757-5682-1 ISBN 978-1-4757-5680-7 (eBook) DOI 10.1007/978-1-4757-5680-7

British Library Cataloguing in Publication Data available Cover design: Sai'd Sayrafiezadeh, em DASH inc. Art direction: Andrea Meyer Copyright © 1997 by Springer Science+Business Media Dordrecht Originally published by Chapman & Hall in 1997. Softcover reprint of the hardcover 1 st edition 1997 Second printing 1999 by Kluwer Academic Publishers

96-22852 CIP

AII rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, mechanical, photo-copying, recording, or otherwise, without the prior written permission of the publisher, Springer-Science+Business Media, B.V.

Printed an acidjree paper.

Contents

Chapter I Electroacoustical Engineering Fundamentals

1.1 Introduction 1.2 A Simple Electrical Series Resonant Network 1.3 A Simple Mechanical Resonant System 1.4 Impedance and Mobility Analogies 1.5 Combining Electrical and Mechanical Domains 1.6 Combining Mechanical and Acoustical Domains 1.7 Directional Characteristics 1.8 Cone Excursion, Power, and Pressure Relationships

Chapter 2 Cone and Dome Drivers

2.1 Introduction 2.2 Mechanical Construction Details of the Cone Driver 2.3 The Moving System 2.4 Variations on the Cone Transducer 2.5 Dome Drivers 2.6 Distortion in Cone and Dome Drivers

Chapter 3 Principles of Magnetics

3.1 Introduction 3.2 Fundamentals: Hysteresis and Load Line 3.3 Details of the Magnetic Circuit 3.4 Linearity Issues 3.5 Temperature Rise and Demagnetization 3.6 Modeling of Magnetic Phenomena 3.7 Magnetic Shielding

Chapter 4 Low-Frequency Systems and Enclosures

4.1 Introduction 4.2 Thiele-Small Parameters 4.3 Sealed Low-Frequency System Analysis 4.4 Ported Low-Frequency System Analysis 4.5 Some Useful Alignments

v

I 3 5 6 6

14 17

21

21 21 25 36 39 42

47

47 47 51 52 53 54 55

57

57 57 59 64 67

vi Contents

4.6 The Passive Radiator 72 4.7 Transmission Line Systems 73 4.8 Curiosities from the Past 74 4.9 Multichamber Bandpass Low-Frequency Systems 75 4.10 Transducers in Acoustical Series and in Parallel 79 4.11 Alignment Shifts 81

Chapter 5 Dividing Networks and Systems Concepts 85

5.1 Introduction 85 5.2 Basic Dividing Networks 85 5.3 Stock Networks and Autotransformers 92 5.4 Combining Acoustical and Electrical Poles 92 5.5 Off-Axis Lobing Effects 92 5.6 Baffle Component Layout and Edge Details 101 5.7 Time Domain Response of Loudspeakers 105 5.8 Loudspeaker Dispersion and Power Response 108

Chapter 6 In-Line and Planar Loudspeaker Arrays 114

6.1 Introduction 114 6.2 Analysis of the Constant Charge ESL Loudspeaker 115 6.3 Electromagnetic Planar Loudspeakers 120 6.4 The Ribbon Tweeter (High-Frequency Unit) 120 6.5 Discrete Line Arrays 121 6.6 Consumer Systems Using Discrete Element Line Arrays 129

Chapter 7 Horn Systems 136

7.1 Introduction 136 7.2 Horn Flare Profiles 136 7.3 The Driving Transducer 139 7.4 Ring Radiators 147 7.5 Families of Horns 147 7.6 Distortion in Horn Systems 160 7.7 Horn Driver Protection 163 7.8 Low Frequency Horns 167 7.9 Horn Arrays 171

Chapter 8 Electronic Interface 174

8.1 Introduction 174 8.2 The Power Amplifier 174 8.3 Line Losses 177 8.4 Matching Loudspeakers and Amplifiers 180 8.5 Amplifier Bridging 181 8.6 Amplifier Paralleling 182 8.7 Biwiring 183

Contents vii

8.8 Multiamping 184 8.9 Electronic Control of Loudspeaker System Performance 185 8.10 Means of Loudspeaker Protection 188

Chapter 9 Thermal Failure Modes of Loudspeakers 190

9.1 Introduction 190 9.2 Basic Heat Transfer Mechanisms 190 9.3 Estimating Values of Thermal Resistance 193 9.4 Low Frequency Performance Shifts 194 9.5 Techniques for Heat Removal 198

Chapter 10 Recording Monitor Loudspeakers 200

10.1 Introduction 200 10.2 Historical Survey 201 10.3 The Modern Era 202 10.4 Monitoring Environments 208 10.5 The Near-Field Monitor 212 10.6 Monitor System Equalization 213

Chapter II Loudspeakers in Sound Reinforcement 219

11.1 Introduction 219 11.2 Systems for Speech Reinforcement 219 11.3 The Role of Signal Delay 221 11.4 Case Studies 222 11.5 Computer Simulation of Loudspeaker Coverage 227 11.6 System Equalization 228 11.7 Measurements and Estimation of System Intelligibility 229 11.8 Electronic Halls 234 11.9 Environmental Effects on Sound Propagation 239 11.1 0 System Stability 242

