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Note: This is a primitive study which is well behind current understanding of this issue, particularly regarding effects on people, but it is important because it is the basis for many current Federal policies regarding aviation noise.  It does have a very complete section on definitions. 

U.S. DEPARTMENT OF COMMERCE
National Technical Information Service

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Table of Contents			i
List of Figures			vi
List of Tables			viii
List of Terms			ix
Section	1.0	General Introduction	1
Section	2.0	Noise Metrics	7
	2.1	Introduction	9
	2.2	Single Event Maximum Sound Level Metrics	9
	2.2.1	A-Weighted Sound Level	9
	2.2.2	D-Weighted Sound Level	11
	2.2.3	Perceived Noise level (PNL)	11
	2.2.4	Tone Corrected Perceived Noise Level (PNLT)	12
	2.3	Single Event Energy Dose Metrics	12
	2.3.1	Effective Perceived Noise Level (EPNL)	12
	2.3.2	Sound Exposure Level (SEL)	12
	2.4	Cumulative Energy Average Metrics	12
	2.4.1	Equivalent Sound Level (Leq)	13
	2.4.2	Yearly Average Day-Night Sound Level (DNL	13
	2.4.3	Community Noise Equivalent level (CNEL)	13
	2.4.4	Noise Exposure Forecast (NEF)	13
	2.5	Cumulative Time Metrics	13
	2.5.1	24-Hour Above (TA)	13
	2.5.2	Day, Evening, Night (TA)	15
	2.6	DNL: The Standard Cumulative Average Energy Metric	15
	2.7	Evaluation of the DNL Metric for Heliport/ Helistop Noise Impact Assessment	15
	2.8	Summary of Noise Metric Policy	17
	2.9	Noise Metrics Applications	17
Section	3.0	Annoyance and Aircraft Noise	19
	3.1	Introduction	20
	3.2	Perception of Noise	20

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	3.3	Variables Affecting Response	20
	3.3.1	Emotional Variables	20
	3.3.2	Physical Variables	21
	3.4	Review of Recent Research	23
	3 5	Conclusion	26
Section	4.0	Different Sources/Different Human Response?	27
	4.1	Introduction	29
	4.2	Schultz - Kryter Debate	29
	4.3	Hall's Research and Analysis	31
	4.4	Conclusion	32
Section	5.0	Hearing and Hearing Loss	33
	5.1	Introduction	35
	5.2	The Hearing Mechanism	35
	5.3	Auditory Range	36
	5.4	Effects of Noise on Hearing	36
	5.4.1	TTS	36
	5.4.2	NIPTS	36
	5.5	Damage Risk Criteria	37
	5.6	Review of Studies	38
	5.6.1	Interior Aircraft Noise	38
	5.6.2	Community Hearing Loss	39
	5.7	Current Standards on Hearing Protection	39
	5.8	Protection of Hearing	41
	5.9	Conclusion	42
Section	6.0	Speech Interference	43
	6.1	Introduction	44
	6.2	Measures of Speech Intelligibility	44
	6.3	Assessing Speech Intelligibility	45

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1.1	Community Response to Aircraft Noise Near Major Airports	3
2.1	Frequency Spectrum	8
2.2	The Metric Family	l0
2.3	A and D weighting Curves	l0
2.4	Typical TA Data Presentation	14
3.1	Community Response to Aircraft Noise Near Major Airports	22
3.2	Community Response to Aircraft Noise --the Netherlands	22
3.3	Community Response to Aircraft Operations— London Heathrow	24
3.4	Comparison of Individual Annoyance and Community Reaction	25
3.5	Attitudes Toward Aircraft Noise	25
4.1	Summary of Annoyance Data from 11 Surveys	28
4.2	Schultz's Synthesis Curve	28
4.3	Hall's Comparison of Air, Road and Schult Synthesis Curve	30
5.1	Cross-Section of the Ear	34
5.2	Cross-Section of the Middle Ear	34
5.3	Damage Risk Criteria Curves	38
5.4	Attenuation by Earplugs	41
5.5	Attenuation by Earmuffs Combined with Earplugs	41
6.1	Calculated AI vs. Effective AI	44
6.2	Noise Criteria Curves	45
6.3	Permissible Distance Between a Speaker and Listeners of Voice and Ambient Level	47

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		PAGE
1.1	Comparative Noise Levels	2
2.1	Noise Metrics Applications	16
5.1	Permissible Noise Exposures	40
5.2	Limiting Values for Total Daily Noise Exposure	40
6.1	Speech Intelligibility Criteria	46
6.2	Recommended Noise Criteria for Offices and Workspaces	48
10.1	Interim Prediction of Effects of Ground Overpressure	74
12.1	Merits and Deficiencies of DNL	83
14.1	Comparison of ANSI and FAA Land Use Guidelines	95
14.2	FAA Land Use Compatibility Guidelines	96
14.3	U.S. Air Force Land Use Objectives Matrix	98
15.1	Damage Estimates for Property Values	101

