Noise control: from concept to application

438 Pages·2014·6.837 MB·English

by  Hansen, Colin H

Noise Control
Also available from Taylor & Francis
Engineering Noise Control
David Bies and Colin Hansen
Spon PressHb: 0–415–26713–7
Pb: 0–415–26714–5
Understanding Active Noise Cancellation
Colin H. Hansen
Spon PressHb: 0–415–23191–4
Pb: 0–415–23192–2
Active Control of Noise and Vibration
Colin Hansen and Scott Snyder
Spon PressHb: 0–419–19390–1
Room Acoustics
Heinrich Kuttruff
Spon PressHb: 0–419–24580–4
Sound Reinforcement Engineering
Wolfgang Ahnert and Frank Steffen
Spon PressHb: 0–415–23870–6
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Noise Control
From concept to application
Colin Hansen

LONDON AND NEW YORK
First published 2005 by Taylor & Francis 2 Park Square, Milton Park, Abingdon, Oxon OX14
4RN
Simultaneously published in the USA and Canada by Taylor & Francis Inc, 270 Madison Ave,
New York, NY 10016, USA
Taylor & Francis is an imprint of the Taylor & Francis Group
This edition published in the Taylor & Francis e-Library, 2005.
“To purchase your own copy of this or any of Taylor & Francis or Routledge's collection of
thousands of eBooks please go to www.eBookstore.tandf.co.uk.”
© 2005 Colin Hansen
Publisher’s Note
This book has been prepared from camera-ready copy supplied by the author
All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or
by any electronic, mechanical, or other means, now known or hereafter invented, including
photocopying and recording, or in any information storage or retrieval system, without permission
in writing from the publishers.
British Library Cataloguing in Publication Data A catalogue record for this book is available from
the British Library
Library of Congress Cataloging in Publication Data Hansen, Colin H., 1951– Noise control: from
concept to application/Colin Hansen. p. cm. Includes bibliographical references and index. 1.
Soundproofing. 2. Noise control. I. Title. TH1725.H36 2005 693.8′34–dc22 2004028048
ISBN 0-203-00481-7 Master e-book ISBN
ISBN 0-415-35860-4 (Hbk)
ISBN 0-415-35861-2 (Print Edition) (Pbk)
Contents

PREFACE vi
ACKNOWLEDGMENTS vii

CHAPTER ONE Fundamentals 1
CHAPTER TWO Noise Criteria and Basic Instrumentation 60
CHAPTER Sound Sources and Sound Power Measurement 101

THREE
CHAPTER Sound Propagation Outdoors and in Rooms 148

FOUR
CHAPTER FIVE Sound Absorbing Materials: Properties and Their 208

Measurement
CHAPTER SIX Partitions, Enclosures and Barriers 246
CHAPTER Muffling Devices 322

SEVEN

APPENDIX A Properties of Materials 413
REFERENCES 415
INDEX 422
Preface

This is a textbook intended for undergraduate or graduate students wanting to learn how
to solve problems in industrial noise control. Occupational Health and Safety engineers
as well as consultants in noise control should also find the book useful. Although this
book may appear similar to the book, Engineering Noise Control by Dr Bies and this
author, it does in fact represent an entirely different approach to the coverage of relevant
material. The concepts discussed in the book are illustrated with many examples that are
worked out in detail. There are very few derivations of equations, but reference is made
to texts where they are derived. Complex analyses are not included and neither are some
of the advanced techniques (such as active control) that are discussed in Engineering
Noise Control. The book is an excellent learning tool for those who wish to apply their
noise control knowledge to real problems.
Acknowledgments

The author would like to express his deep appreciation to his family, particularly his wife
Susan and daughters Kristy and Laura for the patience and support which was freely
given throughout the years taken to complete this book. The author is particularly grateful
to his daughter Kristy for her meticulous proofreading of the manuscript.
This book is dedicated to Susan, to Kristy and to Laura.
CHAPTER ONE
Fundamentals

