Active Noise Control Primer

Abstract

It is rather rare for an active researcher in a particular discipline to be critical about the contributions made by his/her field of research towards technology. As becomes apparent by reading the preface, the author of this book is refreshingly different. He candidly admits that to date the practical (author's emphasis) applications of active noise control are few. However, having said that it is also apparent from the hundreds of archival publications that there are success stories, and to quote the author again `when active noise control works, it really works'. Graduate students and professionals who are new to the field of active control are often faced with the fact that they need a working knowledge of several fields, such as microelectronics and digital signal processing, in addition to being well versed in acoustics and noise control. This book certainly fills the need of such readers and assumes no background in any of the fields mentioned above.The book has been organized into eight chapters. The first chapter is a brief introduction about the organization of the book and suggests advanced references for readers who want to educate themselves more about active noise control. Chapter 2 is an introduction to the fundamentals of sound and its characteristics. While there is adequate coverage of most practical aspects it would have been very useful if the author had included a rather brief description of sound level meters and digital signal analysers used for pressure measurements. The next chapter introduces the reader to the important concepts in noise control such as acoustic power and impedance. The fourth chapter explains passive noise control procedures for free-field radiation and rightly points out that it works better at higher frequencies, thus motivating the requirement for active noise control at lower frequencies. Various issues associated with active noise control in free-field conditions are addressed through a series of seven questions, and in fact I have used this approach to introduce my graduate class in acoustics to the concept of active noise control! From the free-field problems the author moves to enclosed sound fields in chapter 5 and the treatment of passive control measures, which is rather short. In fact this chapter is rather short in its treatment of either active or passive noise control measures, considering that enclosed sound field control has been the motivating factor for active control. However, in the next chapter on duct acoustics, sufficient discussion on the do's and don'ts of active noise control can be found. The final two chapters are really well written and enlighten readers on the digital and signal processing aspects of active control. The final chapter is the longest and is a very good introduction to adaptive feedforward controller characteristics and what is desirable for the design of good controllers. Important issues such as sampling rates, quantization errors, leakage and convergence issues are addressed adequately.In all these chapters the author uses a `side story' to narrate his consulting experiences in the field, which I believe adds value to what he is trying to convey. Furthermore the author has narrated these with considerable wit, making the reading rather pleasurable. Overall, I would recommend this book readily for any serious student embarking on research in the area of active control. This is a good primer before reading more `heavy' books in this area, including one written by the author himself.Mouli Padmanabhan