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AI	Articulation Index
AICUZ	Air Installation Compatible Use Zones
AIR	Aerospace Information Report
ALM	A-Weighted Maximum Sound Level
ANSI	American National Standards Institute
ARP	Aerospace Recommended Practice
CHABA	Committee on Hearing, Bioacoustics and Biomechanics
CNEL	Community Noise Equivalent Level
CNR	Composite Noise Rating
dB	Decibel
DNL	Day-Night Average Noise Level
DOT	Department of Transportation
DRC	Damage Risk Criteria
EPA	Environmental Protection Agency
EPNL	Effective Perceived Noise level
HUD	Housing and Urban Development
Hz	Hertz
ICAO	International Civil Aviation 0rganization
IEC	International Electrotechnical Commission
ISO	International Standards 0rganization
Ldn	Day-Night Average Sound Level
Leq	Equivalent Sound Level
Lx	An Airport Cumulative Metric Derived from dBA

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Section 1.0 General Introduction

Aviation noise significantly affects several million people in the United States. In a great number of instances, aircraft noise simply merges into the urban din, a cacophony of buses, trucks, motorcycles, automobiles and construction noise. However, in locations closer to airports and aircraft flight tracks, aircraft noise becomes more of a concern. The Federal Aviation Administration (FAA) presents this report in an effort to enhance public understanding of the impact of noise on people and to answer many questions that typically arise. Information on aircraft noise indices, human response to noise, and criteria for land use controls is included. Additionally, information on hearing damage is presented, along with occupational health standards for noise exposure.

This document has been developed after reviewing the rather extensive literature in each topical area, including many original research papers, and also by taking advantage of literature searches and reviews carried out under FAA and other Federal funding over the past two decades. Efforts have been made to present the critical findings and conclusions of pertinent research, providing, when possible, a "bottom line" conclusion, criterion, or perspective to the reader concerned with aviation noise.

How to Read This Document

1. If you want only a general, non-technical presentation of the fundamental issues and concerns with aircraft noise, read this introduction and the one-page summaries at the beginning of each section.

2. If you are an engineer, planner, social scientist or an individual conducting an environmental impact, assessment, consider reading each section of interest in its entirety.

3. If you wish to do an in-depth study, assessment or analysis, delve into the text and the references listed. For more information, consider contacting the staff of the FAA 0ffice of Environment and Energy, Noise Abatement Division,, in Washington, D.C. 20591.

What is Sound?

Sound is a complex vibration transmitted through the air which, upon reaching our ears, may be perceived as beautiful, desirable, or unwanted. It is this unwanted sound which people normally refer to as noise.

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Typical Decibel (dBA) Values Encountered in Daily Life and Industry*

Rustling leaves	20 dBA
Room in a quiet dwelling at midnight	32
Soft whispers at 5 feet	34
Men's clothing department of large store	53
Window air conditioner	55
Conversational speech	60
Household department of large store	62
Busy restaurant	65
Typing pool (9 typewriters in use)	65
Vacuum cleaner in private residence (at 10 feet)	69
Ringing alarm clock (at 2 feet)	80
Loudly reproduced orchestral music in large room	82

Beginning of hearing damage if prolonged exposure over 85 dBA

Printing press plant	86
Heavy city traffic	92
Heavy diesel-propelled vehicle (about 25 feet away)	92
Air grinder	95
Cut-off saw	97
Home lawn mower	98
Turbine condenser	98
150 cubic foot air compressor	100
Banging of steel plate	104
Air hammer	107
Jet airliner (500 feet overhead)	115

* When distances are not specified, sound levels are the value at the typical location of the machine operator.

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Sound moves outward from its point of origin in waves just as ripples move outward from the point at which a pebble enters a pond.

Sound, just as the ripple in the pond, requires a medium in which to travel; this medium is usually air.

What is a Decibel?

The decibel (dB) is a shorthand way to express the amplitude of sound (the relative height of those ripples in the pond). Because the "ripples" of sound typically experienced may vary in height from 1 to 100,000 "units", it becomes rather cumbersome to maintain an intuitive feeling for what different values represent. The decibel allows people to understand sound strength using numbers ranging between 20 and 120, a more familiar and manageable set of values. Table 1.1 provides a listing Of some typical sounds and their respective sound levels (expressed in decibels) at given distances.

The decibel also relates well to the way in which people perceive sound. A 10 dB increase in a sound seems twice as loud to the listener, while a 10 dB decrease seems only half as loud. In general, changes in sound level of 3 or 4 dB are barely perceptible.

What is Frequency or Pitch?

Some of the ripples in the pond may be very short; these are analogous to high pitched sounds such as the voice of a soprano. Other wavelets might be very broad; these waves are analogous to a bass or baritone voice. Most sounds we hear are composed of a mixture of these different length sound waves, giving complexity, richness and character to our experience of sound.

