Читать книгу Engineering Acoustics - Malcolm J. Crocker - Страница 12

Preface

Over the past decades, the authors of this book have been working together in several areas of acoustics and vibration, which has led to a number of joint research papers published in scholarly journals and congress proceedings, as well as book chapters. Our goal in writing this book was first to cover the fundamental theory relevant to engineering acoustics, noise, and vibration, and second to describe practical ways in which noise and vibration can be controlled and reduced. Each of the sixteen chapters has several worked examples designed to make the theoretical and empirical prediction methods accessible for readers. This book is aimed at senior undergraduates, graduate students, and practitioners in the noise and vibration fields. Although the use of SI units is emphasized in the book, English units are given in addition in some cases, in particular in Chapter 13, for the convenience of readers in the USA.

The book begins with fundamentals (Chapters 1–3) and continues with human aspects – hearing, speech, and the effects of noise and vibration on people (Chapters 4–6). At this point, two chapters are included on noise measurement (Chapters 7 and 8). Chapter 9 deals with principles of noise and vibration control. The remaining Chapters 10–16 deal with specific practical problems. These chapters include: acoustical design of reactive and passive mufflers and silencers (Chapter 10), control of noise and vibration of machines (Chapter 11), noise and vibration control in buildings (Chapter 12), noise and vibration of air‐conditioning systems (Chapter 13), surface transportation noise (Chapter 14), aircraft and airport noise (Chapter 15), and community noise and vibration (Chapter 16).

The first author has five decades of experience in undergraduate and graduate teaching, research, and consulting in acoustics, noise, and vibration. The research was sponsored by companies and government agencies. The second author has over two decades of experience in undergraduate and graduate teaching, research, and consulting in acoustics, noise, and vibration and in performing research funded by government and private sources. He has also been a consultant with industry in noise and vibration.

Although our understanding of the acoustics, noise, and vibration fundamentals has remained largely unchanged, the last half century (1970–2020) has seen dramatic changes in our ability to make calculations, useful predictions, and measurements. Before the wide availability of electronic calculators (1975), most calculations were made using log tables and slide rules. Large, expensive computers did not appear until the 1960s and 1970s, and it was not until the early 1980s that personal computers and laptops became available. Now computers big and small are everywhere. Computational advances have revolutionized our ability to make acoustics, noise, and vibration calculations.

Because they cover important topics, Chapters 8, 10, 12, and 13 have received expanded treatment in this book. Contracts and grants received by the first author enabled him to conduct research on sound intensity in which he conceived the first use of sound intensity measurements in determining the transmission loss of partitions. During this period, he chaired the ANSI SI‐12 committee which produced the first ever standard, S12‐12‐1992, Engineering Method for the Determination of the Sound Power Levels of Noise Sources Using Sound Intensity. Some of the research results are summarized in Chapter 8.

The first author received a nine‐year contract from a company which produced over 80% of the new mufflers for automobiles manufactured in the USA in the 1960s and 1970s. During this research, he together with a graduate student, C.‐I. J. Young, produced the first acoustical finite element model to predict muffler noise attenuation. This, together with research on measuring source impedance of engines and prediction of the transmission loss of concentric tube resonators with J.W. Sullivan, resulted in improved modeling of the acoustics of exhaust systems. These research results are included in Chapter 10. Intense noise was caused by the Saturn V moon rocket at launch. During the 1960s there was great concern about the vibration and potential for fatigue during the launch of the Saturn V vehicle. First during a 1966–1997 short course – Program for Advanced Study – and then through personal contacts and communications with Richard H. Lyon, the first author began studies on SEA. He and a colleague produced the first papers demonstrating the usefulness of SEA in predicting the transmission of sound through single and double partitions. These results and others are included in Section 12.5 of Chapter 12. The first author also received several research contracts from ASHRAE, AMCA, and ARI to study the acoustics of air‐conditioning systems. These studies resulted in a new in‐duct method of measuring the sound power of fans. During this period, the first author served as chair of the ASHRAE Technical Committee 2.6 Sound and Vibration. This experience and background information has been included in Chapter 13 in addition to some text and figures from an earlier chapter written for CRC Press by A.J. Price and M.J. Crocker.

Chapter 8 reviews the use of sound intensity measurements to determine the sound power of machinery, noise source identification, and the transmission loss of partitions. Accurate sound intensity measurements only became possible with the development of two‐channel mini‐computers, the fast‐Fourier transform and the sound intensity algorithms. The use of sound intensity measurements allows the accurate determination of the sound power of machinery in situ even in the presence of extremely noisy ambient conditions. Sound intensity measurements can also be used to determine the transmission loss of walls without the need for a reception room. In addition, such measurements allow the transmission loss of different parts of a wall partition to be determined, which the conventional two‐room method does not.

Chapter 10 deals with reactive and passive mufflers and silencers. Reactive mufflers are used on all automobiles and trucks, and proper acoustical design is of course most important. Although useful theory and measurements date back to the 1950s, it was not until finite element modeling was first used in 1971 on non‐concentric reactive mufflers that the attenuation of such mufflers could be predicted accurately. This chapter also reviews and compares different attempts to predict the attenuation of passive mufflers used in industrial systems.

Chapter 12 discusses various aspects of sound and vibration in buildings. An important aspect of building acoustics is the unwanted transmission of sound from one room to an adjoining one. One measure of the effectiveness of a party wall to reduce this transmission is the sound reduction index, commonly called the transmission loss (TL). This chapter presents different theoretical models for TL and also measurements of TL for a wide variety of wall structures. A useful theoretical approach to determine the TL of single and multiple layer walls is statistical energy analysis (SEA), as described in Section 12.5 of Chapter 12.

Chapter 13 deals with the noise and vibration generated by air‐conditioning (HVAC) systems in buildings. Although such systems are widely used they are often inadequately or incorrectly designed acoustically. Correct design at the beginning often costs a little more, but corrections made to such systems later, after they are installed, can be very expensive.

Malcolm J. CrockerJorge P. Arenas

30 September 2020