Loudspeaker Physics and Forced Vibration

ISBN-13: 9783030916336 / Angielski / Twarda / 2022

William H. Watkins

Opis

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.

Spis treści

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

O autorze

William H. (Bill) Watkins was a true American audio innovator. Developer of the famous Watkins “Dual-Drive Woofer”, the renowned WE-1 large floor-standing speaker system, the recently introduced compact Generation 4 unit, and numerous other high-performance speakers, he passed away at his home February 1, 2018 in Kingsport, TN.

He was a veteran of the U.S. Army in the Korean War era and served in active duty overseas. In his youth he became an accomplished musician, especially on the mandolin, guitar, and violin.

He was also a long-time member of the Audio Engineering Society, which he originally joined in 1974. He maintained an extensive library of AES publications over a span of several decades, which he heavily utilized in his ongoing audio and electroacoustics research and development activities.

He had been involved in the high-fidelity audio business in Kingsport since the late 1950s, having owned and operated Watkins Stereo, a retail and custom audio firm, and Watkins Engineering, which manufactured several of his later advanced loudspeaker systems, including the highly regarded WE-1 and Generation 4 models. He was granted three U.S. patents in the area of acoustics, including U.S. #3,838,216 in 1974 for the Dual-Drive Woofer concept, which significantly improved low-end performance of an acoustic-suspension system by effectively cancelling the low-frequency resonance impedance peak, thus extending the bass frequency response by close to an octave.

He also authored a landmark article on the technology, "New Loudspeaker with Extended Bass," in the December 1974 edition of Audio magazine. The patented concept was subsequently licensed to Infinity Systems in California for use in many of their high-end speaker systems and soon became widely known as the "Infinity/Watkins" Woofer. In 1982 Watkins collaborated with his son Bill Jr. on a second patent, U.S. #4,443,744, on reviewer-acclaimed sound-damping panels for home listening use, later marketed as the Watkins Echo Muffs. A third patent, on resistively damped crossover networks to optimize speaker transient response, U.S. #4,475,233, was issued to Watkins in 1984.

His prolific speaker design career continued into the 21st century, culminating in the current highly reviewed compact Generation 4, a two-way system incorporating multiple patent-pending features to assure unusually wide, smooth frequency response, along with precise damping and stereo imaging from a small (½ ft³) enclosure.