The Effects of Sound on People (eBook)

James P. Cowan (Autor)

eBook Download: EPUB

2016
John Wiley & Sons (Verlag)
978-1-118-89568-9 (ISBN)

Infos

Provides a summary of current research results on the physiological and psychological effects of sound on people

• Covers how the operation of the hearing mechanism affects our reactions to sounds
• Includes research results from studies on noise sources of public concern such as transportation, public utility, and recreational sources, with emphasis on low frequency sound and infrasound
• Covers sounds that affect some but not others, how sounds can be controlled on a practical level, and how and what sounds are regulated
• Includes coverage of both positive and negative effects of sound

Autor

James P. Cowan is a board-certified noise control engineer with more than 30 years of experience in noise control, architectural acoustics, and environmental noise issues. He has consulted to public agencies, architects, engineers, industrial personnel, and attorneys in all areas of noise control; hearing damage and protection criteria; and acoustic design of all types of spaces. Mr. Cowan has lectured on acoustical topics to thousands of professionals, delivering live seminars and webinars, and teaching courses for universities, professional societies, and private organizations across the US for more than 25 years. In addition to several book chapters and many published articles, Mr. Cowan is the author of Architectural Acoustics Design Guide, published by McGraw-Hill in 2000, Architectural Acoustics, an interactive educational CD set published by McGraw-Hill in 1999, and Handbook of Environmental Acoustics, a reference book in community noise issues published by Van Nostrand Reinhold (subsequently Wiley) in 1994.

