Earg_FM.qxd 15/9/04 4:54 PM Page i THE MICROPHONE BOOK Second edition Earg_FM.qxd 14/9/04 3:11 PM Page ii Earg_FM.qxd 14/9/04 3:11 PM Page iii THE MICROPHONE BOOK Second edition John Eargle AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Focal Press is an imprint of Elsevier Earg_FM.qxd 14/9/04 3:11 PM Page iv Focal Press An imprint of Elsevier Linacre House, Jordan Hill, Oxford OX2 8DP 30 Corporate Drive, Burlington MA 01803 First published 2005 Copyright © 2005, John Eargle. All rights reserved The right of John Eargle to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1T 4LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publisher Permissions may be sought directly from Elsevier’s Science and Technology Rights Department in Oxford, UK: phone: (+44) (0) 1865 843830; fax: (+44) (0) 1865 853333; e-mail: [email protected]. You may also complete your request on-line via the Elsevier homepage (www.elsevier.com), by selecting ‘Customer Support’ and then ‘Obtaining Permissions’ British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress ISBN 02405 1961 2 For information on all Focal Press publications visit our website at: www.focalpress.com Typeset by Newgen Imaging Systems (P) Ltd, Chennai, India Printed and bound in the United States Working together to grow libraries in developing countries www.elsevier.com | www.bookaid.org | www.sabre.org Earg_FM.qxd 15/9/04 4:55 PM Page v CONTENTS Preface to the First Edition vii Preface to the Second Edition ix Symbols Used in This Book x 1 A Short History of the Microphone 1 2 Basic Sound Transmission and Operational Forces on Microphones 7 3 The Pressure Microphone 22 4 The Pressure Gradient Microphone 50 5 First-Order Directional Microphones 66 6 High Directionality Microphones 91 7 Microphone Measurements, Standards, and Specifications 105 8 Electrical Considerations and Electronic Interface 117 9 Overview of Wireless Microphone Technology 142 10 Microphone Accessories 152 11 Basic Stereophonic Recording Techniques 166 12 Stereo Microphones 184 13 Classical Stereo Recording Techniques and Practice 194 14 Studio Recording Techniques 217 15 Surround Sound Microphone Technology 243 16 Surround Recording Case Studies 271 Earg_FM.qxd 14/9/04 3:11 PM Page vi vi Contents 17 A Survey of Microphones in Broadcast and Communications 290 18 Fundamentals of Speech and Music Reinforcement 301 19 Overview of Microphone Arrays and Adaptive Systems 322 20 Care and Maintenance of Microphones 334 21 Classic Microphones: The Author’s View 338 References and Bibliography 367 Index 373 Earg_FM.qxd 14/9/04 3:11 PM Page vii PREFACE TO THE FIRST EDITION Most sound engineers will agree that the microphone is the most important element in any audio chain, and certainly the dazzling array of current models, including many that are half-a-century old, attests to that fact. My love affair with the microphone began when I was in my teens and got my hands on a home-type disc recorder. Its crystal micro- phone was primitive, but I was nonetheless hooked. The sound bug had bitten me, and, years of music schooling not withstanding, it was inevitable that I would one day end up a recording engineer. About thirty years ago I began teaching recording technology at vari- ous summer educational programs, notably those at the Eastman School of Music and later at the Aspen Music Festival and Peabody Conservatory. I made an effort at that time to learn the fundamentals of microphone per- formance and basic design parameters, and my Microphone Handbook, published in 1981, was a big step forward in producing a text for some of the earliest collegiate programs in recording technology. This new book from Focal Press presents the technology in greater depth and detail and, equally important, expands on contemporary usage and applications. The Microphone Book is organized so that both advanced students in engineering and design and young people targeting a career in audio can learn from it. Chapter 1 presents a short history of the microphone. While Chapters 2 through 6 present some mathematically intensive material, their clear graphics will be understandable to those with little technical background. Chapters 7 through 10 deal with practical matters such as standards, the microphone-studio electronic interface, and all types of accessories. Chapters 11 through 17 