I'd like to thank Steve Williams for offering the opportunity of this forum. Much of it will be about field coil drivers and loudspeakers specifically, but my hope is that it will also touch upon many interrelated topics of interest, along the way.
Firstly, I'm not inclined to lecture. Scratch beneath my surface, and within you'll find an artist looking back at you, rather than a scientist or an engineer. Likewise, I don't believe that my ideas or field coils should be preferred by the more civilized among us. The world is full of great loudspeakers, and only a handful of them happen to be electromagnetic. Conversely, field coils are an unfamiliar territory for most of us. It isn't uncommon to find long threads of discussion online in which field coils are enthusiastically embraced or dismissed by audiophiles, often without any first-hand experience of them. What's more, I was surprised to discover this past year how small a percentage of the attendees at shows are aware of what a field coil driver is, or have ever knowingly listened to one. My goal here is to share my own first-hand experience of them with you. In that process, I hope that I can learn a great deal, confer a little knowledge, inspire curiosity, and make field coil loudspeakers a bit more accessible.
I’ll begin with a little about myself first, and my history. My father was an accomplished musician, who started playing piano by ear at age 3. He took piano lessons at age 4 from famous Hungarian concert pianist Madame Lili Keleti, won many awards for his music, and played formally with the Boris Sirpo orchestra. I have him to thank for my lifelong love of music. In college, I myself studied drawing and sculpture, and eventually graduated with a degree in visual design. There isn't a lot of room for painters and sculptors in our modern world however, and over the 20+ following years I worked instead as a software engineer.
The software industry was surprisingly creative. After all, no two people approach a problem in the same way. It also afforded me a good living. My off-hours nonetheless were spent in a variety of creative pursuits, and in my latter years in software I'd found myself increasingly turning toward building loudspeakers as an outlet, using stock drivers. I also found myself consumed by thoughts of creating drivers by hand, and at least one complete loudspeaker based upon them. It grew over time into a creative passion that I felt I needed to pursue.
It was clear to me that, no matter the amount of passion, nothing was going to allow the technical wizardry of a Wilson Audio Chronosonic to simply emerge mythologically from my forehead. In fact, at the stage of life I'd reached, not even rigorous study was likely to achieve that end. If I was to stand any chance of actualizing my goals, what was true for me when I entered software without a computer science degree would also need to be true for this endeavor. That necessary truism was that in many crafts, as in programming, beneath its layers of discourse and intellectual curiosities there are a handful of conceptual pillars. And, if those are internalized and well expressed, success need not require anything else. With nothing more, even an uncredentialed hand can arrive at something very pure, and occasionally, at something extraordinary.
Thankfully, I did find that axiom to be true... at least, for the most part. At some point there may be nothing for a problem other than brain surgery, and that requires knowledge and skill that one has or doesn't have. That said, I began this adventure without even a basic understanding of how a dynamic loudspeaker driver works, and eventually arrived a decade later at what I'd like to hope is one of the better dynamic drivers in the world.
Be that as it may, while field coils have enjoyed a recent renaissance, electromagnetism in its various applications has not become a standard of quality for sound reproduction in loudspeakers. I'd like to offer a few observations about that, in this case limited to dynamic drivers. Firstly, the same manufacturing disadvantages that drove field coils into obscurity in the last mid-century are no less true today. Field coils are expensive and labor intensive to make. They are heavy. They require an external power supply. They can potentially overheat. Of further consideration to modern manufacturers, over time they have become unfamiliar to most of us who love audio.
To be clear, I genuinely celebrate the fact that when all is said and done, the cash value of everything the industry does, from manufacturing to reviewing, is a subjective experience for a listener with art. While there are ever deeper layers of knowledge and richness to expose in that experience, I am (as other makers are) loath to ever suggest that anyone is simply doing it wrong, or even incompletely, for that matter. I'd no more suggest that than I would to anyone that they are viewing a painting or sculpture in 'the wrong way'. I don't feel the slightest need to grade the subjective experiences of listeners.
However, I think a rational and truly useful discussion can be had about things like the physics behind listening experiences, and the properties of differing magnetic materials. In that, I find that manufacturers like myself don't often make the value proposition for what a great field coil has the potential to offer. As an analogy, current data suggests that cheese shows less potential as a material for a rocket fuselage than does titanium, and irrespective of whether we opt for cheese anyway, or of how we feel about the rocket, where it's going, or outer space in general, that distinction need not be considered opaque. It is evident, conversely, that assessing the potential of permanent magnetic materials in audio quickly, and quite understandably, becomes a less clear discussion. Unlike a simple contest between cheese and titanium, there is no end to motor designs in modern drivers, including complex hybrids with several magnetic materials simultaneously in play (even to include electromagnetism, occasionally). Each one of them is task-built to a very specific driver design, and confers its own unique, sonic signature. Which of these complex, modern designs is best? I haven't the slightest idea. I'd suggest that few of us often fully do.
