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ii^.--'_ :^^aB^pit4? ,1-. CO nj tr n~ nj rou i a : o m a ELEMENTS OF Acoustical Engineering p ELEMENTS OF Acoustical Engineering By HARRY F. OLSON, E.E., Ph.D. Acoustic Research Director RCA Manufacturing Company NEW YORK D. VAN NOSTRAND COMPANY, Inc. 250 Fourth Avenue 1940 Copyright, 1940, by D.VANNOSTRAND COMPANY,Inc. AllRightsReserved This book, or any parts thereof, may notbereproducedin anyform without writtenpermissionfromthepublishers PREFACE The reproduction of sound is so commonplace to-day that it is taken for granted by the layman. Nevertheless, the developments during the past two decades in the arts of communications and sound reproduction have been remarkable. In the early stages ofthe present epoch ofprogress the advances were made by pure scientists. As in the metamorphosis of any art, the burden has been gradually shifted to the applied scientist and engineer. These changes have led to a demand for expositions upon the fundamental principles of the new applied science of acoustics from the standpoint of the engineer. Accordingly, this book has been written with the idea of presenting the elements and principles of acoustics to the engineer. This text is the subject matter of thirty lectures prepared for presenta- tion at Columbia University. It is an exposition of the fundamental principles used in modern acoustics and a description ofthe existing acoustical instruments. Particular efforts have been directed towards the develop- ment of analogies between electrical, mechanical and acoustical systems, because engineers have found that the reduction of a vibrating system to the equivalent electrical circuit is a valuable aid in the analysis ofvibrating systems. These methods will become increasingly important as the front of engineering acoustics is broadened. As an aid to the establishment of these analogies an attempt has been made to depict a complete theme in each illustration. The book includes the current acoustic practices in radio, phonograph, sound motion pictures, public address, sound re-enforcing and sound mea- surements. Practically all modern transducers such as microphones, loud speakers, headphones and phonograph pickups are treated from the mechanical or the acoustical impedance viewpoint. A knowledge ofacoustics principles is not required for an understanding of the subject matter. The text may be read and understood by anyone familiar with the principles of elementary physics and simple electric circuit theory. The author wishes to express his gratitude to his wife, Lorene E. Olson, for assistance in the compilation, preparation and correction of the manu- script. PREFACE vi The author wishes to acknowledge the interest given by Messrs. L. M. Clement, Vice President, and E. W. Engstrom, Research Director, of the RCA Manufacturing Company, in this project. KUrry F. Olson January, 1940