SUBJECT TO ER3A.TA CORRECTION
PUBLIC HEALTH AND WELFARE
CRITERIA FOR NOISE
July 27, 1973
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FOREWORD
The Noise Control Act of 1972 requires that the Administrator of The Environmental
Protection Agency (EPA) develop and publish criteria with respect to noise. These criteria are
to "reflect the scientific knowledge most useful in indicating the kind and extent of all identi-
fiable effects of noise on the public health and welfare which may be expected from differing
quantities and qualities of noise." This document meets that requirement.
The terms "criteria and standards" are generally used interchangeably in the scientific
communities concerned with noise and its control. However, in accordance with the intent of
the U.S. Congress, criteria for environmental pollutants are to reflect an honest appraisal of
available knowledge relating to health and welfare effects of pollutants, (in this case, noise).
The criteria are descriptions of cause and effect relationships. Standards and regulations must
take into account not only the health and welfare considerations described in the criteria,
but also, as called for in the Noise Control Act of 1972, technology, and cost of control. This
criteria document, therefore, serves as a basis for the establishment of the recommended envir-
onmental noise level goals to be related to the "Effects Document" called for by Section 5(a)(2)
of the Noise Control Act. That document, along with this criteria document, will become the
basis for standards and regulations called for by Sections 6 and 7 of the Noise Control Act.
Further, the terms "health and welfare," as used in the Noise Control Act include, as in
other environmental legislation, the physical and mental well being of the human populations.
The terms also include other indirect effects, such as annoyance, interference with communica-
tion, and loss of value and utility of property, and effects on other living things.
In preparing this Criteria Document, EPA has taken into account the vast amount of data
in the general professional literature and the information contained in the "Report to the
President and Congress on Noise" and its supporting documents prepared under Title IV, PL 91-
604. To bring to bear the views and opinions of some of the world's leading experts on current
knowledge regarding the effects of noise, EPA sponsored an International Conference on Public
Health Aspects of Noise, in Dubrobnik, Yugoslavia in May 1973. The proceedings of that con-
ference have been applied to the preparation of this document. They are available, as stated in
the Appendix to this document.
The criteria presented herein shall be revised and elaborated upon as the results of continu-
ing investigations on the effects of noise on health and welfare become available.
Foreword-1
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The criteria presented herein shall be revised and elaborated upon as the results of con-
tinuing investigations on the effects of noise on health and welfare become available.
Alvin F. Meyer, Jr.
Deputy Assistant Administrator
for Noise Control Programs
Concur David Dominick
Assistant Administrator for
Hazardous Materials Control
Approved Robert Fri
Acting Administrator
Washington, D.C.
1973
Foreword-2
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TABLE OF CONTENTS
Section Page
Foreword F-l
Abbreviations A-l
NOISE & NOISE EXPOSURES IN RELATION TO PUBLIC HEALTH AND
WELFARE 1-1
HUMAN EXPOSURE AND RESPONSE 1-1
Physiological Response 1-1
Psychological Response 1-3
Speech Interference 1-3
HISTORICAL CONCERN 1-4
PHYSICS OF SOUND 1-4
Sound Waves 1-4
Intensity of Sound . 1-5
Frequency of Sound 1-6
Duration of Sound 1-9
TYPES OF NOISE AFFECTING PUBLIC HEALTH AND WELFARE 1-9
Types of Ongoing Noise 1-9
Impulsive Noise
SUMMARY - TYPES OF NOISE AFFECTING PUBLIC HEALTH
AND WELFARE 1-13
REFERENCES 1-16
2 RATING SCHEMES FOR ENVIRONMENTAL COMMUNITY NOISE 2-1
BASIC PHYSICAL PARAMETERS 2-1
Physical Parameters of Sound and Psychological Perception of Sound 2-2
Equal Loudness Contours 2-3
Perceived Noise Level 2-6
STATISTICAL MEASURES 2-6
The Energy Mean Noise Level (Leq) 2-7
CUMULATIVE MEASURES 2-7
Rosenblith-Stevens Model 2-7
CNR and NEF ' 2-8
Community Noise Equivalent Level 2-8
SUMMARY-RATING SCHEMES FOR ENVIRONMENTAL COMMUNITY
NOISE 2-10
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TABLE OF CONTENTS (con't)
Section Page
REFERENCES 2-10
3 ANNOYANCE AND COMMUNITY RESPONSE 3-1
MEASUREMENT TECHNIQUES FOR ANNOYANCE 3-1
Individual Response 3-1
Earlier Social Surveys 3-1
Recent Social Surveys 3-2
COMMUNITY RESPONSE 3-4
Complaints 3-4
The Rating Scheme
The Borsky Social Survey 3-6
Analysis of Studies 3-6
SUMMARY - ANNOYANCE AND COMMUNITY RESPONSE 3-7
REFERENCES 3-10
4 NORMAL AUDITORY FUNCTION 4-1
NORMAL HEARING IN YOUNG POPULATIONS 4-1
HEARING STUDIES AND RESULTS 4-2
AUDIOLOGICAL UNIFORMITY OF THE POPULATION 4-3
SOURCES OF VARIATION IN HEARLING LEVELS
Individual Variation 4-4
Sex Related Variations 4-4
The Effect of Noise Stimulation on Mediating Mechanisms in the
Middle Ear (Middle Ear Muscle Reflex) 4-6
HEARING LOSS ASSOCIATED WITH OLD AGE 4-8
SUMMARY - NORMAL AUDITORY FUNCTION 4-12
REFERENCES 4-13
5 NOISE-INDUCED HEARING LOSS - TEMPORARY AND PERMANENT
SHIFTS IN AUDITORY THRESHOLD FOLLOWING NOISE EXPOSURE 5-1
TYPES OF ADVERSE EFFECTS ON HEARING 5-2
Noise-Induced Permanent Threshold Shift (NIPTS) 5-2
Noise-Induced Temporary Threshold Shift (NITTS) 5-2
THEORIES RELATING NOISE EXPOSURE AND HEARING LOSS 5-3
The Equal Energy Hypothesis'in Damage Risk Criteria 5-3
The "Equal Temporary Effect" Hypothesis 5-3
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TABLE OF CONTENTS (con't)
Section Page
CHABA Criterion for Steady-State Noise Exposure 5-4
DATA ON EFFECTS OF NOISE ON HEARING 5-4
Ongoing Noise and Hearing Loss 5-4
Industrial Experience . 5-5
Tinnitus Associated with Occupational NIPTS 5-7
Social Significance of Hearing Loss at Retirement 5-7
The Reliability of the Data from Industrial Studies 5-7
EFFECTS OF LOUD MUSIC 5-7
EXPERIMENTAL SUPPORT FOR THE NOISE DAMAGE-RISK
THEORIES 5-8
Burns' Approach 5-8
TT$2 as a Predictor of Hazardous Noise Exposure 5-9
"Equal-Energy" Hypothesis in Predicting TTS and PTS 5-9
Growth of TTS in Constant Noise
TTS from Prolonged Noise Exposure 5-9
Asymptotic TSS as a Function of Noise Level 5-10
Pitfalls of Generalizing from Animal Studies to Man 5-10
Uncertain Relation of PTS to TTS and Cochlear Damage 5-10
Asymptotic TTS in Man 5-11
Miscellaneous Factors Considered in TSS 5-11
IMPULSIVE NOISE
Incidence of NIPTS as a Function of Peak SPL 5-11
Effect of Impulse Duration 5-12
Allowance for Repated Impulses 5-12
High-Frequency Hearing Losses Due to Impulse Noise 5-12
Factors Influencing Hazard Due to Impulse Noise 5-13
Combined Exposure to On-Going Noise with Added Impulsive
Noise - Allowance for Impulsiveness 5-13
Effects Found in Studies of Children 5-13
Methods for Predicting the Expected Hearing Loss Due to Exposure
to Ongoing Noise 5-13
"Industrial" Methods of Predicting Long-term Hazard from Daily
Continuous Noise Exposure 5-14
iii
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TABLE OF CONTENTS (con't)
Section Page
Method and Data of Passchier-Vermeer 5-14
Method of Robinson 5-14
Method of Baughn 5-15
Averaging NIPTS Predictions Over the Three "Industrial" Methods 5-15
Use of Industrial Exposure Tables to Approximate Effect of
Less Uniform Noise Exposures 5-16
Exposures to Continuous Noise Exceeding 8 Hours 5-16
Exposures to Continuous Noise for Periods Less Than 8 Hours 5-18
Allowances for Level Fluctuation or Interruption of Noise 5-18
Intermittent Noise 5-18
Factors Influencing Incidence of NIPTS 5-20
Factors Increasing the Risk of NIPTS , 5-21
Factors Mitigating Risk 5-21
Factors not Directly Affecting Susceptibility to NIPTS 5-21
Differences Related to Sex 5-21
Differences Related to Urban Environment 5-22
Differences Related to Age 5-22
DAMAGE-RISK CRITERIA 5-23
The CHABA Criterion 5-23
Criteria for Steady-State Noise 5-23
"AAOO" and Cognate Criteria 5-24
The Intersociety Committee (1970) Guidelines 5-24
Use of A-Weighted Decibels 5-25
Index of Cumulative Noise Exposure-Robinson's "Sound-Immission"
Ring 5-25
Inadequacy of Conventional "Speech Frequencies" Assessment 5-25
Impulsive Noise 5-26
Impulse Noise and TTS 5-26
Impulses With an Oscillatory Component 5-26
SUMMARY - NO1SB-1NDUCED HEARING LOSS-TEMPORARY AND
PERMANENT SHIFTS IN AUDITORY THRESHOLD FOLLOWING
NOISE EXPOSURE 5-27
REFERENCES 5-28
iv
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TABLE OF CONTENTS (con't)
Section Page
6 MASKING AND SPEECH INTERFERENCE 6-1
INTELLIGIBILITY OF SPEECH 6-1
MEASUREMENT OF SPEECH-INTERFERENCE 6-2
Articulation Index 6-2
Speech Interference Level 6-3
Noise Level, Vocal Effort, and Distance 6-3
Reception of Indoors Speech 6-7
FACTORS IN THE DEGREE OF SPEECH INTERFERENCE 6-7
Characteristics of People (Speech, Age, and Hearing) 6-7
Situational Factors 6-9
Noise Characteristics . 6-9
Acoustic Privacy 6-10
SUMMARY-MASKING AND SPEECH INTERFERENCE 6-10
REFERENCES 6-11
7 ADDITIONAL PHYSIOLOGICAL AND PSYCHOLOGICAL CRITERIA 7-1
PAIN 7-1
Tympanic Membrane 7-1
Inner Ear 7-2
Hearing Aids 7-2
EFFECTS OF NOISE ON EQUILIBRIUM 7-3
ORIENTING AND STARTLE REFLEXES (ACOUSTIC) 7-3
Response In Children 7-4
Adult Response 7-4
Variation In Muscular Response 7-5
INTERNAL MECHANISMS-VEGETATIVE AND STRESS REACTIONS 7-6
Noise and The Nature of Stress 7-6
Stress and the Metabolic System 7-8
Variables In Stress Effects . 7-10
Circulatory System and Vasoconstriction 7-11
Pupillary Dilation 7-11
EFFECTS OF NOISE ON SLEEP 7-13
NATURE OF STIMULUS 7-13
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TABLE OF CONTENTS (con't)
Section Page
STAGES OF SLEEP 7-15
MOTIVATION OF SUBJECT 7-15
DIFFERENCES OF AGE 7-16
DIFFERENCES OF SEX 7-16
Adaption to Noise 7-16
Conclusions 7-16
THE EFFECT OF NOISE ON GENERAL HEALTH AND MENTAL HEALTH 7-17
Fatigue 7-17
General Health Effects 7-18
Mental Health Effects 7-19
SUMMARY-EFFECTS OF NOISE ON AUTONOMIC NERVOUS
SYSTEM FUNCTIONS AND Of HER SYSTEMS 7-20
REFERENCES 7-22
8 EFFECTS OF NOISE ON PERFORMANCE 8-1
Noise and State of Arousal 8-2
Noise as a Distracting Stimulus 8-2
Cumulative Effects 8-3
Aftereffects 8-3
Noise Sensitive Tasks 8-4
Special Effects 8-4
Positive and Neutral Effects 8-5
Problems in Evaluation 8-6
SUMMARY-PERFORMANCE AND WORK EFFICIENCY 8-6
REFERENCES 8-8
9 INTERACTION OF NOISE AND OTHER CONDITIONS OR INFLUENCES 9-1
MEASUREMENT OF EFFECTS 9-1
CHEMICAL AGENTS 9-2
Ototoxic Drugs 9-2
Industrial Chemicals 9-3
Vibration 9-3
HEALTH CONDITIONS 9-4
Mineral and Vitamin Deficiencies 9-4
VI
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TABLE OF CONTENTS (con't)
Section Page
Illnesses 9-4
SUMMARY-INTERACTION OF NOISE AND OTHER CONDITIONS
OR INFLUENCES 9-5
REFERENCES 9-6
10 EFFECTS OF INFRASOUND AND ULTRASOUND 10-1
INFRASOUND 10-1
ULTRASOUND 10-3
Research Problems 10-3
Physiological Effects 10-6
SUMMARY-INFRASOUND AND ULTRASOUND 10-7
REFERENCES 10-8
11 EFFECTS OF NOISE ON WILDLIFE AND OTHER ANIMALS 11-1
EFFECT ON HEARING 11-1
MASKING 11-3
BEHAVIORAL CHANGES 11-3
PHYSIOLOGICAL REACTIONS 11-4
FARM ANIMALS . 11-5
SUMMARY-EFFECTS OF NOISE ON WILDLIFE AND OTHER
ANIMALS 11-6
REFERENCES 11-7
12 EFFECT OF NOISE ON STRUCTURES 12-1
SONIC BOOMS 12-1
Nature of Sonic Booms 12-1
Effects of Sonic Booms 12-2
NOISE INDUCED VIBRATIONS 12-3
Effects on Materials 12-3
Effects on Humans 12-5
SONIC FATIGUE 12-5
EFFECT OF NOISE ON MATERIALS 12-5
Summary 12-5
SUMMARY-EFFECTS OF NOISE ON STRUCTURES 12-6
REFERENCES 12-7
VII
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TABLE OF CONTENTS (con't)
Section Page
GLOSSARY G-l
APPENDIX A A-l
Vlll
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LIST OF ILLUSTRATIONS
.Figure Page
1-1 Functional Diagram of Ear 1-2
1-2 Elements of a Sound Wave 1-5
1-3 Relationship of Sound Pressure to Corresponding Decibel Levels 1-8
1-4 Noise Spectra 1-10
1 -5 Representations of Various Types of Noise 1-12
1-6 Two Principal Types of Impulse Noises (Taken from Ward'') 1-14
2-1 Normal Equal-loudness Contours for Pure Tones (Binaural Free Field
Listening) Developed by Robinson and Dadson in Great Britain 2-4
2-2 IEC Standard A, B, and C, Weighting Curves for Sound Level Meters 2-5
3-1 Percentage of Highly Annoyed Persons in Relation to Noise 3-3
3-2 Intercomparison of Various Measures of Individual Annoyance and
Community Reaction as a Function of the Day-Night Average Noise
Level 3-8
4-1 Functional Diagram of Ear :„ 4-5
4-2 Threshold of Hearing as a Function of Clinically Normal Female
Ears (Random Sample Population) 4-10
5-1 Nomogram for Calculation of Leq Equivalent Continuous Sound Level
(From F = antilog [0.1(L-90)J , Where t is in Hours and F is Functional
Exposure Value 5-19
6-1 Distance at Which Ordinary Speech can be Understood as a Function
of A-Weighted Sound Levels of Masking Noise in the Outdoor
Environment 6-5
10-1 Tolerance Data 10-2
IX
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LIST OF TABLES
Table Page
1-1 Acoustic Power and Sound Levels of Typical Noise Sources 1-7
1-2 Classifications of Ongoing Noise Exposure 1-11
2-1 Factors Considered in Each of Four Methods for Describing the
Intrusiveness of Noise on the Community , 2-9
3-1 Percentages of Persons Highly Annoyed who Register Complaints
as a Function of L^n 3-5
4-1 Glorig's Correction for 3F/3.31 4-9
4-2 Presbycusis Data Upper Register: Median Age-Induced Hearing
Levels (Non-Noise-Exposed Men) Rounded to Nearest Decibel.
^9
From: Passchier-Vermeeroz 4-11
5-1 Summary of Effects Predicted for Continuous Noise Exposure at
Selected Values of A-Weighted* Sound Level 5-17
5-2 Effect of Various Factors on Incidence of NIPTS 5-20
5-3 Comparison of CHABA Damage Risk Criteria and APR 160-3 5-23
6-1 Speech Interference Levels (SIL(.85, 1.7, 3.4)) For Outdoors
Environments that Permit Barely Reliable Conversation, or the
Correct Hearing of Approximately 75% of Phonetically-Balanced
Word Lists, at Various Distances and Voice Levels. From Beranek • 6-6
6-2 Design Objectives for Indoor A-Weighted Sound Levels in Rooms
With Various Uses, as Recommended by an Acoustical Engineering
Firm on the Basis of Experience with Acceptability Limits Exhibited
by the Users of the Rooms. From Beranek et aP " 6-8
10-1 TTS Results 10-t
12-1 Sonic Boom Damage Data in Three Cities 12-4
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ABBREVIATIONS
AAOO American Academy of Ophthalmology and Otolaryngology
AC Air Conduction
APR Air Force Regulation
AHL Average Hearing Level
AI Articulation Index
AMA American Medical Association
ANSI American National Standards Institute (formerly USASI)
BC Bone Conduction
CHABA Committee on Hearing and Bio-Acoustics
dBA A-weighted decibel (decibels)
DRC Damage Risk Criterion
E^ Noise emission level
EPA Environmental Protection Agency
HL Hearing Level
IEC International Electrotechnical Commission
ISO International Organization for Standardization
Leq Equivalent continuous sound level
NIHL Noise-Induced Hearing Loss
NIOSH National Institute for Occupational Safety and Health
NIPTS Noise-Induced Permanent Threshold Shift
NITTS Noise-Induced Temporary Threshold Shift
NPL Noise Pollution Level (also National Physical Laboratory in England)
NR Noise Rating ''
OSHA Occupational Safety and Health Act
PB Phonetically Balanced
PIHO Percent Impairment of Hearing (Overall)
PIHS Percent Impairment of Hearing for Speech
PTS Permanent Threshold Shift
RMS Root Mean Square
SIL Speech Interference Level
A-l
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SIR Speech Impairment Risk
SPL Sound Pressure Level
ITS Temporary Threshold Shift
A-2
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SECTION 1
NOISE & NOISE EXPOSURES IN RELATION TO
PUBLIC HEALTH AND WELFARE
From a strictly scientific position, noise is discordant sound resulting from nonperiodic vibra-
tions in air. In common usage, noise is defined more simply as unwanted sound and has sometimes
been categorized as sound without value or noise pollution. To understand noise as an environ-
mental issue affecting public health and welfare as discussed in this document, one must understand
certain fundamentals of sound and human responses to it. However, a detailed discussion on the
fundamentals of physics and bioacoustics is beyond the scope of this document. The following
material is provided only as a general orientation for those unfamiliar with the subject of noise;
to provide a better understanding of the effects of noise on man and its environment as discussed
in the subsequent sections. Those desiring further information should consult Appendix A, which
lists some of the numerous references available in the current literature. Attnetion is also directed
to the Glossary.
HUMAN EXPOSURE AND RESPONSE
Physiological Response
Sound is generated by a source producing vibrations (sound waves) that may travel through
any media and which, in air, actuate the hearing mechanisms of humans and animals. These vibra-
tions set in motion the ear drum and small bones or ossicles of the middle ear as shown in the
schematic drawing in Figure 1-1. The motion of the ossicles, in turn, produces vibrations in the
fluid in the inner ear's sensory organ, the cochela. The vibrations are then transduced into nerve
impulses by sensory hair cells and transmitted to the brain, where they are perceived as sound or,
depending upon circumstances, as noise.
Central to the health and welfare aspect of noise, is the wide range of response of the human
hearing mechamism. The human ear can discern without pain sounds ranging from a threshold of
detection to sounds ICr ^ times as intense. This should be contrasted with the human eye, which
responds to light intensities from its threshold of response up to an intensity 105 times greater.
This wide range of hearing response and the complexity of the various attributes of that response
1-1
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AUDITORY PRESENTATION OF INFORMATION
MIDDLE INNER
EAR EAR
AUDITORY
NERVE
Figure 1-1. Functional Diagram of Ear
1-2
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is reflected in the systems used in defining and measuring noise, as discussed in Section 2 of this
document and elsewhere herein.
Another major element of public health concern, which is the subject of detailed discussion
in Section 3, is that the hair cells, vital to the hearing process, are nonregenerative. Thus, if they are
damaged or destroyed following certain sound exposures, there is no physiological restoration.
Also of major importance is the fact that the process of hearing (as used here meaning the
perception and understanding of sound) is one of the main sensory contacts of man and other
animals with their environment. Hearing is second only in importance to vision in this regard.
Further, there are extremely complex relationships between these two processes that are far
beyond the scope of this presentation and will not, therefore, be discussed here.
Psychological Response
Beyond the relatively obvious aspects of sensory-environmental contact, there is a deep and
exceptionally intricate human emotional and psychological response to sound. Prayers, hymms,
anthems, the soft and sometimes harsh sounds of nature, the blatancy of martial music, the thunder
of applause, the welcome lilt of a loved one's voice, and the regular occurrence of an expected
tone, such as a distant whistle, are indicative of the capability of sound to produce within people
(and in some animals) profound individual and group responses and reactions. These responses
range from pleasure to fear and include all other aspects of human emotional reaction. Some reac-
tions may be attributed to the message conveyed by the sound, prior experiences and conditioning,
and many other poorly identified processes.
Traditionally, in a great many cultures quiet is used to indicate respect, while loud sounds and
noises are indicative of ridicule disrespect or disapproval. Even here, however, there are contradic-
tions. As an example, a loud cheer indicates approbation but equally loud signals can be and are
used to indicate disapproval.
Speech Interference
The effects of noise on the ability to communicate are perhaps an even greater influence on
the human reactions to noise. These reactions are discussed in much greater detail in the following
sections of this document. Interference with communication may arise either from actual impair-
ment of the hearing process or from intrusions of sound so that the message cannot be understood
by the listener. The expression "I could hardly make myself heard" is an example of a reaction
of frustrations to such situations. It very well may reflect part of the origin of the annoyance
reactions and other nonphysiological responses discussed in this document.
Still another problem is that what is pleasurable sound to a particular listener at a particular
point in time may be noise to some other listener. Further, a pleasurable sound may also be
considered as noise when heard at a different time and under different circumstances. An example
1-3
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of this would be a situation in which a devotee of a particular type of music enjoys it in his domicile
but causes annoyance to his neighbors because of the volume of his sound reproduction equipment.
Later, that individual may himself be annoyed by the same musical composition if it interfered
with his sleep.
HISTORICAL CONCERN
Noise is hardly a new concern for society. It has apparently been a problem for most of man-
kind's existence. There is reportedly an ordinance enacted some 2,500 years ago by the ancient
Greek community of Sybaris banning metal works and the keeping of roosters within the city to
protect against noise that interfered with speech and might distrub sleep. There are many other
examples to show this historical concern with noise. They include Juvenal's statement regarding
noise from wagons and their drivers interfering with sleep in ancient Rome and Chaucer's poem of
around 1350 complaining of noise by blacksmiths and that because of them "no man can get a
night's rest." Also, Benjamin Franklin some 400 years later reputedly moved from one part of
Philadelphia to another because "the din of the market increases upon me; and that has I find made
^
me say somethings twice over."z
Over the past 200 years there has been a steady increase in the magnitude of the impact of
noise, changing the nature and extent of the problem from that of primarily nuisance and annoy-
ance to actual physiological damage. While the sources of noise are different, and their numbers
and the magnitude of sound energy have created a larger impact, the character of the impact of
noise is not new or radically different. It is the addition of new noise sources in already noisy
situations and the proliferation of noise sources of increased output into previously relatively quiet
areas that has stimulated greatly increased public concern and has created the need for increased
governmental action. In many ways, the present situation regarding noise is not different from
that of other pollutants, with the possible exception that, unlike some pollutants, once the noise
source is controlled or reduced, the impact of the noise correspondingly changes almost
immediately.
PHYSICS OF SOUND
Up to this point, some of the considerations of human exposure and response have been dis-
cussed. The following discussion highlights some of the essential information on the physics of
sound, needed for a more complete appreciation of the material in the subsequent sections.
Sound Waves
At the outset of this section, it was stated that sound was the result of a source setting a
medium into vibration. Generally, insofar as noise is concerned, that medium is air; and the follow-
ing discussions are related solely to that medium. However, to a alrge extent, sound is to air what
1-4
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waves are to water. Whenever an object moves back and forth in air, it causes the invisible mole-
cules of the air to likewise move back and forth. This vibration produces, in a cyclical fashion,
alternating bands of relatively dense and sparse particles, spreading outward from the source in the
same way as ripples do on water after an object is thrown into it. This movement of particles is
produced as a result of the energy delivered to a source, such as the clapping of the hand, the beat-
ing on a drumhead, or the pulling of a bow across the strings of a violin. The result of the move-
ment of the particles is a variation in the normal atmospheric pressure, or sound waves. These waves
radiate in all directions from the source and may be reflected and scattered or like other wave actions,
may turn corners, or be refracted. They can be combined with or even be cancelled by other sound
waves. Likewise, the energy contained in the sound can be absorbed. As the waves travel over in-
creasing distances, the amount of energy per unit area contained in them is reduced proportionally
to distance. Once the source ceases to be in motion, the movement of the air particles ceases and
the sound waves almost instantaneously disappear and the sound ceases. Under normal conditions
of temperature, pressure, and humidity at sea levels, these sound waves travel at approximately
1100 feet per second.
Intensity of Sound
Sound may be scientifically described in terms of three variables associated with the character-
istics of waves:
1. Amplitude (intensity)
2. Frequency (pitch)
3. Duration (time)
Figure 1-2 depicts these elements.
Compression Rarefaction
.
•Y
Normal
Atmospheric Pressure
frequency = peno
= penod
Time-
Figure 1-2. Elements of a Sound Wave
1-5
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Sound intensity is the average rate of the sound energy transmitted through a unit area (usually
stated as watts per square meter), (The large range of sound intensity involved in .human response1
is shown in Table 1-1.), There are physical and mathematical relationships that exist between the
energy of sound waves and the resulting variation from atmospheric pressure. Sound pressure
(usually stated in terms of newtons per square meter) is the amplitude or measure of that variation
from atmospheric pressure. Presently, there are no instruments to directly measure sound power
(the total amount of energy radiated per unit time by the sound source) or sound intensity. Accord-
ingly, sound pressure is used as the fundamental measure of sound amplitude and is one of the basic
ingredients of the various measurement and rating schemes in systems described in Section 2.
Earlier in this Section, it was pointed out that the human ear has a wide range of response to
sound. Sharply painful sound is 10 million times greater than the least audible sound (20 x 10'
micro newtons per square meter as compared with 20 micro newtons per square meter). Such a
wide range of values creates problems in measurement and computations associated with noise.
Accordingly, in acoustics as in electrical engineering, the concept of level is used for defining sound
(and thus noise) intensity. The level in this usage is the logarithm of the ratio of a quality (in this
case, sound pressure) to a reference quality of the same kind (for sound pressure, 20 micro newtons
per square meter). The unit of measure is the decibel and the formula for sound pressure level
(SPL) is:
SPL = 10 log (— ^) = 20 log — — , where ?2 is the pressure in newtons per square meter
and Pj is the reference value. (See EPA NTID 300.15, "Fundamentals of Noise Measurement," or
other references cited in Appendix A for details of the relationships between sound intensity in
energy and sound pressure). . : ' '
The relationship of sound pressure in terms of micro newtons per square meter to correspond-
ing decibel levels is shown in Figure 1-3. Note that for each 20-decibel increase there is a corres- ,
ponding 10-fold increase in acoustical pressure and sound pressure. Using this scheme, some i
complications may arise for those not well versed in its fundamentals. As an example, sound pres-
sure levels expressed in decibels are not directly additive. That is, a source producing an 80-dB SPL
when added to another one producing that same SPL at the same distance results in only a 3-d B
increase, not a doubling to 1 60. Further, if there is a difference in the sound pressure level of the
two sources, the amount of increase will be smaller to the point that if such a difference is 10
decibels, the lesser source will virtually be of no consequence in terms of increasing the sound
pressure level.
Frequency of Sound ,
The number of compressions and rarefactions of the air molecule density in a unit of time
associated with a sound wave are described as its frequency. The unit of time is usually one second,
and the term "Hertz" (after an early investigator of the physics of sound) is used to designate these
1-6
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TABLE 1-1
ACOUSTIC POWER AND SOUND LEVELS OF
TYPICAL NOISE SOURCES
Power
"V
watts/mz
100,000
10,000
1,000
100
10
3*
1.0
0.1
0.01
0.001
0.0001
0.00001
0.000001
0.0000001
0.000,000,01
0.000,000,001
Power Level
dBrelO'12
watts/m2
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
Source
Ram jet
Turbojet engine with afterburner
Turbojet engine, 7000 Ib thrust
4-propeller airliner
7 5 -piece orchestra
Peak RMS levels in
Pipe organ 1/8-second intervals
Small aircraft engine
Large chipping hammer '
Piano Peak RMS levels in
Bfib tuba 1/8-second intervals
Blaring radio
Centrifugal ventilating fan (13,000 CFM)
4' loom
Auto on highway
Vaneaxial ventilating fan (1500 CFM)
Voice - shouting (average long-time RMS)
Voice — conversational level
(average long-time RMS)
Voice - very soft whisper
= PWL-30dB;3watts = 94dB;OSPL= 10 X
1-7
-------
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1 Newton /m
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94 dB re 20 micro n/ra2
170 dB " " "
127.6 " " "
Figure 1-3. Relationship of Sound Pressure to Corresponding Decibel Levels
1-8
-------
cycles per second. Again, the human ear and those of most animals have a wide range of response.
Humans can identify sounds with frequencies from about 16 Hz to 20,000 Hz. The musical pitch
"A" above middle "C" is produced on a piano by the key-activated hammer striking a string, which
then oscillates back and forth at a rate of 440 Hz, producing a fundamental frequency of 440 Hz.
Pure tones are relatively rare in real life situations. Most human exposures consist instead of
a complex mixture of many frequencies. Some typical examples are shown in Figure 1-4.
Duration of Sound
The temporal nature of sound relates to the duration of its generation and presence. Contin-
uous sounds are those in which the source is producing sound for relatively long periods in a con-
stant state, such as the noise of a waterfall. Intermittent sounds are those which are produced for
short periods, while impulse sounds are those which are produced in an extremely short span of
time.
TYPES OF NOISE AFFECTING PUBLIC HEALTH AND WELFARE
To evaluate the effect of noise on public health and welfare, it has been necessary to define
different types of noise fairly explicitly, since a complex sound may, and usually does, involve a
mixture of sounds of varying intensity, diverse frequencies and temporal patterns.
Types of noise frequently differentiated are ongoing noise and impulsive noise.
Types of Ongoing Noise
.v
Ongoing noise continues for an appreciable period of time. It is further differentiated into
steady-state, fluctuating, and intermittent noise as described in Table 1-2.
Steady-state noise is noise whose quality and intensity is practically constant (varying less than
±5 dBA) over an appreciable period of time. Different types of steady-state noise are illustrated in
Figure 1-5.
Fluctuating noise is continuous, but its intensity rises or falls more than 5 dBA. Intermittent
noise is discontinuous and differs from impulsive noise in being of longer duration and less
specifically defined.
Impulsive Noise
Impulsive noise is one or more transient acoustical events such as a gunshot, each of which
lasts less than 500 milliseconds and has a magnitude (change in sound pressure level) of at least
40 dB within that time. A single impulse may be heard as a discrete event occurring in otherwise
quiet conditions, or it may be superimposed upon a background of stead-state on-going noise.
It may be characterized by the following basic parameters:
1-9
-------
130 -J
JET AIRCRAFT
100* DISTANCE
BOAT WHISTLE
SUBWAY TRAIN
n>
-4- 2 iio-
s
H
c
o
m
TRAFFIC 100'
DISTANCE
T>
30
4- w 100-
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n
90-
+ r 80-
o
CD
70-
TRUCK
BOAT WHISTLE
a
JET
I
i
HOTEL ROOM
HOTEL
QUIET
RESIDENTIAL
AMBIENT
SUBWAY
\
"-^.
•
x.
\
•
I
r
: i ., i
63 125 250 500 1000 2000 4000 8000
OCTAVE BAND CENTER FREQUENCIES IN CP.S.
TiTni^TTri^•^•n:?! ;-":i ^'M^n^Tl
• llkii -vJ'lJ <•
-------
TABLE 1-2
CLASSIFICATIONS OF ONGOING NOISE EXPOSURE
Type of
Exposure
Description
Typical Examples
Steady-State
Fluctuating Noise
Intermittent Noise
Single continuous daily exposure
(typically 8 hours but may be
shorter or longer) at a constant
level within ±5 dBA.
Noise is continuous but level rises
and falls (rapidly or gradually) more
than 5 dBA during exposure.
Noise is discontinuous: i.e., the level
falls to immeasurable low or to non-
hazardous levels between periods of
noise exposure of which more than
one affects the ear during the day.
Note: This can be regarded as a
a special case of fluctuating noise.
Weaving room noise; sound of
a waterfall; shipboard noise;
interior of a vehicle or aircraft
noise; turbine noise; hum of
electrical sub-station.
Many kinds of processing or
manufacturing noise. Traffic
noise; airport noise; many kinds
of recreational noise (e.g., vehicle-
racing; powered lawnmowing;
radio and TV).
Many kinds of industrial noise
(especially in construction work,
ship building, forestry, aircraft
maintenance, etc.); Many kinds
of recreational noise (e.g., drag
racing, rock concerts, chain-
sawing); light traffic noise;
occasional aircraft flyover noise;
many kinds of domestic noise
(e.g., use of electrical applicances
in the home); school noise.
1-11
-------
Pure Tones
Periodic Noise
A-periodic Noise
White noise
Figure 1-5. Representation of Various Types of Noise
1-12
-------
o
1. Peak sound pressure level (in dB re 0.00002 N/mz). For reasons connected with measure-
ment practice in the English-speaking countries, the over-pressures associated with sonic
booms in aerospace operations are customarily expressed in pounds/ft^ (psf) relative to
atmospheric pressure. This convention is adhered to in this document when citing data
expressed in psf by other authors.
2. Duration (in milliseconds or microseconds)
3. Rise and decay time
4. Type of waveform (time-course)
5. Spectrum (in case of oscillatory events, Type B—see Figure 1-6)
6. Number of impulses
Two types, "A" and "B," are shown in Figure 1-6. In the Type A impulse, there is a rapid rise
to a peak SPL followed by a decay to a negligible magnitude. In the classical "Friedlander" type of
event, a subsequent negative pressure wave occurs, of much smaller magnitude. In evaluating this
. type of wave only the duration of the positive part of the event is counted as the duration of the
impulse. In the single Type B (oscillatory) event, the duration is taken as being the time taken for
the envelope to decay to a value 20 dB below the peak. It is important to appreciate that impulse
noises can be distinguished as to type and properly measured only by oscillographic techniques due
to their short duration.
SUMMARY - TYPES OF NOISE AFFECTING PUBLIC HEALTH AND WELFARE
Historical evidence shows that excessive noise has long been considered a menace to the public
health and welfare. Over the past two centuries, industrial development has resulted in a steady
increase in the extent of noise impact.
Noise can affect the ability to communicate or to understand speech and other signals. This
may arise from either actual impairment of the hearing mechanism,or as a result of intrusions of
sounds such that the desired ones cannot be understood by the listener.
The physics of sound provide the appropriate background for the difficult task of assessing
human response to noise. As sound waves travel over increasing distances, their energy diminishes
proportionally, being spread over an ever increasing area. Once the source ceases to be in motion,
the movement of the air particles ceases and the sound waves usually disappear almost
instantaneously.
Sound may be described scientifically in terms of three variables associated with the character-
istics of waves. These are its amplitude (intensity), its frequency (pitch), and its duration (time).
Sound intensity is the average rate of sound energy transmitted through a unit area. Frequency
is the number of compressions and expansions of the air molecules in a unit of time associated with
a sound wave. The temporal nature of sound relates to the duration of its generation and presence.
The variables of sound make sound measurement a complex problem.
1-13
-------
Id
CO
O
LJ
cr
CO
CO
LJ
cr
CL
CO
LJ
"Z.
<
CO
(a)
TIME
Figure 1-6. Two Principal Types of Impulse Noises
(Taken from Ward3)
1-14
-------
Noise is frequently differentiated into ongoing and impulsive noise, to evaluate its effect on
public health and welfare. Ongoing noise is further differentiated into steady-state, fluctuating,
and intermittent noise.
1-15
-------
, . - REFERENCES
1. Cited in Communication of W. Dixon Ward to EPA, Office of Noise Abatement and Control,
1973.
2. Hilderbrand, James L, "Noise Pollution and the Law" William S. Hien & Co., Buffalo, N.Y.,
1970, p. 22.
3. Ward, W.D. (ed.) PROPOSED DAMAGE-RISK CRITERION FOR IMPULSE NOISE (GUN-
FIRE). Report of Working Group 57, NAS-NRC Committee on Hearing, Bioacoustics, and
Biomechanics (1968).
1-16
-------
Section 2
RATING SCHEMES FOR ENVIRONMENTAL
COMMUNITY NOISE
The description of noise encountered in most living situations must account for:
1. Those parameters of noise that have been shown to contribute to the effects of noise
on man (amplitude, frequency and duration). These parameters have already been discussed
in Section 1.
2. The variety of noises found in the environment (transportation noises, construction, home
appliances and others).
3. The variations in noise levels that occur as a person moves through various locations of the
community.
4. The variations in noise levels associated with the time of day at any given location.
Thus, the task of describing community noise is to determine the time and location variations
in the noise environment throughout the community so that the descriptions are relevant to the
effects of environmental noise on people, whether they are located indoors or outdoors. This chapter
will not completely describe all the schemes that have been developed over the years but, rather,
selects a few rating schemes to illustrate the techniques and problems involved, so as to facilitate
the understanding of the rest of this document. The interested reader can find a complete descrip-
tion of rating schemes in numerous texts such as the Effects of Noise on Man, Fundamentals of
Noise Measurement, Rating Schemes, and Standards? and Transportation Noises^ and others. The
following section of this document will review the actual findings regarding annoyance caused by
noise and the community reaction to that noise.
BASIC PHYSICAL PARAMETERS
As pointed out in Section 1 the basic parameters of sound, in terms of its effects on man and
its environment are:
• The amplitude of sound.
• Frequency content of sound.
• The variation in time.
Thus, a complete physical description of sound must account for its frequency spectrum, its
overall sound pressure level, and the variation of both these quantities with time.
2-1
-------
Because it is difficult and cumbersome to present or to understand data having three dimen-
sions, considerable effort has been expended over the last 50 years to develop scales that reduce
the number of dimensions into a one-number scheme. Most of the effort has been focused on com-
bining measures of the frequency content and overall level into a quantity proportional to the mag-
nitude of sound as heard by a person.
.*f"
Physical Parameters of Sound and Psychological Perception of Sound
There have been many studies as to the relationship between the physical parameters of sound
and the psychological perception of sound.
Although there are disagreements in the results of these studies and in the views of their prin-
cipal investigators regarding the actual values of the constants entering into the function relating
loudness experience and intensity of stimuli, there appears to be some concensus regarding the form
of the relationship. Loudness appears to grow as a power function of sound pressure. Thus, for a
pure tone, loudness is proportional to the sound pressure. This relationship has been called the
Power Law by Stevens.^ In practice what this means is that for a 1000-Hz tone, for example, the
loudness of a tone increases by a factor of two for each 10-dB increase in the intensity of the stim-
ulus.*
, In making loudness measurements one often uses reference sounds. In the earlier work, the
reference was a 1000-Hz tone. The choice of a 1000-Hz tone as the reference has been proposed
originally by Fletcher and Munson. The reason for choosing a 1000-Hz tone is stated by Fletcher
and Munson as follows:
" 1) It is simple to define; 2) it is sometimes used as a standard of reference for pitch;
3) its use makes the mathematical formulae more simple; 4) its range of auditory sen-
sitivities ... is as large and usually larger than for any other type sound; 5) its frequen-
cy is in the mid-range of audible frequencies. "^
When an observer is required to compare the loudness of a tone to that of the reference, the pro-
cess is done by having the listener adjust the intensity level of the tone being rated until its loud-
ness matches that of the reference tone. The result is referred to as loudness level. Loudness level
.is expressed in phons. The .units of the phon are the sound pressure level (SPL) of a 1000-Hz
tone heard in a free field and judged to be equal in loudness to the sound in question.
*Stevens, provides a variety of evidence for this rule. In some of his experiments the subjects were
asked to equate apparent loudness of sound to intensity on some other continua, such as mechan-
ical vibration on the skin, brightness of spots of light, or force of hand grip. Results matched
Stevens predictions based on the relation between the intensity of stimuli and various psycho-
physical scale. For example, it is demonstrated that it requires a change of about 9 dB to double
the perceived brightness of a spot of light, whereas about 10 dB is required to double the loudness
of the 1000-Hz tone.
2-2
-------
Equal Loudness Contours
A number of experiments have concerned themselves with establishing equal loudness relation
for pure tones or for bands of noise. The relationships thus obtained show at what intensities tones
of different frequencies appear equal in loudness to a 1000-Hz tone presented at various intensities.
An example of those are reproduced from Robinson and Dadson in Figure 2-1.
Observation of Figure 2-1 will reveal that the ear is most sensitive in the region between 500-
Hz and 6000-Hz and that at low sound pressure level, the ear normally hears low frequency sound
as less loud for equal sound pressure levels (frequencies below 250-Hz). Further, as the intensity
is increased to moderate levels, the ear gives greater weight to sounds of low frequency. Finally, at
very high intensity, the response of the ear becomes flat, that is the loudness of a pure tone depends
primarily on the sound pressure level and is little affected by frequency.
The findings just described are embodied in the most commonly used instrument for measuring
noise: the sound level meter. The typical sound level meter electronically weighs the amplitudes of
the various frequencies approximately in accordance with a person's hearing sensitivity and sums the
resulting weighted spectrum to obtain a single number. Typically, the sound level meter contains
three different response weighting networks: the A, B and C networks. The A-weighting network is
intended to match the response of the ear to sound of low intensity. The B-weighting network is
intended to match the response of the ear to sound of moderate intensity. The C-weighting network
is intended to match the response of the ear to sound of high intensity. The three weightings of the
sound level meter are illustrated in Figure 2-2. Also shown is the proposed D-weighting curve for
monitoring jet aircraft noise. From the curves it can be seen that for a 50-Hz pure tone the reading
on the A scale (which discriminates against low frequency sounds) would be 30 dB less than the C
scale reading.* \
The most commonly used scale on the sound level meter is the A weighting, since it has been
found to account fairly well, although not perfectly, for man's perception of sound.^
When using the sound level meter on the A-weighting, the quantity obtained is the A weighted
sound level. Its unit is the decibel (dB) often popularly referred to as dBA.
;
Although the A weighting is a good indicator of man's perception of sound, it is not perfect.
For this reason, many other scales have been developed that attempt to better quantify "loudness"
or "noisiness."^ The evolution of only one of these will be presented here as an illustration. The
interested reader is referred to standard texts that have already been listed at the beginning of this
section.
•"International Electrotechnical Commission (IEC) Recommendations 123 and 173 and American
National Standard Institute (ANSI) Standard SI.4-1971.
2-3
-------
ft
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b
CD
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Ul
•^
!• •
_!
al
C/J
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-------
-50
20 50 100 200 500 1000 2000 5000 10,000 20,000
FREQUENCY (Hz.)
Figure 2-2. IEC Standard A, B, and C, Weighting Curves for Sound
Level Meters
2-5
-------
Perceived Noise Level
Kryter, in the late 1950's, developed a new scale of perceived intensity called the Perceived
Noise Level.'" Its units are decibels. It is often popularly referred to as PNdB which:
"Was intended to present the sound pressure level of an octave band of noise at
1000 Hz which would be judged equally noisy to the sound to be rated. Equally
noisy means that in a comparison of sound one would just as soon have one noise
as the other at his home during the day or night."
Later, Kryter and his associates refined this technique further to include discrete frequency
components of tones associated with aircraft flyovers.'' The resulting measure is the Tone
Corrected Perceived Noise Level, abbreviated as PNLT. Finally, since long duration flyovers
appear to be more annoying than short duration flyovers, a new correction was added by Kryter
and Pearsons to account for the duration of the noise signal. This new quantity is called the Effec-
tive Perceived Noise Level (EPNL). This quantity is somewhat more exact than the A-weighting
in relating man's perception of sound to the physical parameters of sound, particularly in the case
of aircraft noise. For this reason, it has become a major element in the procedures utilized by the
1 9
Federal Aviation Administration for the certification of aircraft noise.
For most sounds, the Perceived Noise Level exceeds the A-weighted noise level by 13 dB,
the differences ranging typically between 11 and 17 dB, depending primarily upon the amount of
correction for pure tones.
The Tone Corrected Perceived Noise Level scale requires complex analysis and instrumenta-
tion to define a sound. Thus, it has not been utilized extensively, particularly since in most
instances the simple A-weighted sound level appears to adequately describe environmental noise
at a location, at a given time and does not require particularly complex instrumentation.
STATISTICAL MEASURES
One of the dominant characteristics of environmental noise at any location is that it fluctuates
considerably from quiet at one instance to loud the next. Thus, noise at a location must be des-
cribed by a statistical approach that takes time into account if it is to be accurately described. This
can be achieved by giving the complete curve depicting the cumulative distribution of sound
levels; that is, by showing what percent of the whole observation period each level is exceeded.
Noise levels are often specified in terms of levels exceeded 10 percent of the time, 50 percent of
the time, and 90 percent of the time.
The sound pressure level exceeded 10 percent of the time, expressed as L\Q, gives an approxi-
mate measure of the higher level and short duration noise. A measure of the median sound level is
given by the L5Q and represents the level exceeded 50 percent of the time. The residual sound
level is approximated by L9Q, which is the sound level exceede'd 90 percent of the time.
2-6
-------
The Energy Mean Noise Level
A measure accounting for both the duration and the magnitude of all the sounds occurring
during a given period is the average sound level, sometimes called the equivalent continuous noise
level. It is the continuous A-level that is equivalent in terms of noise energy content to the actual
fluctuating noise existing at a location over the observation period. It is also called the Energy
Mean Noise Level (Leq). By definition, Leq is the level of the steady state continuous noise having
the same energy as the actual time-varying noise. In terms of assessing the effects of noise on humans
Leq is one of the most important measures of environmental noise, since there is experimental
^7
evidence that it accurately describes the onset and progression of hearing loss. ' There is also
considerable evidence that it applies to human annoyance due to noise.
The statistical measures described simplify the problem of quantifying environmental noise
and are used extensively. These measures may, however, be misleading if used exclusively when
comparing two environments differing with respect to how constant or stationary they are during
the observation period.^
CUMULATIVE MEASURES
In most instances the noise problem is twofold. It involves either the constant high-level noise
intrusion of the city or the intermittent single-event noise intrusions in residential areas. With the
advent of jet aircraft, the latter type of problem has grown considerably over the years. Jet aircraft
noise has contributed significantly to data on and insight into community annoyance and has
stimulated the development of indices for assessing the cumulative effect of intrusive noises.
Rosenblith-Stevens Model
Rosenblith and Stevens^ developed, in the early 1950's, a model for relating the probable
community reaction to intrusive aircraft noise. This model included seven factors that were corrected
for.