What is the Most Important Effect of Aviation Noise?

Annoyance is the most prevalent effect of aircraft noise. It is important to note that while the overall, or average, community attitude about a noise level is usually what is reported, some individuals will be much more and others much less upset or annoyed with the sound in question. Figure 1.1 shows this typical response pattern. This variation in response is what makes the science of measuring "community response" a rather complicated matter.

What are Other Principal Effects of Aircraft Noise?

1. speech interference

2. sleep interference

3. hearing damage risk

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_ Ref 1

While hearing damage is not a common result of aircraft noise exposure, speech and sleep interferences are major concerns of neighbors close to airports.

What are Some Less Frequently Identified Effects of Noise on Humans?

1. physiological (cardiovascular and circulatory) problems

2. psychological problems (stemming from intense annoyance)

3. social behavioral problems

At the present time there is no conclusive evidence to link these effects with aircraft noise. As discussed in the text, these topical areas are often rife with conflicting research results and are very controversial. The summary of the non-auditory effects section (Section 8.0) provides current guidance for interpreting these reported effects.

What Other Areas May be Affected by Aircraft Noise?

1. real estate values

2. land use

3. wildlife

4. farm animals

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1. Richards, E. S, and J. B. Ollerhead. Noise Burden Factor-
-New Way of Rating Airport Noise. Sound and Vibration,
V.7, No, 12, December 1973.

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Section 2.0 NOISE METRICS

INTRODUCTION

This section describes the noise metrics utilized in conducting analyses of aircraft noise. While dozens of additional metrics exist, this section focuses on the officially designated family of indices. A working knowledge of these measures is extremely valuable in understanding the remainder of this report.

AVIATION APPLICATIONS/ISSUES

1. Correlation between human response and various measures of sound.

2. Selection of the best metrics for specific applications.

3. Selection of weighting factors for sound occurring at various times of day.

4. Selection of metrics which are accurate, relatively easy to measure, compute and understand.

GUIDANCE/POLICY/EXPERIENCE

1. The fundamental sound level metric designated as the A-Weighted Sound Level, or AL. This metric has often appeared in the literature as dBA. It is designated for measuring noise at an airport and surrounding areas by Part 150.

2. Single event dose or energy metric designated as the Sound Exposure Level or SEL.

3. Airport yearly average noise exposure measure designated as the Yearly Average Day Night Level or DNL. The DNL has often appeared in the literature as Ldn.. Required by Part 150 to measure the exposure of individuals to noise resulting from the operation of an airport.

4. Effective Perceived Noise Level or EPNL designated as the certification metric for large transport turbojet aircraft and helicopters.

5. Time functions of ALm (such as Time Above, TA and L-Values, L-10) identified as supplementary metrics for use in environmental impact analyses.

6. Octave and one-third octave spectra identified as important in specific applications such as sound proofing and speech interference studies.

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(2) Single Event Energy Dose

(3) Cumulative Energy Average Metrics

(4) Cumulative Time Metrics

The paragraphs below describe and differentiate these four generic classes of acoustical metrics. An understanding of these four classes essential for an individual undertaking a comprehensive assessment of noise effects. (For mathematical formulations of each of the noise metrics, the reader is referred to The Handbook of Noise Ratings (Ref. 1).

2.2 SINGLE EVENT MAXIMUM SOUND LEVEL METRICS

The following noise metrics are generally related, each representing a maximum sound level. The applications of these metrics are diagrammed in Figure 2.2.

2.2.1 A-Weighted Sound Level: ALm (Historically dBA), Expressed in dB. The A-weighted Sound Level is the single event maximum sound level metric. A-weighted sound pressure level is sound pressure level which has been filtered or weighted to reduce the influence of the low and high frequency extremes. Because unweighted sound pressure level does not correlate well with human assessment of the loudness of sounds, various weighting networks are added to sound level meters to attenuate low and high frequency noise in accordance with accepted equal loudness contours. One of these weighting networks is designated "A" (shown in Figure 2.3).

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It was originally employed for sounds less than 55 dB in level; now A-level is used for all levels of sound because it has been found to correlate well with people's subjective judgment of the loudness of sounds. Its simplicity and superiority over unweighted SPL in predicting people's responses to noise have contributed to its wide acceptance. The ALM is currently used for noise certification of small propeller-driven aircraft; also, in FAA Advisory Circular 36-3C it is used as the basis for airport access restrictions which discriminate solely on the basis of noise level.

2.2.2 D-Weighted Sound Level: DLm (Historicall dB(D)), Expressed in dB. D-weighted sound pressure level or D-level is sound pressure level which has been frequency-filtered to reduce the effect of the low frequency noise and to recognize the annoyance at higher frequencies. D-level is measured in decibels with a standard sound level meter with contains a "D" weighting network with the response curve shown in Figure 2.3. D-level was developed as a simple approximation of perceived noise level (PNL) for use in assess aircraft noise. PNL, addressed in the next paragraph, can be estimated from the D-level by this equation: PNL = dB(D) + 7.