Inhalt

List of Figures

List of Tables

About the Author

Series Preface

Preface

Chapter 1 Acoustic parameters

1.1 Introduction

1.2 Sound generation

1.2.1 Frequency

1.2.2 Wavelength

1.3 Sound propagation

1.3.1 Unimpeded divergence

1.3.2 Impeded propagation

Reflection

Refraction

Diffraction

Diffusion

1.3.3 Sound behavior indoors

Echo

Room modes

Reverberation

1.3.4 Sound behavior outdoors

Atmospheric absorption

Atmospheric refraction

Ground effects

Vegetation effects

Chapter 2 Sound description

2.1 Introduction

2.2 The decibel scale

2.3 Frequency weighting networks

2.3.1 Loudness

2.3.2 Weighting scales

2.4 Frequency band analysis

2.4.1 Noise by color

2.5 Common sound descriptors

2.5.1 Environmental descriptors

2.5.2 Sound propagation in terms of sound levels

Divergence

Refraction and diffraction

Reverberation

Chapter 3 Sound perception

3.1 Introduction

3.2 Human hearing apparatus and mechanism

3.2.1 Outer ear

3.2.2 Middle ear

3.2.3 Inner ear

3.2.4 Signal processing in the brain

Localization

Masking and audibility

3.2.5 Vestibular system

3.3 Alternate sound perception mechanisms

3.3.1 Bone conduction

3.3.2 Cartilage hearing

3.3.3 Tinnitus

3.34 Electromagnetic hearing

3.4 Hypersensitivities

3.4.1 Hyperacusis/misophonia

3.4.2 Electrohypersensitivity

3.5 Low frequency and infrasound perception

Chapter 4 Physiological effects of sound exposure

4.1 Introduction

4.2 Body resonance and damage potential

4.3 Hearing loss

4.3.1 Presbycusis

4.3.2 Noise-induced hearing loss

4.3.3 Hearing loss from illness or agents

4.4 Cardiovascular disease

4.4.1 Hypertension

4.4.2 Ischaemic diseases

4.5 Vibroacoustic disease

4.6 Low frequency noise concerns

4.7 Infrasound concerns

Chapter 5 Psychological effects of sound exposure

5.1 Introduction

5.2 Annoyance

5.3 Stress

5.4 Sleep disturbance

5.5 Learning disabilities

5.5.1 Cognitive development/school performance

5.5.2 Office/occupational

5.6 Emotional effects

Chapter 6 Sound sources associated with negative effects

6.1 Introduction

6.2 Transportation sources

6.2.1 Roadway

6.2.2 Aircraft

Fixed wing

Rotary wing

6.2.3 Rail

6.3 Industry and utilities

6.3.1 Power plants

6.3.2 Wind farms

6.3.3 Electrical power systems

6.4 Personal/recreational sources

6.4.1 Firearms

6.4.2 Public performances

6.4.3 Toys/ personal listening devices

6.4.4 Appliances/tools

6.5 Hums

6.6 Acoustic weapons

Chapter 7 Positive effects of sound

7.1 Introduction

7.2 Music psychology

7.3 Sound therapies

7.4 Natural sources/soundscapes

7.5 Using sound to influence people

Chapter 8 Sound control and regulation

8.1 Introduction

8.2 Sound control fundamentals

8.2.1 Absorption

8.2.2 Transmission control

8.2.3 Partial barriers

8.2.4 Cancellation

8.2.5 Control at the source

8.2.6 Control in the path between the source and listener

8.2.7 Control at the listener

Acoustic privacy

8.3 Regulations and guidelines

8.3.1 Occupational

8.3.2 Environmental

National

Local

8.4 Current and future research

Glossary

Index

Textauszug

1
Acoustic Parameters

1.1 Introduction

Acoustics is the science of sound. It involves many scientific disciplines, most notably physical, mechanical, electrical, biological, and psychological components. This interdisciplinary branch of science has permitted us to evaluate and control sound both to our advantage and to our detriment. Although hearing is not an essential element in acoustics, it has been the basis for our evaluations of sound over the centuries. As one of the most important mechanisms in our survival, the sense of hearing and the interpretation of sound shape our world.

Any discussion about the effects of sound on people must begin with an explanation of the parameters associated with sound generation, propagation, description, and perception. Without an understanding of these principles, a discussion about the effects of sound would not provide any meaningful information to the reader. This chapter covers sound generation and propagation, describing the most common ways in which a sound wave is altered as it travels from its source to a listener.

1.2 Sound generation

Sound energy is generated when a medium is disturbed by particle motion. This disturbance generates pressure variations in the medium. These pressure variations travel in patterns associated with medium conditions and dissipate as they expand from a local source over an increasingly larger area. A simple two-dimensional representation of this can be visualized when a still body of water is disturbed by a small object or drop of water at a single location, as shown in Figure 1.1. The ripples in the water show peaks and valleys of pressure variations radiating out from the single point of contact.

Figure 1.1 Water disturbance pattern illustrating wave propagation from a point source in two dimensions

Sound energy in air radiates from a stationary source in a similar pressure pattern but in three dimensions. This pattern is characterized mainly by three parameters that are mathematically interdependent – frequency, wavelength, and wave speed. The main distinguishing factor between this type of energy and all others is that it can be detected by a hearing mechanism and interpreted for some form of action or communication. For the purposes of the information in this book, the term “sound” refers to any energy that is capable of stimulating the human hearing mechanism, as described in Chapter 3. The term “noise” refers to a subset of sound that is interpreted by humans as negatively affecting their environment. Sound therefore does not require personal interpretation, as noise is a subjective qualification. Sound exists in the forest if a tree falls and no one is there to hear it, but that same tree falling would not generate noise unless someone is there not only to hear it but also to interpret it as having a negative quality.

Sound requires a medium for the energy to propagate to a listener. It does not exist in a vacuum or in outer space. The big bang at the beginning of our universe generated no sound, although the word “bang” certainly implies the generation of sound. The key attribute of sound is that it its energy is of a form capable of stimulating a hearing mechanism.

1.2.1 Frequency

The simplest sound pressure pattern is generated by a source having pressure variations occurring at a constant rate, known as a pure tone. This would result in a sinusoidal pattern traveling away from the source as a wave, as shown in Figure 1.2, with the acoustic pressure oscillating with respect to equilibrium (the 0 position in Figure 1.2) at atmospheric pressure. This sinusoidal pressure pattern occurs with respect to both time and distance from the source. The time elapsed between repeating parts of the pressure pattern is known as the period of the wave, in units of cycles. The rate at which this pressure variation takes place is the reciprocal of the period, and is designated as the frequency, in units of cycles/second (s). The unit of cycles/s is most commonly denoted as Hertz (Hz), named for the German physicist Heinrich Hertz (1857–1894), who is primarily known for proving the existence of electromagnetic waves.

Figure 1.2 Acoustic pressure pattern for a single frequency (pure tone) with time

Humans can generally hear acoustic energy between 20 and 20,000 Hz but with varying sensitivity in that range. We are most sensitive to sounds in the 2,500–4,000 Hz range due to ear canal amplification (to be discussed further in Chapter 2), which is also the critical frequency range for speech intelligibility through consonant sound recognition. Although we can hear sounds below 20 Hz and above 20,000 Hz, their pressures must be many orders of magnitude higher than those in the 2,000 Hz range to be perceived at the same loudness.