1. Magnitude of the noise.
2. Duration of the intruding noise.
3. Time of the year (winter/summer; windows opened or closed).
4. Time of day (night/day).
5. Outdoor noise level when the intruding noise is not present.
6. History of prior exposure of the community to the intrusive noise.
7. Frequency components in the noise or its impulsive nature.
Other methods have been proposed. Most of these represent some modification of the basic model
of Stevens and Rosenblith.
2-7
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CNR and NEF
The Composite Noise Rating (CNR) was introduced in the early 1950's,16 followed by the
Noise Exposure Forecast (NEF).17 The CNR and NEF are similar, except that NEF accounts for
both duration and pure tone content of each single event, whereas CNR does not.
In the course of the studies relating to aircraft and airport noise, called for by the Noise Con-
trol Act of 1972, an effort has been made by Von Gierke and his staff to develop for EPA a suit-
able and simple method for defining and measuring cumulative noise exposure. This method
utilizes a 24-hour average A-weighted sound level with a penalty of 10 dB applied to nighttime
sound levels. This method, the day/night average sound level (L(jn) will be further discussed in
Section 3.
Community Noise Equivalent Level
i £
Recently, California introduced the Community Noise Equivalent Level (CNEL). This
rating represents the average noise level determined for a 24-hour period, with different weighting
factors for noise levels occurring during the day, evening, and night periods. Essentially, it is an
Leq for a 24-hour period with special corrections of 5 and 10 dB, respectively, for evening and
nighttime. It is designed to account for the increased disturbance caused by noise events during
the evening and the night.
To simplify the understanding of the cumulative methods described, a summary of the
variables included in each is presented in Table 2-1.
While most of the developments described above were performed in the United States,
Robinson, in England, developed a new scale, the Noise Pollution Level (L^p). "»2' This
measure is derived from two terms, one involving the average sound level (Leq) of the noise and
one involving the magnitude of the time variation of the noise level. The Lnp concept embodies
some simple principles:
1. Other things being equal, the higher the noise level, the more the disturbance.
2. Other things being equal, the less steady the noise level, the greater its annoying
quality.
In a more recent work, Robinson has further refined his Noise Pollution Level by taking the levels
of variation of the sound pressure levels and their rate of change into account.
The preceding discussion by no means exhausts the list of various schemes devised in the
ever-continuing efforts to develop new and better noise scales. It is intended to facilitate understand-
ing of the following sections of this document.
2-8
-------
Table 2-1
FACTORS CONSIDERED IN EACH OF FOUR METHODS
FOR DESCRIBING THE INTRUSIVENESS
OF NOISE ON THE COMMUNITY
FACTOR
Basic Measure
Measure of Duration
of Individual Single
Event
Weighting for Time
Period
Number (N) of
Identical Events in
Time Period
Summation of
Contributions
COMPOSITE NOISE
RATING CNR
Maximum Perceived
Noise Level
None
NOISE EXPOSURE
FORECAST
Tone Corrected Per-
ceived Noise Level
Energy Integration
DAY/NIGHT AVERAGE
SOUND LEVEL LDN
A Weighted Noise Level
Energy Integration
day 7 a.m. - 10 p.m.
night 10p.m. - 7 a.m.
Day 0 dB
Night 12 dB
10 Log N
Logarithmic:
Day 0 dB
Night lOdB
COMMUNITY NOISE
EQUIVALENT LEVEL
A Weighted Noise
Level
Energy Integration
day 7 a.m. - 7 p.m.
evening 7 p.m. - 10 p.m.
night 10 p.m. - 7 a.m.
Day 0 dB
Evening 5 dB
Night lOdB
10 Log N
Logarithmic
N)
-------
SUMMARY-RATING SCHEMES FOR ENVIRONMENTAL COMMUNITY NOISE
The description of community noise must account for:
1. Those parameters of noise that have been shown to contribute to the effects of noise
on man.
2. The variety of noises found in the environment.
3. The variations in noise levels that occur as a person moves through the environment.
4. The variations associated with the time of day.
Over the years, considerable effort has been expended to develop scales that reduce the
dimensions of sound and perception into a one-number scheme. Much effort has been focused
on combining measures of frequency content and overall level into a quantity proportional to the
magnitude of sound as heard by a person. An example of this type of rating scheme is embodied
in the sound level meter, although, other rating schemes are reviewed as well. Others have des-
cribed noise by a statistical approach that takes time into account. This is done by giving the
complete curve depicting the cumulative distribution of sound levels. Finally, schemes designed
to assess the effects of the constant high-level noise intrusion or the intermittent single-event
noise intrusion are also reviewed. It is found that to date one measure of noise that appears to be
emerging as one of the most important measures of environmental noise in terms of the effects of
noise on man is the Energy Mean Noise Level, Leg, which by definition is the level of the steady
state continuous noise having the same energy as the actual time-varying noise.
2-10
-------
REFERENCES
1. Kryter, K.D., THE EFFECTS OF NOISE ON MAN, New York: Academic Press, 1970.
2. The National Bureau of Standards, Fundamentals of Noise Measurement, Rating Schemes and
Standards, U.S. Environmental Protection Agency Document, NTID 300.15, 1971.
3. Chalupnick, J.D., (ed.), TRANSPORTATION NOISE, A SYMPOSIUM ON ACCEPTABILITY
DATA, Seattle: University of Washington Press, 1970.
4. Young, R.W. Measurement of Noise Level and Exposure, in TRANSPORTATION NOISES,
Seattle: University of Washington Press, 1970.
5. Wyle Laboratories, Community Noise, U.S. Environmental Protection Agency Document,
NTID 300.3, 1971.
6. Stevens, S.S., Measurement of Loudness, X4S.4, 27, 815, 1955.
7. Stevens, S.S., On the Psychophysical Law,Psychol. Review, 64, 153, 1957.
8. Stevens, S.S., Concerning the Form of Loudness Function, JASA, 29, 603, 1957.
9. Fletcher, H. and Munson, W.A., Loudness Definition, Measurement and Calculation, JASA, 5,
84, 1933.
10. Kryter, K.D., Scaling Human Reactions to the Sound from Aircraft, JASA, 31, 1415, 1959.
11. Kryter, K.D. and Pearsons, K.S., Judged Noisiness of a Band of Random Noise Containing
an Audible Pure Tone, JASA, 38, 1965.
12. Federal Aviation Regulations, Part 36, Noise Standards: Aircraft Type Certification,
November 1969.
13. Robinson, D.W. and Cook, J.P., NPL Aero Report No. Ac31, June 1968, National Physical
Laboratory, England.
14. Meister, F.J., The Influence of the Effective Duration in Acoustic Excitation of the Ear,
Larmbekampfung, 10, June/August 1966.
15. Rosenbl th, W.A., Sevens, K.N., and the Staff of Bolt, Beranek and Newman, Inc., HAND-
BOOK OF ACOUSTIC NOISE CONTROL, vol. 2, Noise and Man, WADC TR-52-204, Wright
Patterson Air Force Base, Ohio, 1953.
16. Galloway, W.J. and Pietrasanta, A.C., Land Use Planning Relating to Aircraft Noise, Tech-
nical Report No. 821, Bolt, Beranek and Newman, Inc., Published by FAA, October 1964.
17. Galloway, W.J. and Bishop, D.E., Noise Exposure Forecasts: Evolution, Evaluation, Exten-
sions and Land Use Interpretations, FAA-NO-70-9, August 1970.
2-11
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18. The Adopted Noise Regulations for California Airports: Title H, Register 70, No. 48-11-28-
70, Subchapter 6, Noise Standards.
19. Von Gierke, H., Impact Characterization of Noise Including Implications of Identifying and
Achieving Levels of Cumulative Noise Exposure, Draft Report, Task Group 3, 1973.
20. Robinson, D.W., The Concept of Noise Pollution Level, National Physical Laboratory, Aero-
dynamics Division, NPL Aero Report Ac 38, March 1969.
21. Robinson, D.W., Towards a Unified System of Noise Assessment, /. of Sound and Vibration,
74,279,1971.
22. Robinson, D.W., Rating the Total Noise Environment, paper presented at the International
Congress on Noise as a Public Health Problem, Dubrovnik, Yugoslavia, May 1973.
2-12
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SECTION 3
ANNOYANCE AND COMMUNITY RESPONSE
Annoyance as a result of exposure to noise is a psychosocial response to an auditory experi-
ence. Annoyance has its roots in the unpleasantness of noise, in the disruption by noise of ongoing
activities, and/or in the meaning or messages carried by a given noise.
The degree of annoyance and whether that annoyance leads to complaints or produces rejec-
tion of or action against a noise source are dependent upon many factors to be discussed subse-
quently. Some of these factors are well understood, others are not.
MEASUREMENT TECHNIQUES FOR ANNOYANCE
Numerous techniques have been devised to measure annoyance, from a simple scale ranging
from not annoyed to highly annoyed to very complicated techniques involving social surveys.
Individual Response
Individual responses of people to noise are often studied in the laboratory. Usually, these
studies involve judgments of individual noise events in controlled environments. Such studies have
been helpful in isolating some of the factors contributing to annoyance by noise. The annoyance
factors include:
• The intensity level and spectral characteristics of the noise.
• The duration of the noise event.
• The presence of discrete frequency components.
• The presence of impulses.
• The abruptness of onset or cessation of the noise event.
• Degree of harshness or roughness of the noise.
• Degree of intermittency in either the loudness.
• The pitch or rhythm.
1 9
• The information content and the degree of interference with activity. > z
Earlier Social Surveys
Community annoyance by noise is usually studied through social surveys. These surveys have
revealed other variables that are important in eliciting annoyance. Such variables include:
1. The noise climate or background noise against which a particular noise event,
such as aircraft flyover, occurs.
3-1
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2. The previous experience of the community with the particular noise.
3. The time of day during which the intruding noise occurs.
4. Attitude of people towards the noise makers.
5. Socioeconomic status of the community.
A number of experimental investigations have been made since the early 1950's that have
attempted to determine how people are affected by the noises they are exposed to and how to
arrive at methodologies that allow predictions of their response from measurements.of the physi-
cal characteristics of noise. Most of these studies have been in the form of social surveys and
have included studies in the United Kingdom,^ •> Sweden, ^» '' Austria, 12> '4 France, 15) 17
the Netherlands18 and the United States.19' ^ 1
The social surveys led to a series of noise ratings discussed in Section 2. Most of the ratings
thus devised were primarily based on investigations of aircraft and traffic noise. While there
was coordination between the various researchers involved in social surveys, less coordination
existed among those involved with the measurement of various environmental noises studied.
As a result, a variety of methods were utilized for measuring and reporting the noise exposures
experienced by the survey respondents. Nevertheless, a number of consistent findings emerged.
These findings are:
1. Even though each rating was developed independently, there exists a high degree
of correlation among all ratings, of the order of 0.90. Further, the community
response criteria derived from these surveys are remarkably similar for a specified
noise exposure.
2. The relationship between the statistical average annoyance experienced by a
collection-of individuals (a community) and the degree of noise exposure
experienced is also highly correlated as shown by Alexandra. This is depicted
in Figure 3-1, which shows the correlation between degree of noise exposure and
average annoyance for five surveys.
3. The individual annoyance response of a person living within a community is not
predicted as accurately as that of the community as a whole. This is reflected
in the poor correlation (correlations under 0.5) that exist between noise ratings
and individual annoyance scores. This particular finding stems from the fact
that there are a number of psychological and social factors that contribute
to the large range in individual sensitivity to annoyance from noise. "
Recent Social Surveys
Some of the criticisms generated by the earlier social surveys of the 1950's and early 1960's
have resulted in new surveys. These new surveys have extended the range of noise sources
3-2
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% ennoytd
so
70
60
.. I
DU U
r. I
10
1 1"
70
CO
I—1-4
~!—
i
I rn
I ..
»*v
20
10
?f tO "90 100 110 120 130 1*0 . CN5 (US)
.v, ..'/ /;• ;:• 5? lev 112 i??.;.':'•..-.••.r.c)
Figure 3-1. Percentage of Highly Annoyed Persons in Relation to Noise
3-3
-------
considered, the noise levels, the mix of noise sources and have included additional questions related
to personal factors into the questionnaire administered to people. ' ™ By and large, the new
surveys have confirmed the findings relative to population average obtained in the previous surveys
and have increased the correlation between individual annoyance scores and noise ratings. In the
studies performed by Tractor, for example, it has been shown that the correlation between indi-
vidual annoyance scores and noise rating is increased, when personal variables are included in the
calculation of annoyance, from 0.37 to 0.79.
Further, the new series of surveys have shed considerable light on the nature of some of the
personal factors that contirbute to a person's reaction to noise. Some of these factors include:
1. Fear associated with activities of noise sources such as fear of crashes in the case
of aircraft noise.
2. Socioeconomic status and educational level.
3. The extent to which residents of a community believe that they are being treated
fairly.
4. Attitude of the community residents regarding the contribution of the activities
associated with the noise source to the general well-being of the community.
5. The extent to which residents of the community believe the noise source could
be controlled.
COMMUNITY RESPONSE
Another important aspect of community noise that has not been discussed has to do with
what the community does about noise or sources. Much of what we know about this aspect of
community reaction to noise comes from studies of complaints from individuals living around
airports.
Complaints
Actions against a noise source may take various forms, ranging from registration of a com-
plaint through a telephone call or a letter to the person or authority responsible for the operation
of the noise source, to actual court action.
In general, people who complain do not appear to be unusual, neither are they particularly
sensitive to noise. Complaints have been found to be only a partial indicator of the number of
persons annoyed in a community. In fact, complaints may represent only a fraction of those
annoyed (2 to 20 percent). This finding is shown in Table 3-1.
The Rating Scheme
A different approach for the assessment of the response of a community to noise was
3-4
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TABLE 3-1
PERCENTAGES OF PERSONS HIGHLY ANNOYED WHO REGISTER COMPLAINTS AS A
FUNCTION OF Ldn.
Percentage of Percentage
°n Highly Annoyed of Complaints
"50 13 Less than 1
55 17 1
60 23 2
65 33 5
70 44 10
75 54 15
80 62 Over 20
3-5
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utilized in pioneering work by Stevens, Rosenblith and Bolt, which culminated in the Community
Noise Rating Scheme referred to in Section 2.^6. 37 ynis rat{ng method was based on an heuristic
assessment of 1) the acoustical parameters thought to influence community response and, 2) the
correlation between these effects and actual case histories of overt community action in response
to noise. In this approach, specific overt responses are observed, and then inferences are drawn
about community annoyance. In other words, there is no attempt to actually measure annoyance.
Community responses mean a scale of complaints by citizens ranging from sporadic to actual law
suits against the noise makers.
The Borsky Social Survey
In the 1950's Borsky began an extensive community noise social survey in response to criti-
cism directed to the rating method developed by Stevens et al. One of the initial survey results,
as has been corroborated in subsequent surveys, showed that overt reaction by a community, as
measured on a complaint type of scale, is clearly an underestimate of the degree of annoyance
existing in a community. This finding is consistent with the finding that even at very low noise
exposures, about 10 to 15 percent of the population will still display a high degree of annoyance
even though no complaints may be registered.
An obvious step in the study of community response to noise was to compare the social sur-
vey results on the relationship between annoyance and noise exposure.* This comparison showed
that criteria for acceptable noise exposures based on annoyance data essentially agree with criteria
based on community reaction observations. ^ From these findings, it is inferred that the varia-
bility in the relationship of community reaction to a specified noise exposure is explainable by
the variability in individual suscept bility to noise as compared with group averages. This hy-
pothesis is clearly in need of further study, but the aggregated data show clearly that the
envelopes of variability are highly correctable, whatever the causal relationships.
Analysis of Studies
One of the real problems in evaluating the general relationship between noise exposure and
community response is the fact that most of the data on which these relationships are based are
primarily related to aircraft noise exposures. This problem is somewhat lessened by the results of
several different analyses. First, the case studies used in developing the CNR system covered a
wide range of noise exposures from transportation to industrial noise sources. The high correlation
between these results and those from the airport related surveys, and the relationship between
annoyance and noise exposure lead to the assumption that for the average response of the commun-
ity, annoyance and community reaction to noise exposure can be predicted independently of the
nature of the noise source. Second, the social surveys related to noise sources other than aircraft
provide essentially identical relationships between annoyance and noise exposure as those found
in the airport studies. "'
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The highly convergent trend of the various investigations of annoyance and community re-
sponse leads to the following conclusions:
1. The degree of annoyance due to noise exposure expressed by the population average
for a community is highly correlated to the magnitude of noise exposure in the com-
TC
munity.
2. Variations in individual annoyance or response, relative to the community average,
are related to individual susceptibilities to noise; and these are highly correlated
7f> ^8 ^Q
with definable personal attitudes about noise/0' J0>
3. The numbers of complaints about noise registered with the authorities is small com-
pared to the number of people annoyed, or who wish to complain. However, the
number of actual complaints is highly correlated with the proportion of people in
the community who express high annoyance. °
4. The high correlation between those noise rating methods that account for the phy-
sical properties of noise exposure over a day's time suggests that the simplest acou-
stical measure that accounts for sound magnitude, frequency distribution, and
temporal characteristics of sound over 24 hours is an adequate measure for noise
exposure in communities.
The preceding factors were taken into account by the members of the Task Force of the EPA
Airport/Aircraft Noise Study in their assessment of the impact of cumulative noise exposure on
annoyance. Their conclusion was that the "energy" equivalent, or average, A-weighted sound
level, taken over a 24 hour period, with a 10-decibel penalty applied to nighttime sound levels, is
the simplest noise measure that provides high correlation with annoyance, complaint behavior, and
40
overt community reaction.HUThis measure was named "day-night average sound level." A sum-
mary of the relationship between this measure and the various responses to noise exposure is shown
shown in Figure 3-2, taken from the Task Group report.
SUMMARY - ANNOYANCE AND COMMUNITY RESPONSE
Numerous techniques have been devised to measure annoyance, from a simple scale of annoy-
ance level to complicated techniques involving social surveys. Laboratory studies of individual
response to noise have helped isolate a number of the factors contributing to annoyance, such as
the intensity level and spectral characteristics of the noise, duration, the presence of impulses,
pitch, information content, and the degree of interference with activity.
Social surveys have revealed several factors related to the level of community annoyance.
Some of these factors include:
1. Fear associated with activities of noise sources such as fear of crashes in the case
of aircraft noise.
3-7
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60
U)
oo'
60
•o
rj
c.
c
c? -
I 20
~
95% Confidence
Interval or Mean
.50 60 70 30' 90
Day-Nighh Average Noise Level, Lj IT
-------
2. Socioeconomic status and educational level.
3. The extent to which community residents believe that the are being treated fairly.
4. Attitude of the community's residents regarding the contribution of the activities
• associated with the noise source to the general well-being of the community.
5. The extent to which residents of the community believe that the noise source could
be controlled.
The highly convergent trend of the various investigations of annoyance and community
response leads to the following conclusions:
1. The degree of annoyance due to noise exposure expressed by the population average
for a community is highly correlated to the magnitude of noise exposure in the com-
oc
munity.
2. Variations in individual annoyance or response, relative to the community average,
are related to individual susceptibilities to noise; and these are highly correlated
*)£ 00 TQ
with definable personal attitudes about noise.' >
3. The numbers of complaints about noise registered with the authorities is small com-
pared to the number of people annoyed, of who wish to complain. However, the
number of actual complaints is highly correlated with the proportion of people in
99
the community who express high annoyance.
4. The high correlation between those noise rating methods that account for the phy-
sical properties of noise exposure over a day's time suggests that the simplest acous-
tical measure that accounts for sound magnitude, frequency distribution, and tem-
poral characteristics of sound over 24 hours is an adequate measure for noise
exposure in communities.
3-9
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REFERENCES
1. Galloway, W.J., Predicting Community Response to Noise from Laboratory Data, Transpor-
tation Noises, A Symposium on Acceptability Data, Chalupnik, J.D., ed., University of
Washington Press, 269-291, Seattle: 197 0.
2. Kryter, K.D., THE EFFECTS OF NOISE ON MAN, Academic Press, New York: 1970.
3. Noise, Final Report, prepared by the Committee on the Problem of Noise and presented to
Parliament in July, 1963, Her Majesty's Stationary Office, London, England, Cmnd. 2056.
4. Parkin, P.H., Purkis, H.S., Stephenson, R.V. and Schlaffenberg, B., London Noise Survey,
Building Research Station Report, S.O. Code No. 67-266, London, England, Her Majesty's
Stationary Office 1968.
5. Purkis, H.J., London Noise Survey: A survey of Noise levels in London, Note No. 6/66,
March 1966, Building Research Station, Garston, Herts., England.
6. Cedarlof, R., Jonsson, E. and Kajlaud, A., Annoyance Reactions to Noise from Motor
Vehicles: An Experimental Study Acustica, 13, 270-279J 1963.
7. Kihlman, Tor, Bjrn Lundquist and Bertil Nordlund, Trafikbullerstudier, Report 38: 1968,
Statous Institute for Byggnadsforskning, Stockholm, Sweden.
8. Fog, H., Jonsson, E., Kajlaud, A., Nilson, A. and Sorensen, S. Traffic Noise in Residential
Areas, Statous Institute for Byggnadsforskning, Stockholm, 1968.
9. Jonsson, E., Erlaud, A., Kaylaud, A., Paccagnells, B. and Sorensen, S., Annoyance Reac-
tions to Traffic Noise in Italy and Sweden, Stockholm: National Institute of Public Health,
Karolinska Institute, University of Stockholm and University of Farrara, Italy.
10. Jonsson, E., Sorensen, S., On the Influence of Altitudes to the Source on Annoyance Reac-
tions to Noise-An Experimental Study, Nordisk Hygienisk Tisdkrift, SL VIII, 35-45, 1967.
11. Cederlof, R., Jonsson, E., Sorensen, S., On the Influence of Altitudes to the Source on
Annoyance Reactions to Noise: A Field Experiment, Nordisk Hygienisk Tidskrift, XLVIII,
46-59 Stockholm, Sweden, 1967.
12. Brukmayer, F., and Laug, J., Disturbance of the Population by Traffic Noise, Oostereiche
Ingenieurfeitschrift, Jg. 1967, H.8, 302-206, H.9,338-344, and H.10, 376-385.
13. Bruckmayer, F., Laug, J., Disturbance Due to Traffic Noise In Schoolrooms, Oosterreichische
Ingenicur-Feitschrift, 11, 73-77, 1968.
14. Bruckmayer, F., Judgement of Noise Annoyance by Reference to the Background Level,
Oosterreichische Ingenicur-Feitschrift, Jg. 1963,315.
15. Auzou, S., Lamura, C., Le Bruiet aux Abords des Autoroutes, Cahiers du Centre Scientifique
et Technique du Batement, 78, 669,1966.
16. Lamure, C., Auzou, S., les Niveaux de Bruiet au Voisinage des Autoroutes Degages, Cahiers
du Centre Scientifique et Technique du Batement, 71, 599, 1964.
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17. . Lamure, C. and Bacelon, M., La Gene due au Bruit de la Circulation Automobile, Cahiers du
Centre Scientiflque et Technique du Bailment, 88, 762, 1967.
18. Urban Traffic Noise, Status of Research and Legislation in Different Countries, Draft Report
of the Consultative group on Transportation Research, DAS/CSI/68.47 Revised, OCED, Paris,
France, 1969.
19. Waters, D.M. and Bottom, C.G., The Influence of Background Noise on Disturbance Due to
Aircraft, Seventh International Congress on Acoustics, Budapest, 1971.
20. Robinson, D.W., The Concept of Noise Pollution Level, National Physical Laboratory Aero
Report Ac 38, Teddington, England, 1969.
21. Seuko, Alexandre, A. and Krishnau, P.V., Urban Noise Survey Methodology, in two volumes,
Report No. H-1262. Goodfriend and Associates, 1971.
22. Schultz, T.J., Technical Background for Noise Abatement in HUD's Operating Programs,
HUD Report No. 2005 R, Washington, D.C., 1971.
23. Galloway, W.J. and Von Gierke, H.E., Individual and Community Reaction to Aircraft Noise;
Present Status and Standardization Efforts, paper presented at the London Conference on
Reduction of Noise and Disturbance Caused by Civil Aircraft, Paper INC/C4/pg, Nov. 1966.
24. Galloway, W.V. and Bishop, D.E., Noise Exposure Forecasts: Evolution, Evaluation, Exten-
sions and Loud Use Interpretation, FAA Rpt No 70-9, 1970.
25. Alexandre, A., Aircraft Noise Annoyance in Europe: Special and Temporal Comparisons,
resulted at the International Congress on Noise as a Public Health Problem, Dubrovuik,
Yugoslavia, 1973.
26. McKennel, A.C., Noise Complaints and Community Action in Transportation Noise, A Sym-
posium on Acceptability Data, Chalupnik, J.D., ed., 228-244, University of Washington
Press, Seattle, 1970.
27. Aubree, D., Auzou, S. and Rapise, J.M. Etud de la Gene due au traffic Automobile Urbaise,
Final report of contract D. G, R.S.T. No. 68-01-389. Centre Scientifique and Technique du
Batiment, Paris, 1971.
28. Auzou, S. and Rapice, J.M., de briect du a la Circulation Automobile su Site Urbaiu: Ses
Characteristiques Physiques et sa Prevision, Centre Scientifique et Technique du Batiment
Etablissement de Grenoble, Division Acoustique, 1971.
29. Tracer, Community reaction to airport Noise NASA report CR-1761, 1971.
30. Second Survey of Aircraft Noise Annoyance around London, (Heathrow), Airport, H.M.S.O.
London, 1971.
31. Anderson, C.M.B., the Measurement of Altitude to Noise and Noises, National Physical
Laboratory Acoustics, Rpt. AC 52, Teddington, England, 1971.
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32. A Study of Annoyance from Motor Vehicle Noise, BB&N, Inc., Rpt No. 2112, 1971.
33. Motor Vehicle Noise: Identification and Analysis of Situations Contributing to Annoyance,
BB&N, Inc., Rpt. No. 2082, 1971.
34. Delauy, M.E., Copeland, W.C., Payne, R.C., Propagation of Traffic Noise in Typical Urban
Situations, National Physical Laboratory Acoustics Rpt A, 54, 1971, England.
35. Report to the President and Congress on Noise by the U.S. Environmental Protection Agency,
Document No. 92-63, Washington, D.C., 1972.
36. Rosenblith, W.A., Stevens, K.N., and the Staff of Bolt Baranck and Newman Inc., Handbook
of Acoustic Noise Control, vol 2, Noise and Man, WADC TR-52-204, Wright Patterson Air
Force Base, Ohio, 1953.
37. Stevens, K.N., Rosenblith, W.A. and Bolt, R.M., A Community's Reaction to Noise: Can it
be Forecast, Noise Control, 1, 63 71, 1955.
38. Borsky, P.N. Community Reaction to Air Force Noise, WADD Technical Rpt. No. 60-689,
Pts 1 and 2, Wright Patterson Air Force Base, Ohio, March 1961.
39. Bolt, Baranck and Newman, Motor Vehicle Noise: Identification and Analysis of Situations
Contributing to Annoyance, prepared for the Automobile Manufacturers Association Inc.
BB&N Rpt. No. 2082.
40. Von Gierke, H.E. Draft Report on Impact Characterization of Noise Including Implications
of Identifying and Achieving Levels of Cumulative Noise Exposure, prepared for U.S.
Environmental Protection Agency, June 1973.
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SECTION 4
NORMAL AUDITORY FUNCTION
Besides being sensitive to an enormous range of acoustic pressure variations, the ear is
capable of precise discriminations of temporal, intensity, and frequency changes. Hearing
is probably the most critical learning sense in childhood and continues in adulthood as the most
frequently used sense for the communication of ideas.
Associated with the auditory portion of the ear is the sense of balance. Although not
specifically a part of auditory function, disorders in the vestibular region of the ear can
adversely affect the operation of the auditory sensor and vice versa.
NORMAL HEARING IN YOUNG POPULATIONS
Hearing normally means being able to detect sounds in the audio-frequency range, namely,
16 to 20,000 Hz (20 kHz), at levels that lie at or within 10 decibels of the normal threshold of
hearing and below the threshold of aural pain in human beings (those boundaries define the
domain of normally audible sounds heard by air conduction.) The human hearing process is
such that at frequencies from 1,000 Hz down to 16 Hz, it takes increasingly more acoustical
energy to produce the same sensation of hearing as at the 1,000 Hz level. Similar increases also
are required with regard to the frequencies from 1,000 to 10,000 Hz but at a lower order of
magnitude.
Many otologists define normal hearing more narrowly as the ability to respond
appropriately to human speech (the spectral components of which are contained largely in
the range 250 to 4000 Hz) in average everyday conditions: others dispute so restrictive a
definition, however. When referred to in this document, hearing level is generally presumed
to be determined by pure-tone audiometry using standardized instrumentation and procedures.
The entire audio-frequency range just defined may be considered to be the domain of
human hearing. The appreciation, by nonauditory sensations in the ear or otherwise, of
air- or structure-borne vibrations at frequencies lower (infrasonics) or higher (ultrasonics)
than the audio-frequency range is not a part of hearing.
As to the boundaries of the domain of hearing, there is no evidence that these vary
significantly between normal human populations around the world. The normal threshold of
hearing for pure tones and the corresponding reference zero for audiometers have received
4-1
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international standardization (ISO, 1961, 1964), which may be taken to apply to the American
population. The upper boundary of normally audible sound (threshold of aural pain) has not
yet received such definitive recognition, but is commonly deemed to lie in the region of 135 dB
SPL, a value that is largely independent of frequency.
It is of interest to note that the typical average level of conversational speech without
undue vocal effort, measured at a customary speaking distance of 1 meter from the speaker,
is about 65 dB SPL. Peak intensities of vocal sounds usually exceed the average level by about
6 dB. A range variation of some 20 dB about the average is to be expected in the normal
speech levels of different speakers.
HEARING STUDIES AND RESULTS
Approximately 5 percent of school age children in the USA had deficient hearing,
^
according to a survey by Kodman and Sperrezzo in 1959. ^ A similar incidence has been
reported in Lebanon by Mikaehan and Barsorimian. There is no evidence that any
significant fraction of this hearing loss in American children below working age is noise-
induced. Rosen and Rosen^ have published a comparative survey of the upper limits of
hearing in school-age children and young people (aged 10 to 19 years) in several countries
in Africa, Europe and North America. That survey suggests that the frequency range of
"normal" hearing in that age group extends to at least 16 kHz (at which frequency, using
a special audiometric technique, the authors obtained nearly 100 percent response in some
of the groups), but that the percentage of children responding (able to detect tones) falls
off rapidly at higher frequencies. A response incidence of less than 50 percent was obtained
from all but one of the nine test groups at 20 kHz. However, responses in the range 0 to
15 percent were obtained at 22 kHz; and responses greater than zero (up to 10 percent in
Maba'an youngsters) in 4 groups even at 24 kHz. Fewer than 4 percent of a group of
American (New York) children responded at that frequency.
Rosen and his co-workers have tentatively suggested that the differences in hearing
level of children of different cultures may be linked with differences in susceptibility to
atherosclerosis and coronary artery disease in later life. Rosen, Olin and Rosen, citing
work in Finland as well as their own studies, have also contended that a low saturated fat
diet, said to protect against coronary artery disease, may also protect against sensorineural
hearing loss.
4-2
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Using a bone-conduction ultrasonic transducer in selected young adults (17 to 24 years
of age), Corso" also found that some hearing sensation exists above 20,000 Hz, above which
frequency there is a fairly abrupt decrease in steepness of the threshold slope (which is
steep-about 50 dB/octave-between 14 and 20 kHz). Corso found that some sensation
persisted on bone conduction testing at high levels of stimulation at ultrasonic frequencies up
to more than 90 kH, but it is very questionable whether this can be regarded as part of
"hearing." There was little difference between the sexes in either sensitivity or range of
sensation.
AUDIOLOGICAL UNIFORMITY OF THE POPULATION.
There is no inherent difference between the races comprising the population of the
United States with regard to hearing levels as a function of either age or noise exposure.
Human ears are much the same around the world. Public hearing surveys may, however,
reveal demographic differences in hearing levels of adults of different races or social
groups.^ Such differences may be attributed to the effect of differing environmental
influences, including non-occupational noise exposure (sociacusis).
Surveys of hearing levels in general populations can yield values that are poorer
(less sensitive hearing) than those obtained from samples, ostensibly from similar populations,
from whom subjects with certain audiological abnormalities (sometimes arbitrarily selected)
have been weeded out by a selection procedure.
SOURCES OF VARIATION IN HEARING LEVELS
Apart from the question of changes in hearing with advancing age, individual, and other
factors, it is to be expected that some statistical variation in threshold will be seen even when
a particular ear is audiometrically retested. The variation arises partly from intrinsic sources
(e.g., changes in the subject's physiological state) but a substantial source of variation in
practice is imperfection in the way in which audiometry is conducted (this is discussed in
detail in the section on Audiometry found in a recent EPA/AMRL publication"). Test-retest
variance can, however, be kept to a minimum when serial audiograms are obtained in
accordance with standard procedures, carried out under properly controlled conditions.
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Individual Variation.
Hearing surveys are always subject to possible bias because of the difficulties of
sampling human populations. In voluntary public hearing surveys, for example, a
substantial proportion of people selected to form a supposedly random sample of the
adult American population may decline to be examined. One cannot know, in that event,
whether or not those who will not be examined have group hearing levels similar to those
who do participate. If, for any reason, those refusing do have different hearing as a group,
then the survey cannot truly reflect the state of hearing of the population sampled. More
reliable data are of course obtainable from "captive" (e.g., industrial or military) populations,
of whom every member can perforce be examined, but such populations do not represent
the general population.
Sex Related Variations •.
From the early teenage years onwards, and particularly in the age range 25 through
65 years, women in industrial countries, including the United States, generally have better
hearing than men. In the elderly, however, above age 75, the difference tends to become insig-
nificant. Paradoxically, the rate of increase in hearing loss in men over 50 years of age declines,
while increasing in women of the same age. Female employees have been found to have better
hearing than male employees, even when they work side by side in noisy industries. ^'
Selection processes and circumstantial factors have been postulated to account for this.
These factors included thoughts that the women were exposed less to non-occupational
sociocoustic influences, such as small-arms noise; that they showed a high absentee rate-
a questionable contention and that they are freer to leave a job in which they find the noise
level objectionable). A more reasonable explanation, however, may be that, in the industries
involved, women may benefit from more liberal and frequent rest periods than are allotted
to men.' ^ The decline in differentiation between the hearing of the two sexes in old age
may be linked with an enhanced aging effect upon the ear associated with post-menopausal
changes in women, '^ although this is admittedly speculative.
-------
AUDITORY PRESENTATION OF INFORMATION
MIDDLE INNER
EAR EAR
AUDITORY
. NERVE
Figure 4-1 Functional Diagram Of Ear
Cited from "Human Engineering Guide to Equipment Decision" Editors - Morgan,
Cook, Chapanis, Lund; McGraw Hill, 1963.
4-5
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The Effect of Noise Stimulation on Mediating Mechanisms in the Middle Ear (Middle
Ear Muscle Reflex).
In the normal auditory mechanism, sound is transmitted to the inner portion of the
ear when sound vibrations imparted to the eardrum are mechanically transported across
the middle ear via three tiny bones; the malleus, incus and stapes (the ossicular chain).
See Figure 4-1.
Then, the inner most bone rocks in and out of its location, transferring the vibrations
to the fluid-filled inner ear region. Attached to the outer and inner bones are the two smallest
muscles in the body. The tensor tympani muscle, attached to the handle of the melleus, serves
to pull the eardrum inward (toward the center of the head) when the muscle is contracted.
The smaller of the two muscles, the stapedius, is located on the back portion of the floor in
the middle ear and attaches to the head region of the stapes. Upon contracting, the muscle
pulls the stapes in a lateral direction causing the eardrum to be moved outward. In effect,
the two muscles work in opposition to each other. Therefore, if they both contract at the
same time, there is a tightening of the ossicular chain into a comparatively rigid condition.
The effect of this tensing of the conductive mechanism is to reduce the amount of sound
energy delivered to the cochlea and thereby protect the inner ear from high intensity
sound.
Contraction of the stapedius muscle is caused by high level sound. A bilateral
neurological reflex arc has been described in which sound arriving at the cochlea is converted
to neurological impulses and carried toward the higher brain centers by the nerve of hearing,
Cranial Nerve VIII.' ^ Ifthe neurological activity is sufficiently intense, stimulation of
descending neurologic pathways of the facial nerve, Cranial Nerve VII, occurs. This set of
nerve fibers serves many areas of the head, including the stapedius muscle. Thus, sound
stimulation can result in the contraction of the stapedius muscle.
The middle ear muscle reflex, a popular name for the above-described activity,
increases and decreases in muscle tension according to the amplitude of the auditory
stimulus that sets off the reflex. According to Reger et al., the shift in transmission
efficiency results in a conductive loss of as much as 35 dB in the lower audiometric
frequencies (250 Hz) but there is little loss in conductive cpapbility for frequencies at
2000 Hz and above. This would indicate that there is relatively minor protective capability
by the muscles for a significant portion of the frequency range at which the ear is maximally
sensitive.
4-6
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Indirectly, Ward ' observed that temporary threshold shift for a 700 Hz pure tone
was reduced when masking noise of sufficient intensity to elicit a muscle reflex was
introduced to the opposite ear from the one receiving the tone. The reduction in
temporary hearing loss was of the same magnitude as one would find if the pure tone
stimulus were approximately 10 dB lower in amplitude. Therefore, it might be concluded
that for the frequency tested, there was a degree of protection afforded by the reflex.
When Ward used a 2000 Hz tone, there was no apparent protection function in that the
temporary threshold shift was the same with or without the reflex. In electrophysiological
18
studies, Wever, et al., ° found that the contraction of the stapedius muscle in cats resulted
in 5.6 dB less transmission of a 300-Hz signal to the cochlea. The tensor tympani muscle
contracting alone reduced the transmission efficiency 1.5 dB. When both muscles were
contracted simultaneously, the resulting transmission loss was found to be 20 dB.
There is no firm agreement in the literature on the threshold of middle ear reflex
activity for "normal" human ears. Perlman " observed that reflex thresholds have been
reported for sounds ranging from 40 dB to 100 dB depending upon the type of sound
used. Thus, there appears to be a wide range of individual variation with respect to the
reflex. In general, however, the reflex occurs when the stimulus is presented at
levels between 75 to 90 dB. Perlman'" has also observed that during continuous
stimulation by sound, the muscles tend to relax. This reduces their protective function.
The onset of muscle responses lags behind the onset of an intense sound by 15 to
90
17 milliseconds or longer/" The muscles reach peak contraction somewhat later.
91
Wersall determined that these peaks occur 6 msec after onset of the stimulus for
the stapedius muscle and 132 msec for the tensor tympani. This being the case, sounds of
sudden onset and of short duration (e.g., gunshots, cap pistols, firecrackers, or stamping
presses) are carried into the ear at full force without alteration by the middle ear muscles.
It is thereby considered that the protective function of middle ear muscles for impulse-
type sounds is nonexistent. Fletcher^ has demonstrated that some protection against
noise can be obtained by introducing a moderate reflex-arousing stimulus prior to the
occurrence of the more intense impulse noise. In industry, this principle has been applied
by constructing a triggering device that presents a reflex-arousing tone to the ear of a
drop forge operator prior to the impact of the forge itself. That this provides protection
9 "3
for the cochlea was dramatically demonstrated in animal experiments by Simmons.
4-7
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He subjected one group of cats to gunfire without using a reflex-arousing stimulus
immediately before each report of the gun. Histologic evidence was obtained that
showed a marked difference in cochlear tissues of the cats receiving the reflex-arousing
stimulus.
A possible additional mediating factor in the onset and extent of the reflex is the
amount of attention one pays to the sound itself. Durant and Shallop^ distracted
subjects by diverting their attention with a mathematical mental task. Their conclusion
was that the protective function of the middle ear muscles may be influenced by central
factors, specifically, the state of attention.
HEARING LOSS ASSOCIATED WITH OLD AGE
The threshold of hearing rises, that is, hearing becomes less sensitive with advancing
years, even in the absence of damaging noise exposure. This effect (presbycusis) involves
primarily, and is most marked at, the higher audiometric frequencies, above about
*? ^
3000 Hz. At least in urbanized western populations, presbycusis appears to be more
pronounced, at a given age, in men than in women, but the difference may be associated
with occupational factors and the differences between the sexes in the pattern of day to
day activity involving noise exposure, rather than with the sex difference per se.
Causes of Presbycusis
The loss of auditory sensitivity with advancing age is believed to be due to central
nervous system deterioration as well as to peripheral changes in the auditory system. "'^'
Aging people are apt to have increasing difficulty in discriminating auditory signals and
in understanding speech heard against a background of noise. This may be due to an
increasing susceptibility to masking by low-frequency (below 500 Hz) noise as well as
to the loss of auditory sensitivity in the speech frequency range.
^o
As Hinchcliffe has remarked in a recent review, physiological aging is accompanied
by degenerative changes affecting not merely the organ of Corti but the whole auditory
system, including its central projections. This may explain some of the features of hearing
handicaps typical of old age, such as loss of discrimination of normal, distorted and noise-
masked speech, which are not amenable to prediction from pure tone audiometry alone.
Rosen believes that degenerative arterial disease in particular is a major factor in the
etiology of presbycusis. Such changes affect individuals diffusely in different ways and
4-8
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do not necessarily involve the Organ of Corti itself. To a marked degree, lesions of that
organ due to noise are characteristically located discretely in the basal turn of the cochlea.
Glorig and Nixon ^ have restricted the definition of the term "presbycusis" to hearing
losses caused by physiological aging, and it is used in this sense in this document, although
some audiologists use it to embrace any sensorineural loss occurring in the elderly.
Presbycusis Corrections
Sufficient data now exists from surveys of general populations to permit estimations of aver-
age hearing loss due to presbycusis. These average hearing loss values due to aging are referred
.to as presbycusis corrections.
Glorig^' estimated a presbycusis correction applicable to the three "speech frequencies"
(500, 1000 and 2000 Hz) important in the assessment of disability due ,to occupational noise-
induced hearing loss. His figures are shown in Table 4-1 to illustrate the magnitude of the
39 ^1
effect. Other presbycusis data, derived from industrial surveysJ<->JJ are shown in Table 4-2.
For comparison, the British dats of Hinchcliffe, which are used by Robinson in his
predictive method are summarized in Figure 4-2.
Table 4-1 . ,
Glorig's correction for 3F/3.
Age (years) 25 30 35 40 45 50 55 60 65 70
Correction (dB) 0 +1 +1 +2 +2 +2 +3 +5 +7 +13
Presbycusis and Other Factors Affecting Hearing
Von Schulthess and Huelsen" and von Schulthess^" have pointed out that, audio-
logically, the endogenous and exogenous factors causing the rise in hearing level with age
are not distinguishable. One can only say that group hearing levels rise naturally with age
(presbycusis), due probably to both peripheral and central aging process, " and that this
effect is enhanced (in a way which for lack of other evidence is generally presumed to be
additive) by noxious environmental, mostly acoustic influences (Glorig's "sociacusis")
and specific exposures to excessive noise.
4-9
-------
15
20
25
Oi
•""ii^ r r
i5
50
55
60
70
»• -4
\
X
\i
E
2346
FREQUEKCY (kHz)
8 12
18 - 2>> Years
35 -
45 - 5*1 Years
55 - 6% Years
65 - 74 Years
Note: Median hearing loss is related to median threshold at 21.5 years of age (Hinchcliffe).25
For the purposes of the present document, clinically normal female ears may be equated
with non-noise exposed clinically normal male ears.
Figure 4-2. Threshold of Hearing as a Function of Clinically Normal
Female Ears (Random Sample Population)
4-10
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TABLE 4-2
PRESBYCUSIS DATA UPPER REGISTER: MEDIAN
AGE-INDUCED HEARING LEVELS (NON-NOISE-EXPOSED MEN)
ROUNDED TO NEAREST DECIBEL. FROM: PASSCHIER-VERMEER.32
Age
(Years)
25
30
35
40
45
50
55
60
65
70
75
Frequency (Hz)
250
0
1
1
2
3
4
5
7
9
12
14
500
0
1
1
2
3
4
6
8
10
13
16
1000
0
1
1
2
3
4
6
8
10
13
17
2000
0
1
2
4
6
8
11
14
18
24
30
3000
0
2
4
6
9
14
18
22
27
33
40
4000
0,
3
6
9
13
18
23
28
33
40
47
6000
0
4
7
.12
16
22
27
33
40
47
55
8000
0
3
16
11
15
22
28
35
43
53
62
Comparable data derived from Schneider et ar* corrected to HL = 0 at Age 25
Age
Frequency (Hz)
(Years)
25
30
35
40
45
50
55
60
65
250
_
-
-
-
-
-
-
-
-
500
0
0
1
1
2
3
4
6
8
1000
0
1
1
2
3
5
7
9
12
2000
0
1
3
4
6
8
12
16
22
3000
0
3
5
8
12
15
20
27
34
4000
0
3
5
9
14
18
25
32
42
6000
0
4
7
10
14
19
25
33
42
8000
0
2
5
9
13
19
25
36
50
4-11
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SUMMARY - NORMAL AUDITORY FUNCTION
Normal hearing is regarded as the ability to detect sounds in the audio-frequency range
(16 Hz to 20 kHz) according to established standards or norms. This range varies little
in human populations around the world. However, there is considerable individual variation
in hearing ability. As a general rule, for example, women in industrial countries typically
have better hearing than men.
In the normal auditory mechanism, sound is transmitted to the inner portion of the ear
when sound vibrations imported to the eardrum are transported across the middle ear.
The stapedius and tensor tympani muscles, when contracting, increase the tension of
the conductive mechanism and thereby reduce the amount of sound energy delivered to the
inner ear. Since high intensity sound causes these contractions, the ear has a limited built-in
protective device. However, there is enough of a lag between sound onset and muscle
contraction, that a sudden impulse is not attenuated by the protective mechanism.
Hearing sensitivity normally diminishes with age, a condition known as presbycusis.
Consequently, corrections for aging should be considered in examining data on hearing
loss due to noise exposure.
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REFERENCES
1. BENOX (Biological effects of Noise) Group (Ades, H.W. & Colleagues) (1 December 1953).
BENNOX REPORTS: An exploratory study of the biological effects of noise. Univ."
Chicago: ONR Proj NR 144079.
2. Kodman, F. Jr., and Sperezzo, A. Hearing factors in school-age children. Acta
Otol. 50, 1959.
3. Mikaeman and Barimian (1971) (see related publication^-*)
4. Rosen, S. & Rosen, Helen V. (1971). High frequency studies in school children in nine
countries. The Laryngoscope, 81, 1007, 1013.
5. Rosen, S., Olin, P. & Rosen, Helen, V. (1970). Dietary prevention of hearing
loss. Acta Otolarying, 70, 242-247.
6. Corso, J.F. (November 1963) Bone-conduction thresholds for sonic and ultrasonic
frequencies. Jacoust Soc Amer, 35 (11), 1738-1743.
7. Roberts, Jean and Bayliss, David. Hearing Levels of Adults by Race, Region,
and Area of Residence, United States 1960-1962. National Center for Health
Statistics, Series 11, Number 26. U.S. Department of Health, Education, and Welfare,
Public Health Service, Washington, D.C. (1967).
8. Environmental Protection Agency/Airforce Aerospace Medical Research Laboratory,
A SCIENTIFIC BASIS FOR LIMITING NOISE EXPOSURE FOR PURPOSES OF
HEARING CONSERVATION. EPA document EPA - 550/9-73-001 (in press) 1973.
19. Riley, E.C., Sterner, J. H., Fassett, D.W. and Sutton, W.L. Ten years' experience
with industrial audiometry. Am. Ind. Hyg. Assoc. J. 22, 151-159 (1961).
