SOUND ANALYSIS AND

NOISE CONTROL

SOUND ANALYSIS AND

NOISE CONTROL

JOHN E. K. FOREMAN, P.Eng. Professor Er.nerftus

Sound and Vibration Laboratory The University of Western Ontario

London, Canada

~ VAN NOSTRAND REINHOLD ~ _______ New York

Copyright © 1990 by Van Nostrand Reinhold

Library of Congress Catalog Card Number 90-11945

ISBN-13: 978-1-4684-6679-9

DOl: 10.1 007/978-1-4684-6677 -5

e-ISBN-13: 978-1-4684-6677-5

All rights reserved. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means-graphic, electronic, or mechanical, including photocopying, recording, taping, or information storage and retrieval systems-without written permission of the publisher.

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16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data

Foreman, John E. K., 1922-Sound analysis and noise control/by John E. K. Foreman.

p. cm. At head of title: University of Western Ontario, Faculty of

Engineering Science.

1. Noise control. 2. Sound. I. University of Western Ontario. Faculty of Engineering Science. II. Title. TD892.F67 1990 620.2'3-dc20 90-11945

CIP

CONTENTS

Preface I xi

Acknowledgments xiii

CHAPTER 1 BASICS OF SOUND I 1

1. 1 Genemtion of Sound / 1 1.2 Equations of Motion of Plane Waves / 3 1.3 Velocity of Plane Waves / 5 1.4 Specific Acoustic Impedance / 6 1.5 Spherical Sound Waves / 6 1.6 Sound Intensity / 7 1. 7 Levels / 9 1.8 Wavefonn, Frequency, Pressure Change / 10 1.9 The Decibel/II 1.10 Frequency Spectm of Sound / 14

References for Chapter 1 / 14

CHAPTER 2 MECHANISM OF HEARING AND SUBJECTIVE RATING I 16

2.1 Construction of the Ear / 16 2.2 Functioning of the Mechanism / 16 2.3 Subjective Response and Units for Rating of Noise / 19 2.4 Loudness; Phons and Sones / 20 2.5 Loudness of Short Dumtion Sounds / 21 2.6 Age-Related Hearing Loss-Presbycusis / 22 2.7 Noise-Induced Hearing Loss / 25

References for Chapter 2 / 26

CHAPTER 3 INSTRUMENTATION FOR NOISE MEASUREMENT / 27

3.1 Geneml / 27 3.2 Microphones / 27 3.3 Sound Level Meters / 35 3.4 Weighting Curves / 35 3.5 Basic Sound Level Meter System / 37 3.6 Vibmtion Tmnsducers / 38 3.7 Frequency Analyzers and Filtering / 40 3.8 Tape Recorders / 43 3.9 Signal Processing / 45

3.9.1 Leq Concept / 45 3.9.2 The LN Concept / 48 3.9.3 Level Recorders / 53

v

vi CONTENTS

3.9.4 Real-Time Analyzers (Digital and FFT) / 53 3.9.5 Sound Intensity Measurements / 62 References for Chapter 3 / 79

CHAPTER 4 SOUND FIELDS I 81

4. 1 Reflected Sound / 81 4.2 Ideal Sound Source / 81 4.3 Practical Sound Source / 82 4.4 Anechoic Rooms / 82 4.5 Reverberant Rooms / 85 4.6 Directivity Index and Directivity Factor / 85 4.7 Attenuation of Sound Pressure with Distance in a Free Field / 87 4.8 Attenuation of Sound Pressure with Distance in an Enclosure / 89 4.9 Propagation of Sound in Air / 93

4.9.1 The Plane Source / 93 4.9.2 The Point Source / 93 4.9.3 The Line Source / 94 4.9.4 4.9.5 4.9.6 4.9.7 4.9.8 4.9.9 4.9.10 4.9.11

General Factors Affecting Sound and Propagation / 94 The Effects of Wind / 94 The Effects of Temperature / 97 Humidity and Precipitation / 98 Absorption by Natural Features / 98 Reflection / 98 Absorption / 99 Diffraction / 100

