• Abstract and Figures
• Public Full-text

MODERN GRAMOPHONES AND ELECTRICAL REPRODUCERS Modern Gramophones and I^Mectrical Reproducers By P. WILSON, M.A, Technical Adviser to The Gramophone and G. W. WEBB Chairman, T'he Gramophone “ Expert Committee ” With 120 Diagrams and Half-Tone Illustrations CASSELL AND COMPANY, LTD London, Toronto, Melbourne and Sydney GRAMOPHONES MODERN TWO First published 1929> Printed in Great Britain. FOREWORD 'riiERE is little for the writer of a Foreword to say on behalf of a book which so completely fulfils its purpose as this one. A combination of Mr. Webb’s vast experience and knowledge, with Mr. Wilson’s mathematical genius for being right could not be improved upon by any combina- tion of experts of which I am aware. It has been my privilege and pleasure for some years now to rely upon the judgment of the two authors in all matters connected with the technicalities of the gramophone. What I should have done without their help and advice, when faced by tlie introduction of electric recording, I tremble to think. The time has long passed when the writer of a Foreword to a book of this size, exclusively about the gramophone, would have begun his address by a defence of the instru- ment itself. We take for granted the value of the gramo- if anybody has any lingering doubt phone nowadays ; but of the gramophone’s importance, he has only to turn over a few pages of this book to be immediately reassured. Mr. Wilson and Mr. Webb would be the last people to claim that they have said the final word about the gramo- this built up phone of to-day ; but they have in volume such a solid foundation that it is not rash to suggest that for some time to come it will not be shaken, and that further information will be in the nature of a supplement v Preface 'riic greatest j‘»ractical advance of all has been in the develop- niciU of electrical an system of recording ; but this is not by any means the only benefit. The application of electrical “ impedance ” methods to mechanical theory has provided a new method of attacking difficult problems which promises to be one of great power. In one sense, it is merely a new notation, a new and simpler way of expressing complicated ideas in a sort of mental shorthand. But in the long run, discoveries of this kind are precisely those which have the greatest effect on technical progress. In this book we have attempted to give an elementary account of the new principles. Though the subject matter is based on a practical experience of gramophones extending over twenty years, the actual arrangement of it, and the theoretical explanations which link together the mass of experimental Jfacts, are the result of researches of the past five or six years only. It is only during that period that the art has also become a science. So far as the authors are aware, this is the first attempt that has been made to give a connected and balanced account of modern gramo- phone technique. There are a number of papers in various scientific journals, but these are either confined to generalities or deal only with certain aspects of the subject. Naturally, in a first attempt of this sort, there will be many things that could have been better said, many ideas that time will show to be merely of ephemeral value, and many omissions to be rectified in the future. Developments are now taking place at such a pace, particularly in regard to electrical reproduction, that the near future may bring new apparatus as superior to our present instruments as these are to the gramophones and phonographs of yesterday. But the authors are confident that the fundamental j^rinciples are now well established and the paths of further progress clear. They trust, therefore, that their account will i)rove of service not only to the ordinary man who wishes to know the secrets behind this remarkable advance, Inil niso to those who are their fellow-workers in the art. I'\)r tliis Vlll Preface reason, the use of mathematical formulae has not been av(u’ded, though it has been kept within small limits and, wherever possible, a verbal explanation has been given to iliusti-ate the particular principle under discussion. In addition, it has been thought desirable to reserve the more complicated calculations for appendices rather than to interrupt the narrative in the text. Acknowledgments are due, and are gratefully given, to the many people who have helped the authors in the ]:»rcparation of the book : to the Gramophone Company (“ H.M.V.”) and the Columbia Graphophone Company, lor their courtesy and kindness in supplying photographs and diagrams ; to Mr. A. Hall, Chief Radio Engineer of Ferranti Ltd., for the oscillographs ; to the Wireless World for permission to include pictures of the H.M.V. Electrical Reproducer and Pick-up which first appeared in