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AVIATION NOISE EFFECTS
FEDERAL AVIATION ADMINISTRATION WASHINGTON, DC MAR 85 U.S. DEPARTMENT OF COMMERCE National Technical Information Service

1

TABLE OF CONTENTS Page

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Table of Contents

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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

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2.4.3

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13

Community Noise Equivalent level (CNEL)

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

i

PAGE

3.3

Variables Affecting Response

20

3.3.1

Emotional Variables

20

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3.3.2 3.4

Physical Variables

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21 23

Review of Recent Research

35

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

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5.4.2 NIPTS

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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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PAGE 6.4 Speech Interference on the Ground 47

6.5

Speech Interference in the Cockpit

49

Section

7.0

Sleep Interference

51

7.1

Introduction

53

7.2

Sleep Disturbance Response

53

7.3 7.3.1 7.3.2 7.3.3

Recent Literature Review Arousal for Sleep Measuring Sleep Interference Adaptation and Habituation

53 54 54 55

7.4

1977 Literature Review

55

75

Summary

57

Section

8.0

Non-Auditory Effects of Noise

59

Case 1:01-cv-00201-VJW 8.1 Introduction

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8.2

Interpretation of Rulings

60

8.3

Review of Studies

60

8.4

Conclusion

61

Section

9.0

Effects of Noise on Wild and Domesticated Animals

63

9.1

Introduction

65

9.2 9.2.1 9.2.2

Wildlife Birds Fish

65 65 65

9.3

Domesticated (Farm) Animals

66

9.4

Laboratory Animals

66

9.5

Conclusion

67

Section

10.0

Effects of Strong Low Frequency Acoustical Energy

69

Case 1:01-cv-00201-VJW 10.1 Introduction

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10.2

Structural Effects iii

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10.3

Annoyance with Structural Vibration

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10.4

Physiological Effects

71

10.5 10.5.1

Criteria for Intense Low Frequency Sound EPA Levels Document

71 71

10.5.2

International Standards Organization

73

10.6

Sonic Boom

73

10.7

Conclusion

75

Section

11.0

Impulsive Noise

77

11.1

Introduction

78

11.2

Review of Studies

78

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11.2.1 11.2.2

1977 French Report

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78 78

1977 U.S. Army Report

11.2.3

1978 NASA Report

78

11.2.4

1981 United Kingdom Paper

78

11.3

Conclusion

79

Section

12.0

Time of Day Weightings for Aircraft Noise

81

12.1

Historical Background

82

12.2

Review of the Choice of DNL

82

12.3

Study Results

84

12.4

Conclusion

85

Section

13.0

Noise contours

87

13.1

Introduction

87

13.2

The Uses and Interpretation of Noise Contours

89

13.3

Application and Interpretation of Noise Contours

90

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13.3.1 13.3.2

DNL 65 Contour DNL 75 Contour

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Section

14.0

Airport Noise Exposure and Land Use Compatibility

93

14.1

Introduction

94

14.2

FAA FAR Part 150 Guidelines

94

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Page 14.3 Federal Interagency Criteria 95

14.4 U.S. Air Force AICUZ Criteria

95

14.5 HUD and VA Criteria

97

14.6 Conclusion

97

Section

15.0 Effects of Aircraft Noise on Real Estate Values

99

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15.1 Introduction

15.2 Research Considerations

l00

15.3 Review of Research

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15.4 Conclusion

101

Further Information

103

v Top Return to NPC Library Return to NPC Home Page LIST OF FIGURES Page

Case 1:01-cv-00201-VJW Document 219-6 Filed 10/05/2006 1.1 Community Response to Aircraft Noise Near Major Airports 2.1 Frequency Spectrum

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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

Case 1:01-cv-00201-VJW 5.1 Cross-Section of the Ear

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5.2 Cross-Section of the Middle Ear

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5.3 Damage Risk Criteria Curves

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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

7.1

Sleep Stages

52

Case 1:01-cv-00201-VJW Document 219-6 7.2 Sleep Disturbance by Noise

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7.3

Composite of Laboratory Data for Sleep Interference

56

9.1

Dose Response of 11 Different Animal Species

64

10.1

Human Tolerance of Structural Vibration

72

10.2

Human Tolerance of Vibration Caused by Concorde

72

10.3

N-Wave Signature

73

10.4

Adverse Reactions to Sonic Booms

75

13.1

Typical Noise Contour

88

13.2

Applications of DNL 65 Contour

91

13.3

Applications of DNL 75 Contour

91

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LIST OF TABLES

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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LIST OF TERMS 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