10. Kylin, B. Temporary threshold shift and auditory trauma following exposures to
steady-state noise. An experimental and field study. Acta Otolarying. Suppl. 152,
1-93(1960).
11. Dieroff, H. G. Sex differences in resistance to noise. Arch. Ohren-Nasen-Kehlkopfheilk.
Ver, z, Hals-Nasen-Ohrenheilk, 177, (1961).
12. Gallo, R. & Glorig, A. (1964). Permanent threshold shift changes produced by noise
exposure and aging. Amer Ind. Hyg. Assoc. J, 25, 237-245.
13. Ward, W. D., Glorig, A. & Sklar, Diane L. (April 1959). Temporary threshold shift
from octave-band noise: applications to damage-risk criteria. J acoust Soc Amer, 31 (4),
522-528
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14. Glorig, A., Wheeler, D., Quiggle, R., Grings, W., and Summerfield, A., 1954 Wisconsin
State Fair Hearing Survey: Statistical treatment of clinical and audiometric data.
American Academy Opthalmology and Otolaryngology and Research Center Subcommittee
on Noise in Industry, Los Angeles, California, 1957.
15. Jepsen, Otto, MODERN DEVELOPMENTS IN AUDIOLOGY, Middle-ear Muscle
Reflexes in Man, in James Jerger, New York: Academic Press, 1963.
16. Reger, S. N., Mensel, O. J., Ickes, W. K. and Steiner, S. J., Changes in Air Conduction
and Bone Conduction Sensitivity Associated with Voluntary Contraction of Middle Ear
Musculature, in SEMINAR ON MIDDLE EAR FUNCTION. Report 576 U. S. Army
Medical Research Laboratory, Fort Knox, Kentucky, J. L. Fletcher, (ed.), 171-180,1963.
17. Ward, W. Dixon, Damage-risk Criteria for Line Spectra,/. Acoust, Soc. Am., 34,
1610-1619, 1967.
18. Weaver, E. G., Vernon, Jack and Lawrence, Merle, The Maximum Strength of the
Typanic Muscles, Ann OR and L. 64, 383-391, 1955.
19. Perlman, H. B., The Place of the Middle Ear Muscle Reflexlin Auditory Research,
Arch. Otolaryngol, 72, 201-206, 1960.
20. Neergard, E. B. and Rasmussen, P. E. Latencies of the Stapedus Muscle Reflex in
Man, Arch. Otolaryngol, 84, 173-180, 1966.
21. Wersall, R., Acta Otolaryngol, 139, Supp., 1958.
22. Fletcher, J. L., Protection from High Intensities of Impulse Noise by way of
Proceeding Noise and Click Stimuli, /. Audit Res., 5. 145-150, 1965.
23. Simmons, F. B., Individual Sound Damage Susceptibility: Role of Middle Ear
Muscles, Ann. Otol. Rhinol. Laryngol., 72, 528-547, 1963.
24. Durrant, J. D. and Schallop, J. K., Effects of Differing States of Attention on
Acoustic Reflex Activity and Temporary Threshold Shift, /. Acoustic. Soc. Amer., 46,
907-913, 1969.
25. Hinchcliffe, R. (1959). The threshold of hearing as a function of age. Acoustica, 9,
303-308.
26. Konig, E. Compt. Rend Seances, 11 Congr. Ord. Soc. Internat. Audiol. pp. 87-97, 1955.
27. Davis, H. and Silverman, S. R. HEARING AND DEAFNESS: New York: Holt, Rinehart
and Winston, 1970.
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28. Hinchcliffe, R. Report from Wales: Some relations between aging noise exposure
and permanent hearing levels changes. Committee S3-W-40 of the American National
Standards Institute, Anderson, Indiana, August 1969.
29. Rosen, Samuel. Noise, Hearing and Cardiovascular Function. In PHYSIOLOGICAL
EFFECTS OF NOISE, Welch and Welch, eds. New York: Plenum Press (1970).
30. Glorig, Aram and Nixon, J. Hearing loss as a function of old age. Laryngoscope, 72
(1962).
31. Glorig, Aram, and Davis, H., Age, noise and hearing loss. AnnOtol 70. 556(1961).
32. Passchier-Vermeer, W. (April 1968). Hearing loss: due to exposure to steady-state
broadband noise. Instituut Voor Gezondheidstechniek, Sound & Light Division,
Rpt. 35, 18pp.
33. Schneider, E. J., Mutchler, J. E. Hoyle, H. R., Ode, E. H. & Holder, B. B. (1970).
The progression of hearing loss from industrial noise exposures. Amer. Ind. Hygiene
Assoc. Jour, 31, May-June, 368-376.
34. Robinson, D.W. Estimating the Risk of Hearing Loss due to Continuous Noise.
In Occupational Hearing Loss, D. W. Robinson, Ed. Academic Press, N. Y., 1971.
35. Schulthess, G. V. & Huelsen, E. (1968). Statistical evaluation of hearing losses in
military pilots. Acta oto laryngologica, 65, 137-145.
36. Schulthess, G. V. (1969) Statistical evaluation of hearing losses in military pilots
(2nd Rpt). Acta oto-laryngologica, 68. 250-256.
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SECTIONS
NOISE-INDUCED HEARING LOSS - TEMPORARY AND
PERMANENT SHIFTS IN AUDITORY THRESHOLD
FOLLOWING NOISE EXPOSURE
The prevalence of hearing loss among workers in noisy industries has been recognized since
ancient times, and a popular description of excessively loud noise is "deafening." Yet, it is
still not adequately appreciated by the general public that there is a causal link between noise
exposure and hearing loss. If the hazard is understood, it is, perhaps, regarded by many as a
remote contingency or as one that has little consequence for those afflicted. It is possible, too,
that while people exposed to intense noise frequently experience a substantial Noise-Induced
Temporary Threshold Shift (NITTS), sometimes accompanied by tinnitus (ringing of the ears),
the fact that very often such symptoms largely disappear within a short time may mislead
people into believing that no permanent damage has been done by the noise.
Observations in animals as well as in man show that noise reaching the inner ear attacks
directly the hair cells of the hearing organ (the organ of Corti). As the intensity of the noise
and the time for which the ear is exposed to it are increased, a greater proportion of the hair ,
cells are damaged or eventually destroyed. The function of the hair cells is to transduce the
mechanical energy reaching the ear into neuro-electrical signals, which are then carried by the
auditory nerves to the brain. In general, progressive loss of hair cells is inevitably accompanied
by progressive loss of hearing as measured audiometrically.
There is a great deal of individual variation in susceptibility to noise damage. However,
any man, woman, or child whose unprotected ears are exposed to noise of sufficient intensity
is, in the long run, likely to suffer some degree of permanent noise-induced hearing loss for
which there is no foreseeable cure.
It remains an open question as to the level of noise which is within safe limits for all ears.
In this connection, it is important to bear in mind the fact that neither the subjective loudness
of a noise, nor the extent to which the noise causes discomfort, annoyance, or interference
with human activity, are reliable indicators of its potential danger to the hearing mechanism.
Clinical observations of noise-induced hearing loss have been reported over more than a
century. However, the problem has received intensive study only during the past three or four
5-1
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decades. Since the World War II, substantial data have been gathered on the effects of intense
. sound (particularly industrial noise) on the ear. Based upon the available data, numerous
criteria and noise limits have been established for the purpose of hearing conservation. Some
of these have received national or international acceptance or standardization and some have
been embodied in state and federal legislation. An important present difficulty for the
legislator, administrator or noise control engineer concerned with protecting human hearing
against noise is the fact that confusing and sometimes conflicting guidance is offered by the
multiplicity of official or semiofficial standards, regulations or guidelines now in existence.
Clearly, there is an urgent need for one set of guidelines to be elevated and urged for
universal adoption. This document should help accomplish that task, since the conclusions
reached in this work apply to both occupational and non-occupational exposure at work,
in the home, in transportation, in recreation, or at large in the street and other public places.
The major topics to be discussed in this section will relate to the degree to which ear
damage occurs in the wake of noise exposure. There will also be some discussion of the
mechanism of noise damage in the ear, damage-risk criteria and related calculation, and
factors influencing the incidence of Noise-Induced Permanent Threshold Shift. (NIPTS)
There are a large number of causes of permanent hearing damage, many of which are
beyond the control of the individual who is victimized by destruction in his ear(s). Noise
exposure, for the most p5rt, can be avoided or reduced in a number of ways. Therefore,
the damaging effects of noise upon the ear must be regarded as a preventable influence-
preventable by abatement of the noise, by alteration of operations in and around the noise,
or by protection of the ear with the use of sound reducing materials or devices.
TYPES OF ADVERSE EFFECTS ON HEARING
Noise-Induced Permanent Threshold Shift (NIPTS).
The permanent loss of hearing ascribable to noise exposure, as opposed to other factors
(aging, drug toxicity, etc.) is called Noise-Induced Permanent Threshold Shift (NIPTS).
The shift in threshold refers to the loss in sensitivity of the ear. Details of hearing test
techniques may be found in a related publication.
Noise-Induced Temporary Threshold Shift (NITTS)
The temporary loss of hearing ascribable to noise exposure is called noise-induced
temporary threshold shift (NITTS) and is mentioned frequently in this chapter.
5-2
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THEORIES RELATING NOISE EXPOSURE AND HEARING LOSS
Because most of our data concerning the long-term hazard of noise come from 8-hour
industrial-type noise exposures, there is a relative lack of information about shorter-term
intermittent or incomplete daily exposures, and virtually no data about continuous exposure
to noise going on longer than 8 hours, or around the clock. One is accordingly driven to
make interpolations and extrapolations on the basis of theories of noise trauma. Two main
theories have been supported by substantial amounts of field observation and experimental
work. A continuing difficulty in setting guidelines for safe noise exposure is that predictions
using these theories conflict in some circumstances. Because the conflict is not resolvable in
many circumstances, an empirical decision has to be faced as to which theory to follow in
evaluating a particular noise hazard.
The Equal Energy Hypothesis in Damage Risk Criteria
The "equal-energy" hypothesis argues that the hazard to the hearing is determined by the
total energy (a product of sound level and duration) entering the ear on a daily basis. This
rule is basic to the damage-risk criteria embodied in certain important and widely used
regulatory or guiding documents, notably the 1956 U. S. Air Force Regulation AF 160-3. ^
The "equal-energy" rule allows a 3-dB increase in sound pressure level (expressed in dB) for
each halving of the duration (below 8 hours) of continuous daily steady-state exposure.
Extrapolation to durations of continuous noise exceeding 8 hours daily exposure and
extension to extremely brief exposures or impulses have only recently been proposed. In
^
practice, a cutoff is introduced by the widely recognized mandatory absolute limit of 135 dB^
for unprotected exposure, irrespective of duration. Botsford^ has remarked, there is still a
lack of experimental or empirical verification of the "equal-energy" hypothesis except
perhaps for overall durations of daily occupational exposures extending over years, the only
application for which the equal energy rule was originally proposed. The theory has the
attractions of simplicity and a certain a priori reasonableness. (See Proceedings of the
International Conference on Noise as a Public Health Problenv).
The "Equal Temporary Effect" Hypothesis
This theory, originally based largely on the work of Ward, et al., '" argues that the long-
term hazard (of PTS) of steady-state noise exposure is predicted by the average TTS produced
by the same daily noise in the healthy young ear. As Botsford^ has noted in a recent review,
this hypothesis is plausible because (unlike the "equal-energy" rule) it relates to an observable
physiological function of the ear. Moreover, recent work suggests that a unifying hypothesis
of metabolic insufficiency induced in the hearing organ by noise may underlie both the
temporary and permanent hearing defects caused by excessive noise. The essence of the
5-3
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supporting data is that noise intense enough to cause PTS in the long run is intense enouch to
produce TTS in the normal ear, while noise that does not produce measurable TTS is not
•7
associated with NIPTS. TTS studies also tend to support the observation (reflected in industrial
studies of PTS) that intermittent noise is less harmful than unbroken exposure to steady-state
O Q
noise at the same level.°'y Adoption of this theory has led to a number of current criteria,
including that of the Committee on Hearing and Bioacoustics of the National Research Council
(1966), considered below.
CHABA Criterion for Steady-State Noise Exposure
CHABA's criterion is based essentially upon the hypothesis of "equal temporary effect"
already alluded to. In essence it states that a noise exposure is unsafe if, upon testing the
normal ear two minutes after the cessation of the exposure, an average TTS2 of 10 dB is exceeded
at audiometric frequencies up to 1000 Hz, 15 dB at 2000 Hz, or 20 dB at 3000 Hz and above.10
According to Ward*' this criterion reflects the empirical observation that in most normal-hearing
people, a TTS2 of 20 dB or less recovers completely within 16 hours (when the worker would
be due to renew a typical 8-hour industrial exposure). The corollary to that is that it is deemed
unlikely that any PTS is building up when the TTS recovers completely before the commencement
of the next waking day. (A fraction of "sensitive" ears, of course, will not recover completely.)
This makes no allowance for post-work, non-occupational exposure, however.
DATA ON EFFECTS OF NOISE ON HEARING
Data on the effects on hearing are given for two main types of noise, namely, continuous
(or steady-state) and impulsive noise. For purposes of hearing conservation criteria, noise refers
to airborne sound contained within the frequency range of 16 Hz to 20,000 Hz (20 kHz). Sound
energy outside that range (ultrasonics, infrasonics, vibration) is considered in a separate chapter.
Although some other noise-measurement units are alluded to, this section, in general, adopts
A-weighted sound level (in dBA) for the specification of steady-state noise levels, and peak
sound pressure level (SPL) in decibels (dB) relative to standard reference sound for the specifica-
tion of impulse noises (see Section 1). When A-weighted sound levels are given, the use of
international standard measurement techniques, instrumentation, and weighting characteristics
is assumed.
Ongoing Noise and Hearing Loss
Procedures for calculating Equivalent Continuous Sound Level (Leq) in dBA, in the cases
of atypical, interrupted or intensity-modulated, steady-state noise exposure are given in a recent
EPA-Air Force publication.' ^ This source also may be used to determine exposures in dBA from
octave-band sound levels measured in decibels relative to 0.00002 N/m .
5-4
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Industrial Experience
There is a plethora of published information about the effects of long-term noise exposure
upon the hearing of workers in the manufacturing and construction industries, as well as that of
.aviators and others in noisy occupations: several recent monographs and surveys have been
published on this topic. ^> *° A recent survey by the National Institute of Occupational Safety
.and Health (NIOSH)'' contains a descriptive summary of some of the more important
audiometric surveys carried out in the United States and abroad during the preceding decade.
Temporary hearing loss attributable to fatigue of the inner ear (or Noise-Induced
Temporary Threshold Shift, NITTS) lasting from a few seconds to a few days can occur after
brief exposure to high sound levels or from day-long exposure to more moderate levels of
on-going noise. Regular (day-by-day) exposure to such levels over a long period (days to
years) can result in damage to the inner ear, a sensorineural hearing loss (NIPTS) that is
permanent and so far as is presently known, irreversible. It can be prevented only by
protecting the ear from excessive noise exposure.
NIPTS is usually preceded by, and may at any time be accompanied by, 2 NITTS. The
typical pattern of NIPTS seen in the audiogram is maximum loss in the range 4000 to 6000 Hz,
with a somewhat smaller loss (initially) at higher and lower test frequencies. Because the loss
is sensorineural, it is seen in both air- and bone-conduction audiograms.
Gallo and Glorig^ examined audiometric data from 400 men (aged 18-65) and 90
women (18-35) exposed regularly to high-level industrial plant noise (102 dB SPL overall;
89, 90, 92, 90, 90 and 88 dB, respectively, in the octave bands spanning 150 to 9600 Hz).
These subjects were selected from larger groups of 1526 male and 650 female employees,
using a screening process designed to exclude otological abnormalities and irrelevent noise
exposure (e.g., to military noise), and to maintain in the men a high correlation between age
and time on the job. The purpose of the study was to look specifically at age and duration
of steady-state noise exposure as factors in PTS. It showed quite clearly that hearing level
tends to rise relatively rapidly over the first 15 years of exposure but then to level off as
reflected in the higher audiometric frequencies, 3, 4 and 6 kHz. By contrast, hearing level at
500 Hz, 1 and 2 kHz rose more slowly but continued to rise in an essentially linear manner
over exposures up to some 40 years.
A comparison of data for 4 kHz in the men with equivalent data from non-noise-exposed
males showed that the effects of the age and noise were not simply additive. Examination
of individual differences showed that the spread of hearing level within groups tends to
increase with both increasing exposure time and with audiometric frequency (a similar effect
has been reported by Taylor, et al. Also, the time and frequency dependence of noise-
induced hearing level change was found to be similar for most subjects. Gallo and Glorig
5-5
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concluded from this study that early evidence of PTS at 4000 Hz is the best indicator of
susceptibility to noise-induced PTS on either a group or individual basis. A cognate study by
Taylor et al.^ in female jute weavers supported Gallo and Glorig's finding that noise-induced
deterioration in hearing takes place rapidly and mainly in the first 10 to 15 years of exposure,
with, however, further deterioration at the speech frequencies continuing in later years.
Taylor, et al. carried out retrospective audiometric studies of groups of women working
in or retired from the jute weaving industry in Scotland. The contributions to their group
hearing levels attributable to the regular noise (99-102 dB SPL overall with higher peaks) to
which they had been exposed were evaluated by comparison with non-noise-exposed control
subjects and by corrections for presbycusis using Hinchcliffe's^ median data. Generally, this
study supported the conclusions of Gallo and Glorig. " Namely, these findings were that the
effect of noise on hearing levels is greatest, earliest and most rapid at the higher audiometric
frequencies (4 and 6 kHz), where it mostly takes place in the first 10 or 15 years of occupa-
tional exposure, -* but that further deterioration involving frequencies in the range of 1 to 3 kHz
(being most marked at 2 kHz) becomes manifest during the third decade of noise exposure.
After as few as 10 years of on the job exposure in areas of high-level (90 dB SPL) industrial
plant noise, men as young as 30 years old may have hearing levels worse than non-noise-exposed
men twice their age and may, in some cases, already suffer impaired speech perception. "
PTS produced by noise exposure and PTS produced by aging (presbycusis) may not be
distinguishable on either a group or individual basis. " NIPTS is found primarily among
industrial workers who have been exposed repeatedly and over a long period to high-intensity
noise. Provided that the ears affected are otologically normal, the PTS found in noise-exposed
people may be attributed to the combined effects of aging and habitual noise exposure. Moreover,
the component attributable to noise exposure may be viewed as the result of repeated noise-
induced TTS. Some audiologists subscribe to the view that noise-exposure merely hastens
the aging process, although such a hypothesis can be based only upon circumstantial evidence.
Gallo and Glorig^ have summarized some general characteristics of NIPTS, as seen in
occupational contexts, namely:
1. The magnitude of the resulting PTS is related to the noise levels to which the ear has
habitually been exposed.
2. The magnitude of the resulting PTS is related to the length of time for which the ear
has habitually been exposed.
3. The growth of occupationally related PTS at 4000 Hz is most rapid during the first
10 to 15 years of exposure, after which it tends to slow down (see also Passchier-
Vermeer").
4. There are large individual differences in susceptibility to noise-induced PTS.
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Comparable variability is seen in individual hearing levels and in the effects of aging
^ A
(presbycusis). Summar and Fletcher^ have contended that age at the time of exposure is
probably not a significant factor in industrial NIPTS.
Tinnitus Associated with Occupational NIPTS
Tinnitus (ringing in the ears) may be, at first, the only symptom in many cases of
9S
occupational hearing loss; and it is fairly frequently associated with the condition. Chadwick
has reported an incidence of 30 per cent in one industrial survey in Britain.
Patients with occupational NIPTS frequently notice symptoms upon changing from one
noisy job to another, or from a noisy job to a quiet one, possibly because they have adapted
to or learned to cope with any handicaps due to the noise in a familiar situation.
Social Significance of Hearing Loss at Retirement
Kell, et a/. 26 have reported that more than two thirds of a surveyed group of elderly (mean
age 64.7 years) women who had worked as weavers (with steady daily noise exposures of
approximately 100 dBA) for up to 50 years had difficulty with such social intercourse as
understanding conversation, using the telephone, and attending to public meetings or church
services. By contrast, fewer than one in six age-matched women who had not been in a noisy
occupation was similarly disadvantaged.
The Reliability of the Data from Industrial Studies
Unfortunately, much hearing loss data from industry is heavily "contaminated by" what
Glorig and others' have called "sociocusis" factors (e.g., undeterminable losses due to non-
occupational noise exposure in military, recreational or other pursuits, or to disease affecting
the ear. The data was further contaminated by the effect of presbycusis, which is inextricably
bound up with the time-dependent effect of noise exposure (and shift presumed largely on
a priori rather than evidential reasoning to be simply additive); and even within the setting of
industrial noise exposure, by lack of continuity (e.g., personnel changing jobs) affecting both
retrospective studies.
EFFECTS OF LOUD MUSIC
Several recent studies have confirmed that the overall sound levels of very loud rock and
roll and similar music frequently exceed current hearing damage-risk criteria and can produce
large amounts of TTS in both musicians and listeners.2'.33 Flugrath's and other measure-
ments have shown that typical rock music can be regarded, when considering the hair cells,
as a steady-state noise with interruptions. Typically, the maximum acoustic output from the
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.bands' amplifiers lies in the region of 2000 Hz. Dey^ found that typical exposures averaging
100 to 110 dBA for up to 2 hours produced TTS2 exceeding 40 dB in 16 percent of young
98
adults tested. Rintlemann and Boruszo measured typical levels of 105 dBA and found that
some 5 percent of musicians (mostly quite young) showed evidence of NIPTS attributable to
.their music. Clearly, the hazard is an occupational one for the performer and usually a
recreational one for the listener.
Lipscomb^"'^' has demonstrated cochlear damage in guinea pigs exposed to 88 hours of
recorded rock and roll music adjusted to peak at 122 dB, a level that can be exceeded at the
ears of musicians and nearby listeners in some instances where excessive amplification of the
music is used in reverberent rooms or dance halls. Dangerous levels can also be reached using
domestic stereos.^4 In a comparative study of the noise hazard in young people's recreation,
Fletcher" found playing rock-bands to be exceeded in degree of hearing hazard only by
motorcycle and drag racing and by intensive sport shooting with inadequate ear protection.
Fletcher showed incidentally, that young men and women are equally at risk of hearing damage
when exposed to over-amplified rock music. A similar conclusion was reached by Smithley and
Rintelmann.
EXPERIMENTAL SUPPORT FOR THE NOISE DAMAGE-RISK THEORIES
Many studies have been carried out in an attempt to obtain scientific support for the equal
energy hypothesis and for the theories that relate TTS and PTS.
Burns' Approach
The search for a reliable prognostic test for individual susceptibility to PTS based on tests
of TTS continues. Some promising findings have recently been published by Burns. He
has developed a relative index (based on the regression of TTS on hearing level) of susceptibility
to TTS (Dy) and, using the predictive method of Robinson, " an index (Dp) of PTS, being the
deviation (dB) of the individual's age-corrected HL from the predicted median value of HL for
his peers in age and noise-exposures to be grouped for purposes of correlation with the TTS
index Dj. Having determined values of Dj for 3 groups of subjects divided by sound level
(LA2 in the range 93 to 104 dB) causing TTS, Burns has performed regression of Dj upon Dp
for numerous combinations of audiometric test frequencies and found a positive if rather low
(not greater than 0.34) correlation coefficient for several such combinations. Somewhat
unexpectedly, the most promising result was found when Dj was based on low audiometric
frequencies (1 and 2 kHz) and Dp on high (3, 4 and 6 kHz), for reasons that the author admitted
remain obscure. Burns considers this test to have potentialities and has suggested possible ways
of strengthening it: its present weakness rests largely in the large residual variance of D-p in
the regression of Dj upon Dp.
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TTS2 as a ^dictor of Hazardous Noise Exposure
Luz and Hodge'*" have recently presented complementary evidence, from studies of
recovery from impulse-noise induced TTS in monkeys and men, to show that the recovery is
not a simple process and that, accordingly, a single measure such as TTS2 may not be a par-
ticularly reliable predictor in the construction of damage-risk criteria for hazardous noise
exposure. Luz and Hodge have described multiple TTS recovery patterns and have postulated
the existence of two types of threshold shifts, due to "metabolic" and "structural" auditory
fatigue respectively. They adduce the "rebound" recovery phenomenon as strong evidence
for a delayed component in recovery from TTS (evident from other work also) and
hypothesize with some conviction that this is related to permanent damage.
"Equal-Energy" Hypothesis in Predicting TTS and PTS
Some recent work by Ward and Nelson4* on noise-induced threshold changes in chinchillas
appears to confirm the observations of Eldredge and Covell4^ in guinea pigs that there is an
equivalence of time and engergy-at least within certain ranges of parameters-for continuous,
uninterrupted noise exposure. In other words, there is probably a limiting constant product
of intensity and time (analogous to Robinson's "immission") for single unbroken exposures.
Ward and Nelson'*' urge caution, however, in extrapolation to repeated or to interrupted
exposures. They cite the findings of Miller, Watson and Covell •* that frequent interruptions
of noise exposure by noise-free periods reduce both the TTS and the PTS produced by the
noise.
Growth of TTS in Constant Noise
Miller, et al. have shown in the chinchilla exposed to constant octave-band (300-600 Hz)
noise at 100 dB SPL that TTS grows in magnitude and in audiometry range with duration of
exposure over the first 1 to 2 days, then remains constant (asymptotic) with continuing ex-
posures up to 7 days. After cessation of exposures of that duration, the TTS decays approxi-
mately exponentially over some 5 days (decay took about 2 days after identical exposures
lasting only 193 minutes). These noise exposures produced demonstrable cochlear damage,
although this was associated with only a small PTS measured 3 months after the noise
exposure. A similar observation was also made by Lipscomb.
TTS from Prolonged Noise Exposure
Recent work in the chinchilla4^ and in man47 has confirmed that TSS due to a maintained
steady-state octave-band noise exposure reaches an asymptotic level after some (up to 12) hours,
and that recovery from asymptotic TTS is slow (3 to 6 days for complete recovery in man) and
expotential in form.
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Asymptotic TSS as a Function of Noise Level
Using behavioral audiometry in monaural chinchillas, Mills has further demonstrated asymp-
totic TTS following 4^kHz octave-band exposures of up to 9 days (see also Carder and Miller**"). The
magnitude of TSS at asymptote (TS4QQ> was found empirically to be predicted by the equation:
TS400=1.7(SPL-47),
where SPL is the sound pressure level in decibels relative at 0.00002 N/m . The frequency distribu-
tion, temporal pattern, and degree of persistence of the TTS were also found to depend on the noise
exposure level. TTS caused by 80-dB noise was purely temporary, decaying from the asymptotic
value to zero in 3 to 6 days. Noise in the range 86 to 98 dB, however, caused a "permanent" com-
ponent to persist in the threshold shift, which had not decayed to zero after 15 days. The magnitude
of this residual ("permanent") threshold shift was related to noise level, being of the order of 10 dB
at the higher audiometric frequencies following 86-dB exposure, about 20 dB following 92-dB expo-
sure, and up to 40 dB (at 5.7 kHz) following 98-dB exposure. It cannot, of course, be inferred that
similar values or temporal patterns of TTS and PTS would be caused by the same exposures in man,
but this work would appear to support a correlation between temporary and persistent threshold
shift, both of which showed a similar dependence of magnitude on the noise exposure level. The
persistent threshold shift found by Mills may reasonably be presumed to be an element of NIPTS.
Pitfalls of Generalizing from Animal Studies to Man
Price^ has shown that, although the cat is regarded as being more susceptible than man to
behaviorally measurable NIPTS (see Miller, Watson and CovelP^), as is the chinchilla, " the cochlear
microphonic in the cat appears to be much more resistant to alteration by noise stress (at 5 kHz)
than is the auditory threshold measured (TTS) in man (although both changes follow a rate law that
is linear with the logarithm of time). Price urges caution in drawing parallels between cochlear micro-
phonic and TTS data, although he suggests that mechanical factors in the peripheral auditory mecha-
nism may explain certain paradoxes in the growth of TTS resulting from high intensity sustained
versus impulse noise exposure (see Ward, et a/., ). Price^ has recently published similar findings
at 500 Hz.
Poche, et al. -^ have shown that impulsive (cap gun) noise and pure tones (2 kHz at 125-130
dB SPL for 4 hours) produce similar patterns of hair cell damage in the guinea pig. They point out,
however, that no firm correlation has yet been established between hair cell damage and hearing loss
either in animals (see Miller, et al.) or in man.
Uncertain Relation of PTS to TTS and Cochlear Damage
Other observations in the chinchilla^ have shown that quite a substantial and slowly decaying
asymptotic TTS, as well as simultaneously induced external hair cell damage of a diffuse and exten-
sive nature, can be associated with only a small (less than 10 dB) residual NIPTS measured
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behaviorally 3 months following exposure to the prolonged causative noise (300-600 Hz octave-
band noise at 100 dB SPL for up to 7 days). Poche, Stockwell and Ades^ have also commented
(following studies of impulsive noise and cochlear damage) on the lack of quantitative evidence
correlating hair cell loss with hearing loss.
t
Asymptotic TTS in Man
In tentative observations upon his own ear, Mills^' has found evidence that TSS in prolonged
(24-48 hour) octave-band noise reaches an asymptote in man, as in the chinchilla. The time to reach
it appears to be in the range 4 to 12 hours for man; and the time required for complete recovery
some 3 to 6 days.
Miscellaneous Factors Considered in TSS
In 1958, Trittipoe^ maintained that pre-exposure non-TTS-producing noise levels as low as
48 dB SPL could enhance subsequent TTS due to a high (118 dB) brief noise exposure. This has
been taken as evidence that there is no threshold of noxiousness for noise hazardous to the ear.
' ^^
This observation and its interpretation have, however, been disputed by Ward. J
Karlovich and Luterman^" have shown that phonation might exert a slight protective effect
against NITTS. They have found that TTS was smaller following a 3-minute exposure to 1000 Hz
tones at 100 dB SPL when the subjects phonated during the noise than when they were silent or
merely whispered the same vowel rather than voicing it. Two possible mechanisms have been sug-
gested to account for this phenomenon:
1. That phonation elicits and maintains the acoustic reflex.
2. That during phonation Z-axis vibrations of the skull "protect" the hearing by causing
changes in the mode of oscillation of the stapes.
IMPULSIVE NOISE
Most of our knowledge of the aural hazard due to impulse noise, and practically all the data
systematically relating exposure parameter to threshold shift, comes from studies of the effects of
gunfire on the ear, with some supporting evidence from industrial data.
incidence of NIPTS as a Function of Peak SPL
If all other characteristics of an impulse noise are held constant, TTS increases with peak SPL.
Presumably, this would be true for NIPTS as well. An estimate of hearing damage-risk following
daily exposure to a nominal 100 rounds of gunfire (rifle) noise at 5-second intervals has been
developed by extropolatia of TTS data. ' An important assumption implicit in their calculations
is that a given TT$2 (TTS measured at 2 minutes after cessation of stimulation) will eventually
lead to an equal NIPTS. Further discussion of Kryter and Garinther's predictions are included in a
recent EPA document.
5-11
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Effect of Impulse Duration
The present state of knowledge indicates that a clear hazard exists and, accordingly, that ear
protection should be in use when impulsive noises exceed a peak sound pressure level of 140 dB at
the ear for more than 5 milliseconds regardless of rise time spectrum, or the presence of oscillatory
transients. As duration decreases below 5 milliseconds, higher peak values may be tolerable.
Exceeding a level of 165 dB SPL for short durations is likely to lead to cochlear damage in at least
50 percent of ears, even in the case of isolated impulses (see Acton, ° and Coles, et al. *').
The figure of 165 dB SPL absolute maximum is considered over-stringent by some authorities,
in relation to extremely brief exposures. Coles and Rice, 59,60 for jnstance, have allowed 172 dB
SPL for single impulses of 100 microseconds duration, and over 180 dB for impulses of less than
half that duration (irrespective of pulse shape). This may be over-lenient.
Allowance for Repeated Impulses
A CHABA Working Group has recently arrived at an empirical weighting factor for reducing
permissible levels of exposure when multiple impulse noises are heard. Essentially, the working
group's current recommendation is to add or subtract 2 decibels from permissible values for each
halving or doubling, respectively, of the number of impulses (or 5 dB for every tenfold change in
the total number in a series of impulses).
High-Frequency Hearing Losses Due to Impulse Noise
Coles, 1 Loeb and Fletcher" ^ have drawn attention to the fact that, although hearing loss due
to many kinds of intense short-lived or impulsive noise appear audiometrically identical with loss due
to continuous noise (showing the characteristic audiometric notch at 4000 Hz and progressive upward
spread), certain kinds of impulsive noise, such as gunfire, are frequently associated with a substantial
immediate TTS and potential permanent loss at higher frequencies (6 to 8 kHz and upward). This
may be associated with particular parameters of the noise exposure such as extremely rapid rise and
high peak level. *
Such high-frequency loss is not predicted, or is not treated as significant, by many of the exist-
ing damage-risk criteria or methods of hazardous noise exposure evaluation, which are narrowly
restricted to the so-called "speech frequencies" below 4000 Hz. Sensitivity for frequencies above
2000 Hz can, however, be vitally important for several purposes in life, especially for the reception
of speech heard against a background of noise. It is also important for the localization and identifica-
tion of faint, high-pitched sounds in a variety of occupational (including military) and social
situations. Thus, high-frequency hearing loss, should be prevented when possible.
-------
Factors Influencing Hazard Due to Impulse Noise
There is no unequivocal evidence that a practical distinction need be made between the
sexes or between age groups when predicting hearing damage risk due to impulse noise as it
is here defined. Nor does any definitive evidence exise for a significantly different degree of
susceptibility to impulse-noise-induced PTS in the case of children or persons with otological
abnormality.
Combined Exposure to On-Going Noise with Added Impulsive Noise - Allowance for Impulsiveness
When impulsive noise exposure takes place at the same time as on-going (steady-state) noise,
the hazard of each element to the hearing mechanism should be evaluated separately against its
respective criterion. A conservative and greatly simplified approach is then to treat combined
hazards as simply additive. For example, if for a given centile of the population at risk, a
continuous noise exposure were predicted to cause NIPTS of 10 dB and a concurrent impulse noise
exposure were predicted to produce 5 dB of NIPTS, then the combination may be predicted to
produce 15 dB of NIPTS at that centile. Aternatively, some authorities might argue in favor of
a logarithmic rule which would be somewhat less conservative.
Effects Found in Studies of Children
Gjavenes"3 has cited Scandinavian data showing that between about 1 and 4 percent of
teenaged childred may show hearing injuries resulting from the impulsive noise from fire-
crackers or other noisy toys. He has also argued that this degree of risk accords with a damage
risk criterion of 155 dB peak pressure for impulsive toy noise. He points out that there is no
evidence that childrens' ears are more easily damaged by impulsive noise than are those of
adults. All the data upon which existing impulse noise damage risk criteria are based have
come, of course, from adults (mostly exposed to gun noise).
Methods for Predicting the Expected Hearing Loss Due to Exposure to Ongoing Noise
In the following paragraphs we present procedures for predicting the risk or amount of
hearing loss to be expected from occupational-type noise exposure. This information is based
upon the work of four international authorities in the field of industrial noise-induced hearing
loss namely Baughn"^ Passchier-Vermeer, >°° Robinson' '»•*" and Kryter. Their methods
may be used to predict the effect upon hearing, at selected centiles, of the adult population -
produced by daily 8-hour exposure to steady-state noise at levels in the range 75 to 90 dBA,
5-13
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sustained for periods up to 50 years. The first three predictive methods summarized in
the following paragraphs have been selected because:
1 . They permit calculation of NIPTS (i.e., the noise-induced part of hearing level) for
designated percentiles of the adult population.
2. They also include data permitting the inclusion of 4000 Hz in the computation,
although they are based mainly upon the audiometric test frequencies 500, 1000
and 2000 Hz ("speech frequencies") currently accepted as essential to the eval-
uation of hearing impairment by most otologists in the United States.
3. They show fair agreement with one another.
Kryter" presents a fourth method that differs significantly from the other methods
summarized here. He proposes 55 dBA as the threshold of significant hearing changes to the
speech frequencies of 0.5, 1.0, 2.0 kHz, a value roughly 20 to 25 dB over the values obtained
with the other commonly used methods. Some aspects of his procedure have been discussed
/TO H 1 • TO
recently in the literature00" and Kryter has responded to these critiques. L
"Industrial" Methods of Predicting Long-term Hazard from Daily Continuous Noise Exposure
These methods permit predictions of the amount of noise-induced change in hearing level to be
predicted for designated fractions of otologically normal working adult populations exposed
day after day to steady-state industrial-type noise, as a function of average noise level (or
equivalent continuous sound level). These techniques are elaborated upon in a recent EPA -
1 7
U. S. Air Force publication, therefore, they will be treated quite briefly here.
Method and Data of Passchier-Vermeer
Passchier-Vermeer^'00 has analyzed the audiometric data from several surveys of
industrial hearing loss. Making allowances for presbycusis, in 1968, she published procedures
with graphs for determining the noise-induced part of hearing level evaluation as a function of
daily noise exposure for the 25th, 50th, and 75th centiles of a working population. In 1971V"
she published some additional data including 10th and 90th centile estimates. Her results are
applicable to daily 8-hour exposures to industrial-type noise up to 100 dBA. (For more detail,
see related document published by
Method of Robinson
Robinson 1 '»^" has devised an idealized method for predicting hearing loss resulting from
noise exposure. His method is based on a unique mathematical relationship (the hyperbolic
tangent I between noise exposure and NIPTS, which is adjusted parumetricully for population
ccntilc and audiometric frequency. The method applies to otologically normal adults
5-14
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exposed to industrial noise for 8 hours per day over a period ranging from 1 month to 50
years. It yields estimates of the percentages of the exposed population that may develop
NIPTS as a function of noise exposure (noise "immission"). Robinson's method has been
criticized on the grounds that:
1. It is based upon a single, although substantial, study of otologically screened
British industrial workers (Hinchcliffe).
2. The mathematical niceness of the predictive theory may not be entirely
justified by the realities of industrial audiometric data and their sources of
variance. (Discussed in detail in a related EPA document'^).
Method of Baughn
Baughn"^ has amassed data from extensive industrial audiometric surveys in the United
States. His work provides insight into how NIPTS develops at various centile points as a
result of typical industrial noise exposure in the range 78 to 92 dBA. The prediction of
NIPTS may in some respects be too high, however, owing to a probable contamination of
the data by residual TTS and masking in the circumstances in which the audiometry was
conducted. In some measurements, only 20 minutes recovery from the industrial noise was
allowed before testing. (This method also is treated in a related EPA document12).
Averaging NIPTS Predictions Over the Three "Industrial" Methods
A summary chart of certain predictions that can be made concerning NIPTS and risk
by combining the predictions of Passchier-Vermeer, Robinson and Baughn is presented in
Table 5-1. (Extracted from a related EPA publication12).
The table gives the NIPTS for three frequency configurations: The average shift
over .5, 1 and 2 KHz denoted by Speech (.5, 1, 2), the average shift over .5, 1,2 and 4 KHz
denoted by Speech (.5, 1, 2, 4) and the shift at 4KHz. A brief explanation of the table follows:
o Maximum NIPTS (90th percentile) The NIPTS that can be expected after 40 years
of noise exposure during adult life for the 90th percentile (i.e., 90 percent of the
population will expect NIPTS less than the value in the Table and 10 percent greater
than the value). This value can be considered a lifetime maximum since little or no
i
further shift will take place due to this type of noise exposure."
o NIPTS (90th percentile) at 10 years. The expected NIPTS after ten years of
exposure during adult life not exceeded by 90 percent of the population.
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• Average NIPTS. The gross average value of NIPTS obtained by averaging over a
40-year exposure duration and also over all the population percentiles.
e Maximum Hearing Risk. Hearing risk is defined as the difference between the
percentage of people with a specified hearing handicap in a noise-exposed
group and the percentage of people with a handicap in a non-noise-exposed (but
otherwise equivalent) group. The hearing risk varies with exposure duration, and
the Maximum Hearing Risk is defined as-the peak value (largest difference) that
occurs during the 40 years of exposure. Normally, but not always, this peak
value occurs after 40 years of exposure.
Use of Industrial Exposure Tables to Approximate Effect of Less Uniform Noise Exposures
Most of our knowledge of the effect of noise upon the human ear comes from industrial
audiological experience. More people are at risk from quasi-steady-state noise exposures of
about 8 hours a day, 5 days a week for a working lifetime than from any other variety of noise
exposure. ^ ^ One method for applying our knowledge of the effects of industrial noise to
non-industrial situations, is to rely on the equal energy hypothesis as an estimate of equivalent
noise exposures.
Exposures to Continuous Noise Exceeding 8 Hours
An equivalent continuous sound level (Leq) in dBA can be calculated for varying exposure '
10
times, based upon a normal daily exposure of 8 hours (discussed in a related EPA document1 z).
For that duration only, Leq is numerically equal to the energy equivalent of a continuous sound
level in dBA. As in the case of unbroken steady-state exposure lasting less than 8 hours the
nomogram (Figure 5-1) may be used to find Leq for unbroken steady-state exposures of more
than 8 hours. For an uninterrupted 24-hour exposure, Leq is 4.8 dB greater than for an 8-hour
exposure (this can be rounded off to 5 dB). Expressed another way, the hazard to hearing
from a continuous 85 dBA noise lasting 24 hours is similar to the hazard of an 8-hour exposure
to 90 dBA, provided, of course, that the noise is steady-state (not fluctuating markedly in level),
broadly distributed (spanning a number of octaves), fairly uniform in spectrum without sub-
stantial discrete tonal components, and free from any significant addition of impulse sounds.
An exposure exceeding 24 hours may be treated as indefinite exposure. Allowances for
level fluctuations in continuous noise, for intermittency (interruptions), and for the significant
presence of simultaneous tonal components or impulses during prolonged exposure may be
considered to obey rules similar to those governing these allowances in the case of exposures
shorter than 8 hours (see below).
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TABLE 5-1
SUMMARY OF EFFECTS PREDICTED FOR CONTINUOUS NOISE
EXPOSURE AT SELECTED VALUES OF A-WEIGHTED* SOUND LEVEL
75 dBA for 8 hours
Max NIPTS (90%-ile)
NIPTS at 10 yrs (90%-ile)
Average NIPTS
Max Hearing Risk**
Max NIPTS (90%-ile)
NIPTS at 10 yrs (90%-ile)
Average NIPTS
Max Hearing Risk**
Max NIPTS (90%-ile)
NIPTS at 10 yrs (90%-ile)
Average NIPTS
Max Hearing Risk**
Max NIPTS (90%-ile)
NIPTS at 10 yrs (90%-ile)
Average NIPTS
Max Hearing Risk**
Speech (.5 ,1,2)
1 dB
0
0
NA***
Speech (.5, 1,2,4)
2dB
I
0
N/A
4kHz
6dB
5
5
1
80 dBA for 8 hours
Speech (.5, 1,2)
IdB
1
0
5%
Speech (.5, 1,2,4)
4dB
3
1
N/A
4kHz
11 dB
9
4
N/A
85 dBA for 8 hours
Speech (.5 ,1,2)
4dB
2
1
12%
Speech (.5. 1,2.4)
7dB
6
3
N/A
4kHz
19 dB
16
9
N/A
90 dBA for 8 hours
Speech (.5, 1,2)
7dB
4
3 '
22.3%
Speech (.5,1, 2,4)
12 dB
9
6
N/A
'4kHz
28 dB
24
15
N/A
* Values given are arithmetic averages obtained from predictions using the methods
of Baughn, Passchier-Vermeer and Robinson (see text).
** 25 dB ISO Fence for Hearing Handicap (re ISO: 1964). Averaged from the methods
of Baughn and Robinson (see text).
*** Not available.
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Exposures to Continuous Noise for Periods Less Than 8 Hours
The risk to hearing in the case of daily exposures to on-going noise for periods (minutes
to hours) less than 8 hours can be evaluated by calculating an equivalent continuous sound
•level, Leq, provided that the noise is approximately steady-state and is free from impulsive com-
• ponents. The calculation of Leq normalizes the daily exposure to a duration of 8 hours for the
purpose of Table 5-L_
Allowances for Level Fluctuation or Interruption of Noise
The 73 International Organization for Standardization (ISO, 1970), in its current Draft
Recommendation (ISO/DR 1999) for assessing noise exposure at work, recommends a method
that embodies the A-weighted equal-energy rule, namely the previously mentioned computation
of an equivalent continuous sound level Leq in dBA (see Figure 5-1). This method is probably
the best available method of predicting the effects of noise on hearing in the case of continuous
noise for which the level fluctuates slowly (seconds to hours) during the working day. It may,
with circumspection, be extrapolated to cover distributed noise of fluctuating levels that go on
for longer than the typical working exposure of 8 hours. The fluctuation in level must be non-
impulsive; i.e., slow enough to be followed by a standard sound level meter on the "slow"
setting.
The arbitrary ISO protective weighting of 10 dBA for impulsiveness in the noise is open to
question. Recent, work by Passchier-Vermeer"" has indicated that this figure may not be realistic
in the case of distributed industrial noise with impulsive components. However, her work does
in general confirm the validity of the equivalent level method based on equal-energy in the case
of ongoing noise with slow but not impulsive fluctuations.
In the case of slowly varying levels in continuous noise with a rate of change less than 40 dB/
second, it is appropriate to determine the equivalent continuous sound level, Leq, in dBA and to
enter the tables at the resulting value when evaluating the hazard or risk of NIPTS due to on-going
noise.
Intermittent Noise
It is reasonable to treat intermittent exposure to steady-state nonimpulsive noise as a
special case of fluctuating level. Intermittent noise is generally regarded as sound undergoing
a substantial change in level from some potentially hazardous level to a very low level (below
55 dBA).
Such intermissions are known to be protective, probably by allowing recovery of normal
physiological functions in the auditory system. Because there is no evidence for a threshold of
noxiousness of noise so far as the hearing organ is concerned, it is desirable that the noise during
any period of relative quiet be measured and included in the computation of Leq. Intermittent
noise may thus be treated in the same way as noise of varying level and may be equated analyti-
cally with continuous noise for the purpose of predicting hazard or risk.
—- • 5-18
-------
L
iw-i
130—;1XO
•'C-05
cm
0-02
0-01
Duration
24-
it.
12-
c-
-------
However, Ward * has drawn attention to the particular weakness of the evidence in rela-
tion to intermittent exposure, pointing out that the equal-energy rule makes no allowance for
different patterns of recovery from ITS in different patterns of intermittency. For example,
the rule cannot distinguish the effect of a single 2-hour exposure from two 1-hour exposures
to the same noise with variable amounts of intervening quiet.
In fact, a number of factors may affect the auditory tolerance of intermittent noise expo-
sure. These include the number and duration of interruptions, > the relationships between
continuous and intermittent noise exposures, ' ' and possibly the level of noise below 80 dBA
during the interruption.
Factors Influencing Incidence of NIPTS
Factors influencing the incidence of NIPTS are listed in Table 5-2. The table shows that
some factors appear to increase the risk of NIPTS while others decrease it; and that some, while
they may be significant factors determining group hearing levels measured in population surveys,
show no clear evidence of being related casually to NIPTS.
