Book description
The Design of Active Crossovers is a unique guide to the design of high-quality circuitry for splitting audio frequencies into separate bands and directing them to different loudspeaker drive units specifically designed for handling their own range of frequencies. Traditionally this has been done by using passive crossover units built into the loudspeaker boxes; this is the simplest solution, but it is also a bundle of compromises. The high cost of passive crossover components, and the power losses in them, means that passive crossovers have to use relatively few parts. This limits how well the crossover can do its basic job.
Active crossovers, sometimes called electronic crossovers, tackle the problem in a much more sophisticated manner. The division of the audio into bands is performed at low signal levels, before the power amplifiers, where it can be done with much greater precision. Very sophisticated filtering and response-shaping networks can be built at comparatively low cost. Time-delay networks that compensate for phyical misalignments in speaker construction can be implemented easily; the equivalent in a passive crossover is impractical because of the large cost and the heavy signal losses. Active crossover technology is also directly applicable to other band-splitting signal-processing devices such as multi-band compressors.
The use of active crossovers is increasing. They are used by almost every sound reinforcement system, by almost every recording studio monitoring set-up, and to a small but growing extent in domestic hifi. There is a growing acceptance in the hifi industry that multi-amplification using active crossovers is the obvious next step (and possibly the last big one) to getting the best possible sound. There is also a large usage of active crossovers in car audio, with the emphasis on routing the bass to enormous low-frequency loudspeakers.
One of the very few drawbacks to using the active crossover approach is that it requires more power amplifiers; these have often been built into the loudspeaker, along with the crossover, and this deprives the customer of the chance to choose their own amplifier, leading to resistance to the whole active crossover philosophy. A comprehensive proposal for solving this problem is an important part of this book.
The design of active crossovers is closely linked with that of the loudspeakers they drive. A chapter gives a concise but complete account of all the loudspeaker design issues that affect the associated active crossover.
This book is packed full of valuable information, with virtually every page revealing nuggets of specialized knowledge never before published. Essential points of theory bearing on practical performance are lucidly and thoroughly explained, with the mathematics kept to an essential minimum. Douglas' background in design for manufacture ensures he keeps a wary eye on the cost of things.
Features:
- Crossover basics and requirements
- The many different crossover types and how they work
- Design almost any kind of active filter with minimal mathematics
- Make crossover filters with very low noise and distortion
- Make high-performance time-delay filters that give a constant delay over a wide range of frequency
- Make a wide variety of audio equaliser stages: shelving, peaking and notch characteristics
- All about active crossover system design for optimal noise and dynamic range
- There is a large amount of new material that has never been published before. A few examples: using capacitance multipliers in biquad equalisers, opamp output biasing to reduce distortion, the design of NTMTM notch crossovers, the design of special filters for filler-driver crossovers, the use of mixed capacitors to reduce filter distortion, differentially elevated internal levels to reduce noise, and so on.
