Active Noise Control Primer

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Springer Science & Business Media, May 5, 2000 - Science - 159 pages
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Active noise control - the reduction of noise by generating an acoustic signal that actively interferes with the noise - has become an active area of basic research and engineering applications. The aim of this book is to present all of the basic knowledge one needs for assessing how useful active noise control will be for a given problem and then to provide some guidance for designing, setting up, and tuning an active noise-control system. Written for students who have no prior knowledge of acoustics, signal processing, or noise control but who do have a reasonable grasp of basic physics and mathematics, the book is short and descriptive. It leaves for more advanced texts or research monographs all mathematical details and proofs concerning vibrations, signal processing and the like. The book can thus be used in independent study, in a classroom with laboratories, or in conjunction with a kit for experiment or demonstration. Topics covered include: basic acoustics; human perception and sound; sound intensity and related concepts; fundamentals of passive noise-control strategies; basics of digital systems; basics of adaptive controllers; and active noise control systems.
 

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Contents

Introduction
1
Chapter Summary
2
Do I Have to Read the Whole Book?
3
Adaptive Feedforward Active Noise Control
4
Advanced Reading
5
Background Fundamentals of Sound
7
What Is Noise?
8
Sound Waves
10
Passive Noise Control Approaches
84
Sidebranch Resonator
85
Expansion Chamber
86
Helmholtz Filter
87
Dissipative Passive Control Techniques
88
Active Noise Control Approaches
89
Reference and Error Signal Quality
90
Reference SensorControl Source Separation Distance
91

Frequency Analysis
14
Sine Waves
15
Fourier Analysis
19
Harmonics
21
1 Anything that Rotates
22
2 Many Devices Which Use Mains Electricity
24
3 Devices Which Are Driven Beyond Their Capabilities
25
Human Perception of Sound
27
Acceptable Sound Levels
30
Fundamentals of Noise Control
36
The Magnitude of Acoustic Power
40
Power Pressure and Hearing Loss
41
Real and Imaginary Impedance
42
What Is Noise Control?
43
What Is Active Noise Control?
44
Free Space Noise Control
46
Active Control Approaches
51
Enclosed Space Noise Control
67
How Does the Sound Get Out Again?
68
How Does the Sound Field Arrange Itself?
69
Passive Noise Control Approaches
74
Active Noise Control Approaches
76
Control of Sound Propagation in Ducts
81
Modes in Ducts
82
Impedance in Ducts
83
Control Source Position in the Duct
92
Active Noise Controller Overview
95
Some Important Facts
96
Controller Output Digital Control Filter Requirements
104
Adaptive Algorithm Requirements
107
Controller Fundamentals
113
General Control System Outlines and Definitions
114
Physical System Limitations
119
Interfacing a Digital System
121
Required Additions for Digital Control
124
Overview of the Controller
127
The Digital Filter What Is a Digital Filter?
128
Specifying the Appropriate Digital Filter
132
Specifying the Digital Filter Length
134
The Adaptive Algorithm Background Making Use of Adaptive Signal Processing
135
Gradient Descent Algorithms
136
Evaluating the Gradient
139
The Convergence Coefficient
140
Quantization Errors and Leakage
143
Slowing Down the Algorithm to Improve Performance
145
Cancellation Path Modeler
146
Selecting the Sample Rate
150
So What Is the Optimum Sample Rate?
154
Index
157
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