Case 1:01-cv-00201-VJW Document 219-6 DNL Day-Night Average Noise Level

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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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Case 1:01-cv-00201-VJW Document 219-6 Filed 10/05/2006 NASA National Aeronautics and Space Administration

Page 18 of 98

NEF

Noise Exposure Forecast

NIPTS

Noise Induced Permanent Threshold Shift

NNI

Noise and Number Index

NREM

Non-Rapid Eye Movement Sleep

NTSB

National Transportation Safety Board

OSHA

Occupational Safety and Health Administration

PNL

Perceived Noise Level

PNLT

Tone Corrected Perceived Noise Level

PSIL

Preferred Speech Interference Level

REM

Rapid Eye Movement Sleep

SAE

Society of Automotive Engineers

SEL

Sound Exposure Level

SIL

Speech Interference Level

SST

Super Sonic Transport

TA

Time Above (a certain noise level)

TTS

Temporary Threshold Shift

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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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TABLE 1.1 Comparative Noise Levels 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

Case 1:01-cv-00201-VJW Ringing alarm clock (at 2 feet)

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Loudly reproduced orchestral music in large room Beginning of hearing damage if prolonged exposure over 85 dBA Printing press plant

82

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. 2

How Does Sound Get Around? 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.

Case 1:01-cv-00201-VJW Document 219-6 Filed 10/05/2006 Page 22 of 98 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

Case 3. wildlife1:01-cv-00201-VJW 4. farm animals

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Years of experience in airport planning and development have resulted in guidelines which match uses of land -- like hospitals or concert halls -- with normally compatible noise levels; these guidelines are published in an FAA regulation called Federal Aviation Regulation (FAR) PART 150. Implementation of an FAR150 study will assist airport operators and neighbors in minimizing the extent of non-compatible land uses. While the reactions of animals to noise have been studied, it is another research area plagued with widely varying results. In all but extreme cases (such as in pristine wilderness or in the case of excessive noise levels) wildlife and domesticated animals rarely display any reactions to aviation noise. How Do You Measure Aircraft Noise? sound is often measured using a sound level meter with a filter which simulates the human hearing response. This filter and the human ear give greater emphasis to sounds in the speech-important frequency bands and less emphasis to the lower and higher frequencies. This differential response in the human ear may have developed over the course of human evolution as a way to filter the sounds of wind and water which might interfere with survival-related communications such as "Here comes a Tyrannosaurus Rex--run for it!" In any event, this filter is called the A-weighting filter, and the sound measured with this filter is called the A-level (AL). Now I Know What AL is, but I Am Confused About "Energy Dose." What Exactly is the Sound Exposure Level (SEL)? When our sound level meter is measuring the AL, think of the sound falling on the microphone like rain or snow. The maximum rate of rainfall is the maximum AL. Now consider the sound level meter as a bucket or pail. After the "noise event" has passed (aircraft flyover or truck passby) the rain or snow collected in the bucket (having passed through the microphone) is the noise dose or Sound Exposure Level (SEL). Essentially, loud noise events create a large bucket (dose) of sound energy, while quieter events create smaller buckets. Now What Do I Do With "Buckets" of Noise (the Leq and DNL)? The buckets are typically collected over a 24-hour time period and are poured into a large container. The total volume collected during the 24-hour time period is averaged to formulate a value called the "Equivalent sound Level", or Leq. When the buckets collected during the nighttime hours are multiplied by 10 (because of greater potential for disturbing people) and then the volume averaged, we formulate a value called the "Average Day Night sound Level" or DNL. The Leq and DNL are values one often encounters in looking at the overall noise exposure from an airport operation.

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REFERENCE 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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Case 1:01-cv-00201-VJW Section 2.0 NOISE METRICS

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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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2.1 INTRODUCTION The topic of noise metrics has traditionally involved a rather confusing proliferation of units and indices. In response to the requirements of the Aviation Safety and Noise Abatement Act of 1979 (P.L 96-193), the FAA established a single system of metrics for measuring and evaluating noise for land use planning and environmental impact assessment. The FAA also has another system of metrics which it employs for certification of commercial aircraft. This section describes both systems of metrics. It also identifies other noise metrics frequently and necessarily employed in noise certification and provides detailed analysis of noise effects such as speech interference, hearing impact and sleep disturbance. Sound measures, or more academically, acoustical metrics, all consist of three basic building blocks: 1) sound pressure level, expressed in decibels, 2) frequency or pitch of the sound, and 3) time. The sound pressure levels at various frequencies (points 1 and 2 above), for a given point in time, are usually combined into a frequency spectrum (see Figure 2.1), which is somewhat analogous to the fingerprint of the sound. This spectrum, which varies with time, represents the real starting point for the metric story (see Figure 2.2). From this point of origin, the following classes of metrics have evolved: (1) Single Event Maximum Sound Levels (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