Douglas wears his learning lightly, and this book features the engaging prose style familiar from his other books The Audio Power Amplifier Design Handbook, Self on Audio, and the recent Small Signal Audio Design.
Table of contents
- Cover
- Halftitle
- Title
- Copyright
- Dedication
- Contents
- Preface
- Acknowledgments
-
Chapter 1: Crossover Basics
- 1.1 What a Crossover Does
- 1.2 Why a Crossover Is Necessary
- 1.3 Beaming and Lobing
- 1.4 Active Crossover Applications
- 1.5 Bi-Amping and Bi-Wiring
- 1.6 Loudspeaker Cables
- 1.7 The Advantages and Disadvantages of Active Crossovers
- 1.8 The Next Step in Hi-Fi
- 1.9 Active Crossover Systems
- 1.10 Matching Crossovers and Loudspeakers
- 1.11 A Modest Proposal: Popularising Active Crossovers
- 1.12 Multi-Way Connectors
- 1.13 Subjectivism
- References
- Chapter 2: How Loudspeakers Work
- Chapter 3: Crossover Requirements
-
Chapter 4: Crossover Types
- 4.1 All-Pole and Non-All-Pole Crossovers
- 4.2 Symmetric and Asymmetric Crossovers
- 4.3 All-Pass and Constant-Power Crossovers
- 4.4 Constant-Voltage Crossovers
- 4.5 First-Order Crossovers
- 4.6 Second-Order Crossovers
- 4.7 Third-Order Crossovers
- 4.8 Fourth-Order Crossovers
- 4.9 Higher-Order Crossovers
- 4.10 Determining Frequency Offsets
- 4.11 Summary of Crossover Properties
- 4.12 Filler-Driver Crossovers
- 4.13 The Duelund Crossover
- 4.14 Crossover Topology
- 4.15 Crossover Conclusions
- References
- Chapter 5: Notch Crossovers
- Chapter 6: Subtractive Crossovers
-
Chapter 7: Lowpass & Highpass Filter Characteristics
- 7.1 Active Filters
- 7.2 Lowpass Filters
- 7.3 Highpass Filters
- 7.4 Bandpass Filters
- 7.5 Notch Filters
- 7.6 Allpass Filters
- 7.7 The Order of a Filter
- 7.8 Filter Cutoff Frequencies and Characteristic Frequencies
- 7.9 First-Order Filters
- 7.10 Second-Order and Higher-Order Filters
- 7.11 Filter Characteristics
- 7.12 Higher-Order Filters
- 7.13 More Complex Filters—Adding Zeros
- 7.14 Some Lesser-Known Filter Characteristics
- 7.15 Other Filter Characteristics
- References
-
Chapter 8: Designing Lowpass and Highpass Filters
- 8.1 Designing Real Filters
- 8.2 Component Sensitivity
- 8.3 First-Order Lowpass and Highpass Filters
- 8.4 Second-Order Filters
- 8.5 Sallen & Key Second-Order Filters
- 8.6 Sallen & Key Lowpass Filter Components
- 8.7 Sallen & Key Second-Order Lowpass: Unity Gain
- 8.8 Sallen & Key Second-Order Lowpass Unity-Gain: Component Sensitivity
- 8.9 Sallen & Key Second-Order Lowpass: Equal-Capacitor
- 8.10 Sallen & Key Second-Order Lowpass Equal-C: Component Sensitivity
- 8.11 Sallen & Key Second-Order Butterworth Lowpass: Defined Gains
- 8.12 Sallen & Key Second-Order Lowpass: Non-Equal Resistors
- 8.13 Sallen & Key Third-Order Lowpass in a Single Stage
- 8.14 Sallen & Key Third-Order Lowpass in a Single Stage: Non-Equal Resistors
- 8.15 Sallen & Key Fourth-Order Lowpass in a Single Stage
- 8.16 Sallen & Key Fourth-Order Lowpass in a Single Stage: Non-Equal Resistors
- 8.17 Sallen & Key Fifth- and Sixth-Order Lowpass in a Single Stage
- 8.18 Sallen & Key Highpass Filters
- 8.19 Sallen & Key Second-Order Highpass: Unity Gain
- 8.20 Sallen & Key Second-Order Highpass: Equal-Resistors
- 8.21 Sallen & Key Second-Order Butterworth Highpass: Defined Gains
- 8.22 Sallen & Key Second-Order Highpass: Non-Equal Capacitors
- 8.23 Sallen & Key Third-Order Highpass in a Single Stage
- 8.24 Sallen & Key Fourth-Order Highpass in a Single Stage
- 8.25 Implementing Linkwitz–Riley with Sallen & Key Filters: Loading Effects
- 8.26 Lowpass Filters with Attenuation
- 8.27 Bandwidth Definition Filters
- 8.28 Distortion in Sallen & Key Filters: Highpass
- 8.29 Distortion in Sallen & Key Filters: Lowpass
- 8.30 Mixed Capacitors in Low-Distortion Sallen & Key Filters
- 8.31 Noise in Sallen & Key Filters: Lowpass
- 8.32 Noise in Sallen & Key Filters: Highpass
- 8.33 Multiple-Feedback Filters
- 8.34 Multiple-Feedback Lowpass Filters