2.2.3 Perceived Noise Level (PNL), Expressed in dB. Perceived Noise Level (PNL) is a rating of the noisiness that has been used almost exclusively in aircraft noise assessment. PNL is computed from sound pressure levels measured in octave or one-third octave frequency bands. This rating is most accurate in estimating the perceived noisiness of broadband sounds of similar time duration which do not contain strong discrete frequency components. Currently it is used by the FAA and foreign governmental agencies in the noise certification process for all turbojet -- powered aircraft and large propeller-driven transports. The perceived noise level is expressed in decibels. These units translate the subjective linearly additive noisiness scale to a logarithmic dB-type

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acoustical energy associated with the fluctuating sound (during the prescribed time period) is equal to the total acoustical energy associated with a steady sound level of Leq for the same period of time. The purpose of Leq is to provide a single number measure of noise averaged over a specified time period.

2.4.2 Day-Night Sound Level (DNL), Expressed in dB. Day-Night Sound Level (DNL) was developed as a single number measure of community noise exposure. It is often referred to as Ldn in the literature. DNL was introduced as a simple method for predicting the effects on a population of the average long term exposure to environmental noise. It is an enhancement of the Equivalent Sound Level (Leq) because a correction for nighttime noise intrusions was added. A 10 dB correction is applied to nighttime (10 p.m. to 7 a.m.) sound levels to account for increased annoyance due to noise during the night hours. DNL uses the same energy equivalent concept as Leq. The specified time integration period is 24 hours. As in the case of Leq, there is no stipulation of a minimum noise sampling threshold. The DNL can be derived directly from the A-weighted sound level or the sound exposure level, as shown in Figure 2.2. For assessing long term noise exposure, the yearly average DNL (DNL y-avg) is the specified metric in the FAA FAR Part 150 noise compatibility planning process. In the remainder of this document, the term DNL will be used (in lieu of DNL y-avg), yearly average being implied.

2.4.3 Community Noise Equivalent Level (CNEL), in dB. CNEL, like DNL, incorporates the energy average A-weighted sound level integrated over a 24-hour period Weightings are applied for the noise levels occurring during the evening (7 p.m. - 10 p.m.) and nighttime (10 p.m. - 7 a.m.). CNEL differs from DNL in the addition of the evening weighting step function of 3 dB which is intended to account for activity interference and annoyance during that time period. It was originally used by the state of California, but it is being phased out.

2.4.4 Noise Exposure Forecast (NEF), in dB. Noise Exposure Forecast performs the same role as DNL or CNEL but is developed using EPNL as the intermediate single event dose metric. The NEF metric incorporates a weighting factor which effectively imposes a 12.2 dB penalty on sound occurring between 10 p.m. and 7 a.m. This corresponds to a nighttime event multiplier of 16.7. NEF correlates extremely well with DNL and the equivalency DNL = NEF + 35 is often used.

2.5 CUMULATIVE TIME METRICS

2.5.1 24-Hour Time Above (TA), Expressed in Minutes. The 24-hour TA metric provides the duration in minutes for which aircraft related noise exceeded specified A-weighted sound levels. An example of a TA contour is shown in Figure 2.4. TA is one of the criteria specified in HUD Circular 1390.2 for determining eligibility for HUD construction funding (Ref. 3). TA'S inverse, the L-value (e.g., L 10) is used (along with Leq) as the FHWA criteria for planning and design of Federal-aid highways. Further, TA can be related directly to some "threshold activated" physiological or annoyance effects.

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2.5.2 Day, Evening, Night (TA), Expressed in Minutes. The Day-TA metrics provide the duration in minutes for which aircraft related noise exceeded specified A-weighted sound levels during the period 7:00 a.m. to 7:00 p.m. The Evening TA metrics provide the duration in minutes for which aircraft related noise exceeded A-weighted sound levels during the period from 7:00 p.m. to 10:00 p.m. The Night TA metrics provide the duration in minutes for which aircraft related noise exceeded A-weighted sound levels during the period from 10:00 p.m. to 7:00 a.m.

2.6 DNL: THE STANDARD CUMULATIVE AVERAGE ENERGY METRIC

The FAA selected DNL as the cumulative average energy metric to be used in airport noise exposure studies. While a dialogue continues within research circles concerning weighting functions, the DNL has emerged as a sound and workable tool for use in land use planning and in relating aircraft noise to community reaction. The substantiating basis for the DNL can perhaps best be summarized as follows:

1) Pragmatically speaking, it works. Engineers and planners have acquired over 30 years working experience with a nominal 10 dB nighttime weighting function. This experience has been successful, contributing to wise zoning and planning decisions.

2) The nominal 10 dB decrease in ambient noise levels in many residential areas at nighttime provides a sensible basis for the weighting factor.