cover the major applications areas, with emphasis on the creative aspects of music recording in stereo and sur- round sound, broadcast/communications, and speech/music reinforce- ment. Chapter 18 presents an overview of advanced development in microphone arrays, and Chapter 19 presents helpful hints on microphone maintenance and checkout. The book ends with a comprehensive micro- phone bibliography and index. Earg_FM.qxd 14/9/04 3:11 PM Page viii viii Preface to the First Edition I owe much to Leo Beranek’s masterful 1954 Acoustics text, A. E. Robertson’s little known work, Microphones, which was written for the BBC in 1951, as well as the American Institute of Physics’ Handbook of Condenser Microphones. As always, Harry Olson’s books came to my aid with their encyclopedic coverage of everything audio. Beyond these four major sources, any writer on microphones must rely on technical journals and on-going discussions with both users and manufacturers in the field. I would like to single out for special thanks the following persons for their extended technical dialogue: Norbert Sobol (AKG Acoustics), Jörg Wuttke (Schoeps GmbH), David Josephson (Josephson Engineering), Keishi Imanaga (Sanken Microphones), and in earlier days Steve Temmer and Hugh Allen of Gotham Audio. Numerous manufacturers have given permission for the use of photographs and drawings, and they are credited with each usage in the book. John Eargle April 2001 Earg_FM.qxd 14/9/04 3:11 PM Page ix PREFACE TO THE SECOND EDITION The second edition of The Microphone Book follows the same broad subject outline as the first edition. Most of the fundamental chapters have been updated to reflect new models and electronic technology, while those chapters dealing with applications have been significantly broadened in their coverage. The rapid growth of surround sound technology merits a new chap- ter of its own, dealing not only with traditional techniques but also with late developments in virtual imaging and the creation of imaging that conveys parallax in the holographic sense. Likewise, the chapter on microphone arrays has been expanded to include discussions of adaptive systems as they involve communications and useful data reduction in music applications. Finally, at the suggestion of many, a chapter on classic microphones has been included. Gathering information on nearly thirty models was a far more difficult task than one would ever have thought, and it was truly a labor of love. John Eargle Los Angeles, June 2004 Earg_FM.qxd 14/9/04 3:11 PM Page x SYMBOLS USED IN THIS BOOK a radius of diaphragm (mm); acceleration (m/s2) A ampere (unit of electrical current) AF audio frequency c speed of sound (334 m/s at normal temperature) ЊC temperature (degrees celsius) d distance (m) dB relative level (decibel) dB(A) A-weighted sound pressure level dBu signal voltage level (re 0.775 volt rms) DC critical distance (m) DI directivity index (dB) E voltage (volt dc) e(t) signal voltage (volt rms) f frequency in hertz (s–1) HF high frequency Hz frequency (hertz, cycles per second) I acoustical intensity (W/m2) I dc electrical current, ampere (Q/s) i(t) signal current (ampere rms) ϫ 2 I0 mechanical moment of inertia (kg m ) j complex algebraic operator, equal to ͙ Ϫ 1 k wave number (2␲/␭) kg mass, kilogram (SI base unit) ЊK temperature (degrees kelvin, SI base unit) LF low frequency ␮ LP sound pressure level (dB re 20 Pa) ␮ LR reverberant sound pressure level (dB re 20 Pa) ␮ LN noise sound pressure level (dB re 20 Pa) m meter (SI base unit) MF mid frequency mm millimeter (m ϫ 10–3) ␮m micrometer or micron (m ϫ 10–6) Earg_FM.qxd 14/9/04 3:11 PM Page xi Symbols Used in This Book xi M microphone system sensitivity, mV/Pa MD capacitor microphone base diaphragm sensitivity, V/Pa N force, newton (kg, m/s2) p; p(t) rms sound pressure (N/m2) P power (watt) Q electrical charge (coulombs, SI base unit) Q directivity factor r distance from sound source (m) R, ⍀ electrical resistance (ohm) R room constant (m3 or ft3) RE random efficiency of microphone (also REE) RF radio frequency RH relative humidity (%) s second (SI base unit) S surface area (m2) T torque (N ϫ m) T, t time (s) T magnetic flux density (tesla) T60 reverberation time (seconds) T0 diaphragm tension (newton/meter) torr atmospheric pressure; equal to mm of mercury (mmHg), or 133.322 Pa