But there are a few things that we surely can say about magnetic materials, and the electromagnetic alternatives to them. One is that every permanent magnet that any of us has ever experienced was made with a powerful field coil. For the purpose of audio, the potential magnetic strength of a field coil is all but limitless. We can also say that the highest saturation and therefore the greatest permeability, the lowest hysteresis, the most uniform gap flux density and the lowest susceptibility to parasitic effects are all attributable to the field generated by a solenoid; for our purposes, the solenoid inside a field coil. And again, just as it is with magnetic strength potential, each of these values comparative to a permanent magnet of any kind or combination isn't a matter of small margins that fall below the threshold of the listening experience - for many listeners, the effect of that delta is immediately and viscerally apparent. Unfortunately, I don't feel like I or other field coil makers deliver that message well.
Another important point I see to mention is that electromagnetism is by no means the only, or necessarily the governing factor in whether a driver ultimately sounds very good at all. Turning to analogy once again, while it is true that reinforced concrete is a stronger foundation to build upon than gravel, it doesn't follow that the more beautiful or lasting structures will be built upon one, and not the other. The dominant factor in my driver for example is the fact that it is a large full-range driver with a whizzer cone, and not that it happens to be a field coil. If one's goal is a thriving loudspeaker enterprise based on a near-occult topology, that's a difficult message to carry. Most of us simply want a clear answer that they should, if discerning enough, appreciate or dismiss the quality of field coil loudspeakers... and of course, that simply can't be said. At shows I, and no doubt some of you, have heard field coil loudspeakers that suffer from any number of subjective deficits... shrill, shouty, thin, fatiguing, etc. I've also heard some that were, at least for me, astonishingly good. In each of those cases, the field coil was only a part of the whole story.
The last factor I'd like to touch on regarding the adoption of field coils is, heretical as it may be to say, measured accuracy of sound reproduction is not necessarily the goal of every listener. Each audiophile loves the experience they've crafted for themselves, and unfailingly each may refer to it as accurate, balanced, neutral and so on... even if objective data doesn't confirm that. I have no doubt that presented with a system that is objectively neutral, some number audiophiles will run rather than walk back to the system they have carefully curated, and prefer. And, I sincerely think that's great; it's just as it should be.
In any case, in this long-winded preface I hope I've given you some idea of where this is all headed. Over the course of a decade I designed and built two critically acclaimed loudspeakers. And, it just so happens that they are based on a wonderful field coil driver.
In the forum posts to come, I'd like to document that journey here.
Firstly, I'm not inclined to lecture. Scratch beneath my surface, and within you'll find an artist looking back at you, rather than a scientist or an engineer. Likewise, I don't believe that my ideas or field coils should be preferred by the more civilized among us. The world is full of great loudspeakers, and only a handful of them happen to be electromagnetic. Conversely, field coils are an unfamiliar territory for most of us. It isn't uncommon to find long threads of discussion online in which field coils are enthusiastically embraced or dismissed by audiophiles, often without any first-hand experience of them. What's more, I was surprised to discover this past year how small a percentage of the attendees at shows are aware of what a field coil driver is, or have ever knowingly listened to one. My goal here is to share my own first-hand experience of them with you. In that process, I hope that I can learn a great deal, confer a little knowledge, inspire curiosity, and make field coil loudspeakers a bit more accessible.
I’ll begin with a little about myself first, and my history. My father was an accomplished musician, who started playing piano by ear at age 3. He took piano lessons at age 4 from famous Hungarian concert pianist Madame Lili Keleti, won many awards for his music, and played formally with the Boris Sirpo orchestra. I have him to thank for my lifelong love of music. In college, I myself studied drawing and sculpture, and eventually graduated with a degree in visual design. There isn't a lot of room for painters and sculptors in our modern world however, and over the 20+ following years I worked instead as a software engineer.
The software industry was surprisingly creative. After all, no two people approach a problem in the same way. It also afforded me a good living. My off-hours nonetheless were spent in a variety of creative pursuits, and in my latter years in software I'd found myself increasingly turning toward building loudspeakers as an outlet, using stock drivers. I also found myself consumed by thoughts of creating drivers by hand, and at least one complete loudspeaker based upon them. It grew over time into a creative passion that I felt I needed to pursue.
It was clear to me that, no matter the amount of passion, nothing was going to allow the technical wizardry of a Wilson Audio Chronosonic to simply emerge mythologically from my forehead. In fact, at the stage of life I'd reached, not even rigorous study was likely to achieve that end. If I was to stand any chance of actualizing my goals, what was true for me when I entered software without a computer science degree would also need to be true for this endeavor. That necessary truism was that in many crafts, as in programming, beneath its layers of discourse and intellectual curiosities there are a handful of conceptual pillars. And, if those are internalized and well expressed, success need not require anything else. With nothing more, even an uncredentialed hand can arrive at something very pure, and occasionally, at something extraordinary.