2.7 EVALUATION OF THE DNL METRIC FOR HELIPORT/HELISTOP NOISE IMPACT ASSESSMENT

With the increase in helicopter operations in and around urban areas, the FAA has sought to include helicopters in the environmental planning process. In this context, the question has arisen of whether or not the average cumulative energy metric DNL, which is used in the analysis of noise from conventional aircraft, would also be appropriate for analysis of helicopter noise. Most commercial airports have hundreds of operations a day, while heliports generally handle fewer than thirty. The metric used to analyze helicopter noise would have to be sensitive enough to accurately reflect community response at comparatively low levels of noise exposure (lower cumulative levels because of fewer flights).

In order to investigate whether or not DNL would be appropriate, the FAA supported a field test program to examine subjective response to helicopter operations. The actual study was conducted by NASA Langley Research Center and is summarized below (Ref. 4). In the study, researchers examined the reaction of community residents to low numbers of helicopter noise events. Residents of the selected community were interviewed twenty-three times about their general noise annoyance on particular days. Unknown to them, on those days helicopter flights had been controlled for the test purpose; the number of flights per day varied from 0 to 32. The exposure varied randomly through each of the

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METRIC	DESCRIPTION
One-third Octave Sound Pressure Levels	The one-third octave band sound pressure levels are the starting point for all other metrics; useful in implementation of soundproofing
PNL	Sound Level from which EPNL was developed
PNLT	Sound Level from which EPNL was developed
EPNL	A maximum sound level single event cumulative metric developed from the PNLT and PNL sound level. Used in FAR Part 36, Appendix C Certification, Advisory Circular 36-lB and Advisory Circular 36-2A.
NEF	An Airport cumulative metric no longer in use in the U.S. but often used in older studies; replaced by DNL (the FAA approved metric)
Alm	A sound level metric applied as follows: Airport Noise Analysis 1050.lC Analysis FAR Part 36 Appendix F Certification Specific eligibility for Soundproofing Implementation of Soundproofing Noise Monitoring Systems FAA Advisory Circular
TA	An airport cumulative metric derived from dB(A) and applied as follows: Airport Noise Analysis l050.lD Analysis Noise Monitoring Systems
Lx	An airport Cumulative metric derived from dB(A) and applied as follows: Airport Noise Analysis l050.lD Analysis Noise Monitoring Systems
SEL	A maximum sound level, single event cumulative metric derived from dB(A) and applied as follows: Airport Noise Analysis Noise Monitoring Systems
Leq	An airport cumulative metric derived from SEL; no application in aviation
DNL	An airport cumulative metric derived from SEL with the following applications: Airport Noise Contours Airport Noise Analysis FAR l050.lD Analysis General Eligibility for Soundproofing Noise Monitoring Systems
CNEL	An airport cumulative metric derived from SEL used only by the state of California; CNEL will be phased out in the next few years.

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1. Pearson, Karl. Handbook of Noise Ratings. Bolt, Beranek and Newman, Inc. NASA CR-2376, April 1974.

2. Hassall, J.R. and K. Zaveri. Acoustic Noise Measurements. Bruel & Kjaer, January 1979.

3. Housing and Urban Development Circular 1390.2.

4. Fields, James M. and Clemans A. Powell. Community Survey of Helicopter Noise Annoyance Conducted Under Controlled Noise Exposure Conditions. Unpublished Report, December 1984.

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Section 3.0 ANNOYANCE AND AIRCRAFT NOISE

INTRODUCTION

The typical response of humans to aircraft noise is annoyance. Annoyance response is remarkably complex and, considered on an individual basis, displays wide variability for any given noise level. Fortunately, when one considers average annoyance reactions within a community, one can develop aggregate annoyance response/noise level relationships. This section introduces the reader to the factors which influence individual annoyance response. Also included are examples of research findings which display aggregate community annoyance responses.

AVIATION APPLICATION/ISSUES

Annoyance is the number one consequence of excessive aircraft noise. The continued growth of the aviation industry and expansion of airport capacity is in part dependent on how well noise compatibility planning is handled.

GUIDANCE/POLICY/EXPERIENCE

It is the charter of the FAA to assure safety and promote civil aviation. Promoting civil aviation means, among other things, addressing the problems of aircraft noise annoyance. The FAA, working with other members of the community, has taken a series of steps designed to bring about greater compatibility between aircraft noise levels and affected individuals. Actions include:

1. Source noise certification regulations
2. FAR Part 150 Airport Noise Exposure / Land Use Compatibility Planning Process
3. Research into the mechanism of annoyance to aircraft noise
4. Advisory publications designed to mitigate aircraft noise impact on noise sensitive areas.

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alienated or of being ignored and abused is the root of many human annoyance reactions. If people feel that those creating the noise care about their welfare and are doing what they can to mitigate the noise, they are usually more tolerant of the noise and are willing and able to accommodate higher noise levels.