4. 10 Outdoor Barriers / 10 1 4.10.1 Introduction / 101 4.10.2 Path Length Difference / 102 4.10.3 Thin Barriers / 102 4.10.4 Thick Barriers / 102 4.10.5 Fresnel Number / 103 4.10.6 Attenuation for Point and Line Sources / 103 4. 10.7 Ground Attenuation / 105

4. 11 Attenuation Provided by Trees / 108 References for Chapter 4 / 109

CHAPTER 5 ABSORPTION, SILENCERS, ROOM ACOUSTICS AND TRANSMISSION LOSS I 110

5.1 Absorption / 11 0 5.1.1 Introduction / 110 5.1.2 Absorption Material / 112 5.1.3 Panel Absorption / 118

5.2 Dissipative, Reactive and Active Silencers / 120 5.2.1 Dissipative Silencers / 121 5.2.2 Reactive Silencers / 125 5.2.3 Active Silencers / 136

5.3 Behavior of Sound in Rooms / 138 5.3.1 Reverberation and Decay of Sound in a Room / 138 5.3.2 Calculation of Reverberation Time / 140 5.3.3 Effect of Air Absorption on Decay Rate and Reverberation Time / 144

CONTENTS vii

5.3.4 Speech Intelligibility and Reverberation Time / 144 5.3.5 Measurement of Random-Incidence Absorption Coefficient / 145 5.3.6 Normal-Incidence Absorption Coefficient / 146

5.4 Sound Transmission Loss and Sound Transmission Class / 148 5.4. 1 Transmission Loss / 148 5.4.2 Sound Transmission Class STC / 153 5.4.3 Transmission Loss of Composite Walls and Effect of Flanking

155 References for Chapter 5 / 162

CHAPTER 6 VIBRATION AND VIBRATION CONTROL / 164

6.1 Introduction / 164 6.2 Equation of Motion for a System Having a Single Degree of Freedom / 164 6.3 Free Vibration without Damping / 165 6.4 Free Vibration with Damping / 166 6.5 Forced Vibrations without Damping / 168 6.6 Transmissibility / 170 6.7 Forced Vibration with Damping / 171 6.8 Motion Disturbance-Single Degree of Freedom / 174 6.9 Isolator Selection / 176 6.10 Types ofIsolators / 178 6.11 A Mass Subjected to Motion in Several Degrees of Freedom-Coupled and

Decoupled Modes / 180 6.12 Vibration Criteria / 182 6.13 Vibration Damping / 185

6.13.1 General / 185 6.13.2 Types of Treatments / 185 6.13 . 3 Performance Characteristics / 186 6.13.4 Frictional Damping / 189 6.13.5 Common Damping Materials / 189 6.13.6 Bonding / 189 6.13.7 Laminates / 189 References for Chapter 6 / 189

CHAPTER 7 NOISE CRITERIA AND REGULATIONS / 191

7. 1 Introduction / 191 7.2 Indices for Environmental Noise / 193

7.2.1 Direct Rating / 193 7.2.2 Perceived Noise Level / 193 7.2.3 Equivalent Sound Level Leq / 194 7.2.4 Day-Night Level Ldn / 194 7.2.5 Exceedance Levels LN / 194 7.2.6 Noise Pollution Level NPL / 195

7.3 Criteria for Indoor Noise Environment / 195 7.3.1 NC, PNC and RC Criteria / 195 7.3.2 Direct Rating Guides and Standards / 198 7.3.3 Speech Interference Level PSIL / 199 7.3.4 Other Criteria (or Guides) for Indoor Environments / 200 7.3.5 Speech Communication and Privacy / 201 7.3.6 Open-Plan Offices / 202

viii CONTENTS

7.4 Regulations of Hearing-Damage Risk in Industry-the U.S. Occupational Safety and Health Act Standards / 204 7.4.1 Background to OSHA Regulations / 205 7.4.2 U.S. Occupational Safety and Health Act of 1970 / 207 7.4.3 Ear Protectors / 211 7.4.4 Recent Studies in Canada Regarding Noise-Induced Hearing Loss

and Damage Risk Criteria / 211 7.5 Outdoor Noise Criteria / 214

7.5. 1 Typical Noise Levels, Statistical Community Noise, and Recommended Outdoor Limits / 214

