So what happens if we use 0.18 Qts driver in open baffle? will there be a hump in response at the lower part of the spectrum?
I wouldn't expect to see that necessarily. However you will see poor bass performance compared to a higher Qts driver, when used in a fairly straightforward open baffle design.
This is a good, free software you might consider using for modeling response of dipole loudspeakers:
https://www.tolvan.com/index.php?page=/basta/basta.php
The learning curve is easy as well. Hope that helps!
This is a good, free software you might consider using for modeling response of dipole loudspeakers:
https://www.tolvan.com/index.php?page=/basta/basta.php
The learning curve is easy as well. Hope that helps!
I wanted to share with the wonderful community here that Enjoy the Music evaluated my S1, and published it for the April issue. It's an amazing milestone in the journey, and I am humbled by it. Cheers, everyone.
https://www.enjoythemusic.com/super...ield_Coil_Point_Source_Loudspeaker_Review.htm
https://www.enjoythemusic.com/super...ield_Coil_Point_Source_Loudspeaker_Review.htm
Very impressive production.
Your vestigial spider is a really imaginative invention. But..... I thought the spider in conventional drivers was the good-guy for providing spring action that is linear compared to the non-linearity expected from half-round rubber surrounds?
The critic said the magnetic field is "thousands" of times stronger than a permanent magnet. What would that be in terms of Bl product or other familiar metrics? After all, folks at DIYaudio are, I am certain, immensely interested in your magnet force and other advantages of a field coil.
Ditto for the moving mass of the cone assembly.
The write-up had no REW or other acoustic measurements. Again, that just doesn't cut it with the measurement-happy crowd around here. Can you please post FR, distortion, and similar parameters that matter to us.
B.
Your vestigial spider is a really imaginative invention. But..... I thought the spider in conventional drivers was the good-guy for providing spring action that is linear compared to the non-linearity expected from half-round rubber surrounds?
The critic said the magnetic field is "thousands" of times stronger than a permanent magnet. What would that be in terms of Bl product or other familiar metrics? After all, folks at DIYaudio are, I am certain, immensely interested in your magnet force and other advantages of a field coil.
Ditto for the moving mass of the cone assembly.
The write-up had no REW or other acoustic measurements. Again, that just doesn't cut it with the measurement-happy crowd around here. Can you please post FR, distortion, and similar parameters that matter to us.
B.
Hey @bentoronto,
Yes, the reviewer made an error there - what he should have said was that the magnetic field is hundreds or thousands of times "stiffer" than a hard magnet, depending on the material that is used. That applies to any field coil, and isn't any special invention of my own - it's simply a reflection of the fact that an electromagnet can achieve very high permeability, because it can reach saturation of whatever the material in question is. In the case of low carbon steel, permendur, iron etc that is a comparatively very high number, which results in a very high degree of control over the moving mass.
You do of course want the greatest degree of linearity possible, however if somehow that could be achieved in the absence of a surround and spider entirely you'd have the ideal circumstance for a dynamic driver. Check out Ilumnia - they do fascinating work in that regard. Anyway... in my view, the goal of the spider should be simply to center the voice coil in the gap, move in a highly compliant and linear manner, and to otherwise be as absent as possible. I'm not sure what you meant regarding the rubber surrounds, I apologize...
If you look back a bit in this thread, you'll find FR, distortion and off-axis measurements, although they are from a past iteration of both the driver and S1 speaker. It's come a very long way over those three years... although, my posts here over that time have been quite infrequent.
Posting measurements certainly takes on a different character for me now, than it used to. That's surely a good topic to expand upon here some day. In any case, if you'd like to see something specific I am happy to share.
Yes, the reviewer made an error there - what he should have said was that the magnetic field is hundreds or thousands of times "stiffer" than a hard magnet, depending on the material that is used. That applies to any field coil, and isn't any special invention of my own - it's simply a reflection of the fact that an electromagnet can achieve very high permeability, because it can reach saturation of whatever the material in question is. In the case of low carbon steel, permendur, iron etc that is a comparatively very high number, which results in a very high degree of control over the moving mass.
You do of course want the greatest degree of linearity possible, however if somehow that could be achieved in the absence of a surround and spider entirely you'd have the ideal circumstance for a dynamic driver. Check out Ilumnia - they do fascinating work in that regard. Anyway... in my view, the goal of the spider should be simply to center the voice coil in the gap, move in a highly compliant and linear manner, and to otherwise be as absent as possible. I'm not sure what you meant regarding the rubber surrounds, I apologize...
If you look back a bit in this thread, you'll find FR, distortion and off-axis measurements, although they are from a past iteration of both the driver and S1 speaker. It's come a very long way over those three years... although, my posts here over that time have been quite infrequent.
Posting measurements certainly takes on a different character for me now, than it used to. That's surely a good topic to expand upon here some day. In any case, if you'd like to see something specific I am happy to share.
Thanks for quick reply.