Sounds with dominant energy below 20 Hz are categorized as infrasound and sounds with dominant energy above 20,000 Hz are labeled as ultrasound. There has been a significant amount of research and attention paid to infrasound and its potential effects on people and this is discussed in later sections of this book. Except at very high levels, infrasound is not audible and can be perceived as vibratory feelings in the body. There is conflicting information in the literature regarding the need for auditory perception for a sound to have any effect on people and this information is discussed in Chapter 4.

Ultrasound is not known to cause any noticeable effects on people but may affect other species due to variations in frequency sensitivities between species. For example, bats and dolphins rely on ultrasound to navigate and communicate, with peak sensitivities in the 20,000–80,000 Hz range [1].

As this book is focused on the human experience, only sound energy dominated in frequencies below 20,000 Hz is discussed. For those with musical knowledge, middle C on the piano keyboard is roughly 262 Hz. The American National Standards Institute has standardized the use of specific preferred frequencies to evaluate sound energy, based on 100.1N (where N is an integer value) [2]. The most common of these are between 63 and 8,000 Hz in constant-percentage frequency bandwidths, with each successive band’s center frequency being twice that of its predecessor. This doubling of frequencies is known as an octave increase, with the most commonly used frequencies being 63, 125, 250, 500, 1,000, 2,000, 4,000, and 8,000 Hz. These are known as the most common octave band center frequencies used to describe sounds perceived by humans.

One important aspect of frequency analysis that seems to be confused in much of the literature is a reference to frequencies without associated intensities. Sound energy in every frequency range is constantly varying around us, but we are only affected when the energy levels associated with those frequencies are high enough to elicit a reaction. For example, if sound energy in the 100 Hz range is of interest for its effects on people, it is inappropriate to consider it an issue without also knowing the magnitude or sound level associated with energy in that frequency range. There is a magnitude threshold below which sound energy will not cause negative effects for most people (although sensitivities vary for each person) and that level varies with frequency.

Pure tones (with dominant acoustic energy at a single frequency) rarely exist in nature and are sometimes generated by man-made sources. For the most part, however, the sounds we are exposed to are composed of contributions from energy at all audible frequencies.

Musical sounds and some sounds generated by machinery are often composed of energy peaks at integer multiples of a base frequency, called the fundamental frequency. The integer multiples of the fundamental frequency are often called harmonics. Harmonics tend to enhance the enjoyment of sounds in music but that is not always the case for other types of sources. Examples of acoustic signatures incorporating harmonics are mentioned in later sections of this book.

1.2.2 Wavelength

As mentioned earlier, the sinusoidal pressure wave pattern for a pure tone occurs in terms of both time and distance. When viewing this variation in terms of distance, as shown in Figure 1.3, the distance between repeating parts of the wave is known as the wavelength. Wavelength is associated with frequency according to the following equation, as long as the speed of the sound wave is constant:

(1.1)

Figure 1.3 Acoustic pressure pattern for a single frequency (pure tone) with distance

where c is the speed of sound, ƒ is the frequency, and λ is the wavelength.

This demonstrates an inverse relationship between frequency and wavelength, which is revealed in Table 1.1 (based on equation 1.1).

Table 1.1 Correlation between frequency and wavelength in air at 20°C

Frequency (Hz)

Wavelength (m)

20

17

100

3.43

343

1

1,000

0.343

4,000

0.086

8,000

0.043

16,000

0.021

Considering that materials effective in controlling sound must at a...

Produkt-Details

• Erscheint lt. Verlag: 22.3.2016
• Reihe/Serie: Wiley Series in Acoustics Noise and Vibration
• Reihe/Serie: Wiley Series in Acoustics Noise and Vibration
• Reihe/Serie: Wiley Series in Acoustics Noise and Vibration
• Sprache: englisch
• Themenwelt: Technik ► Maschinenbau
• Schlagworte: acoustic • Acoustic effects • Acoustic Physics • Control Process & Measurements • effect of sound • Energie • Energie u. Umweltaspekte • Energy • Energy & Environmental Impact • Hearing research • Human Hearing • infrasound effects • low frequency sound effects • Maschinenbau • mechanical engineering • Mess- u. Regeltechnik • negative effects of sound • noise control principles • noise effects • Noise sources • Physics • Physics of Acoustics • Physik • Physik des Schalls • positive effects of sound • Sound Control • sound effects • sound generation • Sound Perception
• ISBN-10: 1-118-89568-1 / 1118895681
• ISBN-13: 978-1-118-89568-9 / 9781118895689