TABLE 5-2
EFFECT OF VARIOUS FACTORS ON INCIDENCE OF NIPTS
FACTOR
INCREASES
DECREASES
NO SIGNIFICANT EFFECT
Age
Sex
Nationality
Race
Physiological state:
i. General Health
ii. Activity
iii. Defensive Mechanisms*
Prolonged exposure
Interrupted or modulated
exposure
Ear protection
Adverse environments:
i. Vibration + noise
ii. Hypoxic states
iii. Ototoxic drugs
"Public awareness"
*Principally the acoustic reflex
5-20
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Factors Increasing the Risk of NIPTS
The only factor known to increase the likelihood of a person developing NIPTS is increased
exposure to hazardous noise. Although it is possible that the older ear may be more susceptible
than the younger ear, such a phenomenon is difficult to distinguish epidemiologically, and the
question of age-enhanced susceptibility to NIPTS remains open. The hypothesis that certain
defects or diseases of the ear, or a poor general state of health might increase predisposition to
NIPTS remains to be proven. There is some evidence that certain ototoxic drugs may act syner-
7Q
gistically with noise to damage the hearing organ.'y (This subject is discussed in detail in Section
1 JC
9.) However, Glorig and Nixon's contention that aging and noise exposure alone determine
group hearing levels in otologically healthy members of the general American population has
received support from more recent data and from industrial experience in other Western coun-
tries, notably, the United Kingdom (Burns and Robinson,1^ and Robinson^).
Factors Mitigating Risk
Physiologically, the acoustic reflex is known to protect, to a limited degree, hearing against
noise. This mechanism was discussed in detail in Section 4.
The use of artificial ear protection (earplugs, earmuffs and kindred devices) substantially
decreases the risk of NIPTS but this again is a difficult factor to allow for in predictive formulas,
because the use of ear protection (especially in non-occupational noise exposure situations) is
neither universal nor uniform. In this connection, however, it is reasonable to presume that,
as the population at large is made increasingly aware of the hearing hazard from noise, the
public response (e.g., use of ear protector as well as noise-avoidance and noise reduction) will
be reflected in a decreasing incidence of NIPTS attributable to environmental noise.
Factors not Directly Affecting Susceptibility to NIPTS
Differences Related to Sex
71
Ward' investigated various aspects of NIPTS in relation to sex differences, finding that,
whereas men were more susceptible to TTS following low-frequency (less than 700 Hz) sounds,
they were less susceptible than women to high-frequency (greater than 2000 Hz) exposures.
Women also appeared to show a greater benefit (in terms of reduced TTS) from intermittency
in the noise exposure. Ward has suggested another explanation for these findings, namely, that
females have a more efficient acoustic reflex than males. However, evidence for sex-linked
differences in the fragility of the hearing organ (or fatigability of the auditory nerve by noise)
was negative in this study.
Generally, it can be argued that intrinsic differences between the sexes are of no practical
significance in relation to hearing hazard in noisy environments, or in relation to the setting
of hearing damage-risk criteria.
5-21
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Differences Related to Urban Environment
Certain primitive people, living in remote areas of the world in which they are not exposed
to the constant din of mechanized civilization, have been found to have unusually sharp hearing
in comparison with urban populations of corresponding ages: in this connection particular atten-
tion has been given to the Maba'an people of Sudan. But it is debatable whether such audiometric
differences are due to the lack of noise exposure alone, for many factors (including cultural,
genetic and general environmental differences) may underlie differences in the pattern of hearing
found between dissimilar communities who are widely separated geographically and culturally. >8
Differences Related to Age
Although it has been suggested that older people are more susceptible to NIPTS°^ it is
debatable whether individual susceptibility to noise-induced hearing loss changes appreciably with
age. Some authors have contended that young ears are more susceptible to noise damage (more
"tender") than older ones.84'86
The evidence, however, is inconclusive, having in some studies been confounded by non-
occupational influences (e.g., noise-exposure in military service) that were not the same for the
87 88
age-groups compared. Recent studies0 > ° indicate that there is probably no casual relationship
between age per se and susceptibility to NIHL, at least in men of working age. This view is sup-
on
ported by the work of Loeb and Fletcher.
That the effect of age on hearing is very difficult to distinguish audiometrically from the
influence of noise exposure and related environmental variables is evident from data summarized
by Burns and Robinson and from several studies dealing with or touching on noise suscepti-
bility as a function of age.
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DAMAGE-RISK CRITERIA
That there is a time/intensity tradeoff for hazardous steady-state noise is well established,
but this has been embodied in existing criteria in different ways. The tradeoff is not a simple
' 0
one and differing theories underlie the various damage risk criteria currently in use. The picture
is complicated when the noise exposure is intermittent, which is frequently the case in practice.
Evidence from TTS experiments generally supports the view that the effect of intermittent
exposures to high levels of noise separated by relative quiet is less than the effect of the same
total noise exposure received unbroken. Moreover, the generation of a given TTS by con-
tinuous noise requires progressively less time as the exposure level is increased.
The CHABA Criterion
The CHABA DRC was based on such observations; its principal assumption was that,
for a given octave of frequency, all noise exposures producing the same TT$2 are equally likely
to produce a given PTS (Kryter, Ward, et al. *). This criterion, in which the trade-off between
time and intensity varies (e. g., between 2 and 7 dB per doubling of time for the 1200-2400 Hz
band), represented a departure from the simple adoption of the "equal-energy" rule (3 dB per
doubling of time) seen in earlier criteria (such as APR 160-3 ). The resulting differences between
DRC's are illustrated in Table 5-3 which compares simply the limiting values for continuous
exposure to an octave band of noise from 1200 to 2400 Hz in CHABA and APR 160-3 criteria.
The latter is more conservative for nearly all durations.
TABLE 5-3
COMPARISON OF CHABA DAMAGE RISK CRITERIA AND APR 160-3
Exposure time
CHABA
APR 160-3
8h
85
85
4h
87
88
2h
91
lOmin
105
5 min
112dB
105 dB
The 5 dB rule adopted under the Walsh-Healey Act in 1969 (Federal Register 34, (96): 7948-
7949 (May 20, 1969) appears to have been an expedient compromise: it has some justification
in that it effectively makes an allowance for intermittency.
Criteria for Steady-State Noise
There is generally firm agreement that, for typical 8-hour everyday exposures to con-
tinuous industrial noises, levels below 80 dBA are, for most hearers innocous. Also, as the
noise level increases, an increasing number of people are put in risk, and the average magnitude
of hearing loss grows commensurately. This picture is well supported by a number of substantial
5-23
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audiometric surveys of industrially exposed people in the United States and elsewhere (Baughn,
Rasschier-Vermeer,23' 66 Robinson17). Based on such evidence, a recent DRC, provided for in
1969 under the Walsh-Healey Act governing the welfare of workers under public contracts, was
adopted in the United States. This allows 90 dBA for continuous 8-hour exposures.
"AAGO" and Cognate Criteria
It is a basic premise of these criteria that the chief (a rigorous interpretation might say the sole)
function of human hearing is to receive speech signals. Arguing that telephoned speech (band-
limited to some 300 to 3000 Hz) is generally intelligible, Fletcher92 introduced his "point-eight"
rule for evaluating hearing damage in accordance with this philosophy. This led to the practice
of averaging hearing levels at 500, 1000, and 2000 Hz.
The AAOO and cognate rules attempt, inter alia, to find pragmatic answers to the following
questions: '
1. How much hearing loss must occur before the person affected notices any difficulty?
2. What values of HL constitute complete loss of hearing?
3. What is the relative importance of different audiometric frequencies?
4. How important is it to have two working ears?
The Intersociety Committee (1970) Guidelines
A group of professional associations (The American Academy of Occupational Medicine;
American Academy of Ophthalmology and Otolaryngology; American Conference of Govern-
mental Industrial Hygienists; Industrial Hygiene Association; and Industrial Medical Association)
concerned with industrial noise recently revised some previously published guidelines intended
".. . to aid industrial management and official agencies in establishing effective hearing
conservation programs." The document has also defined hearing impairment as an average
threshold level in excess of 15 dB (ASA-224.5-1951) which is equivalent to 25 dB, ISO:
1964 at 500, 1000 and 2000 Hz. The guidelines were intended .to prevent the development
of that portion of permanent hearing loss due to occupational exposure to steady-state noise,
continuous or intermittent.
The evaluation of noise in dBA using standard meters and procedures was recommended
by the Committee, as was the determination or estimation of the total time and temporal
distribution of noise exposure "throughout the working day." The guidelines, subject to
revision, contain numerical data and procedures for rating the auditory hazard of occupational
noise exposure in terms of risk as a function of age, noise level and exposure time. Overall,
the Committee in 1970 deemed 90 dBA for 8 working hours of steady-state noise daily,
with a permissible increase of 5 dBA (up to a permissible maximum of 115 dBA) for each
halving of exposure time, to be a "reasonable objective for hearing conservation." It was
pointed out explicitly that the rating procedure applies only to groups,~not to individuals.
5-24
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The document included some general guidance on methods of noise control for hearing con-
.servation in industry and some recommendations concerning audiometry in industrial settings.
The recommended audiometric frequencies adopted by the Intersociety Committee were 500,
1000, 2000, 2000, 4000 and 6000 Hz. The guidelines are subject to triennial review and revision.
Use of A-Weighted Decibels
The Intersociety Committee on Guidelines for Noise Exposure and Control, influenced
mainly by the work of Baughn"^ in the USA and Robinson'' in the United Kingdom, decided
to recommend the use of dBA to yield a single-number rating of continuous noise hazard.
This unit, as recommended in this document, has a number of advantages, including convenience
of measurement using standard sound level meters; and it can, incidentally, be easily related
to the ISO standardized NR numbers using the approximate difference of 5 decibels (dBA »
NR + 5). Measurements on the A-weighting scale may, however, underestimate hazard to
hearing when the noise contains a strong tonal component >'" or a markedly uneven
spectrum.
Index of Cumulative Noise Exposure-Robinson's "Sound-Immission" Rating
Robinson'' and Robinson and Cook™ contended that NIHL is expressible in terms of a
composite noise exposure measure (noise or sound "immission") that is proportional to the
total frequency-weighted sound energy received by the ear over a designated exposure period.
Robinson and Cook-'" have presented industrial hearing level and noise exposure data in support
of this predictive model. The data is valid for 8-hour daily exposures from 1 to 600 months (50
years), to industrial-type noise at levels ranging from 75 to 120 dBA.
Inadequacy of Conventional "Speech Frequencies" Assessment
Harris'" has contended that the widely adopted convention of using the average pure-tone
auditory sensitivity at 500, 1000, and 2000 Hz to predict a person's ability to understand every-
day speech may not be adequate when, as is often the case, the speech is of poor quality, is
interrupted, is distorted, or is noise-masked. From a study of speech intelligibility among 52
subjects with sensorineural hypoacusis, listening to various kinds of degraded speech, he
concluded that a better assessment of hearing disability for realistic everyday speech is obtained
when the audiometric frequencies 1, 2 and 3 kHz are used instead, as is the convention in
British practice. This supports a finding of Kryter, Williams and Green, who reported that
the triad 2, 3 and 4 kHz was the best predictor of speech reception for phonetically balanced
words (not sentences) in subjects with high-tone hearing losses. However, they recommended
as a compromise a triad similar to Harris's in view of the already well-established AMA
convention of 500, 1000 and 2000 Hz. Kryter and his co-workers"^ showed that some speech
5-25
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tests and methods of hearing evaluation hitherto adopted introduce a bias that is apt to lead to
underestimation of the importance of auditory sensitivity at frequencies above 2 kHz. Some
authorities, notably the state of California, include 3000 Hz in the assessment of disability.
Impulsive Noise
Kryter15 has adduced evidence from his own and other recent work to show that TTS2
at 4000 Hz and, by implication, the risk of N1PTS, can in many circumstances be predicted
with fair accuracy from a knowledge of the peak overpressure, spectral composition and number
of impulses. For the noise of gunfire, Kryter maintains that damage risk to hearing can be
evaluated from the peak overpressure and number of impulses. An important assumption
implicit in this data is that a given TTS2 will eventually lead to an equal NIPTS.
Some procedures proposed by Kryter1 ^ and others for predicting damage risk to hearing
due to gunfire and similar noises have been summarized elsewhere.' ^ The risk to hearing from
such noise depends primarily upon the peak overpressure and the number of impulses experienced
and to some degree upon the spectral and temporal characteristics of the noise. Although, in
general terms, the pattern of NIHL produced by impulsive noise is similar to that produced by
steady-state noise, namely, loss beginning and advancing most rapidly at 4 kHz and above, the
different stimulus parameters call for rather different criteria and methods for evaluating impulse
noise. For this reason the current ISO Recommendation (ISO, 1971) on the assessment of
occupational noise-exposure for hearing conservation purposes states specifically that the method
is not applicable to such noises.
Impulse Noise and TTS
In 1962, Ward1' 1 argued that damage-risk criteria for impulsive noise should best be
expressed in terms of the number of impulses rather than exposure time per se. The importance
of number of impulses has again, more recently, been brought out by Coles, etal.,> "" Ward's
argument was based on his observations that the TTS in the range 500 to 13000 Hz (and, by
implication, the PTS) produced by impulse noise is relatively independent of the interval between
pulses—at least for intervals in the range 1 to 9 seconds (a 30-second interval, however,
apparently permitted slight recovery between stimuli).
Impulses With an Oscillatory Component
When the impulse contains an oscillatory component ("Type B" of Coles, etal.), the
assumptions of Kryter1' applying to simple, Type A gun noise may require modification, and
spectral information may be needed in the evaluation of hazard, in addition to a knowledge of
the peak pressure, number, and temporal spacing of impulses (Coles, et a/;"** Kryter, •*
5-26
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Ward;97 Ward, et al.98 (CHABA); Ward, Sellers and Glorig"). Oscillatory waveforms can be
recorded from gunshots fired in reverberant areas and from other sources of impulsive noise.
It has been argued that even spike impulses must generate an oscillatory component upon
entering the ear, by exciting the resonances of the ear canal and middle ear structures. ®® This
would in part explain the general similarities between the patterns of threshold shift produced
by both impulsive and distributed steady-state noise.
SUMMARY - NOISE-INDUCED HEARING LOSS-TEMPORARY AND PERMANENT
SHIFTS IN AUDITORY THRESHOLD FOLLOWING NOISE EXPOSURE
Ongoing noise has been proven to cause permanent hearing loss in industrial settings and
among young people exposed to loud music over extended periods of time. Noise is also known
to cause temporary hearing loss and ringing in the ears (tinnitus).
However, since there is a relative lack of information about the effect of shorter-term
intermittent or incomplete daily exposures, several theories have been postulated to relate
noise exposure to hearing loss in these situations.
One theory that has been fairly widely used is the Equal-Energy Hypothesis, which postulates
that hearing damage is determined by the total sound energy entering the ear on a daily basis.
Another theory suggests that the long term hazard is predicted by the average temporary
threshold shift produced by daily noise exposures. There is evidence to support both of these
theories within reasonable limits of extrapolation.
Impulsive noise (such as gunshots) has also been shown to cause damage. CHABA has
recently developed a noise hazard numerical weighting system that takes into account such factors
as intensity, duration, and number of noise impulses.
Averaging the NIPTS predictions over various industrial noise hazard prediction methods
gives a fairly dependable measure of the hearing risk of noise-exposed populations. Hearing
damage has been noted at levels as low as 75 dBA after 10 years.
The only important factor in increasing hearing risk appears to be noise exposure, and
artificial ear protection devices do appear to be of value in preventing damage. Neither sex-
related nor cultural differences appear to significantly affect hearing risk due to noise-exposure.
It is evident from the noise exposure data that noise can damage hearing and can cause
both N1TTS and NIPTS. The relationship between noise exposure and hearing loss is well
understood in industrial settings and in the case of high intensity impulsive sound (i.e.
gunshots). However, in the case of fluctuating or intermittent noise, data is generally lacking
and it is necessary to rely on data extrapolations to estimate effects.
5-27
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REFERENCES
1. Anon. Hazardous Noise Exposure. Air Force Redulation 160-3, Department of
the Air Force, 1956.
2. BENOX (Biological effects of Noise) Group (Ades, H. W. & Colleagues) (1 December
1953). BENNOX REPOR TS: An Exploratory study of the biological effects of
noise. Univ Chicago: ONR Proj NR 144079.
3. Botsford, J. H. (1970). Damage Risk. In: Transportation Noises: A Symposium on
Acceptability Criteria. Chalupnik, J. D. (ed.) Seattle Univ. Washington Press, pp.
103-113.
4. Environmental Protection Agency. PROCEEDINGS OF THE INTERNATIONAL
CONGRESS ON NOISE AS A PUBLIC HEALTH PROBLEM (W. D. Ward, ed.)
In press, 1973.
5. Ward, W. D., Glorig, A & Sklar, Diane L (June 1959). Temporary threshold shift
produced by intermittent exposure to noise. J acoust Soc Amer, 31 (6), 791-794.
6. Ward, W. D., Glorig, A. & Sklar, D. L. (October 1958). Dependence of temporary
threshold shift at 4 kc on intensity and time. / Acoust. Soc. Amer., 30 (10),
944-954.
7. Ward, W. D. (January 1960). Latent and residual effects in temporary threshold
shift. /. Acoust Soc. Amer., 32, (1), 135-137.
8. Sataloff, J. Vassallo, L. & Menduke, H. (June 1969). Hearing loss from exposure
to interrupted noise. Arch Environ Health, 18, 972-981.
9. Cohen, A, Anticaglia, J. R. & Jones, H. H. (May 1970). Noise-induced hearing loss:
exposures to steady-state noise. Arch Environ Health, 20, 614-623.
10. Kryter, K. D. (April 1966). Review of research and methods for measuring the
loudness and noisiness of complex sounds. NASA Contractor Rpt No. NASA CR-422.
11. Ward, W. D. (March 1970). Temporary threshold shift and damage-risk criteria for
intermittent noise exposures. J acoust Soc Amer. 48 (2 part 2), 561-574.
12. Environmental Protection Agency, U. S. Airforce Aerospace Medical Research
Laboratory, A SCIENTIFIC BASIS FOR LIMITING NOISE EXPOSURE FOR
PURPOSES OF HEARING CONSERVATION. EPA Document Number EPA-
550/9-73-001 (in press.) 1973.
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13. Burns, W. NOISE AND MAN. Philadelphia: Lippencott (1969).
14. Burns, W & Robinson, D. W. (1970). Hearing and noise in industry. London:
Her Majesty's Stationery Office, 43 pp + 16 Appendices.
15. Kryter,Karl THE EFFECTS OF NOISE ON MAN. New York: Academic
Press (1970).
16. Anon. Occupational Safety and Health Standards. Occup. Safety and Health
Admin, DOL, Vol. 36, p. 105, 1971.
17. Robinson, D. W. Estimating the Risk of Hearing Loss due to Continuous Noise.
In Occupational Hearing Loss, D. W. Robinson, Ed. Academic Press, N. Y., 1971.
18. King, P. F. (1971). Hearing conservation in aircrew and ground support personnel.
Aeromedical aspects of vibration & noise, Guignard, J. C. & King, P. F. AGARD-
ograph 151.. Paris: NATO/AGARD. Part 2, Ch. 10-23, pp 204-257.
19. Annon. Criteria for a Recommended Standard — Occupational Exposure to
Noise, NIOSH Department of Health, Education and Welfare (1972).
20. Gallo, R&Glorig, A (1964). Permanent threshold shift changes produced by
noise exposure and aging. Amer Ind. Hyg. Assoc. J. 25, 237-245.
21. Taylor, Wr Pearson, J. Mair, A & Burns, W. (December 1965). Study of noise
and hearing in jute weaving. J Acoust Soc Amer. 38, 113-120.
22. Hinchcliffe, R. (1959). The threshold of hearing as a function of age.
Acoustica, 9, 303-308.
23. Passchier-Vermeer, W. (April 1968). Hearing loss: due to exposure to steady-
state broadband noise. Instituut Voor Gezondheidstechniek, Sound & Light
Division, Rpt 35, 18 pp.
24. Summar, T. and Fletcher, John, 1965 (see related EPA document^-*).
25. Vacated
26. Kell, R. L., J. C. G. Pearson, W. I. Acton, and W. Taylor in Occupational Hearing
Loss, D. W. Robinson (Ed.), (Academic Press, London, 1971) pp. 179-191.
27. Lebo, C.P. and Oliphant, D. S. Music as a source of acoustic trauma.
Laryngoscope, 78, 1968.
28. Rintelmann, W. F. and Borus, J. F. Noise-induced hearing loss and rock and
roll music. Arch. Otolaryngol. 88, 1968.
29. Flugrath, J. M. (November 1969). Modern day rock-and-roll music and damage-
risk criteria. J acoust soc Amer. 45 (3), 704-711.
30. Upscomb, David M. High intensity sounds in the recreational enviornment: a
hazard to young ears. Clin. Pediat. 8 (2) 63-68 (1969).
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31. Upscomb, David M. Ear damage from exposure to rock and roll music.
Arch. Otol. 90: 545-555(1969).
32. Dey, F. L. Auditory fatigue and predicted permanent hearing defects from
rock-and-roll music. New Eng, J. Med. 282 (9): 467-470 (1970).
33. Fletcher, John L. High-frequency hearing and noise exposure. Presented to the
International Congress on Noise as a Public Health Problem, Dubronik, Yugoslavia
(1973).
34. Wood, W. Scott and Lipscomb, David M. Maximum available sound-pressure
levels from stereo components. JASA, 52 (2) 484-487 (1972).
35. Fletcher, J. L. (13 October 1972). Effects of non-occupational noise exposure
on a young population. Rpt for NIOSH, HEW, HSM 099-71-52. 18 pp.
36. Smitley, Ellen K & Rintelmann, W. F (April 1971). Continuous versus intermittent
exposure to rock and roll music: effect upon temporary threshold shift. Arch
Environ Health, 22, 413-420.
37. Burns, W & Robinson, D. W. (1970). Hearing and noise in industry. London:
Her Majesty's Stationery Office, 43 pp + 16 Appendices.
38. Burns, W. The relation of Temporary Threshold Shift in Individuals. In
OCCUPATIONAL HEARING LOSS, D. W., Robinson, (ed.) London: Academic
Press, 1971.
39. Robinson, D. W. & Cook, J. P. (1968). The quantification of noise exposure.
Teddington, Middlesex, England: National Physical Laboratory draft dated
14 June 1968. 8pp.
40. Luz, G. A. & Hodge, D. C. (October 1970). Recovery from impulse-noise induced
TTN, in monkeys and men: a descriptive model. Jacoust Soc Amer, 49, (6 part 2),
1770-1777.
41. Ward, W. D. and D. A. Nelson. On the Equal-Energy Hypothesis Relative to
Damage-Rosk Criteria in the Chinchilla. In Occupational Hearing Loss, D. W.
Robinson, Ed. Acad. Press., N. Y., 1971.
42. Eldredge, D. and Covell (see related EPA document 23).
43. Miller, J. D., Watson, C. S,, and Covell, W. (1963) "Deafening Effects of Noise .
on the Cat," Acta Oto-Laryngol Suppl. 176,91 pp.
44. Miller, J. D., Rothenberg, S. J. & Elderdge, D. H. (June 1971). Preliminary
observations on the effects of exposure to noise for seven days on the hearing
and inner ear of the chinchilla. / Acoust. Soc Amer, 50, (4 part 4) 1199-1203.
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45. Lipscomb, David M. Theoretical consideration in the rise of high frequency hearing
loss in children. Presented to the International Congress on Noise as a Public Health
Problem. Dubrovnik, Yugoslavia (1973).
46. Carder, H. M. & Miller, J. D., (September 1972). Temporary threshold shifts from
prolonged exposure to noise, /. Speech & Hearing Res., 15 (3), 603-623.
47. Mills, J. H., Gengel, R. W., Watson, C. S. & Miller, J. D., (August 1970). Temporary
changes of the auditory system due to exposure to noise for one or two days.
Jacoust Soc Amer, 48, (2 part 2), 524-530.
48. Mills, J. H. (1973), "Temporary and Permanent Threshold Shifts Produced by Nine-Day
Exposures to Noise," /. Speech Hear. Res. (Submitted).
49. Price, G. R. (July 1968). Functional changes in the ear produced by high-intensity
sound. I. 5.0 KHz stimulation. J. qcoustSoc Amer., 44 (6), 1541-1545.
50. Peters, E. N. (May 1965). Temporary shifts in auditory thresholds of chinchilla
after exposure to noise, /. Acoust Soc Amer., 37, (5), 831-833.
51. Ward, W. D., Glorig, A & Selters, W. (February 1960). Temporary threshold shift in a
changing noise level. J acoust Soc Amer, 32 (2) 235-237.
52. Price, G. R. (September 1971). Functional changes in the ear produced by high-
intensity sound. II. 500-Hz stimulation. /. Acoust Soc Amer, 51 (2 part 2), 552-558.
53. Poche, L. B., Stockwell, C. W. & Ades, H. W. (November 1968). Cochlear hair-cell
damage in guinea pigs after exposure to impulse noise. / Acoust Soc Amer, 46 (4
part 2). 947-951.
54. Trittipoe, W. J. (November 1958). Residual effects of low noise levels on the temp-
orary threshold shift,/. Acoust Soc. Amer., 30, (11), 1017-1019.
55. Ward, W. D. (April 1960). Recovery from high values of temporary threshold shift.
/. acoust. Soc. Amer., 32, (4), 497-500.
56. Karlovich, R. S. & Luterman, B. F. (August 1969). Application of the TTS paradigm
for assessing sound transmission in the auditory system during speech production. •
/. Acoust Soc. Amer, 47, (2 part 2), 510-517.
57. Kryter, K. D. and G. Garinther (1966). "Auditory Effects of Acoustic Impulses
from Firearms," Acta Oto-Laryngol. Suppl. 211.
58. Acton, W. I. (1967). A review of hearing damage risk criteria. Ann Occup Hyg, 10,
143-153.
59. Coles and Rice (1970) - see related EPA document 23
60. Coles and Rice (1971) - see related EPA document 23
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61. Coles (1971) - see related EPA document23
62. Loeb, M & Fletcher, J. L. (August 1968). Impulse duration and temporary
threshold shift. /. acoust Soc. Amer., 44, (6), 1524-1528
63. Gjaevenes, K. (1967). Damage-risk criterion for the impulsive noise of "toys".
/ acoust Soc Amer, 42 (1), 268.
64. Coles, R. R. A., Garinther, G. R., Hodge, D. C. & Rice, C. G. (1968) Hazardous
exposure to impulse noise. / acoust Soc Amer, 43 (2), 336-343.
65. Baughn, W. L. (September 1966). Noise Control - percent of population protected.
International Audiology, 5 (3), 331-338.
66. Passchier-Vermeer, W. "Steady-State and Fluctuating Noise: Its Effects on the
Hearing of People" in Occupational Hearing Loss, D. W. Robinson. Ed. Academic
Press, N. Y., 1971.
67. Kryter, Karl. Impairment to hearing from exposure to noise. JASA, 53 (5) 1211-
1234, 1973.
68. Cohen, Alexander. Some general reactions to Kryter's paper "Impairment to
hearing from exposure to noise. JASA, 53 (5) 1235-1236 (1973).
69. Davis, Hollowell. Some comments on "Impairment to hearing from exposure to
noise by K. D. Kryter. JASA, 53 (5) 1237-1238 (1973).
70. Lempeer, Barry L. Technical aspects of Karl Kryter's paper "Impairment to
hearing from exposure to noise" with respect to the NIOSH statistics. JASA,
53(5)1239-1241(1973)
71. Ward, E. Dixon Comments on "Impairment to hearing from exposure to noise"
by K. D. Kryter, JASA, 53 (5) 1242-1243 (1973).
72. Kryter Karl, Reply to the critiques of A. Cohen, H. Davis, B. L. Lembert, and
W. D. Ward of the paper "Impairment to hearing from exposure to noise" JASA
53(5),1244-1254. (1973).
73. Anon. "Assessment of Occupational Noise Exposure for Hearing Conservation
Purposes," ISO Recommendation R1999 pp. 1-11, Switzerland (May 1971).
74. Schmidek, M. Henderson, T & Margolis, B (December 1970). Evaluation of
proposed limits for intermittent noise exposures with temporary threshold shift
as a criterion. Cincinnati: HEW, NIOSH, National Noise Study, 10 pp.
75. Ward, W. D. (1970). Hearing Damage. In: Transportation Noises: A symposium
on acceptability criteria. Chalupnik, J. D. (ed). Seattle & London: Univ
Washington Press, pp. 174-186.
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76. Ward, W. D., Glorig, A & Sklar, Diane L ( June 1959). Temporary threshold
shift produced by intermittent exposure to noise. Jacoust Soc Amer, 31
(6), 791-794.
77. Cohen, A. & Jackson, E. (1968). Threshold shift in hearing as a function of band-
width and mode of noise presentation. /. Auditory Res, 8, 401-414.
78. Schmidek M. Margolis, R & Henderson, Effects on the
level of noise interruptions on temporary threshold shift. Cincinnati; HEW,
Public Health Service, NIOSH rpt, 8 pp.
79. Falk, S. A. Combined effects of noise and ototoxic drugs. Environmental Health
Perspectives. Experimental Issue Number Two, October, 1972 (USPHS, NIH),
5-22.
80. Ward, W. D. (1966). Temporary threshold shift in males and females. Jacoust
Soc Amer, 40 (2), 478-485.
81. Rosen, S. & Rosen, Helen V. (1971). High frequency studies in school children in
nine countries. The Laryngoscope, 81, 1007-1013.
82. Rosen, Samuel, Bergman, Moe, Plester, Daniel, El-Mofty, A. and Satti, M. H.
Presbycusis study of a relatively noise-free population in the Sudan. Ann. Otol.
71:727,743(1962).
83. Kryter, Karl Damage-risk Criteria for Hearing. In NOISE REDUCTION, Leo
Baranek, ed. New York: McGraw-Hill (1960).
84. Schwartz (1962) - see related EPA document 23
85. Kupp( 1966)-see related EPA document23
86. Nowak and Kahl (1969) - see related EPA document 23
87. Julse and Partsch (1970) - see related EPA document 23
88. Schneider, E. J., Mutchler, J. E, Hoyle, H. R., Ode, E. H. & Holder, B. B. (1970).
The progression of hearing loss from industrial noise exposures. Amer. Ind.
Hygiene Assoc. Jour, 31, May-June, 368-376.
89. Loeb, M. and Fletcher, John. Temporary threshold shift for "normal" subjects
as a function of age and sex. /. Aud. Res. 3, 65-72 (1963).
90. Ward, W. Dixon Effect of temporal spacing on temporary threshold shift from
impulses. JASA. 34,1230-1232(1962).
91. Kryter, K. D. et al (1965). Hazardous exposure to intermittent and steady-state
noise. Rpt of Working Group 46, NAS-NRC Comm on Hearing, Bioacoustics &
Biomechanics, ONR Cont No. NONR 2300 (05), 30 pp.
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92. Fletcher, H. and Steinberg, J. C. Loudness of Complex sounds. Phys.
Rec. 24(1924).
93. Mercer, D. M. A. (September 1967). Noise-damage criterion using A-
weighting levels. /. Acoust Soc. Amer., 43, (3), 636-637.
94. Harris, J. D. (May 1965). Pure-tone acuity and the intelligibility of everyday
speech. /. Acoust Soc. Amer., 37(5), 824-830.
95. Kryter, K. D., Williams, C. & Green, D. M. (September 1962). Auditory acuity
and the perception of speech. /. acoust Soc. Amer., 34 (9), 1217-1223.
96. Coles et al (1970 - see related EPA document23)
97. Ward, W. D. (September 1962). Effect of temporal spacing on temporary
threshold shift from impulses. /. acoust Soc. Amer., 34 (9), 1230-1232.
98. Ward, W. D. (ed.) PROPOSED DAMAGE-RISK CRITERION FOR IMPULSE
NOISE (GUNFIRE). Report of Working Group 57, NAS-NRC Committee on
Hearing, Bioacoustics, and Biomechanics (1968).
99. Ward, W. D. Sellers, W. & Glorig, A (June 1961). Exploratory studies on
temporary threshold shift from impulses. / acoust Soc. Amer., 33 (6),
781-793.
100. Muirhead, J. C. (July 1960). Hearing loss due to gun blast. J. acoust Soc. Amer.,
32, 885.
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SECTION 6
MASKING AND SPEECH INTERFERENCE
The one effect of noise of which every person is aware is its interference with the understand-
ing of speech. Technically speaking, such interference is only one aspect of the general phenomenon
of "masking"- - an interaction of two acoustic stimuli whereby one of them:
1. Changes the perceived quality of the other.
2. Shifts its apparent location or loudness.
3. Makes it completely inaudible.
Much information has become available over the past 50 years concerning the masking of fairly
simple signals such as pure tones, noise bands and nonsense syllables by noises of various spectra,
and general laws have been developed that will allow rather accurate prediction of whether or not
a given speech sound will be masked by a particular noise. Recent reviews of masking in general
have been presented by Jeffress1 and Scharf . Both Webster'' ^ and Kryter* summarize much of
the evidence concerning the masking of individual speech sounds by noise.
INTELLIGIBILITY OF SPEECH
Unfortunately, most of this specialized knowledge is often of limited assistance in the predic-
tion of the intelligibility of "ordinary speech" - - speech as it actually occurs in real life. Ordinary
speech consists of a complicated sequence of sounds whose overall intensity and spectral distribu-
tion are constantly varying. Because of this lack of uniformity, some sounds will be masked by a
specific steady noise while others will not. Furthermore, even in a steady noise, the energy in
different frequency regions fluctuates from moment to moment; therefore, a sound that might be
masked at one instant could be clearly perceptible the next. Finally, it is not usually necessary for
the listener to hear all the speech sounds in a sentence because ordinary speech is very redundant -
that is, it contains more information than is necessary for understanding. The listener decodes the
speech by a synthesizing process, only partly understood at present, that depends not only on the
acoustic cues but also on his knowledge of the language and of the context in which the speech
occurs. For example, most people, although actually hearing only " She icked up the baby," would
need no additional information in order to know what was actually said. Thus, even though one
speech sound was missed completely, the sentence would have been correctly understood, and its
intelligibility would be "100%."
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For these reasons, the relations between the spectral and intensive characteristics of noise and
the intelligibility of ordinary simultaneously-presented speech are rather complicated. Often they
must be measured directly instead of being predicted on the basis of results with isolated words,
although conversion charts have been constructed to transform scores on tests involving only words-
to the approximate expected scores for the sentences of ordinary discourse.
Many variables may influence the accuracy of speech communication from talker to listener
in an experiment. In addition to the masking noise present at the listener's ear, all the following
can be important:
• The characteristics of the talker.
• The test materials.
• The transmission path from talker to listener.
• The spatial locations of the talker, noise source, and listener.
• The noise level at the speaker's ear (if different from that at the listener's, particularly),
• The presence or absence of reverberation.
• The integrity of the listener's auditory system.
The outcome of experiments involving noise and speech is usually measured by the percentage
of messages understood, and this percentage is taken as a measure of intelligibility or the "articula-
tion score" of the speech. Other measures are occasionally used; among these are:
• Ratings of the quality or the naturalness of the speech.
• Recognition of the talker.
• Recognition of the personality traits.
• Psychological state of the talker.
MEASUREMENT OF SPEECH-INTERFERENCE
In describing speech interference, the noise concerned can be defined either in terms of its
specific spectrum and level or in terms of any number of summarizing schemes. In addition to
the average A-weighted sound level, the two most generally-used alternative methods of character-;/
izing noises in respect to their speech-masking abilities are:
• The articulation index (AI).
• The speech interference level (SIL).
Articulation Index
The articulation index, initially developed by French and Steinberg", although extended and
somewhat simplified by Kryter , is a very complicated measure that takes into account the fact
that certain frequencies in the masking noise are more effective in masking than other frequencies.
Determination of the AI involves:
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1. Dividing the frequency range in which significant speech energy exists (250 to 7000 Hz)
into 20 bands, each of which contributes 1/20 of the total intelligibility of speech.
2. Determining the difference between the average speech level and the average noise level
(that is, the signal-to-noise ratio) for each of these bands.
3. Combining these numbers to give a single index.
This AI, by essentially predicting how much masking of specific speech sounds will occur,
will therefore predict the intelligibility of "speech" at a given level in a specific noise. Simplified
procedures for estimating the AI from measurements of octave-band levels have also been devel-
oped'. Although the AI is as yet the most accurate measurement to use in predicting the effects of
noise on speech intelligibility, it is difficult to use and more difficult for laymen to interpret.
Speech Interference Level
The SIL, which was introduced by Beranek° in 1947 as a simplified substitute for the AI, is
an indication of only the average general masking capability of the noise. Contributions to intell-
igibility by the lowest and highest frequencies are ignored. As originally formulated, it was defined
as the average of the octave-band SPLs in the 600-1200, 1200-2400 and 2400-4800-Hz octaves.
Since that time, the preferred frequencies for octave bands have been changed. One modern ver-
sion of the SIL is the average of the SPLs in the three octave bands centered at 500, 1000, and
2000 Hz. So many variations of SIL in terms of the specific octave bands to be averaged have been
developed that a shorthand notation is now used. SIL (.5,1, 2) is the average of the SPLs of the
three octave bands centered at 500, 1000 and 2000 Hz; SIL (.25, .5, 1, 2) includes the 250-Hz
band in the average, and so on. The original SIL would be SIL (.85, 1.7, 3.4) in this notation. At
the present time, the American National Standards Institute is promoting the acceptance of SIL
(.5, 1, 2, 4) as providing the best estimate of masking ability of a noise.
The simple A-weighted sound level is also a useful index of the masking ability of a noise.
The A-weighting process emphasizes the median frequencies, as do the various SILs. However, in
contrast to most SIL schemes, A-weighting does not ignore the lowest frequencies completely.
Experiments have shown that the AI is somewhat more accurate than any of the SILs or dBA
(or other similar weighting schemes that were not developed specifically for speech) in predicting
the speech-masking ability of a large variety of noises. Nevertheless, dBA and SIL ratings will
continue to be used, because for most noises of importance, the advantage in accuracy of AI
determinations does not outweigh the ease of measurement of dBA or SILs.
Noise Level, Vocal Effort, and Distance
Since much speech is spoken at a reasonably constant level, and in "ordinary" surroundings,
it is possible to express many of the empirical facts about average speech communication in a
6-3
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single graph. The basic data come from Beranek , and are shown in Table 6-1. These are values
of SIL (.85, 1.7, 3.4) that Beranek estimated would just permit reliable conversation our of doors
(understanding of 95% or more of the key words in a group of sentences), a situation corresponding
to correctly hearing approximately 75% of a list of isolated phonetically-balanced words. Thus,
Table 6-1 indicates that speech when spoken at a normal level can only just be heard at a distance
of 3 feet when the noise has an SIL (.85, 1.7, 3.4) of 55 dB. As voice level is judged to go from
"normal" to "raised", "very loud", and (sustained) "shouting", respectively, Beranek postulates
a four-fold increase in vocal output for each step, or a 6-dB increase in acoustic output. If the
voice rises 6 dB for each step, then, as a first approximation, the noise can also increase by the
same amount without changing the intelligibility of the speech. Therefore, at 3 feet a "raised"
voice can be heard through a 61-dB-SIL (.85, 1.7, 3.4) noise, a "very loud" voice is intelligible in
67 dB SIL, and a "shout" will be understood in 73 dB SIL.
The values for other distances in this table are merely expressions of the well-known inverse
i square law, which is that the sound intensity will drop by a factor of 4 (i.e., the level will drop
6 dB) if one doubles the distance from the source in the free fields (outdoors). If the listener is
6 feet from the talker, therefore, the speech level at his ears will have dropped to 6 dB less than
what it was at 3 feet, hence the noise that will permit normal conversation will also be 6 dB lower,
or 55-6-49 dB SIL (.85, 1.4, 3.4). A chart can, therefore, be constructed showing the relations
of Table 6-1 in graphic form. Further, since it is simpler, for general purposes, to use dBA instead
of SIL, a conversion from SIL to dBA is made for the purpose of this graph (Table 6-1).
Although the difference between the SIL and dBA values of any two noises will ordinarily
not be the same, since this difference will depend on the exact spectrum of each, attempts have
been made to determine an average conversion number for a more or less vaguely-defined "average"
noise. Klumpp and Webster'', for example, showed in their sample of 16 shipboard noises that
SIL (0.5, 1, 2) values averaged about 10 dB lower than corresponding A-weighted sound levels
and about 17 dB lower than C-weighted sounc! levels. Similarly, Kryter selected seven different
common spectra from the research literature and found that for these noises dBA minus SIL was
about 9 dB, dBC minus SIL was 13 dB. For the present purposes, then, it can be assumed that
for not-unusual noises, the A-weighted sound levels that will permit conversation can be derived
by simply adding 10 dB to the values of Table 6-1, and that the overall (C-weighted) levels will be
an additional 5 dB higher, or 15 dB above SIL (.85, 1.7, 3.4).values.
The dashed lines in Figure 6-1 show these converted values. The ordinate is the A-weighted
sound level of the noise at the listener's ears. The abscissa is the distance between talker and
listener in feet, plotted in a logarithmic fashion. The four dashed lines indicate the highest noise
level that will permit near-100 percent understanding of sentences spoken with the effort indicated
on each curve, in the outdoor environment. Thus, in a 70 dBA noise, a normal voice can be heard
6-4
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Figure 6-1. Distance at which ordinary speech can be understood as a function of A-weighted
sound levels of masking noise in the outdoor environment.
-------
TABLE 6-1
SPEECH INTERFERENCE LEVELS (SIL(.85., 1.7, 3.4))
FOR OUTDOORS ENVIRONMENTS THAT PERMIT
BARELY RELIABLE CONVERSATION, OR THE
CORRECT HEARING OF APPROXIMATELY 75J&
OF PHONETICALLY-BALANCED WORD LISTS, AT
VARIOUS DISTANCES AND VOICE LEVELS. FROM BERANEK.10
Distance
between
talker and
listener (ft)
0.5
1
2
3
4
5
6
12
Normal
«
71
65
59
55
53
51
49
43
Voice Level
Raised Very Loud
SIL (in decibels)
77
71
65
61
59
57
55
49
83
77
71
67
65
63
61
55
Shouting
1
89
83
77
73
71
69
67
61
6-6
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at a distance of only 2 feet, a raised voice at 3.5 feet, a very loud voice at 7 feet, and a shout at
15 feet. The curve farthest to the left indicates that in 70-dBA outdoor noise, speech at the
level that is generated when people are engaged in "relaxed conversation" in quiet would be
completely understandable only at a distance of 9 inches or so. Beyond 15 feet, progressively
more and more of even shouted speech is masked, so that at 70 feet (i.e., at the boundary of
the blackened area on the right), a shout may serve to attract a listener's attention, but will
convey little other information. Hence, beyond this point, no voice communication is possible
unless of course, the speech is amplified by one means or another (cupping the hands, using a
megaphone, or employing electronic amplification).
Reception of Indoors Speech
The dashed curves of Figure 6-1 predict fairly accurately how noise will affect the percep-
tion of speech in the outdoor environment (field free). However, the criterion of distance
between the talker and the listener is not valid to assess the intrusion of the outdoor noise levels
on the reception of speech indoors because of the reverberant build up of sound by reflections
from the walls of the room. Over the years, various studies have been concerned with specifi-
cations of values which could be utilized in the design of rooms. An example of such data are
presented in Table 6-2.
The data available in the pertinent literature suggests that, for most instances, a reasonable
value for the design of rooms where oral communication is important is somewhere in the range
between 40-45 dBA. It is found that a steady state noise level that does not exceed this value
will assure a 100 percent sentence intelligibility.
FACTORS IN THE DEGREE OF SPEECH INTERFERENCE
Characteristics of People (Speech, Age, and Hearing)
The contours on Figure 6-1 represent conditions for young adults, speaking the same dia-
lect, when they are in a diffuse noise field. The location of these contours will shift in accord-
ance with many variables. Lower noise levels would be required if the talker has imprecise
speech (poor articulation) or if the talker and the listener speak different dialects. Children
have less precise speech than do adults , and their relative lack of knowledge of language often
makes them less able to "hear" speech when some of the cues in the speech stream are lost.
Thus, adequate speech communication with children requires lower noise levels than are required
for adults. One's ability to understand partially-masked or distorted speech seems to begin to
deteriorate at about age 30 and declines steadily thereafter . Generally, the older the listener,
the lower the background must be for nearly normal communication. Finally, it is well known
that persons with hearing losses require more favorable speech-to-noise ratios than do those
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TABLE 6-2
DESIGN OBJECTIVES FOR INDOOR A-WEIGHTED SOUND LEVELS IN
ROOMS WITH VARIOUS USES, AS RECOMMENDED BY AN
ACOUSTICAL ENGINEERING FIRM ON THE BASIS OF
EXPERIENCE WITH ACCEPTABILITY LIMITS EXHIBITED
BY THE USERS OF THE ROOMS. FROM BERANEK ET AL.16
Type or use of space
Approximate A-weighted
sound level (dBA)
Concert halls, opera houses, recital halls
Large auditoriums, large drama theaters, churches
(for excellent listening conditions)
Broadcast, television and recording studios
Small auditoriums, small theaters, small churches, music
rehearsal rooms, large meeting and conference rooms
(for good listening)
Bedrooms, sleeping quarters, hospitals, residences, apartments,
hotels, motels (for sleeping, resting, relaxing)
Private or semiprivate offices, small conference rooms, class-
rooms, libraries, etc. (for good listening conditions)
Living rooms and similar spaces in dwellings (for conversing
or listening to radio and television)
Large offices, reception areas, retail shops and stores, cafe-
terias, restaurants, etc. (moderately good listening)
Lobbies, laboratory work spaces, drafting and engineering rooms,
general secretarial areas (for fair listening conditions)
Light maintenance shops, office and computer equipment rooms,
kitchens, laundries (moderately fair listening conditions)
Shops, garages, power-plant control rooms, etc. (for just-
acceptable speech and telephone communication)
21 to 30
Not above 30
Not above 34
Not above 42
34 to 47
38 to 47
38 to 47
42 to 52
47 to 56
52 to 61
56 to 66
6-8
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with normal hearing. However, little quantitative data exists to indicate how much the curves
of Figure 6-1 should be shifted for specific values of the factors above.
Situational Factors
Of course, adequate communication in higher noise levels than those indicated on Figure
6-1 can occur if the possible messages are known to be restricted. Thus, at ball games, it is
possible to discriminate the umpire's "ball" and "strike" (assuming that he actually says these
words) at much greater distances and in more intense levels of noise than indicated on the
chart. This factor accounts for the success of communication in many industrial situations
with high levels of noise. Failure may occur, however, when an important but unpredictable
message must be communicated. For example, firemen in a high-level noise may have little
difficulty with standard communications about the use of familiar equipment, but they may
encounter grave difficulty communicating about unexpected events that occur at the scene of
the fire.
The opportunity to lipread or use facial or body gestures in support of hearing will improve
the success of communication in background noise. Almost everyone has some small amount of
lipreading skill that they often use without awareness of its contribution to intelligibility.
Spatial variables also may facilitate or impede speech communication in noise. If the
source of noise is clearly localized in a position different from that of the talker, speech com-
munication may be possible under noise conditions less favorable than those indicated on
Figure 6-1. On the other hand, noise interferes with speech communication more when either
is reverberant (involves echoes).
Noise Characteristics
Finally, it must be remembered that the exact characteristics of the noise are also important
for predicting speech communication. While the A-weighted noise level is an adequate measure
of many noises, some situations and noises demand a more complicated analysis. This is par-
ticularly true of noises that consist almost exclusively of either low frequencies or high frequen-
cies-e.g., the rumble of ships' engines or the hiss of compressed air. A chart similar to Figure
6-1, but with an additional correction based on the difference between the C- and A-weighted
levels of the noise, has been developed by Bostsford. However, in case of a very unusual
noise, it is probably better to calculate the AI if a relatively accurate prediction of speech intel-
ligibility is necessary. A discussion of the use of the various methods of measuring noise to pre-
dict speech interference can be found elsewhere.
I'ijiurc <>-! applies only to reasonably steady noises. Intermittent noises and impulses will,
of course, mask certain signals only while they are present, and noises fluctuating in level will
6-9
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provide variable degrees of masking. Again, speech is redundant enough so that an isolated
1-second burst of noise is unlikely to produce much disruption of the communication process;
however, this probability grows with both the frequency and the duration of the noise-bursts.