Case linearly additive noisiness Document 219-6 Filed 10/05/2006 Page of of 98 subjective1:01-cv-00201-VJW scale to a logarithmic dB-type scale, where an increase 2810 dB in PNL is equivalent to a doubling of its perceived noisiness. Page 11 Top Return to NPC Library Return to NPC Home Page

2.2.4 Tone Corrected Perceived Noise Level (PNLT), PNdB. Tone Corrected Perceived Noise Level is basically the Perceived Noise Level adjusted to account for the presence of discrete frequency components. PNLT was developed to aid in prediction of perceived noisiness for aircraft flyovers and vehicle noise which contain pure tones, or have pronounced irregularities in their spectrum. The method for calculating PNLT adopted by the FAA involves calculation of the PNL of a sound and the addition of a tone correction based on the tonal frequency and the amount that the tone exceeds the noise in the adjacent one-third octave bands. 2.3 SINGLE EVENT ENERGY DOSE METRICS The following noise metrics are generically related, each representing a noise energy dose. Each metric reflects both the maximum sound level and the duration of the event. As shown in Figure 2.2, these metrics are derived from single event sound level metrics. 2.3.1 Effective Perceived Noise Level (EPNL), Expressed in dB or EPNdB. Effective Perceived Noise Level is a single number measure of complex aircraft flyover noise which approximates human annoyance responses. It is derived from PNL and PNLT and includes correction terms for the duration of an aircraft flyover and the presence of audible pure tones or discrete frequencies (such as the whine of a jet aircraft) in the noise signal. The EPNL is used by the FAA as the noise certification metric for large transport and turbojet aircraft and helicopters. 2.3.2 Sound Exposure Level (SEL), Expressed in dB. SEL is a measure of the effect of duration and magnitude for a single event measured in A-weighted sound level above a specified threshold which is at least 10 dB below the maximum value. In typical aircraft noise model calculations, SEL is used in computing aircraft accoustical contribution to the Equivalent Sound Level (Leq) and the Day-Night Sound Level (DNL). 2.4 CUMULATIVE ENERGY AVERAGE METRICS The cumulative energy average noise metrics are usually derived from single event energy dose metrics. These metrics can also be computed from continuous noise measurement data. Cumulative metrics correlate well with aggregate community annoyance response. They were not designed as single source measures, so they do not account adequately for tonal components. Nor do they relate accurately to speech interference, sleep disturbance or other phenomena requiring analysis using single event maximum and energy dose sound level data. In practice, these measures are not used in determining source standards or for certification of product noise. 2.4.1 Equivalent Sound Level (Leq), Expressed in dB. Equivalent sound level, Leq, is the energy average noise level (usually A-weighted) integrated over some specified time. Equivalent signifies that the total

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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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TABLE 2.1 METRIC One-third Octave Sound Pressure Levels DESCRIPTION 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 An airport cumulative metric derived from dB(A) and applied as follows: Airport Noise Analysis l050.lD Analysis Noise Monitoring Systems

TA

Case 1:01-cv-00201-VJW Document 219-6 Filed 10/05/2006 Page 32 of 98 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 An airport cumulative metric derived from SEL; no application in aviation

Leq

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 An airport cumulative metric derived from SEL used only by the state of California; CNEL will be phased out in the next few years.

CNEL

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twenty-three (non-consecutive) test days. It was found that the (1) maximum noise level, (2) the number of noise events, and (3) the duration of the events (reflected in cumulative energy noise indices) correlated well with community annoyance response. The results of this program provided strong evidence that the same analytical tool, the DNL metric, employed at airports with large numbers of operations can be used with confidence in assessing the environmental impact (human response) of comparatively small numbers of helicopter operations. 2.8 SUMMARY OF NOISE METRIC POLICY The FAA noise metric usage policy is presented in Figure 2.2. The figure shows the genealogy of the various types of metrics starting from the one-third octave sound pressure level data. The dBA, PNL and PNLT are identified as pertinent sound levels. SEL and EPNL are identified as significant single event cumulative energy (or dose) metrics while Leq, DNL, CNEL and NEF are recognized as airport cumulative exposure metrics along with TA and Lx. The policy outline reflects the stated position supporting ALm as the single event maximum sound level metric, SEL as the single event dose metric, and DNL as the airport cumulative noise metric. EPNL is retained as a certification noise metric. The SEL, TA and Lx metrics are all descendants of the A-weighted sound level and their use is consistent with stated policy. 2.9 NOISE METRICS APPLICATIONS Each of the noise metrics discussed above has a specific set of applications for which it is most