Chapter 12 Systems for Film and Video 243

12.1 Introduction 243 12.2 Motion Picture Loudspeaker Systems and Environment 243 12.3 System Layout in the Theater 248 12.4 Specific Loudspeaker Models for the Motion Picture Theater 251 12.5 Multichannel Video in the Home 253

Chapter 13 Loudspeaker Measurements and Modeling 257

13.1 Introduction 257 13.2 Frequency Response Measurements 257 13.3 Distortion Measurements 261 13.4 Phase and Group Delay Response of Loudspeakers 265

viii Contents

13.5 Measurement of Directional Data 13.6 The Measuring Environment 13.7 An Overview of Transform Measurement Methods 13.8 Optical Measurement Techniques 13.9 Modeling Techniques 13.10 Destructive Testing

Chapter 14 Loudspeaker Specifications for Professional Applications

14.1 Introduction 14.2 On-Axis Frequency Response 14.3 Impedance 14.4 Reference Sensitivity Ratings 14.5 Power Ratings of Drivers and Systems 14.6 Power Compression 14.7 Distortion 14.8 Directivity Performance of Systems and Components 14.9 Thiele-Small Parameters

Chapter 15 Aspects of the Home Listening Environment

266 268 271 276 280 280

282

282 282 283 283 285 288 289 289 290

291

15.1 Introduction 291 15.2 Listening Room Boundary Conditions: the Laboratory Meets the

Real World 291 15.3 Room Modes 293 15.4 Room Treatments at Mid- and High Frequencies 296 15.5 Optimizing Stereophonic Localization 299 15.6 Loudspeaker Systems for Extended Imaging 301

Chapter 16 A Survey of Exotic Transducers

16.1 Introduction 16.2 Variations on a Magnetic Theme 16.3 Piezoelectric and Related Devices 16.4 Ionized Air Devices 16.5 The Air Modulator 16.6 Rotary Actuators 16.7 Digital Loudspeakers

Index

304

304 305 311 313 315 317 317

321

Preface

The prospect of writing a book on loudspeakers is a daunting one, since only a multivolume encyclopedia could truly do justice to the subject. Authors writing about this subject have generally concentrated on their own areas of expertise, often covering their own specific topics in great detail. This book is no exception; the author's background is largely in professional loudspeaker application and specification, and the emphasis in this book is on basic component design, operation, measurement, and system concepts.

The book falls largely into two sections; the first (Chapters 1-9) emphasizing the building blocks of the art and the second (Chapters 10-16) emphasizing applications, measurements, and modeling. While a thorough understanding of the book requires a basic knowledge of complex algebra, much of it is understandable through referring to the graphics. Every attempt has been made to keep graphics clear and intuitive.

Chapter 1 deals with the basic electro-mechano-acoustical chain between input to the loudspeaker and its useful output, with emphasis on the governing equations and equivalent circuits.

Chapter 2 is a survey of cone and dome drivers, the stock-in-trade of the industry. They are discussed in terms of type, design, performance, and perfor­mance limits.

Chapter 3 deals with magnetics. Once a source of difficulty in loudspeaker design, magnetics today yields easily to modeling techniques.

Chapter 4 discusses low-frequency (LF) system performance, primarily from the viewpoint of Thiele-Small parameters. We also discuss some of the multi­chamber LF systems that became popular during the eighties.

Chapter 5 is devoted to systems concepts. There is more diversity in this area than in any other aspect of loudspeaker design. In this chapter we discuss basic network types, baffle layout considerations, component matching, and system power response.

Chapter 6 discusses line and planar loudspeaker arrays. Such loudspeaker types radiate differently than individual cones and domes. We study arrays of dynamic drivers, as well as electrostatic and magnetic panels.

ix

x Preface

Chapter 7 covers horns and their drivers in detail. Hom systems are essential to professional sound applications and have formed a key element of electroacoustics since its inception.

Chapter 8 discusses the electronic interface, including the proper matching of amplifiers to drivers, series and parallel operation of amplifiers, aspects of multiamplification, and line losses.

Chapter 9 covers the performance shifts in loudspeakers due to the heating that occurs in high-level applications. Techniques for minimizing these effects are examined.

Chapter 10, 11, and 12 examine the application areas of recording and broadcast monitoring, sound reinforcement, and motion picture/video, respectively. Current practice in these areas is reviewed in detail.

Chapter 13 is devoted to loudspeaker measurements and modeling. A quiet revolution has taken place in recent years as measurement systems based on digital transform techniques have virtually displaced analog systems. Both methods are discussed, along with various techniques for modeling loudspeaker performance.

Chapter 14 discusses loudspeaker specifications for professional applications. Data presentation is an important first step in this area. We review current professional standards.

Chapter 15 discusses the home listening environment. Knowing where-and where not-to locate loudspeakers in the home often makes the difference be­tween mediocre and excellent performance. We discuss some useful tech­niques here.

Chapter 16 discusses exotic transducers. These devices have always been on the fringes of the loudspeaker business, and some have been highly successful. We discuss many types in this chapter.

The author would like to thank his many colleagues at JBL and other Harman International companies for their direct help in gathering material for this book and for stimulating discussions over the years. Further recognition is given to those manufacturers who have provided illustrative materials for the book. They are cited in the figure captions.

John Eargle, April 1996