B. Judgment of the Importance and Value of the Activity which is Producing the Noise. If the noise is produced by an activity which people feel is vital, they are not as bothered by it as they would be if the noise-producing activity was considered superfluous.

C. Activity at the Time an Individual Hears a Noise. An individual's sleep,, rest and relaxation have been found to be more easily disrupted by noise than his communication and entertainment activities.

D. Attitudes about Environment. The existence of undesirable features in a person's residential environment will influence the way in which he reacts to a particular intrusion.

E. General Sensitivity to Noise. People vary in their ability to hear sound, their physiological predisposition to noise and their emotional experience of annoyance to a given noise.

F. Belief about the Effect of Noise on Health. The extent to which people believe that exposure to aircraft noise will damage their health affects their response to aviation noise.

G. Feeling of Fear Associated with the Noise. For instance, the extent to which an individual fears physical harm from the source of the noise will affect his attitude toward the noise.

3.3.2 Physical Variables. A number of physical factors have also been identified by researchers as influencing the way in which an individual may react to a noise. These factors include:

A. Type of Neighborhood. Instances of annoyance, disturbance and complaint associated with a particular noise exposure will be greatest in rural areas, followed by suburban and urban residential areas, and then commercial and industrial areas in decreasing order. The type of neighborhood may actually be associated with one's expectations regarding noise there. People expect rural neighborhoods to be quieter than cities. Consequently, a given noise exposure may produce greater negative reaction in a rural area.

B. Time of Day. A number of studies has suggested that noise intrusions are considered more annoying in the early evening and at night than during the day.

C. Season. Noise is considered more disturbing in the summer than in the winter. This is understandable since, during the summer, windows are likely to be open and recreational activities take place out of doors.

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D. Predictability of the Noise. Research has revealed that individuals exposed to unpredictable noise have a lower noise tolerance than those exposed to predictable noise.

E. Control over the Noise Source. A person who has no control over the noise source will be more annoyed than one who is able to exercise some control.

F. Length of Time an Individual Is Exposed to a Noise. There is little evidence supporting the argument that annoyance resulting from noise will decrease with continued exposure; rather, under some circumstances, annoyance may increase the longer one is exposed.

3.4 REVIEW OF RECENT RESEARCH

The inherent variability in the way individuals react to noise makes it impossible to predict accurately how any one individual will respond to a given noise. However, when one considers the community as a whole, trends emerge which relate noise to annoyance. In this way it is possible to correlate DNL with community annoyance. This measure will represent the average annoyance response for the community.

In any community there will be a given percentage of the population highly annoyed, a given percentage mildly annoyed and others who will not be annoyed at all. The changing percentage of population within a given response category is the best indicator of noise annoyance impact.

Various studies have focused on the relationship between annoyance and noise exposure, one researcher, in analyzing the results of numerous social surveys conducted at major airports in several countries, derived the curves shown in Figure 3.1 relating degree of annoyance and percent of population affected with noise exposure expressed in DNL (Ref. 1). A survey conducted in the Netherlands investigated the relationship between the DNL and the percentage of those questioned who suffered feelings of fear, disruption of conversation, sleep or work activities (Ref. 2). Figure 3.2 reflects these findings.

In 1960 the "Wilson Committee" was appointed by the British Government to investigate the nature, sources and effects of the problem of noise (Ref. 3). The final report, published in 1963, included results of extensive examination of community response to aircraft operations at London Heathrow Airport. Figure 3.3, adapted from that report, shows the relationship between DNL and the percent of the population disturbed in various activities including sleep, relaxation, conversation and television viewing. Disturbance response categories for startle and house vibration are also included.

The EPA publication "Information on Levels of Environmental Noise Requisite to Protect Health and Welfare with an Adequate Margin of Safety" provides a relationship between the percent of population highly annoyed and the Day-Night Sound Level (DNL) (Ref. 4). These data are shown in Figure 3.4, along with the relationship between annoyance, complaints and community reaction.

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3.5 CONCLUSION

This section has presented a series of relationships useful in interpreting average community response to aircraft noise. These data should provide the reader with the necessary perspective to begin understanding the human reactions to various levels of cumulative noise exposure (DNL).

1. Richards, E. J, and J. B. 0llerhead. Noise Burden Factor - New Way of Rating Airport Noise. Sound and Vibration, V. 7, No, 12, December 1973.

2. Kryter, Karl D. The Effects of Noise on Man. New York, Academic Press, 1970.

3. Great Britain Committee on the Problem of Noise. Noise, Final Report. Presented to Parliament by the Lord Minister for Science by Command of Her Majesty. London, H. M. Stationery Office, July 1963.

4. U.S. Environmental Protection Agency, Office of Noise Abatement and Control, Washington, D.C. Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety. March 1974.

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Section 4.0 DIFFERENT SOURCES/DIFFERENT HUMAN RESPONSE?

