Master Handbook of Acoustics

Master Handbook of Acoustics

Authors: F. Alton Everest and Ken Pohlmann

Published: June 2009

eISBN: 9780071603331 0071603336 | ISBN: 9780071603324

Contents

Introduction

1 Fundamentals of Sound

The Sine Wave

Sound in Media

Particle Motion

Propagation of Sound

Speed of Sound

Wavelength and Frequency

Complex Waves

Harmonics

Phase

Partials

Octaves

Spectrum

Electrical, Mechanical, and Acoustical Analogs

2 Sound Levels and the Decibel

Ratios versus Differences

Expressing Numbers

Logarithms

Decibels

Reference Levels

Logarithmic and Exponential Forms Compared

Acoustic Power

Using Decibels

Example 1: Sound-Pressure Level

Example 2: Loudspeaker SPL

Example 3: Microphone Specifications

Example 4: Line Amplifier

Example 5: General-Purpose Amplifier

Example 6: Concert Hall

Example 7: Combining Decibels

Measuring Sound-Pressure Level

Sine-Wave Measurements

3 Sound in the Free Field

The Free Field

Sound Divergence

Sound Intensity in the Free Field

Sound Pressure in the Free Field

Examples: Free-Field Sound Divergence

Sound Fields in Enclosed Spaces

Hemispherical Field and Propagation

4 The Perception of Sound

Sensitivity of the Ear

Ear Anatomy

The Outer Ear

Directional Cues: An Experiment

The Ear Canal

The Middle Ear

The Inner Ear

Stereocilia

Loudness versus Frequency

Loudness Control

Area of Audibility

Loudness versus Sound-Pressure Level

Loudness and Bandwidth

Loudness of Impulses

Audibility of Loudness Changes

Pitch versus Frequency

An Experiment in Pitch

The Missing Fundamental

Timbre versus Spectrum

Localization of Sound Sources

Binaural Localization

Law of the First Wavefront

The Franssen Effect

The Precedence Effect

Perception of Reflected Sound

The Cocktail-Party Effect

Aural Nonlinearity

Subjective versus Objective

Occupational and Recreational Deafness

Summary

5 Signals, Speech, Music, and Noise

Sound Spectrograph

Speech

Vocal Tract Molding of Speech

Formation of Voiced Sounds

Formation of Unvoiced Sounds

Frequency Response of Speech

Directionality of Speech

Music

String Instruments

Wind Instruments

Nonharmonic Overtones

Dynamic Range of Speech and Music

Power in Speech and Music

Frequency Range of Speech and Music

Auditory Area of Speech and Music

Noise

Noise Measurements

Random Noise

White and Pink Noise

Signal Distortion

Harmonic Distortion

Resonance

Audio Filters

6 Reflection

Specular Reflections

Flutter Echoes

Doubling of Pressure at Reflection

Reflections from Convex Surfaces

Reflections from Concave Surfaces

Reflections from Parabolic Surfaces

Whispering Galleries

Standing Waves

The Corner Reflector

Mean Free Path

Perception of Sound Reflections

The Effect of Single Reflections

Perception of Spaciousness, Images, and Echoes

Effect of Angle of Incidence, Signal Type, and Spectrum on Audibility of Reflection