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Page 17 Top Return to NPC Library Return to NPC Home Page REFERENCES 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 SUMMARY 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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3.1 INTRODUCTION Responses of annoyance are the most common reaction to aircraft noise. This section discusses, first, how people perceive noisiness, and second, some of the emotional and physical variables which may influence an individual's response to a sound. A review of pertinent research concludes this section. 3.2 PERCEPTION OF NOISE How people perceive loudness or noisiness of any given sound depends on several measurable physical characteristics of the sound. These factors are: A. Intensity. In general, a ten decibel increase in intensity may be considered a doubling of the perceived loudness or noisiness of a sound; however, other psychoacoustic evidence suggests that a somewhat greater than IO decibel increase in peak level of airplane flyover noise is required to produce a perceived doubling of loudness. B. Frequency Content. Sounds with concentration of energy between 2,000 Hz and 8,000 Hz are perceived to be more noisy than sounds of equal sound pressure level outside this range. C. Changes in Sound Pressure Level. Sounds that are increasing in level are judged to be somewhat louder than those decreasing in level (consider police and emergency vehicle sirens). D. Rate of Increase of Sound Pressure Level. Impulsive sound (ones reaching a high peak very abruptly, such as pile drivers or jack hammers) are usually perceived to be very noisy. 3.3 VARIABLES AFFECTING RESPONSE Individual human response to noise is subject to considerable natural variability, over the past 35 years, researchers have identified many of the factors which contribute to the variation in human reaction to noise. 3.3.1 Emotional Variables. Knowledge of the existence of these individual variables helps to understand why it is not possible to state simply that a given noise level from a given noise source will elicit a particular community reaction or have a certain environmental impact. In order to do that, it would be necessary to know how much each variable contributes to human reaction to noise. Research in psychoacoustics has revealed that an individual's attitudes, beliefs and values may greatly influence the degree to which a person considers a given sound annoying. The aggregate emotional response of an individual to noise has been found to depend on: A. Feelings about the Necessity or Preventability of the Noise. If people feel that their needs and concerns are being ignored, they are more likely to feel hostile towards the noise. This feeling of being

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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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Ref 1Ref 2

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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). _ REFERENCES 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? SUMMARY _ 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

Case 1:01-cv-00201-VJW Document 219-6 suggests that because aircraft noise falls over a structure, likeFiled 10/05/2006 opposed to passing a house, equally, as Page 41 of 98 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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_ Ref 4

30 Top Return to NPC Library Return to NPC Home Page Fortunately, other researchers have examined this topic; their views aid in going past the Schultz Kryter stalemate. 4.3 HALL'S RESEARCH AND ANALYSIS In 1981, Fred Hall reported on data which had been collected around the Toronto International Airport (Ref. 4). For the first time, data had been collected on both aircraft and ground traffic noise using comparable questions and measured in DNL, thus alleviating the need for juggling survey results to fit DNL, as Kryter and Schultz had to do. His conclusion was that there is indeed a difference between community responses to aircraft noise and to road traffic noise when each is measured by DNL. Figure 4.3 relates his findings in relation to Schultz's synthesis curve; Hall notes that the aircraft noise curve falls out of proportion with the others. For the same noise level, a greater percentage of people are highly annoyed by aircraft noise. The

Case 1:01-cv-00201-VJW two sources is not difference in annoyance at the Document 219-6 constant but instead increases as Ldn increases. The difference in annoyance is equivalent to about 8 dB at

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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.

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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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Section 5.0 HEARING and HEARING LOSS SUMMARY 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

Case 1:01-cv-00201-VJW Document 219-6 Filed 10/05/2006 Page 44 of environments. These temporary sensitivity shifts are not unusual in the industrial setting and do not 98 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

Case 1:01-cv-00201-VJW Document 219-6 through the oval window, displacing the fluid in the inner ear. Filed 10/05/2006 Page 45 of 98 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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5.3 AUDITORY RANGE The ear is capable of hearing a frequency range of about nine octaves and a dynamic range of more than120 dB. The least pressure needed to make a tone audible (the