LEARNING OBJECTIVES
In this chapter the reader is introduced to:
• fundamentals and basic terminology of noise control;
• noise-control strategies for new and existing facilities;
• the speed of sound and the wave equation;
• plane and spherical waves;
• energy density; sound intensity and sound power;
• decibels and sound level;
• frequency analysis and sound spectra;
• loudness and frequency weighting;
• adding and subtracting sound levels and combining level reductions; and
• three kinds of impedance.
1.1 INTRODUCTION
The World Health Organisation (Goelzer et al.) has recognized noise as the most
significant health hazard to the working population in terms of the number of people
affected. In many industries there is much that can be done to alleviate harmful noise.
Perhaps the most insidious aspect of noise induced hearing loss is that in most cases
damage accumulates over time and is only recognized as a problem when it is too late to
do anything about it.
Noise can also affect our daily living away from the work place. This type of problem
is called environmental noise pollution and it is unhealthy for us in terms of our
psychological well being, which in turn can affect our physical health. In this context,
noise is defined as sound that is unwanted by one or more individuals, even though it
may be wanted by someone else.
When considering noise control, it is well known that the most cost effective solution
to a problem is often to control the noise generating mechanism right at its source. This
often has the added benefit of making the process more efficient in addition to being less
noisy. However, it is often (although not always) only manufacturers of equipment who
can alter the noise generating processes in their equipment, which leaves the engineer
who is responsible for an existing item of noisy machinery to find some other way of
reducing the noise that reaches places or people where it is either a hazard or unwanted.
Noise control 2
Often this treatment takes the form of enclosures, barriers, mufflers or vibration isolation
and is referred to as “add-on” noise-control technology. Poorly designed “add-on”
measures can prove cumbersome in use and are likely to be sabotaged by employees who
see them as adversely affecting their efficiency and productivity.
The purpose of this text is to address the causes and methods of control of both
occupational and environmental noise with many example problems to illustrate the
principles. Much of the background to the discussion presented here is provided in the
more comprehensive text on which this one is based (Bies and Hansen, 2003).
The treatment here is restricted to passive noise control as opposed to active noise
control where “anti-noise” sources are introduced to “cancel” unwanted noise. Active
noise control is very difficult to apply successfully in an industrial environment;
development costs are generally high and on-going maintenance is currently an issue.
The principles of active noise control are discussed in detail in another text (Hansen,
2001).
The discussion in this chapter begins with an outline of noise control strategies and a
discussion of the fundamental principles of acoustics, followed by an explanation of how
noise is quantified, with the intention of providing a basis for understanding the
applications discussed in the remainder of the book. In chapter 2, noise criteria are
discussed and instrumentation for measuring noise is described. Chapter 3 describes the
sound fields produced by different sources and various means for measuring the sound
they produce. Chapter 4 is concerned with sound propagation outdoors and in rooms.
Chapter 5 is a detailed treatment of sound absorbing materials and in particular, their
properties and measurement. Chapter 6 includes methods for calculating the sound
transmission loss of partitions and the design of enclosures, while Chapter 7 is concerned
with the design of dissipative and reactive mufflers.
1.2 NOISE-CONTROL STRATEGIES
Possible strategies for noise control are always more numerous for new facilities and
products than for existing facilities and products. Consequently, it is always more cost
effective to implement noise control at the design stage than to wait for complaints about
a finished facility or product.
In existing facilities, controls may be required in response to specific complaints from
within the work place or from the surrounding community, and excessive noise levels
may be quantified by suitable measurements. In proposed new facilities, possible
complaints must be anticipated, and expected excessive noise levels must be estimated by
some procedure. Often it is not possible to eliminate unwanted noise entirely and more
often to do so is very expensive; thus minimum acceptable levels of noise must be
formulated, and these levels constitute the criteria for acceptability.
Criteria for acceptability are generally established with reference to appropriate
regulations for the work place and community. In addition, for community noise it is
advisable that at worst, any facility should not increase background (or ambient) noise
levels in a community by more than 5 dB(A) over existing levels without the facility,
irrespective of what local regulations may allow. Note that this 5 dB(A) increase applies