If a noise criterion such as "X percent perception of sentences" is adopted, therefore, it will be
necessary to specify those patterns of noise that produce this particular degree of intelligibility
loss. For example, any noise above 70 dBA in level will interfere with conversation, even with
a raised voice. Hence, if a criterion were 90 percent sentence intelligibility, then an 85-dBA
noise would meet the criterion, provided it were on only 10 percent of the time.
Acoustic Privacy
It should be pointed out that not all masking is an unmitigated evil. A noise that can be
ignored may be able to blot out an annoying one. Indeed, offices can be made too quiet, so
that everyone can hear the speech and other sounds produced by everyone else-in which case
the speech in question becomes "noise." In a study of workers in noisy workshops, Matsui
and Sakamoto17 found that just as many persons admitted feelings of irritation about noise in
the 50-dB environment that served as a control situation ("desk work") as those in a 100-dB
environment; in the control case, the irritation was attributed to the rustling of paper.
For "acoustic privacy," therefore, a moderate amount of background noise may be desir-
able. If an office area has been made too quiet, a low level of noise (recorded sounds of surf
or a waterfall would serve as well as the intentionally uninteresting music that is widely employed
in this country) may have to be reintroduced so that its level permits'ordinary conversation at
10 feet or less but requires raising the voice in order to be heard at greater distances. The "opti-
mum" noise level is seldom if ever complete silence.
SUMMARY-MASKING AND SPEECH INTERFERENCE
Speech interference is one aspect of "masking" - an interaction of two acoustic stimuli
whereby one of them changes the perceived quality of the other, shifts its apparent location or
loudness, or makes it completely inaudible. Much information is available concerning the mask-
ing of fairly simple signals such as pure tones, noise bands and nonsense syllables by noises of
various spectra; and general laws have been developed that will allow rather accurate prediction
of whether or not a speech sound will be masked by a particular noise.
In describing speech interference, the noise concerned can be defined either in terms of its
specific spectrum and level or in terms of any number of summarizing schemes. In addition to
the average A-weighted sound level, the two most generally-used .alternative methods of charac-
terizing noises in respect to their speech-masking abilities are the articulation index (Al) and
the speech interference level (SIL). The AI takes into account the fact that certain frequencies
6-10
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in the masking noise are more effective in masking than other frequencies. The SIL is more
simplified, indicating only the average general masking capability of the noise. Since much
speech is spoken at a reasonably constant level, it is possible to express many of the empirical
facts about average speech communication in a single graph showing noise level, vocal effort,
and distance.
Various factors enter into the degree of speech interference. Speech, age, and hearing of
individuals affect communications. Children have less precise speech than adults do. Older
listeners are more susceptible to interference from background noise.
Situational factors influence the degree of speech interference. In some contexts, the
predictability of the message will decrease speech interference. Nonverbal communication and
lipreading have the same effect. Spatial variables may facilitate or impede speech communication
in noise. The exact characteristics of noise are important in predicting speech communication.
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REFERENCES
1. L. A. Jeffress, "Masking," in "Foundations of Modern Auditory Theory, Vol. 1," J. V.
Tobias, Ed., Academic Press, New York (1970).
2. B. Scharf, "Critcial Bands," in "Foundations of Modern Auditory Theory, Vol. 1,"
J. V. Tobias, Ed., Academic Press, New York (1970).
3. J. C. Webster, "Effects of Noise on Speech Intelligibility," in "Noise as a Public Health
Hazard," ASHA Reports No. 4, Am. Speech and Hearing Assoc., Washington (1969).
4. J. C. Webster, "The Effects of Noise on Hearing Speech," Proc. Internat. Congress on
Noise as a Public Health Problem, Govt. Printing Office (1973).
5. K. D. Kryter, "The Effects of Noise on Man," Academic Press, New York (1970).
6. N. R. French and J. C. Steinberg, "Factors governing the intelligibility of speech,"
J. Acoust. Soc. Am. 19, 90-119 (1947).
7. K. D. Kryter, "Methods for the calculation and use of the articulation index," J. Acoust.
Soc. Am. 34, 1689-1697 (1962).
8. L. L. Beranek, "The design of speech communication systems," Proc. Inst. Radio Engrs.
35,880-890(1947).
9. R. G. Klumpp and J. C. Webster, "Physical measurements of equally speech-interfering
Navy noises," J. Acoust. Soc. Am. 35, 1328-1338 (1963).
10. L. L. Beranek, "Noise control in office and factory spaces," 15th Annual Mtg. Chem. Eng.
Conf., Trans. Bull. 18, 26-33 (1950).
11. T. S. Korn, "Effect of psychological feedback on conversational noise reduction in rooms,"
J. Acoust. Soc. Am. 26, 793-794 (1954).
12. Kryter, K. D., Specifying Tolerable Limits of Exposure to Noise, Draft Document for World
Health Organization, Europe, 1973.
13. S. Eguchi and I. J. Hirsh, "Development of speech sounds in children," Acta Oto-Laryngol.
Suppl. 257(1969).
14. A. Palva and K. Jokinen, "Presbyacusis: V. Filtered Speech Test," Acta Oto-Laryngol. 70,
232-241 (1970).
15. J. H. Botsford, "Predicting speech interference and annoyance from A-weighted sound
levels," J. Acoust. Soc. Am. 42, 1151 (1967).
16. L. L. Beranek, W. E. Blazier and J. J. Figwer, "Preferred Noise Criterion (PNC) Curves
and their Application to Rooms," J. Acoust. Soc. Am. 50, 1223-1228 (1971).
17. Matsui, K. and Sakawato, H., The Understanding of Complaints in Noisy Workshop;
Ergonomics, 14, 95-102, 1971.
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Section 7
ADDITIONAL PHYSIOLOGICAL AND PSYCHOLOGICAL CRITERIA
Acoustic stimulation of the ear can affect many parts of the body and nervous system in
addition to the auditory system. These "non-auditory" or "extra-auditory" effects are mediated
through at least three neural systems which are not considered to be an integral part of the auditory
mechanism:
1. The autonomic nervous system controlling general somatic responses and the state of
arousal of the body-the glands, viscera, heart, blood vessels, etc.
2. The reticular nervous system which appears to be involved in the state of arousal of the
higher brain centers of the central nervous system and with sensory inputs related to pain
and pleasure.
3. The cortical and subcortical brain centers concerned with cognition, consciousness, task
performance, "thinking," etc.
It is important, therefore, to consider not only the more overt effects of noise, such as hearing
loss and the masking of speech, but the more subtle effects which noise can produce. These non-
auditory effects can be merely transitory or, in some cases, long-lasting. They usually take place
without conscious knowledge of their occurrence.
PAIN
Tympanic Membrane
There are two general types of aural pain or discomfort. The first type is caused by the
stretching of the tympanic membrane tissues in response to large amplitude sound waves. Although
there is a fairly wide range of individual variability, especially for high-frequency stimuli,' the thres-
hold of pain for normal ears is approximately 135-140 dB SPL. This threshold is essentially inde-
pendent of frequency, and it will occur in totally deaf as well as normally hearing people since it
is not a function of the ear's sensorineural system. A good indication that this reaction is a function
of the tympanic membrane was demonstrated by Ades et al, who found that people without ear-
drums report no sensations of pain to sound levels up to 170 dB SPL. At somewhat lower sound
pressure levels (120 to 130 dB), one may experience some discomfort or a tickling sensation in the
ear canal. Since these levels are considerably above the level of hearing damage risk, aural pain
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should not be considered an early warning signal of excessive noise exposure. However, if aural pain
should occur in an otherwise normal ear, it should be a clear sign that hazardous noise levels are
being experienced.
In special cases, aural pain originating in the eardrum or middle ear may occur in response to
sound levels considerably lower than 130 dB SPL. Davis and Silverman point out that sounds of
moderate intensity can produce pain when middle ear tissues are tender from inflammation and the
eardrum may be tense with pus. Similarly, contraction of the middle ear muscles (elicited at about
80 to 90 dB SPL) can be painful if these muscles are inflamed.
Inner Ear
A second type of aural discomfort occurs as a result of abnormal function in the cochlea or
inner ear. Certain sensorineural disorders, and most frequently noise-induced hearing losses, are
accompanied by a condition called auditory recruitment, a term attributed to Fowler. Recruitment
is defined as an abnormal increase in loudness perception, a condition seen in pathological ears. In
some cases of sensorineural hearing disorders, the condition is more severe, and it can lead to con-
siderably lower thresholds of aural discomfort or pain. Thus, sound levels of only moderate intensity
can occasionally be quite uncomfortable to individuals experiencing auditory recruitment. Davis and
Silverman mention that in special cases of sensorineural hearing disorders with symptoms of
diplacusis (a condition in which a tone is perceived as having a different pitch in the two ears) and
severe tinnitus, subjects can be unusually vulnerable to noise-induced hearing loss. These cases often
display lower thresholds of aural pain that may serve a useful warning function.
Hearing Aids
Another important consideration in the area of aural pain is the effect of noise on hearing aid
users. Discomfort associated with exposures to traffic noise, loud music, and even raised voice levels
is a common complaint among hearing-impaired people who wear hearing aids. Although many
hearing aids have devices which automatically limit output intensity to 120 or 130 dB SPL, the pro-
tection offered may not be sufficient for some recruiting ears. In some cases, in order for speech to
be loud enough to be intelligible, it borders on (or even exceeds) the listener's threshold of discom-
fort. Hearing aid users comprise approximately 1 percent of the American population," and about
50 percent of these are over age 65 and tend to suffer more discomfort from loud sounds than
their younger counterparts. Thus, a passing subway train at 95 dBA or a jet flyover at 105 dBA,
which might be momentarily annoying to a normal listener, could be excruciating when amplified
for a hearing-impaired individual with recruitment.
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EFFECTS OF NOISE ON EQUILIBRIUM
o
Many years ago in Italy, Tullio demonstrated that pigeons could be made to veer off course
by presenting an intense low frequency stimulus during flight. From this it has been concluded that
a direct relationship could be found between acoustic stimulation and vestibular (balance sense)
Q
effects.
Complaints of nystagmus (rapid involuntary side-to-side eye movements), vertigo (dizziness),
and balance problems have been reported under noise conditions in the laboratory as well as in
field situations. The levels needed to cause such effects are quite high, typically 130 dB SPL or
more. Less intense noise conditions in the range of 120 dB SPL, however, can disturb one's
sense of balance, particularly if the noise stimulation is unequal at the two ears. This was demon-
strated in a laboratory study in which subjects were required to balance themselves on rails of differ-
11 19
ent widths. McCabe and Lawrence offered the suggestion that these effects are due to noise
directly stimulating the vestibular sense organs whose receptors are part of the inner ear structure.
1 ^
Recently, Lipscomb and Roettger observed a high degree of swelling of capillary walls in the
region of the vestibular organs of rats exposed to 110 dBA noise for 48 hours. Those effects have
been attributed to reduced blood flow to the sensory regions following substantial noise expo-
sures.
Dieroff and Scholtz attempted to test whether or not there exists a significant correlation
between hearing loss due to steady industrial noise and vestibular function. They conducted various
vestibular tests on 293 men and 51 women with various degrees of noise-induced hearing loss. No
significant correlations were found, indicating that habitual exposure to continuous high-intensity
noise is dangerous only to the auditory system and not to the vestibular system. These findings
were obtained by using vestibular tests when the subjects were no longer in the noise. It would be
important also to assess whether continuous stimulation by moderate levels of noise will create
measurable vestibular conditions while the subject is still in the noisy environment.
Due to the scarcity of available data in the pertinent literature, many questions regarding the
effect of noise exposure on equilibrium remain unanswered.
ORIENTING AND STARTLE REFLEXES (ACOUSTIC)
Man is equipped with an elaborate set of auditory-muscular reflexing capabilities. The orienting
portion of these reflexes serves to turn the head and eyes toward a sharply occurring sound source
in order to locate its origin. The startle reaction (recorded by Molinie), occurs primarily in order
to prepare for action appropriate to a possible dangerous situation signalled by the sound. Accord-
1 f\ IT
ing to Davis and Galambos, et al,l the reflex activity begins to operate even at low levels of
sound energy. The presence of these extrinsic acoustic reflexes is detected either by noting
behavioral clues or by electrophysiological study of muscle tension and activity. With the advent
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of low level sound stimulation that is sufficient in abruptness and information to occasion a
startle reflex, there is often little or no noticeable evidence that a person has experienced some
degree of startle except with the use of electrical measures.
Response In Children
Human response to sound develops at very early childhood. Youngsters in the first two months
of life tend to give an all-or-none response to sound stimuli. At this period, a child will signal having
heard the sound by a startle reflex, a gigantic seizure-type of reaction, or by a number of other
lesser responses such as the eye-blink, crying, diminution of activity or sudden assumption of a
listening attitude. In general, neonates demand a considerable amount of sound prior to giving any
of the above-named responses.' ° Some children, later found to have normal hearing sensitivity, do
not respond well or consistently to sound stimulation during this period. Most small babies, how-
ever, do give some degree of response to auditory stimulation if the sound is raised to between 80
and 100 dB Hearing Level (HL).
With maturity, human response to sound becomes modified and diversified so that a consider-
able number of additional behavioral observations can be made. After the first two months,
small children begin to respond to sound consistently. The sharp startle reaction is reduced, being
reserved only for those times that sound has a disturbing quality.
Adult Response
20
Landis and Hunt have given numerous details regarding the behavioral concomitants of the
startle response in mature humans. These manifestations include:
• The eyeblink (if the eyes are open).
• Firm closure of the eyes (if the eyelids are loosely closed).
• Facial grimaces of a characteristic nature.
• Bending of the knees.
• A general inward flexion of the body.
These events occur in something less than 0.5 sec. Other observers have cited:
• Increased neck and shoulder muscle tension tending to draw the head downward.
• Random foot movement.
• An elevation of the arms bringing the hand toward the face with an inward rolling of
the forearms. '
These sudden body movements are accompanied by a set of physiological reactions:
• Alteration in cardiovascular function.
• Increased endocrine activity.
• Alteration of respiration rate and cessation of gastro-intestinal activity.
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Fortunately, these physiological effects are of short duration and the body returns rapidly to
its previous state within a few seconds (or minutes) after the onset of the startling stimulation.
9O
According to Landis and Hunt, the startle response to sound, such as a nearby gunshot,
may undergo various degrees of diminution with repetition of the sound. This lessening of response
depends upon several factors, including:
• The responsiveness of the individual.
• Repetition rate of the sound.
• The predictability of occurrance of the sound.
In some persons, there is little decrease in reaction from one impulse to the next. With others,
there is a marked reduction in reaction'as repetitions occur. The eyeblink and head movement aspects
of the startle response never habituate completely. Even experienced marksmen exhibit these respon-
22
ses each time they fire a gun. This assertion was confirmed by Davis and Van Liere when they
measured electrical indicators of muscle activity. An early response with a latency of about 0.1
second showed little reduction with repetition of the sound. A later measured element in the muscle
reaction to sound stimulation which had a 0.8 second latency did diminish significantly with repeti-
tion of stimulation.
Variation In Muscular Response
2*2 'Jf.
A series of experiments by R. C. Davis and his colleagues demonstrated that the particular
muscular responses to sound and the way in which these responses will influence the performance of
a motor task depend in detail on:
1. Pattern of muscular tension or posture, prior to the sound.
2. Movements required by the task.
07
3. Auditory-muscular reflexes.
From the standpoint of the interfering characteristics of sudden noises, one of the more impor-
tant findings was that the magnitude of the muscle-tension reflex in response to sound increases
with a rise in resting tension in the muscle itself. (This generalization, of course, would not hold as
a muscle approaches its maximum level of tension). Thus, if a person is required to make a move-
ment requiring flexion and if his posture heightened tension in the appropriate flexor muscle, a
burst of sound, which ordinarily produces the reflex action of flexion, would speed the performance
of the movement. The result of this effect is obvious when one considers that the hand might have
been holding a fluid-filled container. Under other conditions, however, the burst of sound could
greatly interfere with the required movement. As an example, consider that, as before, the required
movement was that of flexion but that the person's posture heightened the resting tension in the
opposing extensor. In this case, a burst of sound would result in a greater response in the extensor
(because of the higher resting tension) than in the flexor. The consequence would be that the required
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and desired flexion activity would be interfered with and delayed. In delicate operations in assembly
plants, etc., these effects could greatly affect quality control and workmanship.
The ebb and flow of muscular activity is closely linked to and influenced by the rise and fall of
sound in an immensely complex manner. Gross body orientation toward an unexpected source of
sound will diminish as the sound becomes familiar and predictable. While some components of the
startle response to sharp sounds will diminish with repetition of the stimulus, the exact amount of
this reduction depends upon a number of variables. Subtle changes in the musculature in response
to sustained sound may persist as long as the sound is present, and the effects will depend in a com-
plicated way on posture, activity, and the characteristics of the sound.
Because of the brief durations involved, there is no concrete evidence that startle and orienting
reflexes have a direct bearing upon the general health of humans. Secondarily, however, being
startled might produce an untoward and uncontrollable muscular reaction which can cause injury
in the event an arm is caused to extend into rapidly moving machinery, if a person is involved in
precarious work, or if sharp items or volatile liquids are being handled.
INTERNAL MECHANISMS-VEGETATIVE AND STRESS REACTIONS
The degree to which a stimulus, such as noise, poses a threat to health and well-being of an indi-
vidual depends upon the exposure characteristics involved. If the experience is of very brief duration,
as was the case with the previously mentioned reactions in this section, the transient nature of the
exposure allows the system to return to a normal or preexposure state. If noise stimulation is sus-
tained or consistently repeated, however, it has been observed that specific changes occur in neuro-
sensory, circulatory, endocrine, sensory and digestive systems. These modifications of a body func-
tion may tend to be less transitory.
Noise and The Nature of Stress
As an adjunct to continuous exposure to noise, the keen balances maintained in body physio-
logy can become disrupted. ° This disturbance may be made known at the conscious level as the
feeling of annoyance, irritation and fatigue which will be discussed later in this section. It generally
holds that the disturbing or stressful characteristics of a sound increase with the loudness level of
the sound. There is also a frequency-dependent aspect. Those sounds whose energy is in the fre-
quencies at or above 2000 Hz are usually more distressing than sounds whose spectrum contains
mostly low-frequency energy. Because of a great range in human variability with respect to the
reaction to sound stimulation, these responses are highly unpredictable. There is an element of wide
variation in the same individual from day to day or from moment to moment as well as variability
between individuals.
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Numerous studies have been undertaken to observe the internal reaction experimental animals
undergo when they have been exposed to intense sound for long durations. Some of these studies
are cited and discussed in detail in the text by Welch and Welch. " Some of these results await
verification by further research efforts. Some of the data has not been supported by subsequent
studies. The trend in the literature appears, however, to indicate that there is a potential for some
alteration of body function during and, sometimes, immediately after noise exposure.
It appears that some aspects of noise exposure (noise bursts, startling sounds, etc.) result in a
form of automatic response in that one's attitude about the exposure conditions tends to have little
or no effect upon the internal, bodily reactivity to the noise stimulation. There is, however, a "stress"
component which is related to the degree to which the noise stimulation is aversive.
One further consideration deserves mention here. There is seldom an instance where a single
stressing condition exists. Often, a combination of stressors occur, of which noise may be only one.
In many situations, the stressor may give rise to fear or anger responses yielding an entirely different
combination of body responses. In that case, the stressor itself may be negligible in its effect, while
the reaction to the stressor may be the major stressing agent.
Stress, according to Selye, is largely non-specific. That is, there is not a set of specific reaction
characteristics in the body for each stressing agent. Rather, Selye and his staff in hundreds of experi-
ments have observed that most stressing agents cause an alarm reaction which consists of three mani-
festations:
1. Thymico-lymphatic involution (shrinking of the thymus gland which is located
immediately over the heart).
2. Gastric ulcers, usually located on the duodenum.
3. Adrenal hypertrophy (swelling of the adrenal glands).
It has been shown at 48 hours exposure to 110 dBA broadband noise stimulation evokes these
reactions in experimental animals. ' It was concluded from that experiment that intense noise, in
the sense of Selye's definition, can be classified as a physiologic stressor.
Short and infrequent periods of stress are usually innocuous by virtue of there being an oppor-
tunity for the relevant opposing forces of the body to regain their balance within a brief period after
exposure. Long-term stress is regarded as posing a potential danger to the health of an individual,
this attitude being largely developed from extensive work on experimental animals. A major question
that does not appear to have been resolved is with regard to the point at which a noise becomes a
stressing agent in man, and what amount of exposure is necessary to cause long-lasting or permanent
physiological changes.
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Stress and the Metabolic System
There is little definitive data on the degree to which the preceding observations relate to
stress in humans, since much of the experimental work, necessarily, has been conducted using
animals. Using the umbrella of "stress theory", however, a number of observations can be made.
Selye3^ has described what he calls the General Adaptation Syndrom (GAS) which occurs in
three steps after the onset of the action of a stressing agent:
1. The alarm stage was described earlier as effecting thymus, duodenal and adrenal
condition. This stage is one where there is considerable activity in the body's defensive
mechanisms as the system begins to muster its defenses against the stressor.
2. The stage of resistance is that period where the body combats the influence of the
stressor. If the stressing agent is relatively weak, it will be overcome during this stage.
3. The stage of exhaustion occurs if the stressor is one of sufficient strength or if the
stress takes place over a long enough time to wear out the defenses of the body. In the
event the stressor is a severe one, the end result of the exhaustion stage would be a
breakdown in body function which could end in death.
Selye points out that during the stage of resistance there occurs a decreased resistance to
infection, also perhaps to specific diseases he has called the diseases of adaptation. Among such
diseases are some types of gastro-intestional ulcers, different varieties of blood pressure elevation,
and possible forms of arthritis.
It should be observed that there is not unanimous agreement among medical authorities relative
to the existence of these diseases of adaptation as defined by Selye. There are those who maintain
that each disease has its own specific cause or set of causes.
A wide variety of stressful stimuli activates the pituitary-adrenal system with increased
secretion of ACTH (adrenocorticotropic hormone) and a consequent increase in adreno-cortical
•jry • . '• •
activity. This includes: j
• Trauma.
• Surgery.
• Infection.
• Cold or heat exposure.
• Forced exercise.
• Hemorrhage hypoxia.
• Burns.
• Hypoglycemia (low blood sugar).
• Pain.
• Immobilization.
• Severe psychological trauma.
• Anticipation of physical injury.
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The ACTH secretion is accomplished by a neurohumoral (chemically mediated) mechanism-'-'
between hypothalamic nuclei and the adenohypophysis-'4 (anterior portion of the pituitary gland).
Noise can be considered one of the nonspecific stressors which cause the release of ACTH from the
pituitary.
Like other stressful stimuli.,35 noise causes a biphasic pattern of ACTH release.^ In the rat,
the corticosterone secretion rate doubles after 30 minutes and triples after one hour of exposure to
a 130 dB tone of 220 Hz. The high rate occurring after a one hour exposure is maintained over 8
hours, but after 12 hours the secretion rate decreases to values at or below control levels only to rise
again to the maximal rate after 24 and 48 hours of repeated exposure.
In the rat, noise exposure of 80 dB (SPL) for 18 days alters adrenal function with a decrease in
ascorbic acid content in the adrenal, a reflection of ACTH stimulation. A level as low as 68 dB
(SPL) for only 30 minutes releases ACTH as measured by a decrease in adrenal ascorbic acid content
and by eosinopenia (low numbers of one type of white blood cells), a peripheral glucocorticoid effect.
Dilation of the capillary bed of zona reticularis (one of the layers of the adrenal gland) and medullar
sinusoids (terminal blood channel in the adrenal gland) occurs after 80 dB (SPL). With higher expo-
sures to 102 dB for 4 hours per day for 11 days, these vascular changes worsen and karyopyknosis
(shrinking of a cell nucleus) occurs in the cells of the zona fasciculata^' (another layer in the adrenal
gland). Other pathological changes include an increase in adrenal weight which can be demonstrated
in mice after only 15 minutes daily exposure for 4 weeks to 110 dB sound ranging between 10-20
kHz. Studies in humans are few but a 65 dB sound of 10 kHz has been found to cause a 53 percent
increase in plasma 17-hydroxycorticosteroids.
There is indirect evidence that noise-induced adrenal changes are transient, disappearing with
cessation of the noise. Eosinopenia, a peripheral glucocorticoid effect, occurs only temporarily after
noise, " and the pathological changes in the adrenal cannot be demonstrated one month after
exposure. As noted, the general adaptation syndrome of Selye4' to chronically maintained stress
consists of three stages of response. However, adaptation to stress is not a constant finding. Plasma
corticosterone levels in rats are persistently elevated during the chronic application of multiple
stresses (sound, flashing lights, and cage oscillation). Likewise, there is no evidence that the
hypothalamo-hypophyseal-adrenal axis, (interaction between the hypothalamous, pituitary gland
and adrenal glands) adapts to the stress of chronically maintained noise.
Noise also affects the adrenal medulla (the inner portion of the adrenal gland). An increased
urinary excretion of epinephrine (a product of the adrenal gland) occurs in the rat in response to
high frequency sound (20 kHz) at 100 dB. Increased urinary excretion of epinephrine and nore-
pinephrine after exposure to 90 dB (2000 Hz) for 30 minutes is a constant finding in normal
humans and in patients with essential hypertension '(high blood pressure without known cause) and
in those recovered from mycordial infraction44 (heart attack).
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Variables In Stress Effects
Stress theory, even as presented by its strongest advocates, is admittedly complicated. There
are complex interactions between conditioning factors that lead to disease, non-specific reactions
to stressing agents and general behavioral concomitants which create an immensely complex
pattern. In view of this, the predictability of body response to any given stressor, including noise, is
impossible.
Whether there is any adaptation or accommodation to an ongoing stressful condition caused
by sound is not well established. Several persons have questioned the ability of the body to adapt
to the stressing effect of an on-going stimulus. It can be reasoned that if adaptation were to occur,
however, each new presentation of a noise stimulus would reestablish the stressing condition. There-
fore, it does not seem likely that the highly variable noise stimulation most people receive can be
easily or effectively accommodated.
It is certain that intense sound can serve as a stressor and, at least for some of the more popu-
lar experimental animals, can lead to some physiological changes. Additionally, it is plausible that
some of the more intense sounds in the environment will act as stressors for people. The conditions
under which this might occur are yet unknown. Factors important to consider are:
• The intensity level of the sound stimulus.
• Its characteristics (sudden vs. gradual rising, etc.).
• The amount of fear or misfeasance engendered by the sound.
• The susceptibility of the individual to emotional and physiological reaction.
The concept that stress is universally bad and unhealthy is misleading. At certain periods in
life, some stressing agents and stressful situations might be construed as necessary (alerting,
orienting, motivating). Thus, although it is plausible that noise can be detrimental as a stressing
agent, there is insufficient data to indicate unequivocably that noise as a stressor is sufficiently
severe to cause seriously untoward reactions. Most studies of noise-induced stress upon internal
body functions have utilized quite high sound intensities. There is however, some evidence that low
level noises create internal physiological changes.
In Czechoslovakia, a study by Kirkova and Kromorova implied that stress reactions may
well become important at high levels. Medical records of 969 workers in 85-to-l 15-dB areas were
compared with those of 689 workers in 70-dB working environments or less. In addition to a higher
incidence of hearing loss, the noise exposed group were found to have a higher prevalence of peptic
ulcers.
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Circulatory System and Vasoconstriction
The effects of noise in the laboratory on gross parameters of the circulatory system-blood
pressure, pulse rate, EKG-are apparently negligible, at least at intensities up to 100 dB (SPI). ° °
Although there are reports that a higher incidence of circulatory problems exists in noise-exposed
steel workers and machine shop operators, it cannot be said with confidence that noise alone
caused the circulatory problems in these populations. It has been observed that the slight differences
in the men exposed to high levels of sound relative to those less exposed in these European studies
could be due to equally small differences in other working conditions such as poor ventilation, heat
or light, stress from other sources such as anxiety over job security, and especially personnel selec-
tion. ' This critique is supported by data advanced by Satalovef al~>^ in which men with the great-
est hearing loss (and who therefore presumably suffered a greater average noise exposure) had blood
pressure figures no higher than those with the most normal hearing, when age was controlled. To
settle this controversy, a well-controlled study for long periods of time is needed to observe heart
problems in American industrial workers who have been exposed to noise.
Associated with ongoing noise exposure, some have found evidence of constriction of blood
vessels which is primarily manifest in the peripheral regions of the body such as fingers, toes, and
earlobes. ^~->" The effect has been noted to be proportional to the number of decibels by which
the overall SPL exceeds 70 dB, up to 110 dB at least, reaching values that represent changes of as
much as 40 percent from resting values. Some observe that vasoconstriction does not completely
adapt with time, either on a short-term or long-term basis, and the effects often persist for consider-
able time after cessation of the noise. Jansen^^ has suggested that vasoconstriction, with its con-
comitant effect on the circulatory system in general, will eventually lead to heart trouble. For this
statement to be verified, however, there must be considerably more confirmative information as to
the lasting (irreversible) effects of noise stimulation upon the cardiovascular system.
As an adjunct to the stress reaction creating a condition of generalized vasoconstriction, obser-
vations have been made wherein capillary loops in the cochlea are constricted. This is hypothesized
as being another means whereby cochlea damage occurs. Rather than intense sound pressure physi-
cally destroying cochlear tissues, these reports indicate a damage mechanism resulting from insuffi-
cient oxygen and other nutrients. In brief, the blood supply for the cochlear cells becomes inadequate
during intense sound stimulation. '""^
Pupillary Dilation
According to Jansen, noise affects the sympathetic part of what he calls the vegetative
nervous system. It is in this realm that he has reported on a number of occasions that eye pupil
dilation occurs as one of myriad body reactions to noise exposure. As is the case with cardio-
vascular effects, the effect is proportional to the intensity of the stimulus in excess of 70 dB SPL,
and grows at least to the 110 dB stimulus level. Adaptation over time does not occur.
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A neurological basis for pupillary dilation is provided through the complex nerve network for
the balance sense. This network, called in part the medial longitudinal fasciculus, sends nervous
impulses from the balance mechanism to the cranial nerve which controls pupillary action (CN III-
the Oculomotor Nerve). In this context, the pupillary activity caused by high levels of noise may,
in fact, be a result of stimulation not of the cochlea but of the vestibular portion of the inner ear
which operates the sense of balance.
The significance of this particular physiological reaction is not well understood. It is cited here
in the event that future study suggests that a definable and important function in noise reaction is
served by pupillary dilation.
Essentially, the reaction to high levels of noise can lead to a condition where the counter
relevant forces within the body compete for control, altering the emotions, the general health and
stability of human organisms. It remains to be proven whether this condition is as deleterious to
health as some have suggested, but there is virtually no support for any notion that this type of
exposure is good for one. At least, the results of the noise exposure may not culminate in a definable
illness, but there is need to discover whether this exposure adds its stressing effects to the body withr
out a person becoming consciously aware that he is being stressed.
It is not difficult to project some of the information contained in this section into a "dooms-
day" prediction. Yet it must be pointed out that the bulk of research on this topic has been con-
ducted with very small nonhuman subjects (rats, guinea pigs, chinchillas). Therefore, the projections
to human reactivity cannot be easily made. The most appropriate interpretation of the data is to
realize that inordinately great exposure to noise has a potentially deleterious effect upon vital
physiological processes and must be avoided if one is to remain free of the types of disturbances
such exposure might cause.
Some would state the interpretation even more cautiously, for they hold that the weight of
even the nonhuman evidence must be further established. Long-term studies are needed which will
ultimately determine whether the alleged devastating side effects of excessive noise exposure are
real. To date, the evidence on either side of the argument is incomplete. Man has never before been
forced to endure an acoustic environment composed of such frequent and high level sounds as in
this age; therefore, his responses to such sound conditions are not fully predictable.
A most important area of investigation is to attempt ways to learn if there is such a thing as a
"threshold" of irreversable physiological damage. As stress occurs, does the body return fully to the
previous state within a reasonable period after the stressing condition? How many recurrences of
noise stress are necessary to bring about some irreversable stress reaction which might lead to any
of several disorder conditions? Answers to these and similar questions must be found prior to our
full understanding of noise as a stressor.
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EFFECTS OF NOISE ON SLEEP
There exists evidence that noise may interfere with sleep. At high noise levels, noise may arouse
a person from sleep, and/or prevent the person from falling asleep. At sub-arousal levels, noise may
shift a person's sleep from a deep, dreamless stage to a lighter stage of sleep. However, much of what
we know about sleep comes from experiments in the laboratory on a few people. Caution must
therefore, be exercized in making generalizations about the general population. During a normal
night as a person relaxes and enters a stage of drowsiness, the EEC pattern shows a transition from
rapid, irregular waves to a regular pattern, known as the alpha rhythm. At this stage, the person is
"asleep." As time progresses, the pattern disappears altogether and is replaced by low-voltage, fast
irregular waves, known as the beta stage of sleep. During this stage, rapid eye movements can be
observed. It is usually considered that during this stage of sleep dreaming occurs.
As time progresses further, the EEC pattern shows quick bursts of longer amplitude, low fre-
quency waves, known as delta waves. Later on, the spindles disappear and are replaced by delta
waves of greater magnitude and lower frequency. The two last stages of sleep, spindles and delta
waves, are known as the deep stages of sleep. 3-65^ -p^g various stages of sleep described above
are referred to as 1,2,3 and 4 stages of sleep with the exception of the second stage which is
normally called REM (rapid eye movement stage).
Normally, a person will go through the progression described above with occasional reversals.
The amount of time spent between deep sleep and lighter stages of sleep is somewhat dependent
upon age; however, it is usually considered that all stages of sleep are necessary for good physiologi-
cal and psychological health.
The effects of acoustic stimulation on sleep depend upon several factors:
1. The nature of the stimulus.
2. The stage of sleep the person is in.
3. Instructions to the subject and his psychophysiological and motivational state.
4. Individual differences, e.g. sex, age, physical condition and psychopathology.
For the purpose of this document we will review the relationship between noise and sleep in
terms of each of the factors listed above.
NATURE OF STIMULUS
The likelihood of noise interference with sleep is greatly dependent upon the noise level.
Studies have indicated that the effect of noise on sleep becomes increasingly apparent as ambient
noise levels exceed about 35 dBA. ' Thiessen found that the probability of subjects being awakened
by a peak sound level of 40 dBA was 5 percent, increasing to 30 percent at 70 dBA. Including con-
sideration of EEC changes, the probability increases to 10 percent for 40 dBA and 60 percent for
70 dBA.°° Karagodina ct a/.,69 observed that subjects who slept well (based on psychomotor
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activity data) at 35 dBA, complained about sleep disturbance and had difficulty in falling asleep at
40 dBA, and at 50 dBA. These subjects took over an hour to fall asleep initially, with awakening
occurring often during the sleep period. These data formed part of the basis for Karagodina's et al
suggestion of 30-35 dBA as the maximum allowable noise limits for noise inside apartments, with
the 30 dBA level applicable to nighttime, when sensitivity to noise is increased.
Grandjean'" proposed that noise should not exceed 35 phons during the night in order to
preserve the beneficial restorative processes of sleep, although individual differences in tolerance to
noise were found to range from 30 to 70 phons. Beland et a/."' also suggest a maximum allowable
steady-state noise level of 35 dBA for sleeping, based on studies of community reaction to aircraft
noises.
There seems to be some agreement that moderate noise levels (70-80 dBA, even as low as 48-62
dBA) result in EEC changes in human sleep patterns, manifested especially by an initial depression or
interruption of alpha rhythm.71 Thiessen found that for sound stimuli at 70 dBA, the most likely
reaction was to awaken, followed by shifts in sleep stages.^ At 50 dBA there was 50 percent chance
that no reaction would occur, with the remaining 50 percent about equally divided between the
following four levels of responses:
1. Slight change in EEC pattern lasting a few seconds and detectable only on the recording
chart.
2. Pattern change lasting up to one minute and usually only detectable on the chart.
3. Sleep level change easily observed by analysis of the magnetic tape record.
4. Awakening.
With 40-45 dBA sound levels there was still a greater than '10 percent probability that a response
would result. This response was either a change in sleep stage or awakening.
It is usually reported that subjects who have been deprived of sleep require more intense
auditory stimuli in order to awaken than do normally rested persons. In addition, if the number
of sound peaks increases, the subject will take longer to fall asleep even if the average sound level
decreases.
It has also been reported that brief acoustic stimuli of low frequencies (100 Hz) and fast rise
time (1 msec) are most effective in eliciting EEG-K-complex in stage 2 of sleep. These findings
have been confirmed by Williams.
Berry and Thiessen compared the effects of impulsive tone bursts with simulated sonic booms
and truck noise (with a maximum intensity of 70 dBA). They observed that frequency of awaken-
ing is lower for impulsive noise. Peak level for impulsive noise has apparently no significant effect on
the response, although increases in level for truck noise and subsonic jet flyover do increase the
frequency of awakenings and shifts in sleep stages.
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Mery et al. used artificial crescendos of white noise, aircraft flyovers, and traffic noise as
stimuli in a number of experiments. They found that everything else being equal, low density traffic
noise are more sleep-disruptive than high density noises.
Other researchers have observed that weak stimuli that are either unexpected or novel may have
an effect on sleep. '~'° Furthermore Williams (1973) reports studies by Buendia et al, 1966 and
Schect et al, 1968 which suggest that differentiated responses acquired during waking to specific
acoustic stimuli persist during sleep in both animals and humans.
The rate or presentation of stimuli has also been found to have a significant effect on sleep. *
Schieber et al found that low density traffic sounds (61 dB) are more disruptive of sleep than high
density traffic, thus confirming the results of Mery et al.
STAGES OF SLEEP
It is found that the effect of noise on sleep is very much dependent upon the stage of sleep.
Results of some studies suggest that thresholds for awakening appear to be lower in sleep stage REM
for both ordinary noise and sonic booms. ' Evans et al. (1966) were able to elicit relatively complex
motor responses to verbal instructions in REM stage of sleep.
Auditory stimuli presented during stages 3 and 4 generally do not result in complete awaken-
ing, but in more than 30 percent of the cases, produce shifts to stage 2.
The amount of accumulated sleep time also affects the probability of awakening, with arousal
more likely to occur after longer periods of sleep, no matter what the stage of sleep. °,73,79
MOTIVATION OF SUBJECT
Motivation or familarity of the subject with the noise source may be a factor in the degree of
arousal during sleep. •* The ability of sleepers to discriminate among stimuli of various sorts has
been observed especially if the discrimination was learned when the subject was awake. '3-84
In general it is found that effects of motivation on sleep disturbance are somewhat dependent
upon the stage of sleep. These results are confirmed by Zung and Wilson who demonstrated that
instructions and financial incentives produce an increase in frequency of stage shifts and awaking
following presentations of moderate sound stimuli.
Instructions given to subjects before sleep may influence the effects of noise on sleep. Re-
searchers at the FAA Civil Aeromedical Institute in Oklahoma City employed simulated booms
which they did not label as sonic booms to investigate the effects of booms on sleep behavior,
moods and performance. They instructed their subjects "to ignore disturbances and attempt to get
the best night's sleep possible." They found that the number of responses to booms were smaller
than those expected on the basis of the data presented by Lukas and Kryter.""
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DIFFERENCES OF AGE
A number of studies have indicated that children and young persons are less affected by noise
in all stages of sleep than middleaged and older persons. There is no evidence that children
are especially sensitive to sleep disturbance by noise. However, since general sleep disturbance,
in the form of nightmares, enuresis, etc., occurs commonly in children aged 4-6 years, it is possible
that noise may have some effect on this age group, especially since this age group appears to be
particularly disturbed by sudden arousal from sleep stage 4.
Although the sleep of very young children is less disturbed by noise than that of adults or the
elderly it has been claimed that babies who have had gestational difficulties or have been brain
injured are particularly sensitive to noise. •*
DIFFERENCES OF SEX
It has been claimed that women are more sensitive to noise during sleep than men. 4,89,94
Lukas and Dobb (1972) found that middle aged women are particularly sensitive to subsonic jet
aircraft flyovers and simulated sonic booms.
Adaption to Noise
The question of whether or not adaptation to noise during sleep takes place is the subject of
considerable debate. Adaptation in this context means whether or not repeated exposure to sound
stimuli during sleep will result in progressively less interference with normal sleep. Lukas and Dobbs
have indicated that some adaptation does take place in studies of sonic booms during stage 2 of
sleep.°5 Bartus has argued on the other hand that adaptation does not occur." Some tests per-
formed by the National Research Council of Canada indicate that awakening response does seem
to lessen with time, but there is not adaptation of the average response.
Ando et al. found, in a study of women who had moved to Itami City, near Osaka Airport in
Japan, during pregnancy, that it was possible that some sort of adaptation occurred in the fetus.
48 percent of the women who had moved to the area in the first 5 months of pregnancy said that
their infants slept soundly on exposure to air craft noise after birth. This was true for less than
15 percent of the infants whose mothers had moved in the latter 5 months of pregnancy.
Conclusions
The discussion above indicates that sleeping in noisy surroundings does produce some effects
on sleep either in the form of awakening, if the noise is loud enough, or in the form of shifts in the
stages of sleep. Usually, however, much of our data comes from laboratory experiments that involve
few people, and "responses" are evaluated in terms of physiological measurements such as EEC.
Caution must therefore be exercised in drawing conclusions regarding the effect of noise on the
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sleep of the general population. Even greater caution must be exercised in making references about
the longrange effect of sleep disturbance since there exist very little experimental data regarding
these longterm effects. We know, however, that sleep may be interfered with by noise and that some
groups (such as the old and middle age and the sick) are particularly sensitive to these effects. Since
sleep is thought to be a restorative process during which the organs of the body renew their supply of
energy and nutritive elements, noise could be a health hazard.
Further, we also know that survey data indicate that sleep disturbance is often the principal
reason given for noise annoyance. ° Since it lowers the quality of life, interference with sleep by
noise constitutes a health hazard within the frame of reference of the World Health Organization
definition of Health.
THE EFFECT OF NOISE ON GENERAL HEALTH AND MENTAL HEALTH
Personal health includes a wide variety of conditions and mental states (see definition of health
in Section 1). The complexity of the human body is great, and coupled with the complexity of
human mental function, it is extremely difficult to quantify "health effects" in the wake of stimula-
tion by noise. Individual variations from day to day in susceptibility to physical and mental health
conditions add a further complicating factor.
It has been said that one person's noise is another's music. Mental set, orientation, personality,
general health, and a myriad of other personal factors confound the attempt to fully and compre-
hensively recognize all of the ramifications of the effect of noise on general health and mental
health. In all, there is relatively little known about the effects of noise upon general health and men-
tal health."
Fatigue
Fatigue, in the sense of subjectively described weariness or nervous exhaustion, is so highly
individualized that a clear understanding of it is difficult to ascertain. Fatigue, in the medical and
physiological sense, is indicated by the occurrence of increased pulse frequency, decrease in pulse
pressure, a rise in pulmonary ventilation and slight augmentation of oxygen consumption.' ®® In
addition, fatigue is described as resulting from the exhaustion of metabolic reserves that leads to
a measurable change in the cardiovascular and respiratory systems. Further, blood glucose levels
decline and serum cholesterol levels increase. Fatigue does not ordinarily impair the ability to com-
plete tasks, rather, it lowers the motivation to perform.1^ (See the discussion on Effects of Noise
on Performance-Section 8).
The extent to which noise exposure contributes to fatigue is difficult to assess. In using
extremely intense levels of infrasound, aerospace researchers1^1 have induced symptoms of
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extreme fatigue in their subjects.' " However, the exposure conditions for those subjects were
highly atypical.
A study was conducted by the U. S. Public Health Service in 1941, to determine the relation-
ship between fatigue and driving conditions among interstate truck drivers. ^ The results of
various psychological and physiological tests demonstrated that, with increasing hours of driving,
there was a gradual and progressive diminution in certain bodily functions. The most consistent
changes were found in certain dexterity test results and manual steadiness. Physiologic changes
recorded after driving for prolonged periods of time included:
• Heart rate.
• Blood pressure.
• White blood cell counts.
Interestingly, the medical findings of fatigue and the drivers' independent judgement of appar-
ent fatigue correlated quite highly. In that study, no attempt was made to relate any of the observa-
tions to noise exposure.
In a more recent study reported by Aston and Janway, truck drivers were subjected to
truck vibration. The results of their investigation led Aston and Janway to conclude that vehicle
vibration is not intense enough to cause the severe conditions created in laboratory studies of
vibration effects on the body. However, they did offer the suggestion that chronic exposure to
vibration, especially of very low frequencies (5-7 Hz), could provide sufficient cumulative insult
that, coupled with other infective or pulmonary disorders, long-term pulmonary debilitation might
occur. (See also Section 10).
General Health Effects
Noise is considered to be a contributor to adverse health influences as well. Numerous condi-
tions have been attributed to noise exposure, such as:
• Nausea.
• Headaches.
• Irritability.
• Instability.
• Argumentativeness.
• Reduction in sexual drive.
• Anxiety.
• Nervousness.
• Insomnia (and its opposite, abnormal somnolence).
• Loss of appetite.
• Other ailments.
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These complaints are difficult to assess, not only because of their essentially subjective nature, but
also because intense noises are often associated with working conditions that, even without noise,
involve stress (including fear) which could account for many of the symptoms with or without the
influence of noise. For example, Jansen's study ^ on workers in high-intensity noise gave evidence
of higher circulatory problems. Higher incidence of fatigue and irritability leading to social conflicts
was also found. By contrast, Felton and Spencer, ^ in a comparison of 50 jet engine testers with
55 control subjects, concluded that noise had nothing to do with morale on the job.
1 07
There are some interesting, but difficult to explain, statistics reported by Carosi and Calabro.
In a comparison of 330 families in Naples in which either the husband or wife worked in noisy indus-
try (metalwork or industrial weaving) with a control group of 200 non-noise-exposed families
matched for age, they found that while 69 percent of the non-noise-exposed families had two or
more children, only 24 percent of the noise-exposed families had that many children. If these data
were taken at face value, one might conclude that high-level industrial noise exposure reduces human
reproductivity or the drive for sexual activity (or both). However, conclusions are premature.
A few attempts have been made to evaluate the health-related aspects of noise stimulation in
1 AQ
special environments. For example, Brewer and Briess u suggested that non-auditory effects of
noise exposure in industry included the development of coughs, hoarseness, lesions, and pains in the
throat caused by the strain of shouting above the noise. In another industrial population, Buyniski
reported that deaf industrial workers made more trips to the dispensary than did their normal-' '^
hearing counterparts. Unfortunately, Buyniski did not define the "deafness" of his subjects.
Some have considered noise in a hospital environment to be detrimental to the recovery process
of patients. "0-112 However, this concern has not been verified by data at the present time.
Goshen 3 has described as erroneous the conception that because ill health produces discomfort,
discomfort can produce ill health. He continued by making the point that sound stimulation, such
as that frequently encountered in the hospital environment, might be just as vital in augmenting the
recovery of patients as some feel it might be in hampering recovery. Kryter™ contended that help-
ful adaptation to noise would occur very rapidly in an organism which, for some physiological or
psychological reason of health, should not be aroused.
Sleep disturbance, the subject of another portion of this chapter, should be mentioned as
another possible contributor to the effects of noise on general health. Several authors' 14-117
have stated that sleep interruption or sleep modification due to noise exposure is one of the most
harmful conditions noise poses for an individual's health.
Mental Health Effects
One of the most serious charges against noise in the environment has been issued by those
who state that noise can adversely affect mental health. A widely-cited report by Abey-Wickrama
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et a/11** stated that aircraft noise contributes to mental illness. In the study, 488 admissions to a
psychiatric hospital were divided into two groups. One group consisted of persons who resided in
what the researchers classified as a "maximum noise area" (MNA) near London's Heathrow Airport.