7.5.2 Rating Procedures / 217 7.5.3 Psychoacoustic Studies on Aversiveness to Typical Noises / 220 References for Chapter 7 / 221

CHAPTER 8 GENERAL REVIEW OF NOISE CONTROL, AND PRACTICAL EXAMPLES I 224

8.1 General Review of Noise Control / 224 8.1.1 General Noise Control Measures / 224 8.1.2 A Program for Noise Control / 232 8.1.3 Methods of Noise Reduction / 233 8.1.4 Noise Measurement / 234

8.2 Practical Examples of Noise Control Techniques / 239

CHAPTER 9 NOISE SOURCE DIAGNOSIS AND CASE STUDIES I 340

9.1 The Use of Sound Power Data in Source Diagnosis / 340 9.2 Further Case Studies in Noise Control / 344

9.2.1 Reduction of Noise Levels in a Food-Packaging Area / 344 9.2.2 Reduction of Engine-Generator Cooling-Fan Noise / 346 9.2.3 Reduction of Noise from a Mine Ventilation Fan / 347 9.2.4 Reduction of Railcar Retarder Noise / 348 9.2.5 Reduction of Mechanical Equipment Noise in a Penthouse

Apartment / 349 9.3 Case Study of Noise Reduction from a Centrifugal Pump and Motor Drive in

a Laboratory / 352 9.3.1 Introduction / 352 9.3.2 The Problem / 352 9.3.3 Suggested Procedure / 352 9.3.4 Instrumentation / 356 9.3.5 Comments on and Results of Typical Measurements / 356 9.3.6 Sample Calculations / 357 9.3.7 Results / 362 9.3.8 Discussion / 362

9.4 Example of Use of Silencer and Silencing Material in Ventilation System 365

9.5 NIOSH Case Histories / 369 9.6 General Texts, Handbooks, and Manuals / 415

CREDITS FOR FIGURES AND TABLES I 419

APPENDIX I GLOSSARY OF ACOUSTICAL TERMS I 423 APPENDIX II CONVERSION FACTORS I 426 APPENDIX III ACOUSTICAL STANDARDS ORGANIZATIONS AND

STANDARD DOCUMENTS I 427 APPENDIX IV USEFUL ACOUSTICS PERIODICALS I 438 APPENDIX V GUIDELINES FOR REGULATORY CONTROL OF

OCCUPATIONAL NOISE EXPOSURE AND HEARING CONSERVATION I 439

APPENDIX VI BUYER'S GUIDE TO PRODUCTS FOR NOISE AND VIBRATION CONTROL I 442

CONTENTS ix

APPENDIX VII DYNAMIC MEASUREMENT INSTRUMENTATION BUYER'S GUIDE I 448

INDEX I 455

PREFACE

This book has been written to provide an intro­duction to the fundamental concepts of sound and a comprehensive coverage whereby un­wanted sound (noise) can be controlled. Al­though there are many notable textbooks which deal primarily with the physics (or theory) of sound, and others which treat noise control in a strictly practical (and sometimes even empir­ical) manner, there are few textbooks that pro­vide a bridging between the necessary under­standing of the fundamentals of sound (its generation, propagation, measurement) and the application of these fundamentals to its control. This book provides that link.

The text presents noise control primarily at the introductory level. As such, the book should be of interest to students in engineering pro­grams at the university level and to students in technology and technician programs at com­munity colleges who need to acquire a basic understanding of noise control principles and applications; it should be of value to the prac­ticing engineer who may have no formal train­ing in noise control but whose responsibilities now involve assessment of noise and imple­mentation of methods to control it; and it should appeal to teachers of a first course in sound analysis and noise control who must rely upon an authoritative and comprehensive text book on the subject.

The development of the presentation of the material in the text has been designed so that the book can serve also as a means of self­study. To this end, worked examples are in­cluded at the appropriate sections throughout the text and in two chapters at the end of the text in order to demonstrate the principles which have been developed. The worked ex­amples are typical of those problems which may be encountered in real situations.