- 8.35 Multiple-Feedback Highpass Filters
- 8.36 Distortion in Multiple-Feedback Filters: Highpass
- 8.37 Distortion in Multiple-Feedback Filters: Lowpass
- 8.38 Noise in Multiple-Feedback Filters: Highpass
- 8.39 Noise in Multiple-Feedback Filters: Lowpass
- 8.40 State-Variable Filters
- 8.41 Variable-Frequency Filters: Sallen and Key
- 8.42 Variable-Frequency Filters: State-Variable Second Order
- 8.43 Variable-Frequency Filters: State-Variable Fourth Order
- 8.44 Variable-Frequency Filters: Other Orders
- References
- Chapter 9: Bandpass & Notch Filters
-
Chapter 10: Time Domain Filters
- 10.1 The Requirement for Delay Compensation
- 10.2 Calculating the Required Delays
- 10.3 Signal Summation
- 10.4 Physical Methods of Delay Compensation
- 10.5 Delay Filter Technology
- 10.6 Sample Crossover and Delay Filter Specification
- 10.7 Allpass Filters in General
- 10.8 Delay Lines for Subtractive Crossovers
- 10.9 Variable Allpass Time Delays
- 10.10 Lowpass Filters for Time Delays
- References
-
Chapter 11: Equalisation
- 11.1 The Need for Equalisation
- 11.2 What Equalisation Can and Can’t Do
- 11.3 Loudspeaker Equalisation
- 11.4 Equalisation Circuits
- 11.5 HF-Boost and LF-Cut Equaliser
- 11.6 HF-Cut and LF-Boost Equaliser
- 11.7 Combined HF-Boost and HF-Cut Equaliser
- 11.8 Adjustable Peak/Dip Equalisers: Fixed Frequency and Low Q
- 11.9 Adjustable Peak/Dip Equalisers: Variable Centre Frequency and Low Q
- 11.10 Adjustable Peak/Dip Equalisers with High Q
- 11.11 The Bridged-T Equaliser
- 11.12 The Biquad Equaliser
- 11.13 Capacitance Multiplication for the Biquad Equaliser
- 11.14 Equalisers with Non-6 dB Slopes
- 11.15 Equalisation by Filter Frequency Offset
- 11.16 Equalisation by Adjusting All Filter Parameters
- References
-
Chapter 12: Passive Components for Active Crossovers
- 12.1 Resistors: Values and Tolerances
- 12.2 Improving Accuracy with Multiple Components: Gaussian Distribution
- 12.3 Resistor Value Distributions
- 12.4 Improving Accuracy with Multiple Components: Uniform Distribution
- 12.5 Obtaining Arbitrary Resistance Values
- 12.6 Resistor Noise: Johnson and Excess Noise
- 12.7 Resistor Non-Linearity
- 12.8 Capacitors: Values and Tolerances
- 12.9 Capacitor Shortcomings
- 12.10 Non-Electrolytic Capacitor Non-Linearity
- 12.11 Electrolytic Capacitor Non-Linearity
- References
-
Chapter 13: Opamps for Active Crossovers
- 13.1 Active Devices for Active Crossovers
-
13.2 Opamp Types
- 13.2.1 Opamp Properties: Noise
- 13.2.2 Opamp Properties: Slew Rate
- 13.2.3 Opamp Properties: Common-Mode Range
- 13.2.4 Opamp Properties: Input Offset Voltage
- 13.2.5 Opamp Properties: Bias Current
- 13.2.6 Opamp Properties: Cost
- 13.2.7 Opamp Properties: Internal Distortion
- 13.2.8 Opamp Properties: Slew-Rate Limiting Distortion
- 13.2.9 Opamp Properties: Distortion Due to Loading
- 13.2.10 Opamp Properties: Common-Mode Distortion
- 13.3 Opamps Surveyed
- 13.4 The TL072 Opamp
- 13.5 The NE5532 and NE5534 Opamps
- 13.6 The 5532 with Shunt Feedback
- 13.7 5532 Output Loading in Shunt-Feedback Mode
- 13.8 The 5532 with Series Feedback
- 13.9 Common-Mode Distortion in the 5532
- 13.10 Reducing 5532 Distortion by Output Biasing
- 13.11 Which 5532?
- 13.12 The 5534 Opamp
- 13.13 The LM4562 Opamp
- 13.14 Common-Mode Distortion in the LM4562
- 13.15 The LME49990 Opamp
- 13.16 Common-Mode Distortion in the LME49990
- 13.17 The AD797 Opamp
- 13.18 Common-Mode Distortion in the AD797
- 13.19 The OP27 Opamp
- 13.20 Opamp Selection
- References
-
Chapter 14: Active Crossover System Design
- 14.1 Crossover Features
- 14.2 Features Usually Absent
- 14.3 Noise, Headroom, and Internal Levels
- 14.4 Circuit Noise and Low-Impedance Design
- 14.5 Using Raised Internal Levels
- 14.6 Placing the Output Attenuator
- 14.7 The Amplitude/Frequency Distribution of Musical Signals and Internal Levels
- 14.8 Gain Structures