Magnet explanations are over my amateur head. Since this is the single most important feature, can you please explain more. BTW, the whole matter of horsepower or force or don't-know-what is badly handled in the audio world. My guess is that another parameter really matters and that is something like "degree of control in proportion to the weight of the cone assembly". That would combine Bl and cone mass and would also permit comparison to motional feedback ("smart") control.
You have to have a force restoring the cone to normal position. If the vestigial spider isn't serving that purpose for you, what is? Do I see you have a 29 Hz resonance in the link? So some spring of almost conventional force is present.
I'll look for those old FR measurements you mention. But any buyer with $35,000 to spend might want to see measurements of your latest offering.
B.
Magnet explanations are over my amateur head. Since this is the single most important feature, can you please explain more. BTW, the whole matter of horsepower or force or don't-know-what is badly handled in the audio world. My guess is that another parameter really matters and that is something like "degree of control in proportion to the weight of the cone assembly". That would combine Bl and cone mass and would also permit comparison to motional feedback ("smart") control.
You have to have a force restoring the cone to normal position. If the vestigial spider isn't serving that purpose for you, what is? Do I see you have a 29 Hz resonance in the link? So some spring of almost conventional force is present.
I'll look for those old FR measurements you mention. But any buyer with $35,000 to spend might want to see measurements of your latest offering.
B.
Post 23 has acoustic measurements but hard for me to digest them - such as how bass was traced.
The FR seems pretty good for a single driver. You seem to have a driver resonance around 50 Hz. Not sure how loud, but with bass distortion below 10%, that pretty good. Distortion, north of the bass seems to run around -40dB (1%) which may be a good achievement for a single driver.
No doubt it has been obvious and maybe posted previously, but a field magnet has an enormous interest for DiYaudio members because - unlike ceramic magnets - simple matter to DIY (OK, maybe not really "simple"). Again thanks for your great work.
The FR seems pretty good for a single driver. You seem to have a driver resonance around 50 Hz. Not sure how loud, but with bass distortion below 10%, that pretty good. Distortion, north of the bass seems to run around -40dB (1%) which may be a good achievement for a single driver.
No doubt it has been obvious and maybe posted previously, but a field magnet has an enormous interest for DiYaudio members because - unlike ceramic magnets - simple matter to DIY (OK, maybe not really "simple"). Again thanks for your great work.
Me too!
The way I view it though is that until neo motors came along recently the only motors capable of < the ~0.18 Qts AlNiCo 515B Altecs I've used were field coils, which typically went down to 0.1 in my (limited) experience and in recent times at least one of the 'FR' field coil drivers touted on the 'FR' forum with published specs.
My pleasure, Ben. It's all ultimately over my head too, if that is of any consolation. I'm anything but a physicist.
Yes, there are two important qualities regarding the magnetic material - limiting it to just the nature of the magnetic field in these comments. Of course the first is the strength, measured in the gap. This driver at maximum recommended current generates a field of about 1.7 Tesla, just a little shy of that - it's quite strong. The other quality is permeability, and the lower that number is, the more elastic the motor control in response to the AC signal running through the voice coil - and that elasticity of motion manifests as a form of distortion. An interesting example of how the two qualities may counterintuitively vary in a material is neodymium, which carries the potential for an even stronger magnetic field, but has a very low permeability - it's no better than ordinary ferrite in that regard, around a 1μ. Alnico is higher, coming in typically between 5-7μ. However, saturated low carbon steel is in the neighborhood of 2000μ - vastly higher - and that means that the accuracy of motion is correspondingly high.
You know, I'd actually say that the governing factor in my driver is that it is a large, full-ranger with a whizzer cone with unusually high compliance and low mass, and not that it's a field coil. Turning to analogy, 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 - there are so many amazing loudspeakers in the world, and only a handful of them use field coils. I have heard some 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.
Indeed, my spider is definitely acting as a restoring force - in fact it's holding the entire moving mass in light tension. Crazy as it may sound, I have found little or no need for pistonic restraint from the spider at all, other than in the sense that the underhung coil must at rest sit in the middle of the gap. If I could somehow at this moment do without the spider, I would - and, you can bet that I spend a lot of time thinking about how. I place all of my trust in the motor, and at least so far, that philosophy hasn't let me down. The free-air resonance of the current driver after a day of break-in is just 17Hz - I'm surrendering as much of the suspension control as I can.
In those older measurements in post 23, bass was measured nearfield right at the phase plug, up to 600Hz. The rest of the range is measured from a typical listening position across a 30° listening window. The better way to have derived that part of the range (and, how I do now) would have been from 1 meter across a 30° window. You're right about the resonance @50hz - it was the result of a poorly considered design feature of the interior cabinet which, naturally, had seemed genius to me at the time. You're right about the distortion, as well. I shoot for 1% or less until I'm south of 100Hz, and aside from a few tiny hiccups here and there my best efforts can get to 60Hz or so before I'm over that figure.
