The Effects of Sound on People

James P. Cowan

• Publisher: Wiley
• Year: 2016
• ISBN:
  9781118895689
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

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

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. Alth...

Table of contents

• Cover
• Title Page
• Table of Contents
• List of Figures
• List of Tables
• About the Author
• Series Preface
• Preface
• 1 Acoustic Parameters
• 2 Sound Description
• 3 Sound Perception
• 4 Physiological Effects of Sound Exposure
• 5 Psychological Effects of Sound Exposure
• 6 Sound Sources Associated with Negative Effects
• 7 Positive Effects of Sound
• 8 Sound Control and Regulation
• Glossary
• Index
• End User License Agreement