The other group were residents of the same borough, but they lived outside the MNA. According to
rough estimates of the total population represented by the groups, the MNA contained approxi-
mately half the number of residents found in the non-MNA. The two groups of psychiatric admis-
sions were equal in number, leading the observers to surmise that the prevalence of mental problems
in the MNA was twice that of the non-MNA. Criticisms of technique, control, and inference by the
scientific community have been sufficiently great that Herridge' ^ has indicated that a much more
tightly controlled survey is currently underway in the same region of London.
One cannot rule out the possibility that noise exposure not only can eventually produce hearing
loss, but also may pose some other health hazard if no attempt is made to reduce individual exposure
to noise. Caution must be exercised in interpreting the results of studies in this realm, however, for
controls are exceptionally difficult to exercise and quantification of the data is far from easy.
SUMMARY-EFFECTS OF NOISE ON AUTONOMIC NERVOUS SYSTEM FUNCTIONS AND
OTHER SYSTEMS
Noise can elicit many different physiological responses. However, no clear evidence exists indi-
cating that the continued activation of these responses leads to irreversible changes and permanent
health effects. Sound of sufficient intensity can cause pain to the auditory systems. Except for
those persons with poorly designed hearing aids, such intense exposures should not normally be
encountered in the non-occupational environment. Noise can also effect the equilibrium of man,
but the scarce data available indicates that the intensities required must be quite high or similar to
the intensities that produce pain.
Noise-induced orienting reflexes serve to locate the source of a sudden sound and, in combina-
tion with the startle reflex, prepare the individual to take appropriate action in the event danger is
present. Apart from possibly increasing the chance of an accident in some situations, there are no
clear indications that the effects are harmful since these effects are of short duration and do not
cause long time body changes.
Noise can interfere with sleep; however, the problem of relating noise exposure level to
quality of sleep is difficult. Even noise of a very moderate level can change the patterns of sleep,
but the determination of the significance of these changes is still an open question.
Noise exposure may cause fatigue, irritability, or insomnia in some individuals, but the quan-
titative evidence in this regard is unclear. No firm relationships between noise and these factors
can be established at this time.
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Noise exposure can be presumed to cause general stress by itself or in conjunction with other
stressors. Neither the relationship between noise exposure and stress nor the threshold noise level
or duration at which stress may appear has been resolved.
Noise exposure to moderate intensities likely to be found in the environment affects the
cardiovascular system in various ways; however, no definite permanent effects on the circulatory
system have been demonstrated. Noise of moderate intensities has been found to cause vasoconstric-
tion of the peripheral areas of the body and pupillary dilation. Although several hypotheses exist,
there is no evidence at this time that these reactions to noisy environments can lead to harmful
consequences over a period of time. Speculations that noise might be a contributory factor to
circulatory difficulties and heart diseases are not yet supported by scientific data.
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REFERENCES
1. Robinson, D.W. and Dadson, R.S., Threshold of Hearing and Equal-loudness Relations for
Pure Tones, and the Loudness Function,/ Acoust. Soc. Amer., 29, 1284-1288, 1957.
2. von Gierke, H.E., Davis, H., Eldredge, D.H. and Hardy, J.D., Aural Pain Produced by Sound,
in BENOX. REPORT: AN EXPLORATORY STUDY OF THE BIOLOGICAL EFFECTS OF
NOISE prepared by Ades, H.W. et al, ONR Project NR 144079, University of Chicago, 1953.
3. Ades, H.W., Graybiel, A., Morill, S., Tolhurst, G., and Niven, J., Non-auditory effects of
High Intensity Sound Stimulation on Deaf Human Subjects, Joint Report No. 5, U. Texas
Southwestern Med. School, Dallas Texas and U.S. Naval School of Aviation Medicine, Pensa-
cola, Fla., 1958.
4. Davis, H. and Silverman, S.R., HEARING AND DEAFNESS, Holt, Rinehart and Winston,
New York, 1970.
5. Fowler, E.P., Marked Deafened Areas in Normal Ears, Arch. Otolarving, 8, 151-155, 1928.
6. 18th Annual Facts and Figures, National Hearing Aid Journal, 6, Nov. 1972.
7. Minnesota Public Interest Research Group, HEARING AIDS AND THE HEARING AID
INDUSTRY IN MINNESOTA, 3036 Univ. Ave. Southeast, Minneapolis, Minn., Nov. 1973.
8. Tullio, P., Sulla Funzione Delle Varie Parti Dell-Orecchio Interne, 1926.
9. Kacker, W.K. and Hinchcliffe, R., Unusual Tullio Phenomena, / Laryng. & Otol, 84, No.
2, 155-166, 1958.
10. Dickson, E.D.D. and Chadwick, D.L., Observations on Disturbances of Equilibrium and
other Symptoms Induced by Jet Engine Noise, /. Laryngol. Otol., 65, 154-165, 1951.
11. Nixon, C.W., Harris, C. and von Gierke, H.E., Rail Test to Evaluate Equilibrium in Low-Level
Wideband Noise, Report AMRL-TR-66-85, U. S. Air Force Aerospace Medical Research
Laboratories, Wright-Patterson Air Force Base, Ohio, 1966.
12. McCabe, B.F. and Lawrence, M., Effects of Intense Sound on Non-Auditory Labyrinth,
Acta Oto-Laryngoi, 49, 147-157, 1958.
13. Lipscomb, David M. and Roettger, Ruby L., Capillary Constriction in Cochlear and Vestibular
Tissues during Intense Noise Stimulation, Laryngoscope, 83, No. 2, 259-263, February, 1973.
14. Dieroff, H.G. and Scholtz, H.J., Zur Frage der Larmbedingten Vestibularisschaden bei
begutachteten Larmarbeitern, Z. Laryngol. Rhirol. Otol., 46. 746-757, 1967.
15. Moline, J., Reflexes Oculaires d'origine Auditive, Rev. Laryng., 1, 385-393, 1916.
7-22
-------
16. Davis, R.C., Motor Responses to Auditory Stimuli above and below Threshold, /. Exp.
Psychol.,40, 107-120.
17. Galambos, Robert, Rosenberg, Philip E. and Glorig, Aram, The Eyeblink Response as a
Test for Hearing, JSHD, 18, 373-378, 1953.
18. Frisina, D. Robert, MODERN DEVELOPMENTS IN AUDIOLOGY, Measurement of Hear-
ing in Children, James Jerger, (ed.), New York: Academic Press, 1963.
19. Gesell, A. and Armatruda, C., DEVELOPMENTAL DIAGNOSIS, New York: Harper
(HOEBER), 1948.
20. Landis, C. and Hunt, W.A., THE STARTLE PATTERN, New York: Farrar and Rinehart,
Inc., 168.
21. Straus H., Landis, C. and Hunt, W.A., Acoustic Motor Reactions Especially the Cochleopal-
pebral Reflex,/Irc/z. Oto. Laryng, 28, 941-945, 1938.
22. Davis, R.C. and Van Liere, D.W., Adaptation of the Muscular Tension Response to Gunfire,
/. Exp. Psychol., 39, 114-117, 1949.
23. Davis, R.C., Motor Effects of Strong Auditory Stimuli, /. Exp. Psychol, 38, 257-275, 1948.
24. Davis, R.C., Response to "Meaningful" and "Meaningless" Sounds, /. Exp. Psychol, 38,
744-756, 1948.
25. Davis, R.C., Buchwald, A.M. and Frankman, R.W., Autonomic and Muscular Responses and
Their Relation to Simple Stimuli, Psychol, Nonographs, 69, No. 405, 1955.
26. Davis, R.C. and Berry, T., Gastronintestinal Reactions to a Response-Contingent Stimulation,
Psychol. Rep., 15, 95-113, 1964.
27. Miller, James, Effects of Noise on People, (NTID 300.7), December 31,1971.
28. Davis, R.C., Buchwald, A.M. and Frankman, R.W., Autonomic and Muscular Responses and
Their Relation to Simple Stimuli, Psychol. Nomographs, 69, No. 405, 1955.
29. Welch, B.L. and Welch A.S., (eds.), PHYSIOLOGICAL EFFECTS OF NOISE, New York:
Plenum Press, 365, 1970.
30. Selye, H., THE STRESS OF LIFE, New York: McGraw-Hill Book Co., 324, 1956.
31. Lipscomb, David M., INDICATORS OF ENVIRONMENTAL NOISE, Indicators of Environ-
mental Noise, William A. Thomas (ed.), New York: Plenum Press, 1972.
32. Sayers G: The adrenal cortex and homeostasis. Physiol Rev 30:241-320, 1950.
33. Harris GW: Neural control of the pituitary gland. Physiol Rev 28:139-179.
34. McCann SM: Effect of hypothalamic lesions on the adrenal cortical response to stress in the
rat. Am J Physiol 175:13-20, 1953.
35. Brodish A, Long CNH: Changes in blood ACTH under various experimental conditions
studied by means or a cross-circulation technique. Endocrinology 59:666-676, 1956.
36. Henkin RI, Knigge KM: Effect of sound on the hypothalamic-pituitary-adrenal axis.
AmJ Physiol 204:710-714, 1963.
7-23
-------
37. Osintseva VP: Noise-induced changes in the adrenals. Gigiena iSanitariya 34:147-151, 1969.
38. Geber WF, Anderson TA, Van Dyne V: Physiologic responses of the albino rat to chronic
noise stress. Arch Environmental Health 12:151-754, 1966.
39. Anthony A, Ackerman E: Effects of noise on the blood eosinophil levels and adrenals of
mice. JAcoustSoc Am 27: \\44-\\49, 1955.
40. Arguelles AE, Ibeas D, Ottone JP, Chekherdemian M: Pituitary-adrenal stimulation by sound
of different frequencies. / Clin Endocrinology 22:846-852, 1962.
41. Selye H: Stress and disease. Science 122:625-631, 1955.
42. Rosecrans JA, Watzman N, Buckley JP: The production of hypertension in male albino rats
subjected to experimental stress. Biochemical Pharmacology 15:1707-1718, 1966.
43. Ogle CW, Lockett M: The urinary changes induced by high pitched sounds (20 kcyc/sec).
J of Endoc 42:253-260.
44. Arguelles AE, Martinez MA, Pucciarelli E, Disisto MV; Endocrine and metabolic effects of
noise in normal, hypertensive and psychotic subjects, in Physiological Effects of Noise,
edited by Welch BL, Welch AS. New York, Plenum Press, 1970, p. 43-55.
45. Jirkova, H. and Krcmarova, B., Studies of the Influence of Noise on the General Health of
Workers in Large Engineering Work, an Attempt at Evaluation (in Polish), Pracooni Lekarstoi,
Prague, 17, No. 4, 147-148, 1965.
46. Etholm B. and Egenberg, K.E., The Influence of Noise on some Circulatory Functions,
Acta Oto-Larynogol., 58, 208-213, 1964.
47. Blazekova, L., Preliminary Results of Investigation of Noise Effect on some Vegetative
Functions, Pracov. Lek., 18, 276-279, 1966.
48. Klein, K. and Grubl, M., Uber Hamodynamische Reaktionen unter Akustischen Reizen,
Hemodynamic Reactions to Acoustic Stimuli, Wien. Klin. Wschr., 81/40, 705-709, 1969,
Exc.Med., 2550, 1970.
49. Jansen, G., Adverse Effects of Noise on Iron and Steel Workers, Stahl. Eisen., 81, 217-220,
1961.
50. Andrinkin, A., Influence of Sound Stimulation on the Development of Hypertension,
(cited in Kryter, 1970), Cor. Et Vasa, 3, 285-293, 1961.
51. Kryter, K., THE EFFECTS OF NOISE ON MAN, New York: Academic Press, 633, 1970.
52. Satalov, N.N., Ostapkovic, V.E. and Ponomareva, N.I., Sostojanie Sluha i Arterial, 'nogo
Davlenija pri Vozdejstvil Intensivnogo Proizvodstvennogo Suma, Hearing and Arterial Blood
Pressure in Persons Exposed to Intense Industrial Noise, Gigiena Truda i Professional'nye
(Moscow), 13, No. 4, 12-15, April, 1969.
53. Lehman, G. and Tamm, J. Changes of Circulatory Dynamics of Resting Men Under the
Effects of Noise, Intern Z. Agnew Physiol, 16, 217-227, 1956.
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54. Jansen, G., Zur Neriosen Belasting durch Laim, Beihefte Zum Zentralblatt fir Arbirts-
medizion und Arbitsschutz, Dr. Dietrich Steinkopff Verlag, Darmstadt, 9, 1967.
55. Jansen, G., Effects of Noise on Physiological State in Noise as a Public Health Hazard,
W. Ward and J. Fricke, (eds.), (ASHA Reports. 4, Amer. Speech Hearing Assoc., Washington,
D.C., 89-98, 1969.
56. Grandjean, E., Physiologische and Psyshologisce Wirkungen des Laerms, Memsch rend Um-
welt, Documenta Geigy, 4, 13-42, 1960.
57. Lawrence, Merle, Effects of Interference with Terminal Blood Supply on Organ of Corti,
Laryngoscope, 76, No. 8, 1318-1337, 1966.
58. Lawrence, Merle, Circulation in the Capillaries of the Basilar Membrane, Laryngoscope, .
80, No. 9, 1364-1375, 1970.
59. Lawrence, Merle, Gonzalez, G. and Hawkins, Joseph E., Jr., Some Physiological Factors in
Noise-Induced Hearing Loss, Am. Indust. Hyg. Assn. J., 28, 1967.
60. Hawkins, J.E., Jr., The Role of Vasoconstriction in Noise-Induced Hearing Loss, Ann. OR.
andL., 80, No. 6, 903-914, February, 1973.
61. Lipscomb, David M. and Roettger, Ruby L., Capillary Constriction in Cochlear and Vestibu-
lar Tissues during Intense Noise Stimulation, Laryngoscope, 83, No. 2, 259-263, February,
1973.
62. Jansen, Gerd, PHYSIOLOGICAL EFFECTS OF NOISE, Relation Between Temporary Thres-
hold Shift and Peripheral Circulatory Effects of Sound, Welch and Welch, (eds.), New York:
Plenum Press, 1970.
63. Dement, W.C. and Klitman, N., Cyclic Variations in EEG During Sleep and their Relation to
Eye Movements, Body Mobility and Dreaming Electroencephal. Clin. Neurophysio 1., 9, p. 673,
1957.
64. Dement, W. Recent Studies on the Biological Role of Rapid Eye Movement Sleep. The Ameri-
can Journal of Psychiatry, 22, p. 404, 1965.
65. Miller, J.D., Effects of Noise on People, U.S. Environmental Protection Agency, NTID 300.7,
1971.
66. Williams, H.L., Effects of Noise on Sleep: a Review, paper presented at the International
Congress on Noise as a Public Health Problem, Dubrovnik, Yugoslavia, 1973.
67. Beland, R.D., Bishop, D.E. and Lafer, S.K., Aircraft Noise Impact-Planning Guidelines for
Local Agencies, South Pasadena, Wiley and Ham, Rept. No. 979-1, HUD contr. No. H-1675,
36-44, 1972.
68. Thiessen, G.J., Effects of Noise from Passing Trucks on Sleep, Rept. Ql presented at 77th
Mtg. Acoustical Society of America, Philadelphia, April, 1969.
69. Karagodina, I.L., Osipov, G.L. and Shishkin, I.A., Effects of Apartment Noise on Sleep, the
Flight Against Noise in Cities, Karagodina, I.L. ed., pg. 38-39 Moscow: 1972.
7-25
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70. Grandjean, E. Biological Effects of Noise, Congr. Kept. II, 4th International Congress of
Acoustics, Copenhagen, August 1962.
71. Andreyeva - Galanina, Y.T., Noise and Noise Disease, Meditsina, 304, Leningrad: 1972.
72. Thiessen, G.V., Effects of Noise during Sleep, in Physiological Effects of Noise, Welch, B.L.
and Walch, A.S. eds., New York: Plenum Press, 1970.
73. Williams, H.L. and Williams, C.L. Noctural EEG profiles and performance, Psychophysiol 3,
164-175, 1966.
74. Vetter, K. and Hor Vath, S.M., Effects of Audiometrie Parameters on K-Complex of Electro-
encephyalogram, Psychiatry and Neurology, 144, 103-109, 1962.
75. Berry, B. and Thiessen, G.J. Effects of Impulsiva Noise on Sleep National Research Council
of Canada, NRC11597, 36, 1970.
76. Mery, J., Muzet, A., and Schieber, J.P., Effects du Bruit d'Avions Sur le Sommeil, in Pro-
ceedings of 7th International Congress of Acoustic, 3, Budapest 509-512, 1971.
77. Oswald, I., Taylor, A.M., and Triesman, M., Discriminative Responses to Stimulation during '
Human Sleep, Brain, 83, 440-553, 1960.
78. Lehmaun, D. and Koukkov, M. Das EEG des Menschon bein Lermen von Nenem and
Bekanntem Material, Anch. Psychiat. Nerveukr., 215, 22-32, 1971.
79. Lukas, V.S. and Kryter, K.D. Awakening Effects of Stimulated Sonic Booms and Subsonic
Aircraft Noise, in Physiological Effects of Noise, Welch, B.L. and Welch, A.S., eds., 283-293
Plenum Press, New York: 1970.
80. Schieber, J.P., Mery, J. and Muzet A., Etide Analytiqueen Laboratoire de 1' Influence du
Bruit Sur le Sommeil, Kept. ofCeutie d' Etudes Biodimatiques du CNRS, Stransbery,
France, 1968.
81. Rice, C.G. Sonic Boom Exposure Effects, / Sound and Vibration, 20, 511-517, 1972.
82. Evans, F.V., Gustafson, L.A., O'Connell, D.N., Orue, M.T. and Shon, R.E., Response During
Sleep with Intervening Waking Amnesia, Science, 152, 666-667, 1966.
83. Bartus, R.T., Hart, F.D. and LeVere, T.E. Bleetioencephalographic and Behavioral Effects
of NoctumaUy-Occuring Jet Sounds, Aerosp.Med., 384-389, 1972.
84. Wilson, W.P. and Zung, W.W.K. Attention, Discrimination and Arousal during Sleep, Anch,
Gen, Psyshiat., 15, 523-528, 1966.
85. Miller, J.D. Effects of Noise on People, U.S. Environmental Protection Agency Document,
NTID 300.7, 1971.
86. Collins, W.E. and lampiateo, P.F. Effects on Sleep of Hourly Presentations of Simulated
Sonic Booms, paper presented at the International Congress on Noise as a Public Health
Problem, Dubrovnik, Yougoslavia, 1973.
87. Dobbs. M.E. Behavioral Responses to Auditory Stimulation during Sleep, /. Sound and
Vibration, 20, 467-476, 1972.
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88. Kramer, M., Roth, T., Trmdar, J. and Cohen, A. Noise Disturbance and Sleep, Final
Report, FAA-No-70-16, p. 175, 1971.
89. Lukas, J.S. Awakening Effects of Simulated Sonic Booms and Aircraft Noise on Men and
Women,/. Sound and Vibration, 20, 457-466, 1972.
90. Lukas, J.S. and Kryter, K.D. Awakening Effects of Simulated Sonic Aircraft Noise on Six
Subjects 7 to 72 years of age. NASA Report No. CR-1599, Washington, D.C., 1970.
91. Nixon, C.W. and Von Gierke, H.E., Human Response to Sonic Boom in the Laboratory and
the Community, NASA, 51, 766-782, 1972.
92. Lukas, J.S. and Kryter, K.D. Disturbance of Human Sleep by Subsonic Jet Aircraft Noise
and Simulated Sonic Booms, NASA Report No. CR-1780, 68, 1971.
93. Murphy, K.P. Differential Diagnosis of Impaired Hearing in Children, Develop. Med. Child.
Neurol., 11, 561, 1969.
94. Steinicke, G. Die Wirkungen von Larm auf den Schlaf des Menschen. Forschvngsberichte
des Wintschaftes-v. Verkehr-Sministenium Nordrhein Weslfalen No. 416, 1957.
95. Lukas, J.S. and Dobbs, M.E. Effects of Aircraft Noise on the Sleep of Women. NASA
Contractor Report CR-2041, 1972.
96. Thiessen, G.J. Noise Interference with Sleep, National Research Council of.Canada, Ottawa,
Canada, 1972.
97. Ando, Y. and Haltori, H. Effects of Intense Noise During Fetal Life upon Postnatal Adapta-
bility, .M&4, 1128-1130, 1970.
98. Alexandra, A. Les Effects du Bruit Seu le Sommeil, Nuisances et Environment August-
September, Paris, France, 1972.
99. Kryter, Karl D. THE EFFECTS OF NOISE ON MAN. New York: Academic Press 1970.
100. Glasser, Otto, MEDICAL PHYSICS, Volume III, Chicago: The Year Book Publishers, Inc.,
1960.
101. Morgan, C.T., Cook, J.S., Chapanis, A., and Lund, M.W. HUMAN ENGINEERING GUIDE
TO EQUIPMENT DESIGN. New York: McGraw-Hill Book Company, Inc. 1963.
102. Mohr, G.C., Cole, J.N., Guild, E. and Von Gierke, H.E., Effects of Low Frequency and In-
frasonic Noise on Man, AMRL-TR-65-69, U.S. Air Force Aerospace Medical Research Lab-
oratories, Wright-Patterson Air Force Base, Ohio 1966.
103. Jones, B.F., Flinn, R.H., and Hammond, E.G. Fatigue and Hours of Service of Interstate
Truck Drivers. U.S. Public Health Bulletin No. 2b5. Government Printing Office, Washing-
ton, D.C. 1941.
104. Aston, Ray and Janeway, R.N., OVER THE ROAD TO PREVENTABLE DISEASE, Total
Body Vibration, compiled by the International Brotherhood of Teamsters, (undated).
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105. Jansen, G., Vegetative Larmwirkungen bei Industriearbeitern, Larmbekampfung, 6, 126-
128, 1962.
106. Felton, J. and Spencer, C., Morale of Workers Exposed to High Levels of Occupational
Noise,ylm. Ind. Hyg. Assoc. J., 22, 136-147, 1961.
107. Carosi, L. and Calabro, F., La Prolificita di Coniugi Operai di Industrie Rumorose (Prolifi-
cacy of Workers in Noisy Industries), Folia Medica, 51, 264-268, 1968.
108. Brewer, D.W. and Briess, F.B. Industrial Noise: laryngeal considerations. N. Y. State J.
Med., 60, 1737-1740 1960.
109. Buyniski, E.F. Noise and Employee Health. Noise Control 4, (6), 45-46, 1958.
110. Bredengerg, V.C. Quiet Please. HospProg. 42, 104-108, 1961.
111. Denzel, H.A. Noise and Health, Science, 43, 992, 1963.
112. Minckley, B.B. A study of noise and its relationship to patient discomfort in the recovery
room. Nurs. Res. 17, 247-250, 1968.
113. Goshen, C.E. Noise, annoyance and progress. Science, 144, 487, 1964.
114. Grandjean, E. Biological effects of noise. Paper presented at Fourth International Congress
on Acoustics, Copenhagen, 1962.
115. Lehmann, G. Sick people and noise. Max-Planck-Institut fur Arbeitsphysiologie, Dortmund,
Germany (undated).
116. Righter, R. Sleep disturbances which we are not aware of caused by traffic noise. EEG Sta-
tion of the Neurological University Clinic, Basel (undated).
117. Jansen, G. and Schulze, J. Beispiele von Scheafstorungen durch gerausche. Klin. Wachr. 3,
132-134, 1964.
118. Abey-Wickrama, I., A'Brook, M.F., Gattoni, F.E.G. and Herridge, C.F., Mental-Hospital
Admissions and Aircraft Noise, Lancet, 297, 1275-1278, December 13, 1968.
119. Herridge, C.F., Observations of the Effect of Aircraft Noise near Heathrow Airport on
Mental Health, International Congress on Noise as a Public Health Problem, Dubrovnik,
May 17, 1973. .
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SECTION 8
EFFECTS OF NOISE ON PERFORMANCE
The effect of noise on the performance of tasks has been studied in the laboratory and in the
actual work situation, with somewhat more emphasis on laboratory research. Comprehensive
reviews of these studies are available. ''''^
It is evident that when a task involves auditory signals, whether speech or nonspeech,
noise at any intensity sufficient to mask or interfere with the perception of these signals will
interfere with the performance of the task. When mental or motor tasks do not involve
auditory signals, the effects of noise on their performance have been difficult to assess.
In many instances, experiments performed to show effects of noise on working efficiency
or productivity have been inconclusive or unreliable. Broadbent, Kryter, and others have
pointed out that there has not always been adequate control of all the numerous physical and
psychological variables that may significantly influence performance. (Much of the preceding
data is from Effects of Noise on People, by James Miller, EPA, NTID 300.7).
Viewed as a whole, the literature on noise and performance shows that sometimes noise
interferes with performance, sometimes it improves it, and usually it causes no significant changes.
A number of general conclusions, however, have emerged:
1. , Steady noises without special meaning do not seem to interfere with human
performance unless the noise level exceeds about 90 dBA and not consistently
even then.'
2
2. Intermittent and impulsive noises are more disruptive than steady-state noises/
Even when the sound levels of irregular bursts are below 90 dBA they may
sometimes interfere with performance of a task.
3. High-frequency components of noise (above about 2000 Hz) usually produce
more interference with performance than low-frequency components of noise.
4. Noise usually does not influence the overall rate of work, but high levels of
noise may increase the variability of the work rate. There may be "noise pauses"
or gaps in response, 'sometimes followed by compensating increases in work rate.
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5. Noise is more likely to reduce the accuracy of work than to reduce the total
quantity of work '» .
6. Complex or demanding tasks are more likely to be adversely influenced by
Q
noise than simple tasks.
Noise and State of Arousal
Noise does, therefore, have an effect on performance in some situations, depending
on the nature of the stimulus, the task involved, and, as some authors have indicated, the
state of the individual affected. In 1955, D.O. Hebb^ proposed that changes in
stimulation not only produce cues for an affected organism, but also activate or arouse
areas of the cerebral cortex which are involved in response to these cues. Physiologically,
this arousal activity originates in the reticular formation, a portion of the central nervous
system, and affects one's psychological state as well as all physiological systems. An
individual's level of arousal has a great deal to do with the performance of a difficult task.
Too little arousal produces inadequate performance, whereas too much arousal interferes
with performance. The optimum is somewhere at the top of an inverted U-shaped curve
where performance efficiency would form the vertical axis and level of arousal would form
the horizontal one. Thus, noise as an arousing stimulus can enhance, fail to affect or
interfere with performance of certain tasks.''
Noise as a Distracting Stimulus
Similarly, noise can act as a distracting stimulus, depending on the meaningfulness
of the stimulus and also the psychophysiological state of the individual. To quote Broadbent
at the Conference on Noise as a Health Problem in Dubrovnik, Yugoslavia, "Human beings
have a limit to the number of features of their surroundings which they can perceive in any
limited period of time; and therefore anything which happens in the environment has to
1 ^ °
compete with other events for our attention." According to Broadbent, the human sensory
system acts as a channel of communication receiving all kinds of information, relevant and
useless alike. In order to screen out useless information, such as noise, there appears to
be a mental "filter". This filter, however, has the following limits:
• It tends to reject or ignore unchanging signals over a period of time, even
though they may be important, as in vigilance tasks.
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• An individual's state of arousal, stress or fatigue can hinder the mental
filter's ability to discriminate.
• The filter can be overridden by irrelevant stimuli which demand attention
because of novelty, intensity or unpredictability.
Thus, distraction can occur if the organism is overloaded with other stimuli, or if it
is in an otherwise unfavorable physiological state, or if the stimulus is unusually demanding of
attention.
Cumulative Effects
1 **?
At the same conference Broadbentlz expanded on his theoretical cause for noise-induced
decrements in performance. He suggested that exposure to noise can produce an actual change
in the state of the individual that is reflected in failures of selective perception. This change is
due to a cumulative effect of noise exposure producing measurable aftereffects in the form of
performance decrements. As supporting evidence Broadbent mentioned the following
studies:
Wilkinson ^measured the combined effects of sleeplessness and exposure to 100 dB
of white noise. He found that relatively short exposures (30 minutes) tended to create a
state of arousal which reduced the negative effect of sleeplessness on performance. These
same levels of noise impaired efficiency if an individual was at an optimal state of arousal.
Significantly, he found that the previously mentioned combination of noise exposure and
sleeplessness had disruptive effects when the task was continued over a prolonged period.
Evidently this is not a new phenomenon, since other researchers have found that continuous
performance in high noise levels (above 90 dBA) may show adverse effects, sometimes after
1/2 hour's exposure. ^> '>'"
Hartley *' studied the effect of previous exposure to noise on a visual perception
task. He exposed one group of subjects to levels of 95 dBC for 20 minutes and another group
to 70 dBC while both were relaxing, reading magazines. Then he exposed bolh groups to
10 minutes of noise at 25 dBC while the test was administered. The group that had been
previously exposed to noise showed significantly greater decrements in performance than those
exposed to the quieter level. Thus, a cumulative effect of noise was clearly evident.
Aftereffects
In addition to the cumulative effects of noise on performance, some researchers have
reported definite aftereffects. Glass and Singer'° recently reported on 24 studies done over
a period of 5 years in which detrimental aftereffects were noticed on such performance
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stimulus to a visual perception task, centrally-located visual signal were more effectively
perceived, whereas peripherally-located signals tended to be ignored. The theory resulting from
these studies is that noise can cause the organism to become selectively perceptive.
Noise Sensitive Tasks
Some tasks have been described in the literature as particularly sensitive to noise. Among
them are tasks of vigilance, information gathering and analytical processes. Vigilance activities
are not repetitive, do not allow for self-pacing, and demand rapid and accurate decisions.
Therefore, they are more adversely affected by distraction than many other activities. Authorities
tend to agree that noise levels above 90 dB Sound Presence Level are more disruptive in these cases
than levels below 90 DB SPL, and that frequencies above 2000 Hz are more disruptive than lower
ones. >24 Interestingly, frequencies above 2000 Hz also make better warning signals since they
elicit a shorter reaction time.
Various experiments have shown the disruptive effects of noise on learning or information
gathering. Wakely points out that noise may interfere by competing for the limited number of
channels available for information input. If the system is already overloaded, an individual
must take more time to evaluate the usefulness of the intruding stimulus or run the risk of making
errors. When tasks are not self-paced, increased errors will result. Jerison^ found that high levels
of noise interfere with short-term memory tasks. Experimenters at the Stanford Research Institute
found that noise from sonic booms at 1.2 psf can interfere with the learning of an eye-hand
coordination skill without impairing the accuracy of the task.
Special Effects
Some particular types of noise give rise to special effects on task performance. Noise of
short or varying duration and impulsive noise tend to produce short residual effects on noise-
97
sensitive tasks. Woodhead^' found that one-second noise bursts can have residual effects on
performance of from 15 to 30 seconds. She also found that sonic booms of .8 to 2.5 psf produce
residual disruptive effects that are thought to be the result of a startle response (as opposed to
the orienting response).
Startle responses from sudden loud noises can conceivably impair safety in such situations
as construction work, window washing, use of dangerous machinery and even automobile
driving. However, field data and reports of accidents show little tangible evidence of this
A "^Q
phenonmenon. Berglund, Rylander and Sorenson/0 found that sonic booms of
approximately .8 to 45 psf that had tangible effects on task performance had no measurable
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tasks as proofreading, difficult graphic puzzles, and competitive response tasks. They concluded
that these aftereffects could be produced by noises of high intensity, and especially by noise
of low predictability and low controllability.
i &
Glass and Singer10 also found that perceived controllability over aversive sound
affected subsequent performance. Experimental subjects were given a switch to pull in order
to provide relief from the noise. Even those who did not pull the switch showed better
performance afterward than the noise exposed subjects who did not have that choice. The
authors hypothesized from the preceding experiments that unpredictability and uncontrollability
lead to a feeling of helplessness and frustration that, in turn, lessens motivation for task
performance.
Positive and Neutral Effects
Just as frustrating circumstances in combination with noise can hinder performance,
positive motivation can enhance it'. Numerous experimenters report that praise, encouragement
and monetary rewards can enhance performance in noise. Broadbent and Little'° report a
situation where workers' efficiency improved even before acoustical material was installed,
presumably because they were pleased that someone was doing something for them.
As previously mentioned, noise does not always degrade performance. It appears
that for the majority of tasks, noise has little if any effect. These are the tracking or controlling
tasks where noise levels are fairly continuous and where average, rather than instantaneous,
levels of performance are sufficient. Many mechanical or repetitive tasks found in factory
work would fall into this category.
In some situations, noise enhances performance. It appears that moderate levels of
noise maintained beneficial arousal levels during monotonous tasks. McGrath ^ found that
various auditory stimuli at 72 dB improved visual vigilance performance. Also, moderate
levels of music or background television have been reported to enhance performance,
especially amoung young people. However, acceptable levels for background stimuli tend to
decrease with the aging process, probably because of the gradually decreasing efficiency of
the central auditory system .
Occasional studies have been reported where noise exposure produces both positive
and negative effects on task performance. Woodhead^' showed that the introduction of noise
during a memory and calculation task adversely affected the calculation portion. However, when
noise was introduced into the calculation phase only, performance was improved. Experiments by
99
Hockey^z showed that sometimes high-priority aspects of a task could be enhanced while
low-priority aspects were diminished by the presence of noise. He found that by adding a noise
8-5
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effects on a tracking test that simulated automobile driving. There is evidence, however, that
very intense noise, (above 120 dB SPL) may affect manual dexterity due to disturbances of
90
vestibular function.
Problems in Evaluation
A very real problem in the evaluation of the effects of noise on performance is the lack of
•j/-\
well-controlled field studies. Cohen-3" has made inroads in this area by reporting on a 5-year
study of medical, attendance, and accident files for approximately 1000 workers in factory situations.
Five hundred of these workers were employed in noise levels of 95 dBA or above and 500 in 80 dBA
or below. The workers located in the higher noise levels showed significantly greater numbers of
job-related accidents, sickness and absenteeism than their counterparts in the quieter jobs.
However, the reader is cautioned against drawing definitive conclusions because, as Cohen pointed
out, the types of jobs in the noisy and quieter areas could not be equated. For example, possibly
the tasks in the noisy areas were inherently more hazardous. More definitive information may be
available as records continue to be examined, since hearing conversation measures have been
initiated, thereby lowering levels of noise exposure. If accident rates, sickness and absenteeism
are diminished it will support the inference that high noise levels were a causative factor.
Cohen ^ points out an important difficulty in generalizing from the laboratory to real-life
situations. He notes that laboratory tasks are novel in nature, thereby causing subjects to be
fairly well motivated. Also, the actual noise exposures are comparatively short. By contrast,
factory and office workers usually work somewhat below their maximum efficiency and respond
to many stimuli besides noise. Thus, there are particular research needs for long-term studies in
real-life situations.
SUMMARY-PERFORMANCE AND WORK EFFICIENCY
Continuous noise levels above 90 dBA appear to have potentially detrimental effects on
human performance, especially on what have been described as noise-sensitive tasks such as
vigilance tasks, information gathering and analytical processes. Effects of noise on more routine
tasks appear to much less important, although cumulative degrading effects have been demonstrated
by researchers. Noise levels of less than 90 dBA can be disruptive, especially if they
have predominantly high frequency components, are intermittent, unexpected, or
controllable. The amount of disruption is highly dependent on:
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• The type of task.
• The state of the human organism.
• The state of morale and motivation.
Noise does not usually influence the overall rate of work, but high levels of noise may
increase the variability of the work rate. There may be "noise pauses" or gaps in response,
sometimes followed by compensating increases in work rate. Noise is more likely to reduce
the accuracy of work than to reduce the total quantity of work. Complex or demanding tasks
are more likely to be adversely effected than are simple tasks. Since laboratory studies
represent idealized situations there is a pressing need for field studies in real-life conditions.
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REFERENCES
1. Broadbent, D.E., Effects of Noise on Behavior, in HANDBOOK OF NOISE CONTROL,
C. M. Harris (Ed.), McGraw-Hill: New York, 1957.
2. Cohen, A., Effects of Noise on Psychological State, in NOISE AS A PUBLIC HEALTH
HAZARD, ASHA REPORTS #4, American Speech and Hearing Association,
Washington, 1969.
3. Kryter, K.D., EFFECTS OF NOISE ON MAN, Chapter 13, Academic Press,
New York: 1970.
4. Guignard, J.C. and King, P.P., Aeromedical Aspects of Vibration and Noise,
A. G. A. R. D.ograph #151, NATO Advisory Group for Aerospace Research and
Development, Neuilly sur Seine, France: 1972.
5. Gulian, E., Psychological Consequences of Exposure to Noise, Facts and Explanations,
paper presented at the International Congress on Noise as a Public Health Problem,
Dubrovnik, Yugoslavia: 1973.
6. Sanders, A. F., The Influence of Noise on Two Discrimination
Tasks, Ergonomics 4,235, 1961.
7. Carpenter, A., Effects of Noise on Performance and Productivity, in CONTROL OF
NOISE, Symposium No. 12, 297-310, H. M. Stationary Office: London, 1962.
8. Fornwalt, N.E., Investigation into the Effect of Intermittent Noise of Constant
Periodicity vs. Random Periodicity on the Performance of an Industrial Task,
Master's thesis, Dept. Industrial Engineering, Texas Tech. Coll., 1965.
9. Boggs, D. H. and Simon, J. R., Differential Effect of Noise on Tasks of Varying
Complexity, /. Applied Psychol, 52, 148-153,1968.
10. Hebb, D. O., Drives and the C. N. S., Psychological Review, 62, 243-254,1955.
11. Wakely, H. C., Noise and Human Behavior, in the Proceedings of the Symposium On
Environmental Noise - Its Human Economic Effects, 27-34, Chicago Hearing Society,
Chicago, 1970.
12. Broadbent, D. E., Factors Increasing and Decreasing the Effects of Noise, paper
presented at the International Congress On Noise As A Public Health Problem,
Dubrovnik, Yugoslavia, 1973.
13. Broadbent, D. E., PERCEPTION AND COMMUNICATION, Pergmon Press:
London, 1958.
14. Wilkinson, R. T., Interaction of Noise with Knowledge of Results and Sleep
Deprivation, /. Experimental Psychology, 66, 332-337,1963.
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15. Wilkinson, R. T., Some Factors Influencing the Effect of Environmental Stressors Upon
Performance, Psychol. Bull, 72, 260-272,1969.
16. Jerison, H. J., and Wing, S., Effects of Noise and Fatigue on a Complex Vigilance Task,
WADC Technical Report 57-14, Wright Air Development Center, Wright Patterson AFB,
Ohio, 1957.
17. Hartley, L. R., Similar and Opposing Effects of Noise on Performance, paper presented
at the International Congress On Noise As A Public Health Problem, Dubrovnik,
Yugoslavia, 1973.
18. Glass, D. C. and Singer, J. E., Behavioral Effects and Aftereffects of Noise, paper
presented at the International Congress On Noise As A Public Health Problem,
Dubrovnik, Yugoslavia, 1973.
19. Broadbent, D. E. and Little, E.A.J., Effects of Noise Reduction in a Work Situation,
Occupational Psychology, 34, 133,1960.
20. McGrath, J. J., Irrelevant Stimulation and Vigilance Performance, in VIGILANCE A
SYMPOSIUM, Bucknier, D. N. and McGrath, J. J. (eds), McGraw-Hill, New York: 1963.
21. Woodhead, M. M., The Effect of Bursts of Noise on an Arithmetic Task, American
Psychology, 77, 627-633,1964.
22. Hockey, G. R. J., Effects of Noise on Human Efficiency and Some Individual
Differences, /. Sound and Vibration, 20, 299-304, 1972.
23. Broadbent, D. E., Noise, Paced Performance and Vigilance Tasks, Brit. J. Psychol., 44,
295-303,1953.
24. Broadbent, D. E., Effects of Noises of High and Low Frequency on Behaviour,
Ergonomics, 1, 21-29,1957.
25. Jerison, H. J., Paced Performances on a Complex Counting Task under Noise and
Fatigue Conditions, Amer. Psychol. 9, 399-400,1954.
26. Lukas, J. S., Peeler, D. J. and Kryter, K. D., Effects of Sonic Booms and Subsonic
Jet Flyover Noise on Skeletal Muscle Tension and a Paced Tracing Task, National
Aeronautics and Space Administration, Contractor Report NASA, CR-1522,
Washington, D. C., 1970.
27. Woodhead, M. M., The Effects of Bursts of Loud Noise on a Continuous Visual
Task, Brit, J. IndustrialMed., 15, 120-125,1958.
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28. Berglund, K. Rylander, R. and Sorensen, S., Experiments on the Effects of Sonic-Boom
Exposure on Humans, J Acoustical Soc. Amer., 51, 790-798,1972.
29. Harris, C. S., The Effects of High Intensity Noise on Human Performance, Technical
'Report AMRL-TR-67-119, USAF Aerospace Medical Research Laboratories,
Wright-Patterson AFB, Ohio, 1968.
30. Cohen, A., Industrial Noise and Medical, Absence, and Accident Record Data on Exposed
Workers, paper presented at the International Congress On Noise As A Public Health
Problem, Dubrovnik, Yugoslavia, 1973.
8-10
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Section 9
INTERACTION OF NOISE AND OTHER CONDITIONS OR INFLUENCES
i The preceding chapters have dealt primarily with noise as a single agent as it effects hearing
or other physiological or psychological functions. They have also considered mainly the effects of
noise on groups or given percentages of the population in what might be considered average condi-
tions. Real life, however, is much more complex than the laboratory, and individuals can be vastly
different from the norm. Predictions based on the assumption of normal conditions could miss the
mark widely when applied to an individual case or to a group of people with unusual characteristics
in common. This chapter will briefly discuss the interactive effects of noise with other agents and
conditions that often characterize real life situations.
MEASUREMENT OF EFFECTS
Determination of how other agents or conditions interact with noise in producing a given effect
requires three separate experiments, in which is measured:
1. The magnitude (N) of the effect produced by the noise alone.
2. The magnitude (A) of the effect produced by the other agent alone.
3. The magnitude (J) of the effect produced by the joint action of the agent plus the
noise.
, The specific types of interaction that can occur from a comparison of these three results include
the following:
1 1. Indifferent: the joint effect (J) does not differ significantly from the single effect of either
noise or another agent (N or A) whichever is the greater.
J * N or J - A
2. Additive: the joint effect (J) is approximately equal to the sum of the effect of noise
(N) and the effect of the other agent (A).
! J = N + A
3. Synergistic: the joint effect (J) is significantly greater than the sum of the other effects
(N+A).
J > N + A
9-1
-------
4. Ameliorative: the joint effect (J) is significantly smaller than the larger effect of either
noise alone (N) or the other agent alone (A).
J < N or J < A
An enormous number of possible physical and chemical stressors, vitamin or mineral deficien-
cies, and illnesses exist, all of which could conceivably have some degree of influence-additive,
synergistic or ameliorative-on the effects of noise. Furthermore, it is possible that a given agent
might have an additive action on one particular effect of noise, a synergistic action on another, and
be indifferent as far as a third was concerned. Unfortunately, research in interactive effects has
been very sparse. Therefore a brief summary of relevant material is all that can be accomplished
at this time.
CHEMICAL AGENTS
Ototoxic Drugs
It is reasonable to expect either an additive or synergistic action from an agent that acts
directly on the same physiological elements as noise. For example, agents that are known to be
damaging to the hearing mechanism (ototoxic) can be assumed to produce at least an additive effect
when combined with noise exposure. Ototoxic drugs-salicylates and quinine, certain diuretics, and
aminiglycosidic antibiotics-are known to produce cochlear cell damage and consequent high-fre-
quency hearing loss similar to that produced by noise. There is evidence that a synergistic effect
does occur, at least in experimental animals. Quante et a/.,' for example, compared cochlear damage
1. From 90-, 100-, and 110-dB pink noise exposure (see Glossary).
2. From 8 days of kanamycin therapy.
3. From their combination.
Neither the exposure at 90 dB nor the kanamycin therapy produced noticeable changes in the
cochlea when administered separately, but animals given the combination showed extensive damage
to the outer hair cells. A similar synergistic effect of kanamycin and noise was also shown by
o ^
Dayal et al. Both studies confirm a similar study by Darrouzet and Sobrinho. A similar result
was reported by Jauhiainen et a/.4 for neomycin. Sato5 has reported previously a synergistic action
of noise and quinine, salicylic acid or dihidromycin. This literature has recently been reviewed in
greater detail by Falk" and by Haider.
To date there is no definitive data on the interactive effects of ototoxic drugs and noise on
humans. There are instances in which a person, during or shortly after a period of medication,
o
definitely suffered a hearing loss when exposed to noise. It is possible that the noise exposure
alone may have been severe enough to produce the same loss in the unmedieated person.
9-2
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However, it does seem reasonable to advise persons being treated with ototoxic drugs to be particu-
larly careful about noise exposures.
Industrial Chemicals
In an extensive review of industrial hearing loss, Lehnhardt" has summarized the action of
various industrial chemicals. Because hearing losses develop in noisy industrial situations in which
such substances as carbon disulphide, nitrobenzol, carbon monoxide, trichlorethylene, lead, mer-
cury, arsenic compounds and others are found, there is a possibility that such agents may act
additively or synergistically with the noise. Not only hearing damage but also other effects such as
cardiovascular problems may be produced.'" However, as Lehnhardt, and later, Haider have
pointed out, there still exists no conclusive evidence that the hearing losses in these situations are
any greater than would be predicted on the basis of noise exposure alone. It is extremely difficult
to match different groups of workers in all respects except the agent in question. In short, then,
evidence that exposure to industrial chemicals aggravates hearing losses or non-auditory effects of
noise is as yet uncertain.
Vibration
Noise and vibration often occur together, particularly in connection with chain saws, pneu-
matic hammers and drills. In this case, the possibility of a reciprocally synergistic effect exists.
Not only might vibration accentuate the hearing loss produced by the noise, but also the noise
could hasten the development of peripheral circulatory problems such as Raynaud's syndrome by
inducing vasoconstriction. This condition is one in which the fingers lose their sensitivity, and
which is common among operators of pneumatic hammers and drills. The possibility of such an
interaction was considered as long as 40 years ago.' *
As stated previously, successfully matching groups of workers who differ only in their exposure
to one agent is difficult. The most recent attempt to study the interaction of noise and vibration
is recounted by Pinter.' ^ Large numbers of tractor drivers and chain saw operators exposed to
both noise and vibration in the forestry industry were matched, in terms of total estimated cumula-
tive noise exposure, with an equally large number of workers in a furniture industry and a textile
mill, respectively. When audiometric results were adjusted for age, the noise plus vibration-exposed
populations showed more noise-induced hearing losses than those exposed only to noise. Pinter
concludes that vibration enhances the effect of noise on hearing.
Cohen has pointed out the advantage of measuring the combined effects of noise and other
agents using ear protective devices with otherwise equally matched groups. This way, there can
be a fairly predictable noise reduction in one group. Although this method has not been used ex-
tensively to date, it would seem to be quite helpful in providing future information on the inter-
active effects of noise and vibration, as well as other agents.
9-3
-------
As for effects on other physiological parameters, vibration is usually much more potent than
noise. Consequently, most recent studies measure the effects of vibration first alone, and then in
combination with noise. A recent study using this technique'^ has yielded negative results-i.e., the
addition of noise to vibration (and incidentally to heat stress) produced no significant difference on
various performance tasks and physiological measures.
HEALTH CONDITIONS
Mineral and Vitamin Deficiencies
Many people in the world probably suffer from a chronic deficiency in certain minerals or
vitamins because of improper diets. Little research has been done, however, on the effect of such
deficiencies on susceptibility to noise. Although there is a wealth of literature on the effects of various
vitamins and minerals on ITS, nearly all such experiments involved massive doses of the substance
in question, given to presumably otherwise-normal animals. There is a possibility that occasional
ameliorative results may in some cases be attributed to an unrecognized deficiency of the substance
in the control group.
