The Effects of Noise on Man PDF
Preview The Effects of Noise on Man
ENVIRONMENTAL SCIENCES An Interdisciplinary Monograph Series EDITORS DOUGLAS H. K. LEE E. WENDELL HEWSON C. FRED GURNHAM National Institute of Department of Meteorology Department of Environmental Environmental Health Sciences and Oceanography Engineering, Illinois Institute of Research Triangle Park The University of Michigan Technology, Chicago, Illinois North Carolina Ann Arbor, Michigan ARTHUR C. STERN, editor, AIR POLLUTION, Second Edition. In three volumes, 1968 DOUGLAS H. K. LEE E. WENDELL HEWSON DANIEL OKUN National Institute of Department of Meteorology University of North Carolina Environmental Health Sciences and Oceanography Department of Environmental Research Triangle Park The University of Michigan Sciences and Engineering North Carolina Ann Arbor, Michigan Chapel Hill, North Carolina L. FISHBEIN, W. G. FLAMM, and H. L. FALK, CHEMICAL MUTAGENS: Environ- mental Effects on Biological Systems, 1970 DOUGLAS H. K. LEE and DAVID MINARD, editors, PHYSIOLOGY, ENVIRON- MENT, and MAN, 1970 KARL D. KRYTER, THE EFFECTS OF NOISE ON MAN, 1970 In preparation R. E. MUNN, BIOMETEOROLOGICAL METHODS THE EFFECTS OF NOISE ON MAN KARL D. KRYTER Stanford Research Institute Menlo Park, California 1970 ACADEMIC PRESS New York and London Copyright © 1970, by Academic Press, Inc. ALL RIGHTS RESERVED. NO PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORM, BY PHOTOSTAT, MICROFILM, RETRIEVAL SYSTEM, OR ANY OTHER MEANS, WITHOUT WRITTEN PERMISSION FROM THE PUBLISHERS. ACADEMIC PRESS, INC. Ill Fifth Avenue, New York, New York 10003 United Kingdom Edition published by ACADEMIC PRESS, INC. (LONDON) LTD. Berkeley Square House, London WIX 6BA Library of Congress Catalog Card Number: 74-117112 Printed in the United States of America For my wife Grace and daughters Dianne, Victoria and Kathryn PREFACE Several years ago, when I was at Bolt Beranek and Newman Inc. in Cambridge, Massachusetts and was under contract to the Office of the Surgeon General of the Army, I began to update a monograph, published in 1950, titled "The Effects of Noise on Man." This effort was continued and eventually completed at Stanford Research Institute, under contract to the National Aeronautics and Space Administration. Some of the sections concerning concepts and data related to noise-induced deafness are from papers prepared under a research grant from the National Institutes of Health. An attempt has been made to provide a critical and historical (dating from 1950) analysis of the relevant literature in the field and, as warranted, to derive new or modify existing techniques for the evaluation of environmental noise in terms of its effects on man. In Parts I and II of this book, fundamental definitions of sound, its measurement, and concepts of the basic functioning and attributes of the auditory system are provided. These chapters also present, along with their experimental basis, procedures for estimating from physical measures of noise its effects on man's auditory system and speech com- munications. Part III is devoted to man's nonauditory system responses and includes information about the effects of noise on such things as work performance, sleep, feelings of pain, vision, and blood circulation. It is clear that some of the more complex, and perhaps more important from a health viewpoint, effects of noise have to do with these somewhat second-order reactions. Tolerable limits of noise with respect to its effects on man's auditory and nonauditory systems are suggested at various places. The bibliography consists of those items referred to in the text, plus some additional items that are particularly pertinent to given points or that are important general sources of relevant information. In the preparation of this book some 4000 articles were, except for many of the non-English publications, read or reviewed. A limited number of copies of the original draft bibliography, which is organized around 24 subtopics, can be obtained by writing to me at the Stanford Research Institute. I regret that space does not permit the inclusion of a larger bibliography. XV ACKNOWLEDGMENTS* Grateful acknowledgment is given to the numerous authors and editors of journals and books for permission to reproduce their figures. I owe many thanks to Miss Dorian Doebler, my secretary, for her skills and great patience during innumerable typings of the manuscript and to Mrs. Margaret Troy and Mrs. Natalie McDonald for editing the major portion of the