Description
This book is a study of the workings of dynamic loudspeakers and dynamically forced vibration. With its wealth of practical observations and real-life examples, this work will prove invaluable to the practicing motor design or loudspeaker design engineer, as well as researchers and students in electroacoustics. The book is based on a lifetime’s accumulated knowledge by acclaimed speaker designer William H. (Bill) Watkins. It differs from the usual tone of most technical books on this subject by initially presenting, and analyzing in full, the function of each key parameter of a reference dynamic loudspeaker. Each parameter’s value is then calculated and also confirmed via lab measurements to vividly illustrate all energy-transduction facets of loudspeaker operation and the forced vibration. This presentation style makes the analysis both more engaging, intuitive, and easier to comprehend compared to most previous works in the field. The principles of this book apply to all direct reciprocating motors, not just those in a dynamic loudspeaker. Unique to the book is an entire chapter dedicated to the discussion of back-EMF voltage, discussed from several technical points of view and analyzed in depth as related to the dynamic transfer of energy between the mechanical and electrical domains. Another unique feature is a detailed discussion of Watkins’ patented dual-motor concept to achieve high dynamic speaker performance in the region of its low-frequency resonance. Chapter 1. Glossary and Prologue 1.1 Glossary of symbols 1.2 Introduction 1.3 Elaboration Chapter 2. Preliminaries 2.1 Procedure 2.2 Assumptions and limitations 2.3 Electrical, mechanical, and acoustic analogies 2.4 Power to loss ratio and volume acceleration 2.5 Terminology Chapter 3. Analogous Electrical circuit 3.1 Analogous circuit and discussion 3.2 Reference driver magnitudes in the analogous circuit Chapter 4. Electrical impedance 4.1 Coil Resistance 4.2 Resistance due to the mechanical and acoustic load 4.3 Core resistance 4.4 Blocked coil measurement 4.5 Source and total resistance 4.6 Reactance 4.7 Inductance 4.8 Impedance expressions 4.9 Voltage and power expressions Chapter 5. Efficiency and the mechanical response function 5.1 Efficiency at the working frequency 5.2 The mechanical response function 5.3 Relation to parameters and power 5.4 Correlation with Kinsler, Kloss, and Small 5.5 Efficiency expressions and loss 5.6 Efficiency, bass extension, and enclosure size Chapter 6. Back emf 6.1 Faraday and Lenz’s laws 6.2 Transfer of energy 6.3 Degree of current flow 6.4 Newton’s laws 6.5 Conservation of energy 6.6 Back emf and power transfer Chapter 7. Mechanical and acoustic load impedance 7.1 Mechanical plus acoustic impedance 7.2 Equivalent mechanical resistance 7.3 Air load resistance 7.4 Mechanical resistance Chapter 8. Mechanical and acoustic power 8.1 Electric power factor 8.2 Mechanical power factor 8.3 Mechanical plus acoustic power 8.4 Relations of acoustic power 8.5 Energy and power distribution Chapter 9. Low frequency response 9.1 Half-power point 9.2 Maximum amplitude Chapter 10. Force 10.1 The Lorentz force law 10.2 Motor resistance and electromagnetic damping 10.3 Correlation with Beranek’s velocity expression 10.4 Relation to the power-to-loss ratio 10.5 Force expressions Chapter 11. Velocity 11.1 Average and RMS velocity 11.2 Velocity relationships and expressions 11.3 Measuring velocity 11.4 Recoil velocity 11.5 Volume velocity Chapter 12. Energy 12.1 General considerations 12.2 Kinetic energy 12.3 Relation of kinetic energy to power from the source Chapter 13. Work, efficiency, and power 13.1 Work done heating the coil and core 13.2 Work done on the mechanical and acoustic side 13.3 Relation to power and the power-to-loss ratio Chapter 14. Resonance, Q, and measurements 14.1 Mass, compliance, and mechanical resonance 14.2 Bandwidth 14.3 Quality factors at resonance Chapter 15. Related parameters and measurements 15.1 Acceleration 15.2 Amplitude 15.3 SPL 15.4 Motor strength 15.5 Measuring with precision 15.6 Momentum 15.7 Pressure Chapter 16. Circumventing Efficiency and Bass Extension Limitations 16.1 Efficiency and bass extension limitations 16.2 Back EMF 16.3 Dominant parameters 16.4 The trade-off 16.5 Dual motors 16.6 Technical details 16.7 Summary Chapter 17. Appendix 17.1 Parameter magnitudes 17.2 Parameter tables Chapter 18. References