Research with vitamin A provides an example. Ruedi' * found that injections of vitamin A pro-
duced a decrease in temporary threshold shift. However, a controlled doubleblind study using univer-
sity students revealed no effect on TTS attributable to the vitamin A, a result later confirmed by
Dieroff'' for noise-induced permanent threshold shifts (NIPTS). A possible explanation of Ruedi's
results is that an excess of vitamin A may, in reality, produce no change in susceptibility, whereas a
deficiency in vitamin A may actually increase susceptibility to TTS.
Similarly, indication of a slight ameliorative action on TTS for such substances as nicotinic
acid, vitamin B ], hydrochloricpapaverin, nylindrin, thioctic acid and chlorpromazine has recently
been reported by Nakamura; for adenosine triphosphate by Faltynek and Vesely, for ephedrine
by Stange and Beickert, 0 for Hydergine by Plester;^! and for destran by Kellerhalse/ al. How-
ever, considerable effort must still be expended before any of these drugs can be proven generally
beneficial.
Illnesses
Whether or not illness affects an individual's susceptibility to various effects of noise is another
instance of a reasonable hypothesis with as yet little empirical confirmation. Of course, any condi-
tion that increases the amount of energy reaching the cochlea, such as Bell's Palsy, which includes
among its symptoms a paralysis of the stapedius muscle, should result in larger TTS's and NIPTS's,
and the general consensus is that it does. ,24
9-4
-------
9 ^
The reverse is also true, at least to a limited extent. Dieroff showed that in persons with
unilateral otosclerosis, which acts much like an earplug in reducing the flow of airborne energy to
the cochlea, the "protected" ear has significantly less sensorineural loss. Dohi^" also showed that
a chronic perforation of the eardrum reduced the noise-induced hearing losses suffered by industrial
workers.
On the other hand, the possibility exists that middle ear diseases which invade the cochlea might
cause sufficient changes in the cochlear chemistry and blood supply to increase susceptibility to
noise-induced hearing loss. This possibility awaits further exploration. It may, however, account for
the fact that when audiometric results of workers are categorized only very broadly, so that all
types of "chronic middle ear" problems are thrown into a single group, protection of the affected
ear is not always demonstrated. ^'
Despite the largely inconclusive outcome of this review of interactive effects, it still appears '
reasonable that both synergistic and ameliorative influences by other agents on the effects of noise
will eventually be identified and quantified. Properly planned and executed experiments on the
interaction of noise with other stressors is greatly needed if defensible criteria for noise exposure in
the presence of such conditions are to be proposed.
SUMMARY-INTERACTION OF NOISE AND OTHER CONDITIONS OR INFLUENCES
Determination of how various agents or conditions interact with noise in producing a given
effect requires three separate experiments measuring the effect produced by the noise alone, the
effect produced by the other agent alone, and the effect produced by the joint action of the agent
and the noise. These results indicate whether the joint effect is indifferent, additive, synergistic, or
ameliorative.
Chemical agents may have a joint effect with noise. Ototoxic drugs that are known to be
damaging to the hearing mechanism can be assumed to produce at least an additive effect on hearing
when combined with noise exposure. There are instances in which individuals using medication
temporarily suffer a hearing loss when exposed to noise, but there is no definitive data on the inter-
active effects of ototoxic drugs and noise on humans. Evidence.linking exposure to noise plus
industrial chemicals with hearing loss is also inconclusive.
The possibility of a reciprocally synergistic effect exists when noise and vibration occur to-
gether. Vibration is usually more potent than noise in effecting physiological parameters. There
appears to be consensus that vibration increases the effect of noise on hearing.
Health conditions may interact with noise to produce a hearing loss. Mineral and vitamin
deficiencies are one example but little research has been done on the effect of such deficiencies on
susceptibility to noise. Another reasonable hypothesis is that illness increases an individual's sus-
ceptibility to the adverse effects of noise. However, as with the other hypotheses, conclusive
evidence is lacking.
9-5
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REFERENCES
1. Quante, M., Stupp, H. and Brun, J.P., Ototoxikosen Unter Larmbelastung, Archiv. fur Klinische
und Experiment die Ohren-, Nasen-, und Kehikopfheilkunde, 196, 233, 1970.
2. Dayal, V.S., Kokshanian, A. and Mitchell, D.P., Combined Effects of Noise and Kanamycin,
Ann. Otol., 80, 897-902, 1971.
3. Darrouzet, J. and Sobrinho, E.D.L., Inner Ear, Kanamycin, and Acoustic Trauma, Experimental
Study, Rev. Bras. Cirurg., 46, 120, 1963.
4. Jauhiainen, T., A. Kohonen and M. Jauhiainen. Combined Effect of Noise and Neomycin on the
Cochlea. A eta Otolaryngol, 73, 387-390, 1972.
5. Sato, T.A. Study on Experimental Acoustic Trauma in Animals Treated with Specific Poisons
for Auditory Organ. /. Oto-rhino-laryng. Soc. Jap. 60, Abstr. 31-32, 1957, ref. ZHNO 60, 231,
1958.
6. Falk, S.A. Combined Effects of Noise and Ototoxic Drugs, Environmental Health Perspectives,
Experimental Issue Number Two, 5-22, Oct. 1972.
7. Haider, M., Influences of Chemical Agents on Hearing Loss, paper presented at the International
Congress on Noise as a Public Health Problem, Dubrovnik, Yugoslavia, 1973.
8. Darrouzet, J., Essais de Protection de 1'Organe de Corti contre 1' Ototoxicite Antibiotiques,
Etude Experimentelle, Acta Otolaryng., 63, 49-64, 1967.
9. Lehnhardt, E., Die Berufsschaden des Ohres, Arch. f. Ohr.- Nas. u. Kehlk.- Heilk., 185, 11-242,
1965.
10. Zenk, H., Die Begutachtung Cochlearer Schaden Infolge Beruflicher Intoxikationen und Infek-
tionen. Arbeitsmed., Socialmed., Arbeitshyg. 2, 358-362, 1967.
11. Temkin, Jakob. Die Schadigung des Ohres durch Larm und Erschutterung. Mschr. Ohrenheilk. u.
Laryngo-Rhinologie 67, 257-299, 450-479, 527-553, 705-736, 823-834, 1933.
12. Pinter, I. Hearing of Forest Workers and Tractor Operators, Interaction of Noise with Vibration,
paper presented at the International Congress on Noise as a Public Health Problem, Dubrovnik,
Yugoslavia, 1973.
13. Cohen, A., Industrial Noise and Medical, Absence and Accident Record Data on Exposed Work-
ers, paper presented at the International Congress on Noise as a Public Health Problem, Dubrov-
nik, Yugoslavia, 1973.
14. Grether, W.F., Harris C.S., Ohlbaum, M., Sampson, P.A. and Guignard, J.C., Further Study of
Combined Heat, Noise and Vibration Stress,/ Aerospace Med. 43, 641-645, 1972.
9-6
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15. Ruedi, L., Wirkungen des Vitamin A im Menschlichen und lierischen Gehbrgang, Schweiz.
Med. Wschr. 84, 1411-1414, 1954.
16. Ward, W.D. and Glorig, A., The Relation between Vitamin A and Temporary Threshold
Shift, Ada Otolaryng. 52, 72-78, 1960.
17. Dieroff, H.G., Der Einfluss des Vitamins A auf die Larmschwerhorigkeit, HNO (Berlin), 10,
323-325, 1962.
18. Nakamura, S., Some of the Basic Problems in Noise Trauma, Jap. J. Otol, 67, 1669-1684,
1964.
19. Faltynek, L., and Vesely, C., Zur Restitution der Mikrophonpotentiale des Meerschweinchens
nach kurzfristiger Larmbelastung, Arch Ohr. Nas. Kehlkopfheilk, 184, 109-114, 1964.
20. Stange, G., and Beickert, P., Adaptation sverhalten des cortischen Organs nach Ephedrin und
Beschallung, Arch. Ohr. Nas. Kehlkopfheilk, 184, 483-495, 1965.
21. Plester, D., Der Einfluss vegetativ wirksamer Pharmaka auf die Adaptation bezw. Horermu-
dung, Archiv, Ohren-Nasen-Kehlkopfhlk, 162, 463-487, 1953.
22. Kellerhals, B., Hippert, F. and Pfaltz, C.R., Treatment of Acute Acoustic Trauma with Low
Molecular Weight Dextran,/Vac/. ORL, 33, 260-264, 1971.
23. Ward, W.D. Studies on the Aural Reflex, II, Reduction of Temporary Threshold Shift from
Intermittent Noise by Reflex Activity; Implications for Damage-Risk Criteria,/ Acoust.
Soc. Am., 34, 234-241, 1962.
24. Mills, J.H. and Lilly, D.J. Temporary Threshold Shifts Produced by Pure Tones and by
Noise in the Absence of an Acoustic Reflex,/. Acoust. Soc. Am. 50, 1556-1558, 1971.
25. Dieroff, H.G., Die Schalleitungsschwerhorigkeit als Larmschutz, Z. Laryngol. Rhinol. Otol,
43, 690-698, 1964.
26. Dohi, K. Influence of Impared Tympanic Membrane on Occupational Deafness, /. Otorhino-
laryng. Soc. Jap. 56: 39, 1953, ref. ZNHO, 5, 319, 1954-1955.
27. Mounier-Kuhn, P., Gaillard, J. Martin, H. and Bonnefoy, J., The Influence of the Earlier
Condition of the Ear on the Development of Deafness due to Noise Trauma (French),
Acta Oto-Rhino-Laryng, Belg, 14/2, 176-185, 1960.
9-7
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Section 10
EFFECTS OF INFRASOUND AND ULTRASOUND
The audio frequency range is generally considered to be 20 to 20,000 Hz. Frequencies below
16 Hz are referred to as infrasonic frequencies. Frequencies above 20,000 Hz are referred to as
ultrasonic frequencies.
INFRASOUND
Infrasound occurs in nature at relatively low intensities. Sources of natural infrasonic frequen-
cies are:
• Earthquakes.
1 9
• Volcanic erruptions. '
• Winds.
• Air turbulence.
• Thunder.
• Large waterfalls.
• Impact of waves on beaches.
There are also manmade sources of infrasonic sound such as:
• Air heating and air conditioning systems.
• All transportation systems including jet aircraft.
• High powered propulsion systems utilized in space flights. >-*'"
Man-made infrasound occurs at higher intensity levels than those found in nature. It is there-
fore conceivable that with the increase in man-made sources, there may exist potential danger to
man's health. Stephens and Bryan have reported complaints of people about infrasound, including
disorientation, nausea and general feelings of discomfort. In short, responses generally resemble
those seen during whole-body vibration, and are mostly of a non-specific nature, resembling reactions
O Q
to mild stress or alarm.°>y
Data obtained in comprehensive experiments by Mohr et al, reveal that exposures to high inten-
sity infrasonics (100 db-160 db) for short duration (two minutes) have adverse effects on man.
Results of these studies are summarized in Figure 10-1.
10-1
-------
TOLERANCE DATA
INFRASOUNO
E;:F OSURE
OBSERVED BEHAVIOR
m
o
K
y 160
CM
O
O
o
b
o
w
CD
•o
140
120
>
LJ
100
O
LJ
Q.
80
PURE TONES
-NARROW
BANDS
OCTAVE BANDS
I 1 I
IO 40 100
FREQUENCY (Hz)
1000
C to 5u Hz
Up to 145 dB
50 {<• 100 Hz
Up t> 154 d B
Discnte
Freqj mcies
IOC H? «" 153 d B
60Hz«t 154dB
73to<" 130dB
Chest Wall Vibration. Gag Sensations.
Respiratory Rhythnr. Changes. Post-
Exposure Fatigue; Voluntary Tolerance
Not Exceeded
Headache. Choking, Coughing. Visual
Blurring and Fatigue; Voluntary
ToleranceLin.it Reached
ToleranceLirr.it Symptoms
Mild Nausea, Giddiness. SubCostal
Discomfort, Cutaneous Flushing
Coughing, Severe Suosternal Pressu.
Choking Respiration, Salivation, Pain
On Swallowing. Giddiness
REPRESENTATIVE LOW FREQUENCY AND
INFRASONIC TEST ENVIRONMENTS
MOHR »t ol
JAMA, 1965
Figure 10-1
-------
Mohr et al's data have been confirmed by Nixon. ^ Whether or not symptoms similar to
those described in Figure 10-1 would occur for prolonged exposure to low intensities of infrasound
still remains an open question. There is, however, a report by Green and Dunn which shows that
there exists a correlation (0.5) between infrasound exposure and disturbance of certain activities,
such as increase in absenteeism in school children and unskilled workers and a higher rate of
automobile accidents during periods of higher infrasonic exposure. * *
A variety of bizarre sensations in the ear have also been reported during exposure to airborne
infrasonic waves. These include fluttering or pulsating sensations.
There is some evidence that intense infrasound (120db Sound Pressure Level or above) can
stimulate the vestibular system, as can low-frequency vibration, leading to disequilibrium if the
stimulation is intense enough; nevertheless, there is no evidence that the hearing organ may be
O Q
affected by exposures to infrasonic waves encountered in real-life situations.0'^ However,
Guignard and Coles (1965) have demonstrated that a very high-frequency mechanical vibration
may produce a small TTS involving the lower audiometric frequencies and from this it may be
inferred that airborne infrasound could possibly also have an effect on hearing.' •*
Various experiments have attempted to shed light on this problem.^ Results are presented
in Table 10-1. The data contained in Table 10-1 reveals that:
1. Only small, if any, TTS can be observed following exposures to moderate and intense
infrasonics.
2. Recovery to pre-exposure hearing levels is rapid when TTS do occur.
The data available suggests that infrasonics do not pose a serious problem to the hearing
mechanism when intensities are below 130 db SPL (which is generally the case); however, where
high intensities are present (above 130 dB SPL) there may exist a serious hazard.
ULTRASOUND
It will be recalled that ultrasonic frequencies are those above 20,000 Hz. Ultrasonics are pro-
duced by a variety of equipment and in industry, such apparatus as:
• High speed drills.'
• Cleaning devices.
• Dicing equipment.
• Emulsification and mixing devices.
Research Problems
Ultrasonic waves became recognized as a potential health problem with the advent of jet
outlines when a number of persons working in the vicinity of jet engines reported symptoms of
10-3
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TABLE 10-1
INVESTIGATOR
EXPOSURE
HEARING RESPONSE
RECOVERY
Tonndorf (17)
Mohr. et al (9)
Jorger, ct al (6)
Nixon (11)
Nixon (II)
Submarine Diesel Room
10 Hz-20 Hz. No Level Given
Discrete Tones; Narrow Band Noise
in 10 Hz-20 Hz Region. 150-154
dB Exposures of About 2 Minutes
Successive 3 Minute Whole Body
Exposures, 7-12 Hz; 119- 144 dB
Pistonphone Coupled to Ear via
Earmuff. 18 Hz at 135 dB. Series
of 6, 5 Minute Exposures Rapid in
Succession
Pistonphone Coupled to Ear via
Earmuff. 14 Hz at 140 dB. Six
Individual Exposures of 5, 10, 15,
20. 25 and 30 Minutes
Depression of Upper Limits of Hear-
ing as Measured by Number of Seconds
a Tuning Fork was Heard - No Conver-
sion to MAP
No Change in Hearing Sensitivity
Reported by Subjects; No TTS
Measured About One Hours Post Ex-
posure .
TTS in 3000 - 6000 Hz Range For I 1
of 19 Subjects (TTS of 10 dB - 22
dB)
Average TTS of 0 - 15 dB After 30
Minute Exposures
Three Experienced Subjects No TTS
in One; Slight TTS in One; 20 - 25
dB TTS in One
Recovery in Few Hours Outside of
Diesel Room
Recovery Within Hours
Recovery Within 30 Minutes
Recovery Within 30 Minutes
According to Nixon and Johnson, 1973
-------
TABLE 10-1 (Continued)
INVESTIGATOR
EXPOSURE
HEARING RESPONSE
RECOVERY
Johnson (7)
Ear Only: Pressure Chamber
Coupled to Ear via Tuned Hose
and Muff
171 dB (1-10 Hz) 26 sec, Is
168dB(7 Hz) 1 min, Is
155 dB (7 Hz) 5 min. 2s
I40dB(4.7,12 Hz)30min, Is
140dB(4.7.12 Hz)5 min, 8s
135 dB (.6. 1.6, 2.9 Hz) 5 min, 1 2s
126dB(.6. 1.6, 2.9 Hz) 16 min, I Is
Whole Body: All Exposures, 2s:
8 min at 8 Hz at SPL's of I 20, I 26,
132, 138
8 min at 1,2,4.6,8,10 Hz at 144 dB
8 min at 12,16,20 Hz at 135 dB to
142 dB
NOTTS
NOTTS
NOTTS
14-17dBTTS
8 dB TTS for 1 Subject
NoTTS
No TTS
NoTTS
NOTTS
NOTTS
Recovery Within 30 Minutes
Recovery Within 30 Minutes
-------
excessive fatigue, nausea, headache and even vomiting. »'* These responses resemble those
found during stress. The problem, however, is difficult to study because of two factors:
1. Ultrasonic waves are highly absorbed by air and, therefore, are of significance only near
a source.
2. Airborne ultrasonics from ordinary sources are often accompanied by broadband noise
and by sub-harmonics, both of which fall into the audible range.'"
For the reasons just stated, it was thought that the effects reported by various personnel
working near jet engines were due to stimulation of the vestibular system by intense acoustic stimu-
lation, and the matter did not receive much attention. ^»'' However, consideration of the subject
was revived in the mid-50's by Crawford. °
Physiological Effects
In man, there have been reports of blood sugar level decrease following exposure to ultra-
sonics , however, there are also reports of increased blood sugar level. There are also reports of
electrolyte balance changes in the tissues of the nervous system. A major problem with these
studies is that neither the sound levels nor the frequencies utilized in these experiments are men-
tioned.
In a study by Batolska, it is cautioned that some of the effects that have been attributed to
exposure to ultrasonic waves are similar to those produced by potential toxic agents that often are
found in working places.
In work by Grigoreva, no significant physiological changes were found in subjects exposed to
sound ranging between 110 dB and 115 dB SPL for 1 hour at 20,000 Hz.23'24 Parrack, on the
other hand, has shown a mild warming of the surface of the body following exposure to 159 dB,
and a loss of equilibrium and dizziness has been shown following exposures to a 20-KHz tone at
levels of 160 to 165dB.25 '.
A number of studies designed to assess the effects of ultrasonics on the hearing mechanism
are reported in a review paper by Action/6 as follows:
"An investigation to determine if the noise from industrial ultrasonic devices caused
auditory effects was described by Acton and Carson (1967). The hearing threshold
levels of 16 subjects (31 ears) were measured in the frequency range 2 to 12 KHz be-
fore and after exposure to the noise over a working day. No significant temporary
threshold shifts were detected (Figure 2). On the assumption that if a noise exposure
is not severe enough to cause a temporary threshold shift, then it cannot produce
permanent damage, it was cniK'tmloil that hearing damage duo to exposure to the noise
from industrial ultrasonic devices is unlikely. A parallel retrospective investigation by
KNIGHT (1968) on a group of 18 young normal subjects using ultrasonic devices showed
10-6
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a median hearing level within 5 dB of that of a matched control group of hospital staff
except, at 4 KHz where the departure was 7 dB. It was concluded that it would have
been difficult to attribute this exposure solely to ultrasonic radiation. In addition, no
abnormal vestibular function test (caloric test) results were found.
"Some temporary threshold shifts have been reported as a result of exposures to ultra-
sound under laboratory conditions (Parrack, 1966, Dobroserdov, 1967, Smith
1967).
"The exposures used by Dobroserdov were at high audible frequencies, and those by
Smith contained high audible frequency noise. The results due to Parrack are interesting
in that he exposed subjects to discrete frequencies mainly in the ultrasonic region, and
measured temporary threshold shifts at sub-harmonics of one half of the fundamental
and occasionally at lower sub-harmonic frequencies as a result of 5 minute exposures
to discrete frequencies in the range 17 to 37 KHz at levels of 148 to 154 dB. Sub-har-
monic distortion products have been reported in the cochlear-microphic potentials of
guinea pigs (Dallos and Linnel, 1966a) and have also been monitored in the sound field
in front of the eardrum using a probe-tube microphone (Dallos and Linnel, 1966b).
They were believed to result from non-liner amplitude distortion of the ear drum, and
they appeared at a magnitude of the same order as that of the fundamental. This ob-
servation may help to explain Parrack's findings."
The discussion above reveals that exposure to high levels of ultrasound (above 105 dB SPL) may
have some effects on man; however, it is important to recognize that a hazard also arises from ex-
posure to the high levels of components in the audible range that often accompany ultrasonic waves.
At levels below 105 dB SPL there does not appear to be significant danger.
SUMMARY-INFRASOUND AND ULTRASOUND
Frequencies below 16 Hz are referred to as infrasonic frequencies. Sources of infrasonic fre-
quencies include earthquakes, winds, thunder, and jet aircraft. Man-made infrasound occurs at
higher intensity levels than those found in nature. Complaints associated with infrasound resemble mild
stress reactions and bizarre auditory sensations, such as pulsating and fluttering. It does not appear, how-
ever, that exposure to infrasound, at intensities below 130 dB SPL, present a serious health hazard.
Ultrasonic frequencies are those above 20,000 Hz. They are produced by a variety of indus-
trial equipment and jet engines, the effects of exposure to high intensity ultrasound (above 105
dB SPL) also resemble those observed during stress. However, there are experimental difficulties in
assessing the effects of ultrasound. Since:
1. Ultrasonic waves are highly absorbed by air.
2. Ultrasonic waves are often accompanied by broadband noise and by sub-harmonics.
At levels below 105 dB SPL there have been no observed adverse effects.
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REFERENCES
1. Cook, R.K. Radiation of Sound by Earthquakes, 5th International Congress on Acoustics,
Liege, Sept. 1965.
2. Hinde, B.J. and Graunt, D.I., Micnoseims, Contemporary Physics, 8, 267, 1967.
3. Fehr, V., Measurements of Infrasound from Artificial and Natural Sources of Low Frequency
Sound, Proceedings of Fall Meeting of British Acoustical Society, 71-105, Nov. 1971.
4. Stephens, R.W.B., Sources of Low Frequency Sound, Proceedings of Fall Meeting of British
Acoustical Society, 71-105, Nov. 1971.
5. Stephens, R.W.B., Very Low Frequency Vibrations and Their Mechanical and Biological
Effects. Seventh International Congress on Acoustics, 26-G-l, Budapest 1971.
6. Tempest, W. Low Frequency Noise on Road Vehicles. Proceedings of Fall Meeting of British
Acoustical Society, 71-106, Nov. 1971.
7. Stephens, R.W.B. and Bryan, M.E. Annoyance Effects Due to Low Frequency Sound, Pro-
ceedings of Fall Meeting of British Acoustical Society, 71-109, Nov. 1971.
8. Mohr, G.C., Cole, J.N., Guild, E.G. and Von Gierke, M.E., Effects of Low Frequency and In-
frasonic Noise on Man, Aerospace Medicine, 36, 817-824, 1965.
9. Nixon, W. and Johnson, D.L. Infrasound and Hearing, paper presented at the International
Congress on Noise as a Public Health Problem, Dubrovnik, Yugoslavia, 1973.
10. 'Nixon, C.W., Some Effects of Noise on Man. Proceedings of 1971 Intersociety Energy Conver-
sion Engineering Conference, Boston, Mass., August 1971.
11. Green, J.E. and Dunn, F. Correlation of Naturally Occuring Infrasonics and Selected Human
Behavior, JASA, 44, 1456, 1968.
12. Yeowart, N.S., Bryan, M.E., and Tempest, W., The Monaural M.A.P. Threshold of Hearing at
Frequencies from 1.5 to 100 c/s. J. Sound and Vibration, 6, 335-342, 1967.
13. Guignard, J.C. and Coles, R.R.A., Fifth International Congress on Acoustics, Liege, Sept.
1965.
14. Davis, H., Biological and Psychological Effects of Ultrasonics, JASA, 20, 605, 1948.
15. Parrack, H., Ultrasound and Industrial Medicine, Ind. Med. and Surgery, 21, 156, 1952.
16. Acton, W.I., The Effects of Airborne Ultrasound and Near-Ultrasound. Paper presented at the
International Congress on Noise as a Health Problem, Dubrovnik, Yugoslavia, 1973.
17. Davis, H., Parrack, H.D., and Eldredge, D.H., Hazards of Intense Sound and Ultrasound, Annal
of Otology, 58, 732, 1949.
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18. Crawford, A.E., Ultrasonic Engineering, Butterworth, London: 1955.
19. Asbel, F.F., The Effects of Ultrasound and High Frequency Noise on Blood Sugar Level,
Occupational Safety and Health Abstracts, 4, 104, 1966.
20. Byalko, N. Certain Biochemical Abnomalitics in Workers Exposed to High Frequency Noise,
Excerpta. Medico, 17, 570, 1964.
21. Angeluscheff, F.D., Ultrasonics, Resonance and Deafness, Revue de Laryng, d' Otol, et de
Rhinol, July 1957.
22. Batolska, A., Occupational Disorders Due to Ultrasound, Work of the Scientific Research Insti-
tute of Labor Protection and Occupational Diseases, Sofia, 19, 63-69, 1969.
23. Grigoreva, V.M., Ultrasound and the Question of Occupational Hazards, abstracted in Ultra-
sonics, 4,214, 1966.
24. Grigoreva, V.M., Effect of Ultrasonic Vibrations on Personnel Working with Ultrasonic Equip-
ment, Soviet Physics, Acoustics, 11, 426, 1966.
25. Parrack, H.D., Physiological and Psychological Effects of Noise, Proceedings of Second Annual
National Noise Abatement Symposium, Chicago, 111., 1951.
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SECTION 11
EFFECTS OF NOISE ON WILDLIFE AND OTHER ANIMALS
In recent years the effect of noise on wildlife and other animals has become a matter of
serious concern for several reasons. As our American civilization proliferates, we find that areas
previously considered tranquil and remote are now being exposed to various kinds and amounts
of noise. The effects that increased noise levels have on wildlife in these areas are practically
unknown. (Much of the following material can be found in Effects of Noise on Wildlife and
Other Animals, prepared by John Fletcher, et al., EPA NTID 300.5, 1971).
This section will present an overview of the documented and suspected effects of noise on
animals. Laboratory animals will be discussed briefly, insofar as their reaction to noise is of
interest in assessing the effects on wildlife and farm animals. (Of course the primary reason for
studying the effect of noise on laboratory animals has been to throw light on the human reaction).
Noise exposures of farm animals will be discussed briefly with respect to possible changes in
size, weight, reproductivity, and behavior. Effects of noise on wildlife will be dealt with throughout,
although this area is probably the most complex and least documented of the three.
Noise produces the same general categories of effects on animals as it does on humans. For
purposes of this document, these categories will be classified as auditory, masking, behavioral,
and physiological. The actual effects, although they are somewhat more basic, are in many ways
analagous to human life. Reduction of sensitivity in animals may create a particular hardship
for those animals that rely on auditory signals for staking out territory, courtship and mating
behavior, and locating both prey and predators. Masking of signals can also inhibit these
activities in a similar way. Behavioral effects may include panicking and crowding in severe
cases, with aversive reactions being more common. Disruption of breeding and nesting habits
are occasional consequences of noise exposure, along with possible changes in migratory patterns.
Documented physiological changes have been observed almost entirely in laboratory animals. They
consist of the general pattern of response to stress including changes in blood pressure and chemistry,
hormonal changes and changes in reproductivity.
EFFECT ON HEARING
In assessing the effects of noise on the auditory system of animals, it is important to determine
what the particular animal in question can hear. Although the auditory range of most birds and
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reptiles lies within the human range, 2'^ some animals, such as dogs, bats, and rodents, possess
hearing sensitivity which we would consider ultrasonic. Sewell (1970) reported that certain
rodents both emit and respond to frequencies up to 40,000 Hz, and even up to 80,000 Hz in
special cases. Various procedures have been devised to elicit auditory responses from animals.
The Preyer or ear-twitch reflex is a reliable but not very sensitive test of hearing.-' Many laboratory
animals have been conditioned quite well to respond behaviorally to auditory stimuli. Their
cochlear and neural activity in response to sound can be monitored electronically, and also, they
can be sacrificed and examined histologically to observe the condition of the auditory mechanism.
Poche, Stockwell and Ades" found that quinea pigs exposed to impulsive noise averaging 153 dB
Sound Pressure Level, 1 to 5 seconds apart over a 45 minute period showed histological damage
in a narrow band midway along the organ of Corti. Similarily, Majeau-Chargois, Berlin, and
i-i
Whitehouse' studied the effect on guinea pigs of 1000 simulated sonic booms at approximately
130 dB, at the rate of one boom per second. Although the Preyer reflex did not reveal any changes
in hearing sensitivity, histological examination showed considerable loss of sensory cells in the
inner ear.
Benitez, Eldredge, and Templer° studied the effects of narrowband noise on chinchillas. They
found a temporary threshold shift of 48 dB, with eventual behavioral recovery in response to
48 to 72 hours of an octave-band noise centered at 500 Hz at 95 dB SPL. Similarily, Miller,
Rothenberg, and Eldredge9 obtained TTSs of 50 dB during 7 days of exposure to a 300-600 Hz
octave-band at 100 dB SPL. Although behavioral recovery was nearly complete, histological
examination revealed that sensory cells were lost.
In examining the effects of broad-band noise, Miller, Watson, and Covelr ^ exposed cats to
noise of 115 dB for 15 minutes with a resulting permanent threshold shift of 5.6 dB, and then for
8 hours with a resulting permanent threshold of as much as 40.6 dB. The same exposure broken
up into small doses produced considerably less hearing loss.
By exposing guinea pigs to loud music peaking occasionally as high as 122 dB on an irregular
schedule, Lipscomb ' found extensive cochlear cell damage. In a similar series of studies, octave-
band noise of 110 dB for 8-hour exposure periods was found to create widespread damage
throughout the cochlea, regardless of the center-frequency of the noise bands, when guinea pigs
17 1 ^
were used. This condition was slightly less widespread in the case of chinchillas. •*
As expected, the extent of noise-induced hearing loss in animals depends upon the intensity,
spectrum, and duration of the stimulus and on the pattern of exposure and individual susceptibility.
A table of damage-risk contours for various animals would be in order at this point, but to date,
this topic has not been as thoroughly explored for animals as it has for humans.
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MASKING
Masking of auditory signals can interfere with some animals' communication of necessary
information, such as danger, distress, warnings about territorial boundaries, recognition of a mate
or of young, etc.
Much of the research on the effects of masking has been to evaluate the effectiveness of
commercial units which produce jamming or other aversive signals to repel unwanted animals.
Some animals are more resistant to masking than others. Griffin, McCue, and Grinnell14 showed
that bats resist jamming by orienting themselves so that noise and signal are received from different
angles. Potash* •> reported that Japanese quail responded to an increase in ambient noise levels
from 36 to 63 dBA by increasing the frequency of their separation cells, (i.e., the number of
calls in time), thereby improving the signal to noise ratio. However, rabbits, deer, and some species
of birds have been repelled by a commercial jamming signal which produces signals of 2,000
and 4,000 Hz which are amplitude and frequency modulated. ^"
BEHAVIORAL CHANGES
Behavioral changes are perhaps the most observable effects of noise on wild animals. It seems
that many animals learn to differentiate among acoustic stimuli. Deer have been observed grazing
1 7
close to the runway of a busy heliport,1' whereas other deer have been noticeably scarce at the
first crack of a rifle during the hunting season. ° Birds have also been seen to react in an adaptive
way. Starlings have been repelled by tape-recorded starling distress-calls only to reinfest the
area after cessation of the signal. A study by Thompson, Grant, Pearson, and Corner^ showed,
by telemetric monitoring of heart rate, that starlings reacted differently to various aversive and neutral
stimuli, and habituation to the stimuli occurred at various rates. In order to effectively scare
birds, the Committee on the Problem of Noise^ * reported that a noise level of 85 dB SPL at the
bird's ear was required. Since birds seem to adapt quickly, the Committee reported that the
signals should be used sporadically throughout the day.
00
More serious aversive behavior has been observed in some animals. Greaves and Rowez/ found
that wild Norway rats and house mice, when exposed to pulsed ultrasound, displayed aversion to
93
the sonic field and did not re-enter the testing ground after exposure. Cutkomp J reported that
ultrasonic pulses at 65 dB SPL produced aversive behavior in certain species of moths, as well as
reduced longevity. Of greater concern are effects reported by Shaw^ who found that adult
condors were very sensitive to noise and abandoned their nests when disturbed by blasting, sonic
booms, or even traffic noise. As reported by Bell ^ and Henkin^" the most harmful effects
attributed to sonic booms were mass hatching failures of sooty terns in Florida, where 50 years
of breeding success were followed by a 99 percent failure of terns' eggs to hatch in 1969. It is
thought that extremely low-altitude supersonic flights over the area may have driven the birds
off their nests and damaged the uncovered eggs.
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PHYSIOLOGICAL REACTIONS
As stated earlier, the physiological response to noise follows the general pattern of response
to stress, which can be an extremely difficult parameter to measure. Undoubtedly, susceptibility
to different stressors is variable among animals, as are stressful conditions. Wild animals, of
necessity, are more sensitive to a variety of environmental stimuli than most domestic animals^'.
However, an animal raised under conditions that protect it from stress can become extremely
susceptible to disease under even mildly stressful situations. ^ The actual significance of physiological
response to stress for an individual animal is not adequately understood.
It must be noted that most of the physiological effects described are the result of relatively
brief exposures to very high noise levels. These exposures could be considered acute, and the
chances for duplication in real-life situations are fairly slim. Levels cited are sometimes as high
as 160 dB, with most in excess of 100 dB, considerably above what we would normally find
around airfields, industries, highways or other intrusions of people into the natural habitat of
animals. Fletcher et al. * point out the difficulty in generalizing from high level, acute exposures
to the more realistic low level, chronic ones, as well as the difficulty in generalizing from laboratory
animals to wild animals in their natural habitat
Laboratory experiments have shown that exposure to a 120 Hz tone at 100 dB SPL for
intervals of 5 minutes per day for 15 days produced higher adrenal weights and ascorbic acid values
and lower blood glutathione levels in experimental rats as opposed to their controls . Hrubes and
Benes found that white rats repeatedly subjected to 95 dB noise levels developed increased
uremic catecholamines, increased free fatty acid in blood plasma, and increased suprarenal size.
Friedman, Byers and Brown^O exposed rats and rabbits to white noise of 102 dB SPL continuously
for 3 and 10 weeks, respectively, with a randomly interspersed 200 Hz tone at 114 dB SPL.
Although few differences were noted in the rats, the rabbits showed significantly more aortic
atherosclerosis and a higher cholesterol content than their controls, along with deposits of fat
in the irises of the eyes. The authors concluded that auditory stress can produce changes in
the organism's handling of fat.
Although experimental results are not always consistent, auditory stress can also cause changes
in reproductive glands and functions. Anthony and Harclerode^ reported no significant changes
in the sexual behavior of male guinea pigs exposed to 300-48000 Hz band of noise at 139-144 dB
SPL for 20 minutes out of each 30 minute period, daily for 12 weeks. (Of course, the animals
could have been deafened fairly quickly by such intense exposures, thereby preventing changes
which might otherwise have occurred). Experiments by Zondek and Isachar^ found considerably
more effect of auditory stress on female rats and rabbits than in the males. Exposure to a stimulus
of approximately 100 dB at 4000 Hz for one minute out of every 10, continuously for 9 days,
produced enlargement of the ovaries, persistent estrus and follicle hematoma. Exposure to a similar
stress caused a significant reduction in both m;ile and female fertility in white ruts.
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Laboratory studies have also shown that auditory stress can sometimes produce harmful effects
in pregnancy. Ishii and Yokobori^ found that female mice exposed to white noise at the 90, 100,
and 110 phon levels for 5 days during pregnancy produced more malformed, still-born, and smaller
young than did their controls. More serious effects were found by Ward, Barletta and Kaye,^ who
exposed female mice to a 320-580 Hz stimulus at 82-85 dB SPL for 60-75 percent of each hour for
5 hour periods at different stages during pregnancy. Although moderate noise levels were used, 40
percent of the litters were resorbed when exposure occurred during certain periods of pregnancy,
and 100 percent of the Utters were resorbed when exposure occurred during more critical periods.
The authors felt that these effects were due to decreased uterine and placental blood flow, as the
result of stress.
Interesting results have been obtained by Anthony, Ackerman, and Lloyd in their study of
adreno-cortical activation in rats, mice and guinea pigs. The authors found that these animals could
adapt successfully to fairly high levels of noise, but that when audiogenic stress occurred in combi-
nation with another stress, such as restriction of food, the animal's life span could be decreased.
These findings, along with those which show changes in animals' ability to handle fat, could provide
important implications for wildlife, especially during the lean months of late winter.
As mentioned previously, there is little direct information on the physiological response of wild-
life to noise. The study of Thompson, Grant, Pearson and Corner2^ showed changes in the heart
rate of birds by telemetric monitoring, although the long term consequences of this type of stress
are still unknown. Studies of fish exposed to noise are not conclusive. A report of the FAO
Fisheries^" shows that fish respond to the noise of fishing vessels by diving and by changing direc-
tion. The same report states that low frequency noise appears to be more frightening than high
frequency noise. Fish kills resulting from underwater explosions are thought to be due to pressure
waves rather than acoustic stimulation. A number of studies of the effect of sonic boom on fish
egg hatchability failed to show any adverse results.
FARM ANIMALS
Possible effects of noise on farm animals include changes in:
• Milk production
• Egg hatchability
• Mating behavior
• The animal's size and weight
It appears that some animals are more sensitive to meaningful sound stimuli, such as distress
signals. However, the majority of studies of the effects of noise on farm mammals have produced
negligible results. 9,40,41,42 Bond^ did find a mild reaction to noise in dairy and beef cattle;
however, reactions to low subsonic aircraft noise exceeded the reactions to sonic booms. Further-
more, the same reactions were elicited in response to flying paper, strange persons, or other moving
objects.
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The reaction of poultry is a slightly different matter. Although noise seems to have little
effect on the hatchability of eggs or the quality of chicks hatched, it does appear to affect the
hen's inclination to incubate her eggs. Stadelman'" exposed hens to aircraft noise of approximately
120 dB at intervals of 8 dB.
SUMMARY - EFFECTS OF NOISE ON WILDLIFE AND OTHER ANIMALS
Noise produces the same general types of effects on animals as it does on humans, namely:
auditory, masking of communication, behavioral, and physiological.
As previously mentioned, the most observable effects of noise on farm and wild animals seem
to be behavioral. Clearly, noise of sufficient intensity or noise of adversive character can disrupt
normal patterns of animal existence. Exploratory behavior can be curtailed, avoidance behavior
can limit access to food and shelter, and breeding habits can be disrupted. Hearing loss and the
masking of auditory signals, as mentioned before, can further complicate an animal's efforts to recog-
nize its young, detect and locate prey, and evade predators. Competition for food and space in an
"ecological niche" results in complex interrelationships and, hence, a complex balance.
Many laboratory studies have indicated temporary and permanent noise-induced threshold
shifts. However, damage-risk criteria for various species have not yet been developed. Masking of
auditory signals has been demonstrated by commercial jamming signals, which are amplitude and
frequency modulated.
Physiological effects of noise exposure, such as changes in blood pressure and chemistry, hor-
monal balance, and reproductivity, have been demonstrated in laboratory animals and, to some
extent, in farm animals. But these effects are understandably difficult to assess in wildlife. Also,
the amount of physiological and behavioral adaptation that occurs in response to noise stimuli is as
yet unknown.
Considerable research needs to be accomplished before more definitive criteria can be developed.
The basic needs are:
1. More thorough investigations to determine the point at which various species incur hearing
loss.
2. Studies to determine the effects on animals of low-level, chronic noise exposures.
3. Comprehensive studies on the effects of noise on animals in their natural habitats. Such
variables as the extent of aversive reactions, physiological changes, and predator-prey
relationships should be examined.
Until more information exists, judgments of environmental impact must be made on existing
information, however incomplete.
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REFERENCES
1. Memphis State University, Effects of Noise on Wildlife and Other Animals, U.S. Environmental
Protection Agency, Document, NTID 300.5, 1971.
2. Konishi, Masakazu, Comparative Neurophysiological Studies of Hearing and Vocalizations in
Songbirds, Zeitschrift fuer Vergleichende Physiologic, 67, 363-381, 1970.
3. Manley, Geoffrey, Comparative Studies of Auditory Physiology in Reptiles, Zeitschrift fuer
Vergleichende Physiologic, 67, 363-381, 1970.
4. Sewell, G.D., Ultrasonic Signals from Rodents, Ultrasonics, 8, 26-30, 1970.
5. Memphis State University, Effects of Noise on Wildlife and Other Animals, U.S. Environmental
Protection Agency, Document, NTID 300.5, 1971.
6. Poche, L.B., Stockwell, C.W. and Ades, H., Cochlear Hair Cell Damage in Guinea Pigs after
Exposure to Impulse Noise, The Journal of the Acoustical Society of America, 46, 947-951,
1969.
7. Majeau-Chargois, D.A., Berlin, C.I. and Whitehouse, G.D., Sonic Boom Effects on the Organ
of Corti, The Laryngoscope, 80, 620-630, 1970.
8. Benitez, L.D., Eldridge, D.H. and Templer, J.W., Electrophysiological Correlates of Behavioral
Temporary Threshold Shifts in Chinchilla, Paper presented at the 80th meeting of the Acoustical
Society of America, Houston, November 1970.
9. Miller, J.D., Rothenberg, S.J. and Eldredge, D.H., Preliminary Observations on the Effects of
Exposure to Noise for Seven Days on the Hearing and Inner Ear of the Chinchilla, The Journal
of the Acoustical Society of America, 50, 111 9-1203, 1971.
10. Miller, J.D., Watson, C.S. and Covell, W.P., Deafening Effects of Noise on the Cat, Acta Oto-
laryngologica, Suppl., 176, 91, 1963.
11. Lipscomb, D.M., Ear Damage from Exposure to Rock and Roll Music, Arch. Otol, 90,
545-555, 1969,
12. Lipscomb, D.M., Noise Exposure and Its Effects, Scand., Audiol, 1, No. 3, 119-124, September
1972.
13. Lipscomb, D.M., Theoretical Considerations in the Apparent Rise of High Frequency Hearing
Loss in Young Persons, Presented to the International Congress of Noise as a Public Health
Problem, Dubrovnik, Yugoslavia, May 15, 1973.
14. Griffin, D.R., McCue, J.J.G. and Grinnel, A.D., The Resistance of Bats to Jamming, Journal
of Experimental Zoology, 152, 229-250, 1963.
15. Potash, L.M., A Signal Detection Problem and Possible Solution in Japanese Quail, Animal
Behavior, 20, 1972.
16. Crummett, J.G., Acoustic Information Denial as a Means for Vertebrate Pest Control, Paper
presented at the 80th meeting of the Acoustical Society of America, Houston, November 1970.
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17. Fletcher, J., Agricultural and Recreational Use Noise, Statement at U. S. Environmental
Protection Agency Public Hearings on Noise Abatement and Control, Denver, Colorado,
V, 45, 1971.
18. Michener, R., Agricultural and Recreational Use Noise, Statement at U.S. Environmental
Protection Agency Public Hearings on Noise Abatement and Control, Denver, Colorado,
V, 42-46, 1971.
19. Block, B.C., Williamsport, Pennsylvania Tries Starling Control With Distress Calls, Pest
Control, 34, 24-30, 1966.
20. Thompson, R. D., Grant, C. V., Pearson, E. W. and Corner, G. W., Differential Heart Rate
Response of Starlings to Sound Stimuli of Biological Origin, The Journal of Wildlife
Management, 32, 888-893, 1968.
21. Committee on the Problem of Noise, Final Report, Presented to Parliament July, 1963,
London: Her Majesty's Stationery Office, Cmnd. 2056, 19s bd. net.
22. Greaves, J. H. and Rowe, F. P., Responses of Confined Rodent Populations to an Ultra-
sound Generator, Journal of Wildlife Management, 33, 409-417, 1969.
23. Cutkomp, L. K., Effects of Ultrasonic Energy on Storage Insects, Agriculture Department
Cooperative State Research Service, Minnesota, 1969.
24. Shaw, E. W., California Condor, Library of Congress Legislative Reference Service, SK351,
70-127, 1950.
25. Bell, W. B., Animal Response to Sonic Boom, Paper presented at the 80th meeting of the
Acoustical Society of America, Houston, November 1970.
26. Henkin, H., The Death of Birds, Environment, Jl.Sl, 1969.
27. Goetz, B., Agricultural and Recreational Use Noise, Statement at U. S. Environmental
Protection Agency Public Hearings on Noise Abatement and Control, Denver, Colorado,
V, 91-96, 1971.
28. Jurtshuk, P., Weltman, A. S. and Sackler, A. M., Biochemical Responses of Rats to Audi-
tory Stress, Science, 129, 1424-1425, 1959.
29. Hrubes, V. and Benes, V., The Influence of Repeated Noise Stress on Rats, Acta Biologica et
Medico Germanica, 15, 592-596, 1965.
30. Friedman, M., Byers, S. O. and Brown, A. E., Plasma Lipid Responses of Rats and Rabbits
to an Auditory Stimulus, American Journal of Physiology, 212, 1174-1178, 1967.
31. Anthony, A. and Harclerode, J. E., Noise Stress in Laboratory Rodents, II. Effects of
Chronic Noise Exposures on Sexual Performance and Reproductive Function of Guinea
Pigs, Journal of the Acoustical Society of America, 31,1437-1440, 1959.
32. Zoiulck, B. and Isachar, T.. Effect of Audiogenic Stimulation on Genital Function and
Reproduction, A eta Endocrinologka, 45, 227-234, 1964.
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33. Ishii, H. and Yokobori, K., Experimental Studies on Teratogenic Activity of Noise Stimu-
lation, Gunma Journal of Medical Sciences, 9, 153-167, 1960.
34. Ward, C. O., Barletta, M. A. and Kaye, T., Teratogenic Effects of Audiogenic Stress in
Albino Mice, Journal of Pharmaceutical Sciences, 59, 1661-1662, 1970.
35. Anthony, A., Ackerman, E. and Lloyd, J.A., Noise Stress in Laboratory Rodents, I,
Behavioral and Endocrine Response of Mice, Rats, and Guinea Pigs, Journal of the Acous-
ticalSociety of America, 31, 1430-1437, 1959.
36. F A O Fisheries Report No. 76, Report on a Meeting for Consultations on Underwater
Noise, Food and Agriculture Organization of the United Nations, April 1970.
37. Rucker, R. R., Effect of Sonic Boom on Fish, Federal Aviation Administration Systems
Research and Development Service, Report No. FAA-RD-73-29, 1973.
38. Bugard, P., Henry, M., Bernard, C. and Labie, C., Aspects Neuro-Endocriniens et Metaboli-
ques de 1'Agression Souore, Revue de Pathologic Gienerale et de Physiologic Clinique, 60,
1683-1707,1960.
39. Bond, J., Winchester, C. F., Campbell, L. E. and Webb, J. C., Effects of Loud Sounds on
the Physiology and Behavior of Swine, U. S. Department of Agriculture, Agricultural
Research Service Technical Bulletin, No. 1280, 1963.
40. Bond, J., Effects of Noise on the Physiological and Behavior of Farm-raised Animals,
PHYSIOLOGICAL EFFECTS OF NOISE, Welch and Welch, (eds.), New York: Plenum
Press, 295-306, 1970.