7 Diffraction

Wavefront Propagation and Diffraction

Wavelength and Diffraction

Diffraction of Sound by Obstacles

Diffraction of Sound by Apertures

Diffraction of Sound by a Slit

Diffraction by the Zone Plate

Diffraction around the Human Head

Diffraction by Loudspeaker Cabinet Edges

Diffraction by Various Objects

8 Refraction

The Nature of Refraction

Refraction of Sound in Solids

Refraction of Sound in the Atmosphere

Refraction of Sound in Enclosed Spaces

Refraction of Sound in the Ocean

9 Diffusion

The Perfectly Diffuse Sound Field

Evaluating Diffusion in a Room

Steady-State Measurements

Decay Beats

Exponential Decay

Spatial Uniformity of Reverberation Time

Geometrical Irregularities

Absorbent in Patches

Concave Surfaces

Convex Surfaces: The Polycylindrical Diffuser

Plane Surfaces

10 Comb-Filter Effects

Comb Filters

Superposition of Sound

Tonal Signals and Comb Filters

Combing of Music and Speech Signals

Combing of Direct and Reflected Sound

Comb Filters and Critical Bands

Comb Filters in Multichannel Playback

Reflections and Spaciousness

Comb Filters in Microphone Placement

Comb-Filter Effects in Practice: Six Examples

Estimating Comb-Filter Response

11 Reverberation

Growth of Sound in a Room

Decay of Sound in a Room

Idealized Growth and Decay of Sound

Calculating Reverberation Time

Sabine Equation

Eyring-Norris Equation

Air Absorption

Measuring Reverberation Time

Impulse Sources

Steady-State Sources

Measuring Equipment

Measurement Procedure

Reverberation and Normal Modes

Analysis of Decay Traces

Mode Decay Variations

Frequency Effect

Reverberation Characteristic

Reverberation Time Variation with Position

Decay Rate and the Reverberant Field

Acoustically Coupled Spaces

Electroacoustically Coupled Spaces

Eliminating Decay Fluctuations

Influence of Reverberation on Speech

Influence of Reverberation on Music

Optimum Reverberation Time

Bass Rise of Reverberation Time

Initial Time-Delay Gap

Listening Room Reverberation Time

Artificial Reverberation

Reverberation Time Calculations

Example 1: Untreated Room

Example 2: Modified Room

12 Absorption

Dissipation of Sound Energy

Absorption Coefficients

Reverberation Chamber Method

Impedance Tube Method

Tone-Burst Method

Mounting of Absorbents

Mid/High-Frequency Absorption by Porosity

Glass Fiber Insulation Materials

Glass Fiber: Boards

Glass Fiber: Acoustical Tile

Effect of Thickness of Absorbent

Effect of Airspace behind Absorbent

Effect of Density of Absorbent

Open-Cell Foams

Drapes as Sound Absorbers

Carpet as Sound Absorber

Effect of Carpet Type on Absorbance

Effect of Carpet Underlay on Absorbance

Carpet Absorption Coefficients

Sound Absorption by People

Sound Absorption in Air

Panel (Diaphragmatic) Absorbers

Polycylindrical Absorbers

Poly Construction

Bass Traps: Low-Frequency Absorption by Resonance

Helmholtz (Volume) Resonators

Perforated Panel Absorbers

Slat Absorbers

Placement of Materials

Reverberation Time of Helmholtz Resonators

Reducing Room Modes with Absorbers

Increasing Reverberation Time

Modules

13 Modal Resonances

Early Experiments and Examples

Resonance in a Pipe

Reflections Indoors

Two-Wall Resonance

Frequency Regions

Room-Mode Equation

Mode Calculations—An Example

Experimental Verification

Mode Decay

Mode Bandwidth

Mode Pressure Plots

Mode Density

Mode Spacing and Timbral Defects

Audibility of Timbral Defects

Optimal Room Shape

The Bonello Criterion

Splaying Room Surfaces

Nonrectangular Rooms

Controlling Problem Modes

Simplified Axial Mode Analysis

Summary

14 Schroeder Diffusers

Experimentation

Reflection Phase-Grating Diffusers

Quadratic-Residue Diffusers

Primitive-Root Diffusers

Performance of Diffraction-Grating Diffusers

Reflection Phase-Grating Diffuser Applications

Flutter Echo

Application of Fractals

Diffusion in Three Dimensions

Diffusing Concrete Blocks

Measuring Diffusion Efficiency

Comparison of Gratings with Conventional Approaches

15 Adjustable Acoustics

Draperies

Adjustable Panels: Absorption

Hinged Panels

Louvered Panels

Absorption/Diffusion Adjustable Panels

Variable Resonant Devices

Rotating Elements