Thankfully, I did find that axiom to be true... at least, for the most part. At some point there may be nothing for a problem other than brain surgery, and that requires knowledge and skill that one has or doesn't have. That said, I began this adventure without even a basic understanding of how a dynamic loudspeaker driver works, and eventually arrived a decade later at what I'd like to hope is one of the better dynamic drivers in the world.
Be that as it may, while field coils have enjoyed a recent renaissance, electromagnetism in its various applications has not become a standard of quality for sound reproduction in loudspeakers. I'd like to offer a few observations about that, in this case limited to dynamic drivers. Firstly, the same manufacturing disadvantages that drove field coils into obscurity in the last mid-century are no less true today. Field coils are expensive and labor intensive to make. They are heavy. They require an external power supply. They can potentially overheat. Of further consideration to modern manufacturers, over time they have become unfamiliar to most of us who love audio.
To be clear, I genuinely celebrate the fact that when all is said and done, the cash value of everything the industry does, from manufacturing to reviewing, is a subjective experience for a listener with art. While there are ever deeper layers of knowledge and richness to expose in that experience, I am (as other makers are) loath to ever suggest that anyone is simply doing it wrong, or even incompletely, for that matter. I'd no more suggest that than I would to anyone that they are viewing a painting or sculpture in 'the wrong way'. I don't feel the slightest need to grade the subjective experiences of listeners.
However, I think a rational and truly useful discussion can be had about things like the physics behind listening experiences, and the properties of differing magnetic materials. In that, I find that manufacturers like myself don't often make the value proposition for what a great field coil has the potential to offer. As an analogy, current data suggests that cheese shows less potential as a material for a rocket fuselage than does titanium, and irrespective of whether we opt for cheese anyway, or of how we feel about the rocket, where it's going, or outer space in general, that distinction need not be considered opaque. It is evident, conversely, that assessing the potential of permanent magnetic materials in audio quickly, and quite understandably, becomes a less clear discussion. Unlike a simple contest between cheese and titanium, there is no end to motor designs in modern drivers, including complex hybrids with several magnetic materials simultaneously in play (even to include electromagnetism, occasionally). Each one of them is task-built to a very specific driver design, and confers its own unique, sonic signature. Which of these complex, modern designs is best? I haven't the slightest idea. I'd suggest that few of us often fully do.
But there are a few things that we surely can say about magnetic materials, and the electromagnetic alternatives to them. One is that every permanent magnet that any of us has ever experienced was made with a powerful field coil. For the purpose of audio, the potential magnetic strength of a field coil is all but limitless. We can also say that the highest saturation and therefore the greatest permeability, the lowest hysteresis, the most uniform gap flux density and the lowest susceptibility to parasitic effects are all attributable to the field generated by a solenoid; for our purposes, the solenoid inside a field coil. And again, just as it is with magnetic strength potential, each of these values comparative to a permanent magnet of any kind or combination isn't a matter of small margins that fall below the threshold of the listening experience - for many listeners, the effect of that delta is immediately and viscerally apparent. Unfortunately, I don't feel like I or other field coil makers deliver that message well.
Another important point I see to mention is that electromagnetism is by no means the only, or necessarily the governing factor in whether a driver ultimately sounds very good at all. Turning to analogy once again, while it is true that reinforced concrete is a stronger foundation to build upon than gravel, it doesn't follow that the more beautiful or lasting structures will be built upon one, and not the other. The dominant factor in my driver for example is the fact that it is a large full-range driver with a whizzer cone, and not that it happens to be a field coil. If one's goal is a thriving loudspeaker enterprise based on a near-occult topology, that's a difficult message to carry. Most of us simply want a clear answer that they should, if discerning enough, appreciate or dismiss the quality of field coil loudspeakers... and of course, that simply can't be said. At shows I, and no doubt some of you, have heard field coil loudspeakers that suffer from any number of subjective deficits... shrill, shouty, thin, fatiguing, etc. I've also heard some that were, at least for me, astonishingly good. In each of those cases, the field coil was only a part of the whole story.
The last factor I'd like to touch on regarding the adoption of field coils is, heretical as it may be to say, measured accuracy of sound reproduction is not necessarily the goal of every listener. Each audiophile loves the experience they've crafted for themselves, and unfailingly each may refer to it as accurate, balanced, neutral and so on... even if objective data doesn't confirm that. I have no doubt that presented with a system that is objectively neutral, some number audiophiles will run rather than walk back to the system they have carefully curated, and prefer. And, I sincerely think that's great; it's just as it should be.
In any case, in this long-winded preface I hope I've given you some idea of where this is all headed. Over the course of a decade I designed and built two critically acclaimed loudspeakers. And, it just so happens that they are based on a wonderful field coil driver.
In the forum posts to come, I'd like to document that journey here.
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