INTRODUCTION

This section addresses a fundamental question raised from time to time in connection with aviation noise related law suits, environmental impact assessments, and research studies. It has been suggested that aircraft noise levels should be treated as more annoying to people than the same sound levels generated by other sources. A review of the research shows that very strong positions have been taken both supporting and opposing the theory. The most recent papers appearing in the scientific journals concede that a differential in response may exist but it can not be shown to be statistically significant.

AVIATION APPLICATIONS/ISSUES

Should aircraft noise be considered as comparable to noise from other sources in the land use planning and environmental assessment process?

GUIDANCE/POLICY/EXPERIENCE

In the general application of noise exposure/land use criteria, aircraft noise should be considered in the same manner as noise from other sources.

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4.1 INTRODUCTION

In assessing comparative contributions to the overall annoyance with noise experienced by an individual, the issue of whether or not aircraft noise should be compared with other ambient sources continues to arise. The issue is an important one in terms of establishing acceptable cumulative noise exposure levels for various land use categories. This section reviews current literature on this controversial topic.

4.2 SCHULTZ - KRYTER DEBATE

In 1978, Theodore Schultz published an article synthesizing results from many social surveys on noise annoyance. In this article he stated that it is possible to compare aircraft and other transportation noise equally, and to find and use a median annoyance response curve for them (Ref. 1). In order to compare these various results, Schultz developed some theories and formulas with which he determined which parts of each survey would fall into the "highly annoyed" category. He also figured the DNL indices for these surveys and plotted them (see Figure 4.1). Figure 4.2 reproduces Schultz's "synthesis curve", the median of all the noise surveys.

Karl Kryter, responding in 1982 to Schultz's article, proposed a different relationship (Ref. 2).. While Schultz only considered people who were highly annoyed, Kryter stated that all individuals annoyed should be considered in these comparisons. He also developed the DNL values for each study differently, so his values varied significantly from those of Schultz. Kryter also attempted to explain the poor correlation between noise exposure and annoyance in individuals by explaining that, while it is assumed that noise exposure is homogeneous over a given neighborhood, an individual's particular dose of noise may vary quite a bit.

Kryter cited Grandjean (Ref. 3), another researcher who found that aircraft noise is significantly more disturbing than other noise. This Swiss study stated that it took a DNL of 10 to 15 dB higher for road traffic noise to cause equal disturbance as aircraft. Kryter then explained his concept of the "effective exposure" of noise, rather than the exposure that may actually be measured or reported. Kryter suggests that because aircraft noise falls over a structure, like a house, equally, as opposed to passing through interfering structures as traffic noise would do (as in moving from the front to the back of a house), the "effective noise exposure" would be greater than that of traffic noise. Kryter further submits that, for a house facing the road, residents in the back yard would experience diminished noise from those in the front yard; however, they would all experience equal aircraft noise. Likewise, each room in the house would experience nearly identical exposure to aircraft noise (Kryter evidently only considered single - level homes). Kryter found a front to back of house difference of 17 - 21 dB for road traffic and only 0.3 dB for aircraft noise. Thus, Kryter suggests that aircraft noise must be considered separately from other transportation noise.

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For the same noise level, a greater percentage of
people are highly annoyed by aircraft noise. The
difference in annoyance at the two sources is not
constant but instead increases as Ldn increases. The
difference in annoyance is equivalent to about 8 dB at
Ldn of 55 dB increasing to about 15 dB at Ldn of 65 dB.

Hall puts forth some possible explanations of these variations. For example, the sporadic time pattern of aircraft noise differs from the relatively steady noise of road traffic. Thus, maximum levels for aircraft noise will be higher. Hall suggests that until further work can be done, "Ldn is a reasonable predictor of response to any particular source, but there are differences in response to different sources at the same Ldn value." Hall concluded that the best thing to do, then, would be to use separate functions to estimate community response to different types of noise.

In a later article (published in December 1984), Hall further addressed this complex issue, substantially altering his previous conclusions (Ref. 5). He references about a dozen papers published on this subject over the last five years. Hall suggests that intrinsic differences may exist but can not be substantiated as statistically significant. His summary statements are excerpted below:

The overwhelming conclusion from the recent literature is that different studies have led to different dose-response functions. This has happened for different sources, for different types of one source, and even for different studies at the same location (e.g., Heathrow). There is some consistency of evidence that the annoyance response function for rail noise is lower than for road or aircraft noise. (Rohrmann reaches the same conclusion in his review of relevant literature.) There is also some indication, but with fewer studies pertaining to it, that the aircraft annoyance function is higher than that for road traffic. However, the evidence is not strong enough to totally reject the hypothesis that all of this is just random variation about the "average" response.