bibliography. Michael Hecker, Manfred Heckle, Eric Rathe and Henning von Gierke graciously translated or furnished me translations of portions of some of those articles reviewed that were published in German. I am also deeply indebted to Drs. Frank R. Clarke and James R. Young, Stanford Research Institute, Professor James P. Egan, University of Washington, and Professor Walter A. Rosenblith, Massachusetts Institute of Technology, for reviewing various portions of the manuscript. Their detection of errors and constructive suggestions were invaluable; some of their suggestions could not be utilized however because of limited time and ability on my part. Finally, I wish to express gratitude for the encouragement and support I received in this endeavor from Colonel William Hausman and Dr. Glen R. Hawkes of the Office of the Surgeon General of the Army, Dr. Gilbert Tolhurst of the Office of Naval Research, and Mr. Harvey Hubbard and Mr. Phillip Edge of the National Aeronautics and Space Administration. I can only hope that this book partially justifies the support they have given me. *We have reproduced, with their permission, some figures and tables from the documents of the American National Standard Institute. Copies of those documents may be purchased from that organization at 1430 Broadway St., New York, New York. xvii PART I AUDITORY SYSTEM RESPONSES TO NOISE Introduction In the fields of electronics, neurophysiology, and communication theory, noise means signals that bear no information and whose intensities usually vary randomly in time. The word noise is used in this sense in acoustics, but more often it is used to mean sound that is unwanted by the listener, presumably because it is unpleasant or bothersome, it interferes with the perception of wanted sound, or it is physiologically harmful. Noise, as unwanted sound, does not necessarily have any particular physical characteristic (such as randomness) to distinguish it from wanted sound. For example, an information-bearing signal such as speech may be so intense that it is subjectively unwanted and may even be harmful to the ear of the listener, whereas a sound such as so-called "white" noise that is random, or nearly so, in the physical sense may be subjectively quite acceptable, particularly if it serves to mask other sounds that, if audible, would be bothersome. As far as man's auditory system is concerned, there is no distinction to be made between sound and so-called noise, and in the text to follow the word "noise" is often used in place of "sound" merely to draw attention to the theme of the book. There are certain unwanted effects of sounds that appear to be related rather precisely to physical characteristics of the sound in ways that are more or less universal and invariant for all people. The effects we refer to are (a) the masking of wanted sounds, particularly speech, (b) auditory fatigue and damage to hearing, (c) excessive loudness, (d) some general quality of bothersomeness or noisiness, and (e) startle. These unwanted effects of sound upon man's peripheral and subjective auditory response system are mainly what this book is about. Because the effects are (a) similar for all people, (b) neither primarily dependent on learning, nor, except to some extent for startle, able to be unlearned, and (c) quantitatively related to the physical nature of sounds, they deserve the attention and 1 2 The Effects of Noise on Man understanding of persons interested or involved in the design of devices that generate sound, in the control of the sound during its transmission, or in the protection of the health and well-being of people exposed to the sound. Indeed, nearly all measurements made of sound by acoustical engineers are made for the immediate or ultimate purpose of evaluating or controlling the effects of the sound on man. Chapters 1 through 3 of this book are concerned with basic and somewhat academic (except to the research worker) information concerning noise and functioning of the ear. Some readers may wish to turn immediately to Chapter 4, the start of the material on noise damage to the ear, or even to Part II of the book, Subjective Responses to Noise. However, all parts are interrelated and a fuller understanding of the state-of-the-art and problems in this field is to be had from reading the whole book. Chapter 1 Analysis of Sound by the Ear Definitions of Sound For the human listener, sound in the frequency domain is defined as acoustic energy between 2 Hz and 20,000 Hz, the typical frequency limits of the