Acoustics and Psychoacoustics

David M. Howard, Jamie Angus

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781317508298
• Edition: 5
• Topic: Technologie et ingénierie
• Subtopic: Ingénierie de l'acoustique

The acoustics of a space can have a real impact on the sounds you create and capture. Acoustics and Psychoacoustics, Fifth Edition provides supportive tools and exercises to help you understand how music sounds and behaves in different spaces, whether during a performance or a recording, when planning a control room or listening space, and how it is perceived by performers, listeners, and recording engineers.

With their clear and simple style, Howard and Angus cover both theory and practice by addressing the science of sound engineering and music production, the acoustics of musical instruments, the ways in which we hear musical sounds, the underlying principles of sound processing, and the application of these concepts to music spaces to create professional sound. This new edition is fully revised to reflect new psychoacoustic information related to timbre and temporal perception, including an updated discussion of vocal fold vibration principles, samples of recent acoustic treatments, and a description of variable acoustics in spaces, as well as coverage of the environment's effect on production listening, sonification, and other topics.

Devoted to the teaching of musical understanding, an accompanying website (www.routledge.com/cw/howard) features various audio clips, tutorial sheets, questions and answers, and trainings that will take your perception of sound to the next level.

This book will help you:

• 
  
  

• Gain a basic grounding in acoustics and psychoacoustics with respect to music audio technology systems

• 
  
  

• Incorporate knowledge of psychoacoustics in future music technology system designs as appropriate

• 
  
  

• Understand how we hear pitch, loudness, and timbre

• 
  
  

• Learn to influence the acoustics of an enclosed space through designed physical modifications

Chapter 1

Introduction to Sound

Chapter Contents

• 1.1 Pressure Waves and Sound Transmission
  • 1.1.1 The Nature of Sound Waves
  • 1.1.2 The Velocity of Sound Waves
  • 1.1.3 The Velocity of Sound in Air
  • 1.1.4 Transverse and Other Types of Waves
  • 1.1.5 The Velocity of Transverse Waves
  • 1.1.6 Waves in Bars and Panels
  • 1.1.7 The Wavelength and Frequency of Sound Waves
  • 1.1.8 The Wavenumber of Sound Waves
  • 1.1.9 The Relationship between Pressure, Velocity and Impedance in Sound Waves
• 1.2 Sound Intensity, Power and Pressure Level
  • 1.2.1 Sound Intensity Level
  • 1.2.2 Sound Power Level
  • 1.2.3 Sound Pressure Level
• 1.3 Adding Sounds Together
  • 1.3.1 The Level When Correlated Sounds Add
  • 1.3.2 The Level When Uncorrelated Sounds Add
  • 1.3.3 Adding Decibels Together
• 1.4 The Inverse Square Law
  • 1.4.1 The Effect of Boundaries
• 1.5 Sound Interactions
  • 1.5.1 Superposition
  • 1.5.2 Sound Refraction
  • 1.5.3 Sound Absorption
  • 1.5.4 Sound Reflection from Hard Boundaries
  • 1.5.5 Sound Reflection from Bounded to Unbounded Boundaries
  • 1.5.6 Sound Interference
  • 1.5.7 Standing Waves at Hard Boundaries (Modes)
  • 1.5.8 Standing Waves at Other Boundaries
  • 1.5.9 Sound Diffraction
  • 1.5.10 Sound Scattering
• 1.6 Time and Frequency Domains
  • 1.6.1 What Is Fourier Theory?
  • 1.6.2 The Spectrum of Periodic Sound Waves
  • 1.6.3 The Effect of Phase
  • 1.6.4 The Spectrum of Nonperiodic Sound Waves
• 1.7 Analyzing Spectra
  • 1.7.1 Filters and Filter Types
  • 1.7.2 Filter Time Responses
  • 1.7.3 Time Responses of Acoustic Systems
  • 1.7.4 Time and Frequency Representations of Sounds
• Bibliography

Sound is something most people take for granted. Our environment is full of noises, which we have been exposed to from before birth. What is sound, how does it propagate and how can it be quantified? The purpose of this chapter is to introduce the reader to the basic elements of sound, the way it propagates and related topics. This will help us understand both the nature of sound and its behavior in a variety of acoustic contexts and allow us to understand both the operation of musical instruments and the interaction of sound with our hearing.

1.1 Pressure Waves and Sound Transmission

At a physical level, sound is simply a mechanical disturbance of the medium, which may be air, or a solid, liquid or other gas. However, such a simplistic description is not very useful, as it provides no information about the way this disturbance travels or any of its characteristics other than the requirement for a medium in order for it to propagate. What is required is a more accurate description that can be used to make predictions of the behavior of sound in a variety of contexts.

Figure 1.1 Golf Ball-and-Spring Model of a Sound-Propagating Material

1.1.1 The Nature of Sound Waves

Consider the simple mechanical model of the propagation of sound through some physical medium, shown in Figure 1.1. This shows a simple one-dimensional model of a physical medium, such as air, which we call the golf ball-and-spring model because it consists of a series of masses, for example, golf balls, connected by springs. The golf balls represent the point masses of the molecules in a real material, and the springs represent the intermolecular forces between them. If the golf ball at the end is pushed toward the others, then the spring linking it to the next golf ball will be compressed and will push at the next golf ball in the line, which will compress the next spring, and so on.

Because of the mass of the golf balls, there will be a time lag before they start moving from the action of the connecting springs. This means that the disturbance caused by moving the first golf ball will take some time to travel down to the other end. If the golf ball at the beginning is returned to its original position, the whole process just described will happen again, except that the golf balls will be pulled rather than pushed and the connecting springs will have to expand rather than compress. At the end of all this, the system will end up with the golf balls having the same average spacing that they had before they were pushed and pulled.

The region where the golf balls are pushed together is known as a “compression,” whereas the region where they are pulled apart is known as a “rarefaction,” and the golf balls themselves are the propagating medium. In a real propagating medium, such as air, a disturbance would naturally consist of either a com...