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Lastly, an "average" dose-response function appears to be useful in two contexts, both defined by limited information. The first is the general situation we are now in, in which it appears that different dose-response functions are warranted, but we cannot specify precisely the conditions calling for each. Although we suspect the variance in results is not simply random, it almost behaves as if it were, in which case the "average" function represents our best current estimate. The second situation will arise in the future, when we may be able to specify clearly the conditions calling for separate dose-response functions. Even then, there will undoubtedly be conditions which we cannot categorize, in which case again the "average" response function would be. the best one to use.

4.4 CONCLUSION

For matters of policy, there does not exist at this time enough evidence to support the requirement of a differential for comparing aircraft noise with noise from other sources. All transportation and other ambient noise sources therefore can be treated as comparable when considering aviation noise impact.

1. Schultz, Theodore. Synthesis of Social Surveys on Noise Annoyance. J. Acoust. Soc. Am. 64, 1978.

2. Kryter, Karl D. Community Annoyance from Aircraft and Ground Vehicle Noise. J. Acoust. Soc. Am. 72 (4), October 1982.

3. Grandjean, P. Graf, A. Lauber, H.P. Meier, and R. Huller. Survey on the Effects of Aircraft Noise in Switzerland. Inter-Noise 76, Washington, D.C., April 1976.

4. Hall, Fred L., Susan E. Bernie, Martin Taylor, and John E. Palmer. Direct Comparison of Community Response to Road Traffic Noise and to Aircraft Noise. J. Acoust, Soc. Am. 70 (6), December 1981.

5. Hall, Fred L. Community Response to Noise: Is All Noise the Same? J. Acoust. Soc. Am. 76 (4), October 1984.

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INTRODUCTION

This section describes the human hearing mechanism and the processes of temporary and permanent hearing loss. The results of research are presented and the potential for hearing loss in aviation noise environments evaluated. OSHA hearing protection criteria are also addressed.

AVIATION APPLICATIONS/ISSUES

1. Permanent or temporary hearing loss.
a. cockpit crew
b. flight attendants
c. passengers
d. persons in communities exposed to aircraft
overflight

2. Temporary hearing loss for the same categories of individuals listed above.

GUIDANCE/POLICY/EXPERIENCE

1. FAA-sponsored research results show that permanent hearing loss is not a likelihood for a) cockpit crew, b) flight attendants, c) passengers, d) people exposed to overflights.

2. Temporary hearing loss (up to several hours recovery time) may occur in commercial aviation noise environments. These temporary sensitivity shifts are not unusual in the industrial setting and do not exceed OSHA criteria.

3. Persons on the ground exposed to aircraft overflights would typically not experience any temporary hearing loss due to the relatively short duration of the noise exposure.

4. A greater degree of temporary and possible permanent hearing loss can result in the case of long exposure times in certain small propeller driven aircraft.

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5.1 INTRODUCTION

It is well established that continuous exposure to high levels of noise will damage human hearing. This section begins with a description of the hearing mechanism, followed by discussion of the effects of noise on hearing, along with criteria for hearing protection established by the military, the FAA and OSHA. Finally, methods for protection of hearing are discussed.

5.2 THE HEARING MECHANISM

The ear is an external sense organ designed to receive and respond to air-borne acoustic vibratory energy. Figure 5.1 provides a schematic cross section showing the outer, middle and inner ears. The external ear, made up of the auricle (the outer portion of the ear) and the ear canal, transmits sounds to the eardrum. The eardrum, which is a very thin membrane that moves very slightly in response to sound pressure levels, separates the ear canal from the middle ear.

The middle ear is an air-filled cavity that lies between the outer and the inner ear (see Figure 5.2). It acts as a mechanical amplifier of the air pressure vibrations from the eardrum and through a series of bones called the ossicles. Air pressure vibrations displace the eardrum, which then displaces the ossicles, a link of three small bones which reach across the middle ear cavity to the delicate, fluid-filled membranes of the inner ear. The ossicles, made up of the malleus, the incus and the stapes, rest against the opening to the inner ear, the oval window; when the ossicles are displaced, the stapes pushes through the oval window, displacing the fluid in the inner ear.

The middle ear allows pressure variations in air to be transmitted into pressure variations in fluid with very little loss of energy. This is due in part to the relative size difference between the eardrum and the oval window (the eardrum has an area 20 times that of the oval window). Thus, the force exerted on the inner ear fluid by the stapes is about the same as the force exerted on the eardrum by the sound wave in the air, but the resulting pressure is much greater -- as much as a ratio of 22 to 1.

The inner ear contains the final section of the organ of hearing, the cochlea, which rests, coiled like a snail, against the oval window. As the stapes forces the oval window in and out, the fluid of the cochlea is also moved. About thirty thousand hair cells (called cilia) located in the cochlea react to the fluid motions, translating them to nerve impulses (and converting them from mechanical to electrical energy), then transmitting the impulses to the brain for interpretation.

Acoustical energy may also be conducted to the inner ear through vibration of bone. An example is the sound of one's own voice. Bone-conducted vibrations set up similar patterns of vibration of the cochlear partition as does air-conducted sound.

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