Portable Units

16 Control of Interfering Noise

Approaches to Noise Control

Airborne Noise

Transmission Loss

Effect of Mass and Frequency

Coincidence Effect

Separation of Mass

Composite Partitions

Porous Materials

Sound Transmission Class

Comparison of Wall Structures

Sound-Insulating Windows

Sound-Insulating Doors

Structureborne Noise

Noise Transmitted by Diaphragm Action

Floating Floors

Floating Walls and Ceiling

Noise and Room Resonances

Noise Standards and Specifications

17 Noise Control in Ventilating Systems

Selection of Noise Criterion

Fan Noise

Machinery Noise and Vibration

Air Velocity

Natural Attenuation

Duct Lining

Plenum Silencers

Packaged Attenuators

Reactive Silencers

Tuned Silencers

Duct Location

ASHRAE

Active Noise Control

Some Practical Suggestions

18 Acoustics of Listening Rooms

Playback Criteria

Peculiarities of Small-Room Acoustics

Room Size and Proportion

Reverberation Time

Low Frequency Considerations

Modal Anomalies

Control of Modal Resonances

Bass Traps for the Listening Room

Mid-High Frequency Considerations

Identification and Treatment of Reflection Points

Lateral Reflections and Control of Spaciousness

Loudspeaker Placement

19 Acoustics of Small Recording Studios

Ambient Noise Requirements

Acoustical Characteristics of a Studio

Direct and Indirect Sound

Role of Room Treatment

Room Modes and Room Volume

Mode Analysis for Different Room Sizes

Reverberation Time

Reverberation in Small Rooms

Optimal Reverberation Time

Diffusion

Noise

Studio Design Example

Absorption Design Goal

Proposed Room Treatment

20 Acoustics of Control Rooms

Initial Time-Delay Gap

Live End-Dead End

Specular Reflections versus Diffusion

Low-Frequency Resonances in the Control Room

Initial Time-Delay Gaps in Practice

Loudspeaker Placement and Reflection Paths

The Reflection-Free-Zone Control Room

Control-Room Frequency Range

Outer Shell and Inner Shell of the Control Room

21 Acoustics of Audio/Video Rooms

Design Factors

Acoustical Treatment

Audio/Video Work Place Example

Appraisal of Room Resonances

Control of Room Resonances

Absorption Calculation

Proposed Treatment

Specialized Treatment

Voice-Over Booth

Dead versus Live Ambience

Early Reflections

Live End-Dead End Voice Studio

22 Acoustics of Large Halls

Essential Design Criteria

Reverberation and Echo Control

Hall Design for Speech

Volume

Hall Geometry

Absorption Treatment

Ceiling, Walls, and Floor

Speech Intelligibility

Speech Frequencies and Duration

Subject-Based Measures

Analytical Measures

Concert Hall Acoustical Design

Reverberation

Clarity

Brilliance

Gain

Seating Capacity

Volume

Spaciousness

Apparent Source Width

Initial Time-Delay Gap

Bass Ratio and Warmth

Concert Hall Architectural Design

Balcony

Ceiling and Walls

Raked Floor

Virtual Image Source Analysis

Hall Design Procedure

Case Studies

23 Acoustic Distortion

Acoustic Distortion and the Perception of Sound

Sources of Acoustic Distortion

Coupling of Room Modes

Speaker-Boundary Interference Response

Comb Filtering

Diffusion

Diffusion Measurement

Design Approach

24 Room Acoustics Measurement Software

Acoustic Measurements

Basic Analysis Instruments

Time-Delay Spectrometry Techniques

Maximum-Length Sequence Techniques

AcoustiSoft ETF Program

Frequency-Response Measurements

Resonance Measurements

Fractional-Octave Measurements

Energy-Time Curve Measurements

Reverberation Time

25 Room Optimizer

Modal Response

Speaker-Boundary Interference Response

Optimization

Theory of Operation

Prediction of Room Response

Optimizing Procedure

Cost Parameter

Optimization Procedure

Results of Operation

Stereo Pair

Stereo Pair with Two Woofers per Loudspeaker

5.1-Channel Home Theater with Dipole Surrounds

5.1-Channel Home Theater with Matched Satellites

Subwoofer

Summary

26 Room Auralization

History of Acoustic Modeling

The Auralization Process

Scattering Coefficients

Receiver Characterization

Echogram Processing

Room Model Data

Room Model Mapping

Binaural Playback

Summary

Biblography

Appendix

Glossary

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

V

W

Index