Chapter 1 deals with the basics of sound, in order to inform the reader of some of the phys­ics associated with sound phenomena.

Chapter 2 deals with the mechanism of hear­ing and the subjective rating of sound, includ­ing age-related and noise-induced hearing loss.

Assessment of any noise problem involves a knowledge of the instrumentation available for measurements, the limitations of this instru­mentation, the appropriate procedures for mak­ing the measurements with the instrumentation, and the methods by which the measured data can be analyzed. Chapter 3 provides an up-to­date coverage of these requirements, including a section on one of the newest and most valu­able tools in noise studies-sound intensity measurement. The capability of being able to measure sound intensity as compared with con­ventional sound pressure has given the noise engineer a means of dealing with noise prob­lems which had heretofore been denied-par­ticularly noise source identification.

Chapter 4 concerns the propagation and at­tenuation of sound in free fields (e.g., outdoors with no reflecting surfaces) and the attenuation of sound in an enclosure. Outdoor barriers are also discussed in this chapter.

Chapter 5, one of the most important in the book, deals with absorption of sound in enclo­sures, reverberation in enclosures (and its ap­plication) and sound transmission loss through barriers.

Noise is the result of surface radiation, i.e., the surface moves back and forth (a seemingly infinitesimally small amount at times), which in tum excites a pressure propagation (sound wave) due to molecular interaction and excita­tion of the air adjacent to the surface. This sur­face excitation is often the result of structure­borne vibration due to rotating or reciprocating machines. Where such conditions can exist, it is imperative that the vibrating machine be iso­lated (or decoupled) from its attachment so as to alleviate as much as possible the excitation of adjacent surfaces, as mentioned above. Chapter 6 deals with the theory of vibration and

xi

xii PREFACE

vibration control, including applications as to the appropriate vibrating isolators and/or damping material to be used to reduce struc­ture-borne vibration.

The situation regarding noise criteria and regulations, as they have historically evolved in the U.S.A. and as they currently pertain in Canada, is discussed in Chapter 7. Criteria for indoor noise environment, hearing-damage risk and criteria at the workplace (industry), and outdoor noise criteria are extensively covered.

Notable aspects of this text are found in the last two chapters. Chapter 8 covers a review of general noise control measures and a program for noise control in industry; it also outlines a large number of practical examples involving noise situations and noise control techniques.

Chapter 9 discusses the use of sound power data in noise source diagnosis and presents a wide range of in-depth case studies of noise problems-all representative of situations en­countered in practice.

Included in the appendices are a complete

listing of acoustical standards organizations and acoustical standards, useful acoustical periodi­cals, anq a list of suppliers of acoustical ma­terials and measuring instruments.

The writing and completion of this book would not have been possible without the val­uable assistance of the many experts in the field of sound analysis and noise control mentioned throughout the text and the references; the crit­ical comments by uncountable numbers of stu­dents who have worked with the author in lec­tures, laboratories and tutorials on sound analysis and noise control over the years; the many typists who endured the largely indeci­pherable handwriting of the author, and who, with perseverance and admirable expertise, translated concepts into readable text; and the author's family who, besides being supportive, also endured many months of having the dining room table littered with all sorts of paper, books, periodicals, files, pencils, rulers, pens, scissors, glue bottles, and whatever was re­quired in putting together a book of this nature.

ACKNOWLEDGMENTS

In the preface, I mentioned those people who played a part in the development of this text. I wish to single out, in particular, all of the la­dies to whom I am indebted.

First of all, my wife, Jan, whose support during the arduous years of writing and final­izing the book meant so much to me.

Then come the many ladies who have trans­lated my thoughts on paper into the text which

now follows. These are Elizabeth, Cathie, San­dra, Jacquie, and Pennie.

And finally, I wish to acknowledge, in par­ticular, Mary, who, when introduced to this project, quickly assessed the essence of what was required in making this book viable, and in fact became a welcome and valuable assis­tant to me.

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SOUND ANALYSIS AND

NOISE CONTROL