41. Parker, J. B. and Bayley, N. D., Investigation on Effects of Aircraft Sound on Milk Pro-
duction of Dairy Cattle, 1957-1958, United States Department of Agriculture, Agriculture
Research Service, Animal Husbandry Research Division, 1960.
42. Casady, R. B. and Lehmann, R. P., Responses of Farm Animals to Sonic Booms, Sonic
Boom Experiments at Edwards Air Force Base, Annex H., U. S. Department of Agriculture,
Agriculture Research Service, Animal Husbandry Research Division, Beltsville, Maryland,
September 20, 1966.
43. Bond, J., Responses of Man and Lower Animals to Acoustical Stimuli, U. S. Department
of Agriculture, Agricultural Research Service, Animal and Poultry Husbandry Research
Branch, Beltsville, Maryland, October 1, 1956.
44. Stadelman, W. J., The Effects of Sounds of Varying Intensity on Hatchability of Chicken
Egg, Poultry Science, 37, 166-169, 1958.
45. Jeannoutot, D. W. and Adams, J. L., Progestergone Versus Treatment by High Intensity
Sound as Methods of Controlling Broodiness in Broad Breasted Bronze Turkeys, Poultry
Science, 40,512-521, 1961.
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Section 12
EFFECT OF NOISE ON STRUCTURES
Airborne noise normally encountered in real life does not normally carry sufficient energy
to cause damage to most structures. The major exceptions to this general statement come from
the sonic boom, which produces sudden and considerable changes in atmospheric pressure and
from low frequency sound produced by large rocket-engine and certain types of construction
equipment. Most of our data on the effects of noise on structures comes from studies of sonic
booms generated by super-sonic aircraft, or from studies of structures located near low frequency
sound sources.
In the preparation of this document, a review has been made of the effects of sonic booms
on structure and the effects of noise induced vibrations.
SONIC BOOMS
Attempts have been made to clarify two issues within the constraints of currently avail-
able literature. These issues are summarized in the following questions:
1. What are the over-pressures produced by sonic booms generated by present
military and commercial aircraft and how does the pressure vary with time?
2. What are the effects of these levels on physical structures?
Nature of Sonic Booms
The passage of an aircraft at speed greater than the local speed of sound in the atmosphere
generates an impulsive noise called a sonic boom. The boom is observable at ground level as a
succession of two sharp bangs, separated by a short time interval. Different parts of an aircraft
radiate strong pressure waves in the air that grow into shocks known as leading shock and trail-
ing shock. These two shocks form cones in the atmosphere that interest the surface of the
earth in hyperbolas. These interactions trace out a path called the "boom carpet." The length
of the boom carpet may be thousands of miles.
Since it is often thought that sonic booms occur only as a supersonic aircraft passes the
speed of sound, it should be emphasized that sonic booms occur at all times that a super sonic
aircraft travels at faster speed than the speed of sound.
At the surface of the earth, the passage of a sonic boom is registered as an abrupt increase
in pressure called the over-pressure, followed by a decrease in pressure below that of atmospheric
pressure, thence a return to ambient or atmospheric pressure.
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The intensity of a sonic boom is determined by the airplane characteristics and atmospheric
conditions. ^ The over-pressure for a supersonic bomber or an SST is typically around 100
9 9
newtons/mz (or about 2 Ib/ft ) at the center of the boom carpet when cruising in level flight at
an altitude of 60,000 ft and at a speed of Mach 2. In this example, the width of the boom car-
pet would be around 90 nautical miles, and the interval between shocks would be about 300
msec.
Although a sonic boom is heard as two sharp bangs, most of the energy carried by a sonic
boom is contained in a very low frequency range (often below 5 H_).
£
Effects of Sonic Booms
The impulse from a sonic boom may set the components of a structure into vibration.
Further, if the natural frequency of a structural component matches that of the impulse, the
response of this component is greatly increased.
Further, reflections from rigid surfaces present on the ground and/or focusing effects can
also amplify the intensity of the wave. >" The point is that, because of possible changes in the
impulse intensity from factors cited above, the response of a particular structure to sonic booms
may be unpredictable. However, the response of a large collection of structures, such as various
buildings in a community, can be fairly well predicted in a statistical sense.
Much of what we know about the effects of sonic booms on structures comes from studies
conducted by the Air Force in the United States and some studies in Sweden, Britain and
France over the last 10 years.
Field studies carried out in the United States involved sonic boom effects in three cities:
St. Louis, Oklahoma City and Chicago. Each of these cities was subjected to systematic over-
flights in a period ranging between 1961 and 1965. From these studies it appears that structures
most susceptible to damage by sonic booms are secondary structural components such as windows
and plaster. The over pressures tested were of the order of 50 to 150 newtons/rh.^ These results
have been confirmed in some British studies.
In a study by Parrot, data indicated that window glass can sustain air pressures up to 1000
newtons/m^ without any damage. " These results have been confirmed by ICAO Sonic Boom
Panel. These findings imply that a supersonic aircraft under normal conditions is not likely
f\
to give rise to over-pressures at ground level greater than 1000 newtons/m and would not,
therefore, cause serious damage to most structures. Caution must be exercised, however, in reach-
ing such conclusions, since it is known that some atmospheric effects and/or factors, such as those
cited previously, could lead to a magnification of boom over-pressures which could have serious
effects on some structures. This could be particularly critical when some structures are already
weakened because of some imperfection (such as misaligned windows) which renders the structure
12-2
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more susceptible to unusual changes in pressures, even though the changes are small. An example
of an unanticipated problem can be found in an incident which occurred in 1959 in Ottawa,
Canada. In this instance, a supersonic aircraft was maneuvering at low altitude at speed below
that of sound, when it accidentally went supersonic for a brief time. In the process, it caused
1 9
damage estimated at $300,000 to the window glass of Ottawa new airport terminal. However,
by and large, the effect of sonic boom can be accurately predicted, on a statistical basis.
The results of some of the studies discussed are summarized in Table 12-1.
There has been only very scarce data on the effects of sonic booms on historical monuments
and archeological structures; however, these structures are usually old and have sustained some
damage from various environmental conditions, such as high winds, temperature and humidity
fluctuations. It is, therefore, possible that repeated sonic booms may be an additional factor
which, when added to the other environmental factors, could accelerate the "aging" of these
structures. An answer to this question must, however, await further research on the long range
effects of sonic booms.
NOISE INDUCED VIBRATIONS
High intensity, low frequency acoustical energy has been observed to set structural com-
ponents, such as windows, light aluminum, or other flat materials, into sympathetic vibratory
motions. As it is difficult to determine the transition between noise and vibration, many dam-
aging effects may be the result of a complex interreaction between these two factors.
Effects on Materials
Measurable effects of noise on structure, while not common in most environmental situa-
tions, do occur in special circumstances. The heavy concentration of construction equipment in
certain urban areas may produce a combination of vibratory energy transmission through the
soil, supporting structures, and the air, which could conceivably affect fragile structures. Little
research, however, has been accomplished to identify such effects. The launches of Saturn
Rockets from Cape Kennedy have provided some data. From experimental and theoretical cal-
culations of window glass breakage, one percent of the windows excited to the critical frequency
of 30 Hz at 130 dB SPL (re. 0002 dynes/cm2) would be expected to break, and at 147 dB, 90
percent of the windows would be predicted to break. These effects occur only at certain fre-
quencies, and would not appear if the excitation were at some higher frequencies until the
sound pressure level was increased considerably.
Possible seismic motion from the sound of rocket launches has been measured and found
negligible even at distances of 400 ft. from the launching site.
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TABLE 12-1
SONIC BOOM DAMAGE DATA IN THREE CITIES*
Boom
Dates
Location
St. Louis
1961-1962
Oklahoma
City
1964
Chicago
1965
Total
Metropol-
itan Popu-
lation
2,600,000
512,000
6,221,000
9,333,000
Total
Super-
sonic
Over
Flights
150
1,253
49
1,452
Maxi-
mum
Peak
Over
Pres-
sure
86
58
86
84+
No. of
Com-
plaints
5,000
15,452
7,116
27,568
No.
Com-
plaints
Filed
1,624
4,901
2,964
9,489
No.
Claims
Paid
825
289
1,442
2,556
Value
Claims
Pd. in $
58,648
123,061
114,763
296,472
This table is based on Table 1 of United States Environmental Protection Agency
Publication NTID 300.12, 1971.
+Average for the three cities
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Effects on Humans
Vibration of buildings produced either by impulse noise, such as those associated with
sonic booms, or certain types of construction equipment or low frequency noise from aircraft,
rocket launches, construction equipment, heavy trucks or trains can produce reactions such as
startle, discomfort, or interference with activities in humans. These effects have been recog-
nized, and criteria has been proposed for human exposure.'^'16
SONIC FATIGUE
Sonic fatigue is a well known and well documented phenomonen. Fatigue, in general,
occurs in ductile materials, such as metals, when subjected to repeated stresses of sufficient
magnitude. Noise of high intensities can cause such stresses through sympathetic vibrations.
These repeated stresses, in turn, produce failure in the material below its normal design load.
The design engineer must take such effects into account when designing structures, such as air-
craft and rockets, that may be subject to intense noise. However, the intensities encountered
in most environmental noises are relatively low; therefore, in most instances, sonic fatigue will
not be a problem, since the noise intensities must be above 140 dB SPL for sonic fatigue to
occur.
EFFECT OF NOISE ON MATERIALS
Summary
The three general types of effects of noise on material are: sonic boom effects, noise in-
duced vibration, and sonic fatigue. These are secondary effects of noise on the health and wel-
fare of man. Sound can also excite buildings to vibrate, which can cause direct effects on man.
The effects caused by sonic booms are the most significant from an environmental stand-
point. Sonic booms of sufficient intensity not only can break windows, but can damage
building structures as well. Nevertheless, as with noise in general, the intensity of sonic booms
can be controlled to levels that are completely innocuous with respect to material or structures.
Noise induced vibration can cause noticeable effects on community windows near large
rocket launch sites. Construction may also cause such effects, but such relationships are poorly
defined at this time.
Sonic fatigue is a very real problem where material is used near intense sound sources.
However, such considerations are normally the responsibility of a design engineer and do not
cause environmental problems.
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Building vibrations excited by impulse noise such as sonic booms or from low frequency
noise from aircraft or rockets can result in human reactions such as startle, discomfort or inter-
ference with some tasks. These effects occur primarily in the infrasound range and point toward
the close relationship between sound and vibration. Criteria for human exposure to vibration
are available but not discussed in this report.
SUMMARY-EFFECTS OF NOISE ON STRUCTURES
Airborne sound normally encountered in real life does not usually carry sufficient energy
to cause damage to most structures. The major exceptions to this are sonic booms produced by
supersonic aircraft, low frequency sound produced by rocket engines and some construction
equipment, and sonic fatigue.
From an environmental point of view, the most significant effects are those caused by
sonic booms on the secondary components of structures. These effects include the breaking
of windows and cracking of plaster. Effects such as these have led to the speculation that
historical monuments and archeological structures may age more rapidly when exposed to
repeated sonic booms.
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REFERENCES
1. Garrick, E. D. Atmospheric Effects of Sonic Boom, NASA document SP-180, 1969.
2. Maglieri, D. J. Sonic Boom Ground Pressure Measurements for Flights at Altitudes in Excess
of 70,000 feet and at Mach Numbers up to 3.0, NASA document SP-180, 19-27, 1968.
3. National Bureau of Standards, The Effects of Sonic Boom and Similar Impulsive Noise on
Structures, V. S. Environmental Protection Agency, 1971.
4. Slutsky, S. and Arnold, L. Coupled Elastic and Acoustic Response of Room Interiors to
Sonic Booms, NASA document SP-155, 227-240, 1970.
5. Pierce, A. D., Maximum Overpressures of Sonic Boom Near the Cusps of Caustics, paper
presented at Purdue Noise Control Conference, Purdue University, 1971.
6. Warren, C. H. E. Recent Sonic Bang Studies in the United Kingdom, paper presented at
Sonic Boom Symposium 11, Houston, Texas, 1970.
7. Wiggins, J. H. Jr., Effects of Sonic Boom on Structural Behavior, Material Research and
Standards, 7, 235-245, 1967.
8. McKinlye, R. W., Response of Glass in Windows to Sonic Booms, Material Research and
Standards, 4, 594-600, 1964.
9. Warren, C. H. E. Recent Sonic Bang Studies in the United Kingdom, JASA, SI.
10. Parrott, T. L., Experimental Studies of Glass Breakage due to Sonic Booms sound, J,
18-21, 1972.
11. ICAO Sonic Boom Panel Report doc 6649, SBP/11,1970 reprinted in Noise Control 1971.
12. Ramsey, A. W. Damage to Ottawa Air Terminal Building produced by a sonic boom,
Material Research and Standards, 4, 612, 1964.
13. Hershey, R. L., & Wiggins, J. H. Jr., Statistical Prediction Model for Glass Breakage from
Nominal Sonic Booms Loads, FAA report No. FAA RD-73-79, 1973.
14. Sinex, C. H., Effects of Saturn Vehicle Launch Noise on Window Glass, TR-99-1, Dec 15,
1965, Safety Office, John F. Kennedy Space Center.
15. Von Gierke, H. E., on Noise and Vibration Exposure Criteria, Archives of Environmental
Health, 11, 327-339, Sept. 1965.
16. ISO guide for the Evaluation of Human Exposure to Whole-Body Vibration, ISO/DIS
2631. 1972.
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GLOSSARY
The following explanations of terms are provided to assist the reader in understanding some
terms used in this publication:
A-WEIGHTED SOUND LEVEL-The ear does not respond equally to frequencies, but is less
efficient at low and high frequencies than it is at medium or speech range frequencies. Thus, to ob-
tain a single number representing the sound level of a noise containing a wide range of frequencies
in a manner representative of the ear's response, it is necessary to reduce, or weight, the effects of
the low and high frequencies with respect to the medium frequencies. The resultant sound level is
said to be A-weighted, and the units are dB. A popular method of indicating the units, dBA, is used
in this Digest. The A-weighted sound level is also called the noise level. Sound level meters have an
A-weighting network for measuring A-weighted sound level.
ABSCISSA—The horizontal axis on a chart or graph.
ACOUSTICS-( 1) The science of sound, including the generation, transmission, and effects of
sound waves, both audible and inaudible. (2) The physical qualities of a room or other enclosure
(such as size, shape, amount of sound absorption, and amount of noise) which determine the audi-
bility and perception of speech and music.
ACOUSTIC REFLEX—The involuntary contraction of the muscles (stapedius and/or tensor
tympani) of the middle ear in response to acoustic or mechanical stimuli.
ACOUSTIC TRAUMA-Damage to the hearing mechanism caused by a sudden burst of intense
noise, or by blast. Note: The term usually implies a single traumatic event.
AIRBORNE SOUND—Sound that reaches the point of interest by propagation through air.
AIR CONDUCTION (AC)-The process by which sound is normally conducted to the inner
ear through the air in the external auditory meatus and the structures of the middle ear.
AMBIENT NOISE (RESIDUAL NOISE; BACKGROUND NOISE)-Noise of a measurable
intensity that is normally present.
ARTICULATION INDEX (AI)-A numerically calculated measure of the intelligibility of
transmitted or processed speech. It takes into account the limitations of the transmission path and
the background noise. The articulation index can range in magnitude between 0 and 1.0. If the AI
is loss than 0.1, speech intelligibility is generally low. If it is above 0.6, speech intelligibility is
generally high.
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AUDIBLE RANGE (OF FREQUENCY) (AUDIO-FREQUENCY RANGE)-The frequency
range 16 Hz to 20,000 Hz (20 kHz). Note: This is conventionally taken to be the normal fre-
quency range of human hearing.
AUDIOGRAM—A chart, table, or graph showing hearing threshold level as a function of
frequency.
AUDIOMETER—An instrument for measuring the threshold or sensitivity of hearing.
AUDIOMETRY-The measurement of hearing.
AUDITORY TRAUMA-Damage to the hearing mechanism resulting in some dregree of per-
manent or temporary hearing loss. Note: Auditory trauma may be caused by agents other than
noise, e.g., head injury; burns; sudden or excessive changes of atmospheric pressure (cf. acoustic
trauma).
AURAL—Of or pertaining to the ear or hearing.
BACKGROUND NOISE-The total of all noise in a system or situation, independent of the
presence of the desired signal. In acoustical measurements, strictly speaking, the term "background
noise" means electrical noise in the measurement system. However, in popular usage the term
"background noise" is also used with the same meaning as "residual noise."
BAND CENTER FREQUENCY-The designated (geometric) mean frequency of a band of
noise or other signal. For example, 1000 Hz is the band center frequency for the octave band that
extends from 707 Hz to 1414 Hz, or for the third-octave band that extends from 891 Hz to 1123
Hz.
BAND PRESSURE (OR POWER) LEVEL-The pressure (or power) level for the sound con-
tained within a specified frequency band. The band may be specified either by its lower and upper
cut-off frequencies, or by its geometric center frequency. The width of the band is often indicated
by a prefatory modifier; e.g., octave band, third-octave band, 10-Hz band.
BASELINE AUDIOGRAM-An audiogram obtained on testing after a prescribed period of
quiet (at least 12 hours).
BONE CONDUCTION (BC)-The process by which sound is transmitted to the inner ear
through the bones of the skull (cf. air conduction).
BOOM CARPET—The area on the ground underneath an aircraft flying at supersonic speeds
that is hit by a sonic boom of specified magnitude.
BROADBAND NOISE—Noise whose energy is distributed over a broad range of frequency
(generally speaking, more than one octave).
C-WEIGHTED SOUND LEVEL (dBC)-A quantity, in decibels, read from a standard sound-
level meter that is switched to the weighting network labeled "C". The C-weighting network
weights the frequencies between 70 Hz and 4000 Hz uniformly, but below and above these limits
frequencies arc slightly discriminated against. Generally, C-weighted measurements are essentially
the same as overall sound-pressure levels, which require no discrimination at any frequency.
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CENTRAL HEARING LOSS-Hearing loss resulting from injury or disease involving the
auditory pathways or the auditory center of the brain or from a psychoneurotic disorder. Note:
Central hearing loss can occur in the absence of any damage or deficiency in the peripheral hearing
mechanism.
COCHLEA-A spirally wound tube, resembling a snail shell, which forms part of the inner ear
and contains the end organ of hearing.
COMMUNITY NOISE EQUIVALENT LEVEL-Community Noise Equivalent Level (CNEL)
is a scale which takes account of all the A-weighted acoustic energy received at a point, from all noise
events causing noise levels above some prescribed value. Weighting factors are included which place
greater importance upon noise events occurring during the evening hours (7:00 p.m. to 10:00 p.m.)
and even greater importance upon noise events at night (10:00 p.m. to 6:00 a.m.).
COMPOSITE NOISE RATING-Composite noise rating (CNR) is a scale which takes account
of the totality of all aircraft operations at an airport in quantifying the total aircraft noise environ-
ment. It was the earliest method for evaluating compatible land use around airports and is still in
wide use by the Department of Defense in predicting noise environments around military airfields.
Basically, to calculate a CNR value one begins with a measure of the maximum noise magni-
tude from each aircraft flyby and adds weighting factors which sum the cumulative effect of all
flights. The scale used to describe individual noise events is perceived noise level (in PNdB); the
term accounting for number of flights is 10 logjQN (where N is the number of flight operations),
and each night operation counts as much as 10 daytime operations. Very approximately, the noise
exposure level at a point expressed in the CNR scale will be numerically 35-37 dB higher than if
expressed in the CNEL scale.
CONDUCTIVE HEARING LOSS (CONDUCTIVE DEAFNESS)-Hearing loss resulting from
a lesion in the air-conduction mechanism of the ear.
CONTINUOUS NOISE—On-going noise, the intensity of which remains at a measurable level
(which may vary) without interruption over an indefinite period or a specified period of time.
Loosely, nonimpulsive noise.
CYCLES PER SECOND—A measure of frequency numerically equivalent to Hertz.
DAMAGE RISK CRITERION (DRC)-A graphical or other expression of sound levels above
which a designated or a general population incurs a specified risk of noise-induced hearing loss.
DEAFNESS-100 percent impairment of hearing associated with an otological condition.
Note: This is defined for medicological and cognate purposes in terms of the hearing threshold
level for speech or the average hearing threshold level for pure tones of 500, 1000, and 2000 Hz
in excess of 92 dB.
DECIBEL-The decibel (abbreviated "dB") is a measure, on a logarithmic scale, of the magni-
tude of a particular quantity (such as sound prmure, y>und t)ow«r, :m
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DOSEMETER (NOISE DOSIMETER)-An instrument which registers the occurrence and
cumulative duration of noise exceeding a predetermined level at a chosen point in the environment
or on a person.
EAR DEFENDER (EAR PROTECTOR)-A device inserted into or placed over the ear in
order to attenuate air-conducted sounds.
EARMUFF-An ear defender that encloses the entire outer ear (pinna). Note: Earmuffs are
customarily mounted as a pair on a headband or in a helmet.
EARPLUG—An ear defender, having specified or standard acoustic characteristics, which
upon insertion occludes the external auditory meatus. Note:Earplugs should be properly designed,
made of suitable material, and correctly fitted to insure that they are acoustically effective and do
not harm the ear.
EFFECTIVE PERCEIVED NOISE LEVEL (EPNL)-A physical measure designed to estimate
the effective "noisiness" of a single noise event, usually an aircraft flyover; it is derived from instan-
taneous Perceived Noise Level (PNL) values by applying corrections for pure tones and for the
duration of the noise.
FENCE—(Slang.) An arbitrary hearing level, greater than OdB, below which no hearing im-
pairment is deemed to have occurred ("low fence") or at which complete (100%) hearing impair-
ment is deemed to have occurred ("high fence").
FILTER-A device that transmits certain frequency components of the signal (sound or
electrical) incident upon it, and rejects other frequency components of the incident signal.
FLUCTUATING NOISE-Continuous noise whose level varies appreciably (more than +5
dB) with time.
FREE SOUND FIELD (FREE FIELD)-In practice, a sound field in which the effects of
spatial boundaries or obstacles are negligible.
FREQUENCY—The number of times per second that the sine-wave of sound repeats itself,
or that the sine-wave of a vibrating object repeats itself. Now expressed in Hertz (Hz), formerly in
cycles per second (cps).
HAIR CELL—Sensory cells in the cochlea which transform the acoustically derived disturbance
of the cochlea into a nerve impulse.
HANDICAP (HEARING HANDICAP)-The occupational and social difficulty experienced by
a person who has a hearing loss.
HARD OF HEARING—Having more than zero but less than 100 percent impairment of hear-
ing for everyday speech or for pure tones of 500, 1000, and 2000 Hz. Note: This is defined, accord-
ing to various standards, in terms of an elevated hearing threshold level of which the elevation is
less than that defining deafness.
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HEARING CONSERVATION (HEARING CONSERVATION PROGRAM)-Those measures
which are taken to reduce the risk of noise-induced hearing loss.
HEARING DISABILITY—Hearing handicap prejudicing employment at full wages.
HEARING IMPAIRMENT-Hearing loss exceeding a designated criterion (commonly 25
dB, averaged from the threshold levels at 500, 1000 and 2000 Hz).
HEARING LEVEL—The difference in sound pressure level between the threshold sound for
a person for the average for a group and the reference sound pressure level defining a standard
audiometric threshold.
HEARING LOSS-Impairment of auditory sensitivity: an elevation of a hearing threshold
level with respect to the standard reference zero.
HEARING THRESHOLD LEVEL-The amount by which the threshold of hearing for an ear
exceeds a standard audiometric reference zero. Units: decibels.
HEARING THRESHOLD LEVEL FOR SPEECH-An estimate of the amount of socially
significant hearing loss in decibels. Note: This is measured by speech audiometry or estimated by
averaging the hearing threshold level for pure tones of 500, 1000, and 2000 Hz.
HERTZ-Unit of measurement of frequency, numerically equal to cycles per second.
IMPULSE NOISE (IMPULSIVE NOISE)-Noise of short duration (typically, less than one
second) especially of high intensity, abrupt onset and rapid decay, and often rapidly changing
spectral composition. Note: Impulse noise is characteristically associated with such sources as
explosions, impacts, the discharge of firearms, the passage of supersonic aircraft (sonic boom),
and many industrial processes.
INDUSTRIAL DEAFNESS-Syn. occupational hearing loss.
INFRASONIC-Having a frequency below the audible range for man (customarily deemed
to cut off at 16 Hz).
INTERMITTENT NOISE-Fluctuating noise whose level falls once or more times to very
low or unmeasurable values during an exposure.
INTERRUPTED NOISE-Syn. Intermittent noise (deprecated).
INVERSE-SQUARE LAW—The inverse-square law describes that acoustic situation where the
mean-square pressure changes in inverse proportion to the square of the distance from the source.
Under this condition the sound-pressure level decreases 6 decibels with each doubling of distance
from the source. See also spherical divergence.
LIQ LEVEL—The sound level exceeded 10 percent of the time. Corresponds to peaks of
noise in the time history of environmental noise in a particular setting.
LSQ LEVEL—The sound level exceeded 50 percent of the time. Corresponds to the average
level of noise in a particular setting, over time.
L9Q LEVEL-The sound level exceeded 90 percent of the time. Corresponds to the residual
noise level.
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LEVEL—The value of a quantity in decibels. The level of an acoustical quantity (sound
pressure or sound power), in decibels, is 10 times the logarithm (base 10) of the ratio of the
quantity to a reference quantity of the same physical kind.
LOUDNESS—The judgment of intensity of a sound by a human being. Loudness de-
pends primarily upon the sound pressure of the stimulus. Over much of the loudness range it
takes about a threefold increase in sound pressure (approx. 10 dB) to produce a doubling of
loudness.
LOUDNESS LEVEL—The loudness level of a sound, in phons, is numerically equal to the
median sound pressure level, in decibels, relative to 0.0002 microbar, of a free progressive
wave of frequency 1000 Hz presented to listeners facing the source, which in a number of
trials is judged by the listeners to be equally loud.
MASKING—The action of bringing one sound (audible when heard alone) to inaudibility
or to unintelligibih'ty by the introduction of another sound. It is most marked when the
masked sound is of higher frequency than the masking sound.
MICRO BAR—A microbar is a unit of pressure, equal to one dyne per square centi-
meter.
MICROPHONE-An electroacoustic transducer that responds to sound waves and delivers
essentially equivalent electric waves.
MIDDLE EAR—A small cavity next to the ear drum in which is located the ossicular
chain and associated structures.
MIXED HEARING LOSS—Hearing loss due to a combination of conductive and sen-
sorineural deficit.
NARROW-BAND NOISE-A relative term describing the pass-band of a filter or the
spectral distribution of a noise. Note: The term commonly implies a bandwidth of 1/3 octave
or less (cf. Broad-band noise).
NOISE—Disturbing, harmful, or unwanted sound.
NOISE EXPOSURE-The total effective acoustic stimulation reaching the ear or the
person over a specified period of time (e.g., a work shift, a day, a working life, or a lifetime).
NOISE EXPOSURE FORECAST-Noise exposure forecast (NEF) is a scale (analogous to
CNEL and CNR) which has been used by the federal government in land use planning guides
for use in connection with airports.
In the NEF scale, the basic measure of magnitude for individual noise events is the effective
perceived noise level (EPNL), in units of EPNdB. This magnitude measure includes the effect of
duration per event. The terms accounting for number of flights and for weighting by time period
are the same as in the CNR scale. Very approximately, the noise exposure level at a point ex-
pressed in the NEF scale will be numerically about 33 dB lower than if expressed in the CNEL
scale.
NOISE HAZARD (HAZARDOUS NOISE)-Acoustic stimulation of the ear which is likely to
produce noise-induced permanent threshold shift in some fraction of a population.
-------
NOISE-INDUCED HEARING LOSS (NIHL)-A sensorineural hearing loss caused by
acoustic stimulation.
NOISE-INDUCED PERMANENT THRESHOLD SHIFT (NIPTS)-Permanent threshold shift
caused by noise exposure.
NOISE-INDUCED TEMPORARY THRESHOLD SHIFT (NITTS)-Temporary threshold shift
caused by noise exposure.
NOISE LEVEL—(Slang.) An averaged sound level (weighted sound pressure level). Note: The
weighting must be specified.
NOISE LIMIT (NOISE EMISSION STANDARD)-A graphical, tabular, or other numerical
expression of the permissible amount of noise which may be produced by a practical source (e.g.,
a vehicle or an appliance) or which may invade a specified point in a living or working environ-
ment (e.g., in a workplace or residence) in prescribed conditions of measurement.
NOISE AND NUMBER INDEX (NNI)-A measure based on Perceived Noise Level, and with
weighting factors added to account for the number of noise events, and used (in some European
countries) for rating the noise environment near airports.
NOISE POLLUTION LEVEL (Ljsjp or NPL)-A measure of the total community noise,
postulated to be applicable to both traffic noise and aircraft noise. It is computed from the "energy
average" of the noise level and the standard deviation of the time-varying noise level.
NOISE RATING (NR) NUMBERS (CONTOURS)-An empirically established set of standard
values of octave-band sound pressure level, expressed as functions of octave-band center frequency,
intended as general noise limits for the protection of populations from hazardous noise, speech
interference and community disturbance. Note: The NR number is numerically equal to the sound
pressure level in decibels at the intersection of the so designated NR contour with the ordinate at 1000 Hz.
NOISE SUSCEPTIBILITY-A predisposition to noise-induced hearing loss, particularly of an
individual compared with the average.
NON-ORGANIC HEARING LOSS (NOHL)-That portion of a hearing loss for which no
otological or organic cause can be found. Hearing loss other than conductive or sensorineural.
NONSTEADY NOISE-Noise whose level varies substantially or significantly with time (e.g.,
aircraft flyover noise). (Syn: fluctuating noise.)
NORMAL HEARING-The standardized range of auditory sensitivity of a specified population
of healthy, otologically normal people determined in prescribed conditions of testing. (Deprecated.)
NORMAL THRESHOLD OF HEARING-Syn. Standard audiometric threshold.
OCCUPATIONAL HEARING LOSS-A permanent hearing loss sustained in the course of
following an occupation or employment. 7Vo/e:While noise is usually presumed to be the cause,
other causes are possible (e.g., head injury).
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OCTAVE-An octave is the interval between two sounds having a basic frequency ratio of two.
For example, there are 8 octaves on the keyboard of a standard piano.
OCTAVE BAND—All of the components, in a sound spectrum, whose frequencies are between
two sine wave components separated by an octave.
OCTAVE-BAND SOUND PRESSURE LEVEL-The integrated sound pressure level of only those
sine-wave components in a specified octave band, for a noise or sound having a wide spectrum.
ORDINATE—The vertical axis on a chart of graph.
ORGAN OF CORTI-The end organ of hearing made up of hair cells and their associated and
supportive structures.
OTOLOGICALLY NORMAL-Enjoying normal health and freedom from all clinical manifesta-
tions and history of ear disease or injury; and having a patent (waxfree) external auditory meatus.
PEAK SOUND PRESSURE-The absolute maximum value (magnitude) of the instantaneous
sound pressure occurring in a specified period of time.
PERCEIVED NOISE LEVEL (PNL)-A quantity expressed in decibels that provides a subjective
assessment of the perceived "noisiness" of aircraft noise. The units of Perceived Noise Level are
Perceived Noise Decibels, PNdB.
PERCENT HANDICAP-Syn. Percent impairment of hearing.
PERCENT IMPAIRMENT OF HEARING (OVERALL) (PIHO)-The estimated percentage by
which a person's hearing is impaired, based upon audiometric determinations of the hearing threshold
level at 500, 1000 and 2000 Hz (cf. Percent impairment of hearing for speech).
PERCENT IMPAIRMENT OF HEARING FOR SPEECH (PIHS)-An estimate of the percentage
by which a person's hearing is impaired, particularly at the frequencies (500, 1000, and 2000 Hz)
deemed important for the perception of speech. Note:The scale 0 to 100 percent is arbitrarily set to
correspond linearly with a standard range of values of hearing threshold level for speech in decibels
(more than one standard has been used). The percent impairment of hearing increases by approxi-
mately 1.5 percent for each decibel of elevation of the estimated hearing threshold level for speech
(average of 500, 1000 and 2000 Hz) in the standard ranges.
PERCEPTIVE HEARING LOSS-Syn. Sensorineural hearing loss. (Obs.)
PERMANENT HEARING LOSS-Hearing loss deemed to be irrecoverable.
PERMANENT THRESHOLD SHIFT (PTS)-That component of threshold shift which shows
no progressive reduction with the passage of time when the putative cause has been removed.
PERSISTENT THRESHOLD SHIFT-Threshold shift remaining at least 48 hours after
exposure of the affected ear to noise.
PHON- Tlii- unit of measurement for loudness level. Phon = 40 + lojo sone.
PINK NOISE- Noise where level decreases wilh increasing frequency to yield constant energy
per octave of bandwidth.
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PITCH—A listener's perception of the frequency of a pure tone; the higher the frequency,
the higher the pitch.
PNdB—See perceived noise level.
PRESBYCUSIS—The decline in hearing acuity that normally occurs as a person grows older.
PURE TONE—A sound wave whose waveform is that of a sine-wave.
RECRUITMENT—The unusually great increase in loudness with rising sound levels.
RESONANCE—The relatively large amplitude of vibration produced when the frequency of
some source of sound or vibration "matches" or synchronizes with the natural frequency of vibra-
tion of some object, component, or system.
RISK-That percentage of a population whose hearing level, as a result of a given influence,
exceeds the specified value, minus that percentage whose hearing level would have exceeded the
specified value in the absence of that influence, other factors remaining the same. Note:The influ-
ence may be noise, age, disease, or a combination of factors.
SEMI-INSERT EAR DEFENDER-An ear defender which, supported by a headband, occludes
the external auditory meatus at the entrance to the ear canal.
SENSORINEURAL HEARING LOSS-Hearing loss resulting from a lesion of the cochlear end-
organ (organ of Corti) or its nerve supply.
SHORT-LIVED NOISE-Noise of measurable intensity lasting without interruption (although
the level may vary) for more than half one second but less than one minute (cf. Continuous noise;
impulsive noise).
SOCIOCUSIS—Elevation of hearing threshold level resulting from or ascribed to non-occupa-
tional noise exposure associated with the general social environment and exclusive of elevation
associated with aging.
SONE—The unit of measurement for loudness. One sone is the loudness of a sound whose
level is 40 phons.
SONIC BOOM—The pressure transient produced at an observing point by a vehicle that is
moving past (or over) it faster than the speed of sound.
SOUND-See acoustics (1).
SOUND LEVEL (NOISE LEVEL)-The weighted sound pressure level obtained by use of a
sound level meter having a standard frequency-filter for attenuating part of the sound spectrum.
SOUND LEVEL METER—An instrument, comprising a microphone, an amplifier, an output
meter, and frequency-weighting networks, that is used for the measurement of noise and sound
levels in a specified manner.
SOUND POWER—Of a source of sound, the total amount of acoustical energy radiated into
the atmospheric air per unit time.
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SOUND POWER LEVEL—The level of sound power, averaged over a period of time, the refer-
ence being 1CP ^ watts.
SOUND PRESSURE—(1) The minute fluctuations in atmospheric pressure which accompany
the passage of a sound wave; the pressure fluctuations on the tympanic membrane are transmitted
to the inner ear and give rise to the sensation of audible sound. (2) For a steady sound, the value
of the sound pressure averaged over a period of time. (3) Sound pressure is usually measured (a) in
dynes per square centimeter (dyn/cm^), or (b) in newtons per square meter (N/m^). 1 N/m^ =
10 dyn/cm^ 10"^ times the atmospheric pressure.
SOUND PRESSURE LEVEL (SPL)-20 times the logarithm to the base 10 of the ratio of the
sound pressure in question to the standard reference pressure of 0.00002 N/m . Units: decibels (dB).
SPECTRUM—Of a sound wave, the description of its resolution into components, each of
different frequency and (usually) different amplitude and phase.
SPEECH AUDIOMETRY-A technique in which speech signals are used to test a person's aural
capacity to perceive speech in prescribed conditions of testing.
SPEECH DISCRIMINATION-The ability to distinguish and understand speech signals.
SPEECH-INTERFERENCE LEVEL (SIL)-A calculated quantity providing a guide to the
interfering effect of a noise on reception of speech communication. The speech-interference level is
the arithmetic average of the octave-band sound-pressure levels of the interfering noise in the most
important part of the speech frequency range. The levels in the three octave-frequency bands
centered at 500, 1000, and 2000 Hz are commonly averaged to determine the speech-interference
level. Numerically, the magnitudes of aircraft sounds in the Speech-Interference Level scale are
approximately 18 to 22 dB less than the same sounds in the Perceived Noise Level scale in PNdB,
depending on the spectrum of the sound.
SPEED (VELOCITY) OF SOUND IN AIR-The speed of sound in air is 344 m/sec or 1128 ft/sec
at78°F.
SPL—See sound pressure level.
STANDARD—(1) A prescribed method of measuring acoustical quantities. Standards in this
sense are promulgated by professional and scientific societies like ANSI, SAE, ISO, etc., as well as
by other groups. (2) In the sense used in Federal environmental statutes, a standard is a specific
statement of permitted environmental conditions.
STANDARD AUDIOMETRIC THRESHOLD-A standardized set of values of sound pressure
level as a function of frequency serving as the reference zero for determinations of hearing threshold
level by pure-tone audiometry.
STAPEDIUS REFLEX (STAPEDIAL REFLEX)-(Likewise, tensor tympani reflex.) The reflex
response of the stapedius (likewise, tensor tympani) muscle to acoustic or mechanical stimulation.
t \Miimouly. synonymous with iivoustic reflex.
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STEADY NOISE (STEADY-STATE NOISE)-Noise whose level varies negligibly within a
given period of time.
TEMPORARY THRESHOLD SHIFT (TTS)-That component of threshold shift which
shows a progressive reduction with the passage of time after the apparent cause has been removed.
THRESHOLD OF HEARING (AUDIBILITY)-The minimum effective sound pressure level
of an acoustic signal capable of exciting the sensation of hearing in a specified proportion of trials
in prescribed conditions of listening.
THRESHOLD OF FEELING (TICKLE)-The minimum effective sound pressure level of an
auditory signal capable of exciting a sensation of feeling or tickle in the ear which is distinct from
the sensation of hearing.
THRESHOLD OF PAIN (AURAL PAIN)-The minimum effective sound pressure level of an
auditory signal at the external auditory meatus which is capable of eliciting pain in the ear as distinct
from sensations of feeling, tickle, or discomfort.
THRESHOLD SHIFT-An elevation of the threshold of hearing of an ear at a specified fre-
quency. Units: Decibels.
TINNITUS-Ringing in the ear or noise sensed in the head. Onset may be due to noise exposure
and persist after a causative noise has ceased, or occur in the absence of acoustical stimulation (in
which case it may indicate a lesion of the auditory system).
TONE—A sound of definite pitch. A pure tone has a sinusoidal waveform.
TTS-See temporary threshold shift.
ULTRASONIC—Pertaining to sound frequencies above the audible sound spectrum (in general,
higher than 20,000 Hz).
VASOCONSTRICTION-The diminution of the caliber of vessels, arteris and arterioles.
VESTIBULAR MECHANISM (SYSTEM)-The sensory mechanism which has to do with balance,
locomotion, orientation, acceleration and desceleration.
WEIGHTING (FREQUENCY WEIGHTING)-The selective modification of the values of a
complex signal or function for purposes or analysis or evaluation, in accordance with prescribed
or standardized rules or formulae. Note: This may be done by computation or by the use of speci-
fied weighting networks inserted into electronic instrumentation so as to transform input signals.
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APPENDIX A
Some Source References - Acoustics and Noise
GOOD INTRODUCTORY ARTICLES ON
POTENTIAL SOLUTIONS
Mecklin, John M., It's Time to Turn Down All
That Noise, Fortune, October, 1969.
Bcranek, L.L., Noise, Scientific American,
December, 1966.
GENERAL INTEREST BOOKS
^Report to the President and Congress on
Noise, NRC 500.1, U.S. Environmental Pro-
tection Agency, Office of Noise Abatement
and Control, December 31, 1971.
Bragdon, Clifford, Noise Pollution: The Un-
quiet Crisis, University of Pennsylvania Press,
Philadelphia, 1972.
Berland, Theodore, The Fight for. Quiet, En-
glewood Cliffs, Prentice-Hall, 1970.
Still, Henry,/« Quest of Quiet, Harrisburg, Pa.
Stackpole Books, 1970.
Baron, Robert Alex, The Tyranny of Noise,
New York, St. Martin's Press, 1970.
Burns, William, Noise and Man, Philadelphia,
Pa., Lippincott, 1969.
EFFECTS OF NOISE ON PEOPLE
* Effects of Noise on People, NTID 300.7, U.S.
Environmental Protection Agency, Office of
Noise Abatement and Control, Technical
Document, December 31. 1971.
Proceedings, Conference on Noise as a Public
Health Hazard, June, 1968, American Speech
and Hearing Association, 9030 Old George-
town Road, Washington, D.C. 20014 ($5.00).
Proceedings, American Association for the
Advancement of Science International Sym-
posium on Extra-Auditory Physiological Ef-
fects of Audible Sound, Boston, Massachu-
setts, December, 1969. Obtain from Plenum
Press, 227 West 17th Street, New York 10011
($15.00).
Kryter, K., Effects of Noise on Man, Aca-
demic Press. 1970 ($19.50).
Stevens, S. S. and Warshofsky, Fred, Sound
and Hearing, Time-Life Books (Life Science
Library Series). New York, 1970.
LEGISLATION
*Laws and Regulatory Schemes for Noise
Abatement, NTID 300.4, U.S. Environmen-
tal Protection Agency, Office of Noise Abate-
ment and Control, Technical Document, De-
cember 31, 1971.
*Statc and Municipal Non-occupational Noise
Programs, NTID 300.8, U.S. Environmental
Protection Agency, Office of Noise Abate-
ment and Control, Technical Document, De-
cember 31, 1971.
Hildebrand, James L. (ed.), Noise Pollution
and the Law, William S. Hein & Co., Inc.,
Law Book Publishers, Buffalo, New York,
1970.
Working Paper jor the Noise Legislation
Workshop, The National Symposium on State
Environmental Legislation sponsored by the
Council of State Governments, Washington,
March 16-18, 1972. (Obtain from EPA, Of-
fice of Noise Abatement and Control, Wash-
ington, D.C. 20460.)
The Noise Around Us: Findings and Recom-
mendations, Report of the Panel on Noise
Abatement to the Commerce Technical Ad-
visory Board, U.S. Department of Commerce,
September 1970 (Obtained from U.S. Gov-
ernment Printing Office, Washington, D.C.
20402—$.50). Full report of the committee
available as COM-71-00147, from National
Technical Information Service, Springfield,
Virginia 22151—$6.00.
A Report to the 1971 Legislature on the Sub-
ject of Noise, Pursuant to Assembly Concur-
rent Resolution 165, 1970, California De-
partment of Public Health, 2151 Berkeley
Way, Berkeley, California. (Released March
22,1971)
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Toward a Quieter City, report of the Mayor's
Task Force on Noise, City of New York,
1970. (Obtain from N.Y. Board of Trade,
295 Fifth Avenue, New York City, $1.50)
Transportation Noise Pollution: Control and
Abatement. NASA Langley Research Center
and Old Dominion University, 1970 (obtain
from Dr. Gene Golia, Old Dominion Univer-
sity, P.O. Box 6173, Norfolk, Virginia 23508.)
A Brief Study of a Rational Approach to
Legislative Control of Noise. National Re-
search Council of Canada, NRC 10577, Ot-
tawa, 1968.
OF SPECIAL INTEREST TO DESIGNERS,
ARCHITECTS AND URBAN PLANNERS
Beranek, Leo L. (ed.). Noise and Vibration
Control, McGraw-Hill Book Co., New York,
1971.
*The Effect of Sonic Boom and Similar Impul-
sive Noise on Structures, NTID 300.12, U.S.
Environmental Protection Agency, Office of
Noise Abatement and Control, Technical
Document, December 31, 1971.
^Community Noise, NTID 300.3, U.S. Envi-
ronmental Protection Agency, Office of Noise
Abatement and Control, Technical Document,
December 31, 1971.
*Transportation Noise & Noise from Equip-
ment Powered by Internal Combustion En-
gines, NTID 300.13, U.S. Environmental Pro-
tection Agency, Office of Noise Abatement
and Control, Technical Document, December
31, 1971.
* Noise from Construction Equipment & Oper-
ations, Building Equipment, & Home Appli-
ances, NTID 300.1, U.S. Environmental Pro-
"These reports are available from the National Tech-
nical Information Service. 5258 Port Royal Road.
Springfield. Virginia 22151; and from the Superin-
tendent of Documents. U.S. Government Printing
Office. Washington. D.C. 20402. They will not be
available from the EPA directly.
tection Agency. Office of Noise Abatement
and Control, December 31. 1971.
*Fundamentals of Noise: Measurement, Rat-
ing Schemes. & Standards. NTID 300.15,
U.S. Environmental Protection Agency, Of-
fice of Noise Abatement and Control, Decem-
ber 31, 1971.
Department of Housing and Urban Develop-
ment: 1. Circular 1390.2. Subject: Noise
Abatement and Control: Departmental Policy.
Implementation Responsibilities, and Stand-
ards, 1971. 2. Noixe Assessment Guidelines.
August 1917. in furtherance of Section 4a of
the above mentioned Circular, available from
the Superintendent of Documents. U.S. Gov-
ernment Printing Office, Washington. D.C.
20402. price 70 cents. Stock Number 2300-
1194.
Berendt, R. I)., Winzer, C. E. and Burroughs,
C. B., A Guide to Airborne. Impact ami
Structure-h<>rni' Noise Control in Multi-ftimilv
Dwellings, FHA Report FT-TS-24. January,
1968.
Meyer, Harold B. and Goodfriend, Lewis,
Acoustics for the Architect. Rcinhold Pub-
lishing Co., New York, 1957.
Solutions to Noise Control Problems in the
Construction of Houses, Apartments, Motels
and Hotels, AIA Files No. 39-E, Owens-
Corning Fiberglass Corporation, Toledo, Ohio
1963.
Building Code Section on Noise Insulation
Requirements in Multifamily Dwellings. Local
Law No. 76 for 1968, City of New York.
Proceedings, Conference on Noise as a Public
Health Hazard, June. 1968. Amer. Speech &
Hearing Assoc., 9030 Old Georgetown Road,
Washington, D.C. 20014. (Especially see Mc-
Grath, Dorn, "City Planning and Noise.")
Land Use Planning with Respect to Aircraft
Noise, October 1964. Can be obtained from
A-2
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the Federal Aviation Administration; the Na-
tional Technical Information Service. 5285
Port Royal Road, Springfield, Virginia 22151;
and the U.S. Air Force, refer to AFM 86-5,
TM 5-365. NAVDOCKS P-98.
Harris, C. H., ed., Haiulhook of M>/\<- Con-
trol, McGraw-Hill Book Co.. 1957 (includes
chapters on community noise and city plan-
ning, anti-noise ordinances, and noise control
requirements in building codes).
PERIODICALS
Noise/News, published bi-monthly by the In-
stitute of Noise Control Engineering. For in-
formation contact Circulation Department.
P.O. Box 1758. Poughkeepsie, N.Y. 12601.
(This is a new newsletter dedicated to publi-
cation of news items related to the scientific
and engineering aspect of noise, its control.
and its effects on people.)
Sound and Vibration, published monthly. For
informatixin contact Sound and Vibration,
27101 E. Oviatt Road, Bay Village, Ohio
44140.
TVASNAC 'Quotes,' Town-Village Aircraft
Safety & Noise Abatement Committee News-
letter, published monthly. For information
contact Editor, TVASNAC Quotes. 196 Cen-
tral Avenue. Lawrence, N.Y. 11559.
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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