that paper ; and above all, to Mr. Compton Mackenzie, Mr. Christopher Stone and the “ Expert Committee ” of The Gramophone for encouragement and assistance both in the past and in the actual preparation of the book. To Mr. FI. F. V. Little, B.Sc., Mr. J. Ainger Hall, B.Sc., who kindly read both manuscript and proofs, and to Mr. W. C. Wilson, who prepared the majority of the diagrams, we owe a special word of thanks. IX —- CONTENTS CHAPTER I PAGE Sounds and Sound-Waves i Sound-waves—Wave-front—Velocity, Wave-length, Fre- quency, Amplitude—Simple and Complex Waves ; Phase—Analysis of Sounds—Musical Sounds—Tran- sients—Sensitivity of the Ear—Requirements for Perfect Reproduction—Permissible Errors in Repro- duction. CHAPTER II Records AND Recording Systems .... 20 Production of Mechanical Vibrations—Early Recording Systems—Ideal Response to Sound-Resonance and Damping—Electrical Recording—Electrical and Me- chanical Analogies—The Electromagnetic Recorder —Lateral-cut and Hill-and-Dale Records—Constant Amplitude Recording. Appendix.—Note on Electrical Circuits. CHAPTER HI Reproducing Systems -43 Historical Summary—The Scientific Stage—Even Re- sponse — Limitations of Mechanical Reproduction Electrical Reproduction—Advantages of Electrical Reproduction. CHAPTER IV Sound-boxes 61 Essential Features—Motion of a Diaphragm—The Air- chamber—Action of the Stylus-bar—The Electrical Analogy — Stylus-bar Mountings — Back-plate and Gaskets—Miscellaneous Attachments. Appendix.—Example of Sound-box Design. CHAPTER V Horns ......... 90 Function of the Horn—Properties required of a Horn— Contour of a Horn—The Exponential or Logarithmic Horn—Another Approximation—Size of Mouth Open- ing—Non-circular Section—Folded Horns—Bifurcated Horns—Material of Horns. Appendix (i). —Example of Folded Horn Design. Appendix (ii).-—Theory of the Modified Exponential Horn. XI — (hulenis riiAPi'iCR v[ PAGE loNi; AKMS ........ I2I ( i ( Is’iM'di (I I nuvr lia I .M (c'l ihI It :i ( hmhiic 1 1 ir.) I Kr< [iiii cuicnts Arnii;.l i( ,il Kc‘( | ii i i ri nrii I IV1(‘( Imnical ('onsideralions lour aim Malriial ( 'ai ryiii(.;ai ms lor Idcdric l^icU-ups. ClIAPTltR Vlf l\M-.coin> Wi'AK, Nickducs, Sukkace-noise . M3 1' I ir.lioiKil Wi^ar —K.cactivc Wear—Needles—Surface-noise. CHAPTER VIII ludccTRic Pick-ups . ...... 155 I'linctions—Types—-Velocity and Displacement Devices —IClectromagnetic Pick-nps—Half-Rocker Moving-Iron i*ick-ups—Other Types—Possible Developments. A})pcndix. —Force Equations of the Half-rocker Pick-up. CHAPTER IX Loud-Speakers ....... 173 General Principles—Reed-driven Mechanisms—Moving- coil Mechanisms—Diaphragm Effects—Large Dia- phragms—The Outlook. CHAPTER X Electric Amplifiers ...... 193 Thermionic Valves — Valve Characteristics — Intervalve Couplings—The Output Stage—Special Conditions for Reception of Broadcasting—Low-Frequency Amplifier Design—Volume Controls—Mains Units or Battery Eliminators. Appendix.—Design of Amplifier Units. CHAPTER XI Miscellaneous Hints ...... 236 Practical Considerations—Motors—Parts of a Spring Motor—Care of the Motor—Electric Motors—Speed Regulation—Levelling the Gramophone—Record Faults —Record Storage and Indexing. Bibliography 257 Index 267 xii : ERRATA p. 32 Fig. 15 {Caption) : For Zc read Ze. p. 39 Line 18 should read : 2 7T f L = L that is, f — — , when = 2 7T f C 'ITT p. 40 Add footnote to line 7 .• It should be noted, however, that in combining impedances account has to be taken of phase relations. But by writing Z = R -j- X, where j stands for and denotes ; ^ _ j that the reactance X is 90° out of phase with the resistance R, we can perform the algebraic operations indicated on pages 40, 41 and 42 and the phases will take care of themselves. If the resultant impedance is then expressed in similar form, this will indicate directly its resistance and reactance components, p. 85 Line ii .* Delete cm-. A ^ A Last line : For -— read 42-8 42-8 p. 115 Line 20 should read ; where m -f- n = M. etc. Line 26 should read : ^og (OP) - m = log (op)„ p. 217 Fig. 102 {Caption) : Sth line : For inpedance read impedance, yth and gth lines : For value read valve, Lootnote : For Davy read Davey. p. 268 2.nd Col. line 4 should read , stiffness/mass ratio. LIST OF ILLUSTRATIONS HALF-TONE PLATES Plate I. Two Modern Gramophones. Frontispiece (i) E.M.G. External Horn Model (ii) H.M.V. “Re-entrant’' (Phantom view) Facing page Plate II. Recording Instruments. ... 20 (i) Two Columbia Mechanical Re- corders (ii) Electromagnetic Recorder with rubber loading 1 ’late hi. Old Recording Conditions. ... 22 (i) Jos6 Collins (ii) A Jazz Band Plate IV. New Recording Conditions (Electrical). 28 The Halle Orchestra, in Free Trade Hall, Manchester Plate V. Historical Gramophones. .44 (i) Treadle Machine Graphophone (ii) Berliner Gramophone (iii) H.M.V.

Load more

  296

Copy Link