ear. The lowest frequency of sound that has a pitch-like quality is about 20 Hz and the upper frequency audible to the average adult is about 10,000 Hz. Hertz (Hz) is the name, by international agreement, for the number of repetitions of similar pressure variations per second of time; this unit of frequency was previously called "cycles per second" (cps or c/s). The decibel (dB) is the common unit of measurement of sound pressure. It is 20 log of the ratio between the 10 root-mean-square (rms) pressure of a given sound and usually, and for this document, the reference rms pressure of 0.0002 microbar (jubar). While the unit //bar, and another unit, dynes per square centimeter (dyne/cm2), are in common use, the unit newtons per square meter (N/m 2 ) is becoming the international standard unit of sound pressure. These units are related to each other as follows: 0.1 N/m2 = 1 dyne/cm2 = 1016 jubar. In the temporal domain, the rise time of a sound is the time required for a sound to go from ambient air pressure to the first occurrence of its peak pressure. The duration of a sound is the time in seconds from the start of the rise in pressure to the time the pressure envelope starts again to stay at ambient. In the intensity-time dimensions, sounds are labeled as being either "impulsive" or "nonimpulsive." Impulse sound, for this document, is defined as a change in rms air pressure greater than 40 dB per 0.5 sec; all other 0.5-sec intervals of sound are nonimpulsive. Nonimpulsive intervals may be described as changing in level or steady-state. Sound is here said to be steady-state when the rms pressure remains relatively constant (within ±5 dB) for successive periods of 0.5 sec. A sound, unless shorter in total duration than 0.5 sec, can go from impulsive to nonimpulsive and vice versa during its existence. The amplitude-phase relations between frequency components, and the 3 4 The Effects of Noise on Man number of components (bandwidth) of a sound will determine the moment-to-moment fluctuations to be expected in rms pressure taken over all frequencies. Therefore, the specification of a ±5 dB tolerance for steady-state level is suggested as a practical range. Theoretical calculations and actual measurements of random noise show that variations of ±5 dB or less are to be expected with 95% certainty for frequency bands wider than about 10 Hz, and ±2 dB or less for bandwidths wider than about 100 Hz (see Fig. 1 from Galloway [272]). Because of this unavoidable fluctuating of relatively narrow bands of random noise, it is the practice to use a sound level meter which has a pressure averaging time constant of 0.5 sec for making band spectral analysis of noise in order to achieve reasonably reliable measurements. Pressure-Temporal-Spectral Response Characteristics of the Ear to Sound Figure 2 is a schematic drawing showing the path and means by which sound enters the human ear, where it is transduced into motion in the fluid (perilymph) of the cochlea. This fluid action causes nerve fibers on the basilar membrane to send impulses to higher nerve centers where the impulses are perceived or interpreted as sound. The analysis of sound, in classical auditory theory, takes place in the ear with respect to the physical dimensions of frequency and intensity. Except for special circumstances, some of which will be discussed later, phase information appears to be of little significance to the subjective response to sounds. The primary psychological aspects of frequency and intensity are pitch and loudness. Psychological dimensions other than pitch or loudness - for example, density, volume (size), and perceived noisiness — have also been related to the frequency-intensity characteristics of sounds. These will be discussed later. The attribute of pitch has been ascribed in the past to possible cues of place of stimulation on the basilar membrane of the cochlea and rate of firing of peripheral neural units; the attribute of loudness has been ascribed to the rate at which neural impulses are generated in the cochlea. It is, however, the perception of the patterns of complex pitch and loudness in the flow of time that makes audition such a useful and pervasive part of man's consciousness. Critical Bandwidth of the Ear The abilities of the ear to perceive pitch as a function of frequency and loudness as a function of intensity, and to detect small changes in these attributes, were well mapped out prior to 1950. However, the ability of the ear
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