- 14.9 Noise Gain
- 14.10 Active Gain-Controls
- 14.11 Filter Order in the Signal Path
- 14.12 Output Level Controls
- 14.13 Mute Switches
- 14.14 Phase-Invert Switches
- 14.15 Distributed Peak Detection
- 14.16 Power Amplifier Considerations
- References
-
Chapter 15: Subwoofer Crossovers
- 15.1 Subwoofer Applications
- 15.2 Subwoofer Technologies
- 15.3 Subwoofer Drive Units
- 15.4 Hi-fi Subwoofers
-
15.5 Home Entertainment Subwoofers
- 15.5.1 Low-Level Inputs (Unbalanced)
- 15.5.2 Low-Level Inputs (Balanced)
- 15.5.3 High-Level Inputs
- 15.5.4 High-Level Outputs
- 15.5.5 Mono Summing
- 15.5.6 LFE Input
- 15.5.7 Level Control
- 15.5.8 Crossover In/Out Switch
- 15.5.9 Crossover Frequency Control (Lowpass Filter)
- 15.5.10 Highpass Subsonic Filter
- 15.5.11 Phase Switch (Normal/Inverted)
- 15.5.12 Variable Phase Control
- 15.5.13 Signal Activation Out of Standby
- 15.6 Home Entertainment Crossovers
- 15.7 Power Amplifiers for Home Entertainment Subwoofers
- 15.8 Subwoofer Integration
- 15.9 Sound Reinforcement Subwoofers
- 15.10 Automotive Audio Subwoofers
- References
-
Chapter 16: Line Inputs and Outputs
- 16.1 External Signal Levels
- 16.2 Internal Signal Levels
- 16.3 Input Amplifier Functions
- 16.4 Unbalanced Inputs
- 16.5 Balanced Interconnections
- 16.6 The Advantages of Balanced Interconnections
- 16.7 The Disadvantages of Balanced Interconnections
- 16.8 Balanced Cables and Interference
- 16.9 Balanced Connectors
- 16.10 Balanced Signal Levels
- 16.11 Electronic versus Transformer Balanced Inputs
- 16.12 Common Mode Rejection Ratio (CMRR)
- 16.13 The Basic Electronic Balanced Input
- 16.14 Common-Mode Rejection Ratio: Opamp Gain
- 16.15 Common-Mode Rejection Ratio: Opamp Frequency Response
- 16.16 Common-Mode Rejection Ratio: Opamp CMRR
- 16.17 Common-Mode Rejection Ratio: Amplifier Component Mismatches
- 16.18 A Practical Balanced Input
- 16.19 Variations on the Balanced Input Stage
- 16.20 Combined Unbalanced and Balanced Inputs
- 16.21 The Superbal Input
- 16.22 Switched Gain Balanced Inputs
- 16.23 Variable-Gain Balanced Inputs
- 16.24 High Input Impedance Balanced Inputs
- 16.25 The Instrumentation Amplifier
- 16.26 Transformer Balanced Inputs
- 16.27 Input Overvoltage Protection
- 16.28 Noise and Balanced Inputs
- 16.29 Low-Noise Balanced Inputs
- 16.30 Low-Noise Balanced Inputs in Real Life
- 16.31 Ultra-Low-Noise Balanced Inputs
- References
- Chapter 17: Line Outputs
- Chapter 18: Power Supply Design
-
Chapter 19: An Active Crossover Design
- 19.1 Design Principles
- 19.2 Example Crossover Specification
- 19.3 The Gain Structure
- 19.4 Resistor Selection
- 19.5 Capacitor Selection
- 19.6 The Balanced Line Input Stage
- 19.7 The Bandwidth Definition Filter
- 19.8 The HF Path: 3 kHz Linkwitz–Riley Highpass Filter
- 19.9 The HF Path: Time Delay Compensation
- 19.10 The MID Path: Topology
- 19.11 The MID Path: 400 Hz Linkwitz–Riley Highpass Filter
- 19.12 The MID Path: 3 kHz Linkwitz–Riley Lowpass Filter
- 19.13 The MID Path: Time Delay Compensation
- 19.14 The LF Path: 400 Hz Linkwitz–Riley Lowpass Filter
- 19.15 The LF Path: No Time Delay Compensation
- 19.16 Output Attenuators and Level Trim Controls
- 19.17 Balanced Outputs
- 19.18 Crossover Programming
- 19.19 Noise Analysis: Input Circuitry
- 19.20 Noise Analysis: HF Path
- 19.21 Noise Analysis: MID Path
- 19.22 Noise Analysis: LF Path
- 19.23 Improving the Noise Performance: The MID Path
- 19.24 Improving the Noise Performance: The Input Circuitry
- 19.25 The Noise Performance: Comparisons with Power Amplifier Noise
- 19.26 Conclusion
- Reference
- Appendix 1 Crossover Design References
- Appendix 2 Loudspeaker Design References
- Index
Product information
- Title: The Design of Active Crossovers
- Author(s):
- Release date: August 2012
- Publisher(s): Focal Press
- ISBN: 9781136111891
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