Finn Jacobsen - Fundamentals of General Linear Acoustics

This edition first published 2013

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Library of Congress Cataloging-in-Publication Data

Jacobsen, Finn.

Fundamentals of general linear acoustics / Finn Jacobsen, Peter Moller Juhl.

pages cm

Includes bibliographical references and index.

ISBN 978-1-118-34641-9 (hardback)

1. Sound-wavesTransmissionTextbooks. 2. Wave-motion, Theory ofTextbooks. I. Juhl, Peter Moller. II. Title.

QC243.J33 2013

620.2dc23

2013005223

A catalogue record for this book is available from the British Library.

ISBN: 9781118346419

The cover picture shows the output of a circular delay-and-sum beamformer. The picture is adapted from Stewart Holmes' MSc Thesis entitled Spheriodal Beamforming (Department of Electrical Engineering, Technical University of Denmark, 2012), in which beamforming with microphones in circular configurations in different baffles is analysed in detail.

Finn Jacobsen received an MSc in Electrical Engineering in 1974 and a PhD in Acoustics in 1981, both from the Technical University of Denmark (DTU). In 1996 he was awarded the degree of Doctor Technices by the Technical University of Denmark. In 1985 he became an Associate Professor in the Department of Acoustic Technology, DTU where he was Head of Department from 1989 to 1997. He is currently Head of Acoustic Technology, which is now a group within the Department of Electrical Engineering at DTU. His research interests include general linear acoustics, acoustic measurement techniques and signal processing, transducer technology, and statistical methods in acoustics. He has published approximately 100 papers in refereed journals and a similar amount of conference papers.

Finn Jacobsen has more than 25 years' experience with teaching acoustics at MSc level, and more than 15 years' experience with teaching fundamentals of acoustics at BSc level. He has supervised and co-supervised about 100 Masters thesis projects on acoustic topics. In the early 1990s he produced a set of lecture notes in Danish. From the end of the 1990s all lectures were given exclusively in English in the Acoustic Technology group at DTU, and Finn Jacobsen produced a completely new set of lecture notes which form the basis of this book and have frequently been updated and improved on the basis of comments from students.

Peter Mller Juhl obtained an MSc in electrical engineering from the Technical University of Denmark (DTU) in 1991 and in 1994 he received a PhD in numerical acoustics. He is currently an Associate Professor at the University of Southern Denmark, where he has had a key role in establishing the profile of acoustics in the BSc and MSc programmes in Physics and Technology. His research areas are general linear acoustics, mathematical and numerical modeling in acoustics, and source identification techniques such as beamforming and acoustic holography.

Peter Mller Juhl has 15 years of experience of teaching both basic and advanced acoustics to engineering students. Additionally he has taught physics at BSc level, and he has experience with teaching acoustics to students in the field of audiology. He has supervised approximately 50 BSc and MSc projects in acoustics. In his teaching he makes use of computer programs to visualise the theory and strengthen the understanding of the link between model, mathematical description and physical behaviour. Many of the figures in the present book have been created with these computer programs.

This book is a textbook on fundamentals of acoustic wave motion, and the topics covered by the book include duct acoustics, sound in enclosures, and sound radiation and scattering. Non-linear effects are only mentioned, and the effects of viscosity, heat conduction and mean flow are only touched upon. On the other hand, we have included classical expansions, because in our opinion there is an obvious link between technological possibilities and the relevance of theory. For more than ten years microphone array-based measurement techniques such as beamforming and holography, and loudspeaker array-based sound recording and reproduction techniques such as ambisonics, have made extensive use of results from classical analysis of sound fields (e.g., decompositions into spherical and cylindrical harmonics), which therefore have become more relevant than they seemed to be 30 years ago. Finally, measurements are important in acoustics, and therefore we have not only included a chapter on fundamentals of acoustic measurement techniques but also an appendix on applied signal analysis.

Acoustics is an interdisciplinary field, and throughout the world acoustic research at university level is carried out in relatively small groups, typically placed in departments focused on electrical engineering, applied physics, mechanical engineering, audiovisual engineering, or civil and environmental engineering. It has been our intention that the book should be equally accessible to readers with a background in electrical engineering, signal processing, physics and mechanical engineering.

The book is based on a number of lecture notes developed over many years and tested by numerous students. The notes have frequently been updated and improved on the basis of questions and critical comments from the students. We are grateful for the many generations of students whose comments have certainly improved the book.

We would also like to thank Jonas Brunskog for critical comments on the first draft of the book.