I'm torn about sharing measurements these days... it's a topic that I could and still may write about here, at length. They are the essential foundation of sound decision-making, effective troubleshooting, voicing and so on during development, and yet not the final arbiter of what the subjective listening experience will be, for any given individual. What's more, while you bring obvious acumen with you, many do not... and the idea of litigating the more narrow views on the topic in a forum thread... ugh. What you may find surprising is that the buyer with $35k is usually what I'd describe as a music lover, and not an audiophile. In any case, I'm thankfully wise enough to know that hiding any real defects I find in measurement is of no value. And conversely, I love hosting people for listening sessions - it's wonderful to watch people react to the work, especially those that have never experienced a well-made field coil driver. Exhibiting at shows this past year was a joy.
I'll be at THE Show and PAF in June, and then likely at CAF in November. Come for a listen, Ben...
Yes, there are two important qualities regarding the magnetic material - limiting it to just the nature of the magnetic field in these comments. Of course the first is the strength, measured in the gap. This driver at maximum recommended current generates a field of about 1.7 Tesla, just a little shy of that - it's quite strong. The other quality is permeability, and the lower that number is, the more elastic the motor control in response to the AC signal running through the voice coil - and that elasticity of motion manifests as a form of distortion. An interesting example of how the two qualities may counterintuitively vary in a material is neodymium, which carries the potential for an even stronger magnetic field, but has a very low permeability - it's no better than ordinary ferrite in that regard, around a 1μ. Alnico is higher, coming in typically between 5-7μ. However, saturated low carbon steel is in the neighborhood of 2000μ - vastly higher - and that means that the accuracy of motion is correspondingly high.
You know, I'd actually say that the governing factor in my driver is that it is a large, full-ranger with a whizzer cone with unusually high compliance and low mass, and not that it's a field coil. Turning to analogy, 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 - there are so many amazing loudspeakers in the world, and only a handful of them use field coils. I have heard some 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.
Indeed, my spider is definitely acting as a restoring force - in fact it's holding the entire moving mass in light tension. Crazy as it may sound, I have found little or no need for pistonic restraint from the spider at all, other than in the sense that the underhung coil must at rest sit in the middle of the gap. If I could somehow at this moment do without the spider, I would - and, you can bet that I spend a lot of time thinking about how. I place all of my trust in the motor, and at least so far, that philosophy hasn't let me down. The free-air resonance of the current driver after a day of break-in is just 17Hz - I'm surrendering as much of the suspension control as I can.
In those older measurements in post 23, bass was measured nearfield right at the phase plug, up to 600Hz. The rest of the range is measured from a typical listening position across a 30° listening window. The better way to have derived that part of the range (and, how I do now) would have been from 1 meter across a 30° window. You're right about the resonance @50hz - it was the result of a poorly considered design feature of the interior cabinet which, naturally, had seemed genius to me at the time. You're right about the distortion, as well. I shoot for 1% or less until I'm south of 100Hz, and aside from a few tiny hiccups here and there my best efforts can get to 60Hz or so before I'm over that figure.
I'm torn about sharing measurements these days... it's a topic that I could and still may write about here, at length. They are the essential foundation of sound decision-making, effective troubleshooting, voicing and so on during development, and yet not the final arbiter of what the subjective listening experience will be, for any given individual. What's more, while you bring obvious acumen with you, many do not... and the idea of litigating the more narrow views on the topic in a forum thread... ugh. What you may find surprising is that the buyer with $35k is usually what I'd describe as a music lover, and not an audiophile. In any case, I'm thankfully wise enough to know that hiding any real defects I find in measurement is of no value. And conversely, I love hosting people for listening sessions - it's wonderful to watch people react to the work, especially those that have never experienced a well-made field coil driver. Exhibiting at shows this past year was a joy.
I'll be at THE Show and PAF in June, and then likely at CAF in November. Come for a listen, Ben...
I was thinking about the bulk of magnets, with respect to backwave reflection and the inevitable lumps and bumps in the response. Some magnet assemblies are bigger than the cone! So I searched for field coils... sort of
I was slightly surprised to read of permanent field coils - i.e. DC powered. I can see why they would sound better, getting the magnet metal away from the coils - not sure about the pole piece but not really relevant to my point here.
My thoughts were about eliminating the magnet, to remove the obstacle to the backwave, so instead of being 'dealt with' (reflected back through the cone) by a steel basket with holes in and a giant slab of steel, it was free to be absorbed/used in the cabinet, properly.
So my question is this: Why use a DC electromagnet - why not simply remove the magnet and put a slightly bigger speaker coil in it's place, driven by the amplifier in the opposite direction to the one glued to the cone tube?
So there is no DC, just two coils in opposition, one glued to a thin (wooden?) frame, the other glued to the cone tube, and maybe even put a small spider right at the end too (Surround -> cone -> tube -> coil(s) -> spider)
I'm guessing it's going to be an efficiency thing, but in this case - does it actually matter?
Has anyone tried it? Thanks
I was slightly surprised to read of permanent field coils - i.e. DC powered. I can see why they would sound better, getting the magnet metal away from the coils - not sure about the pole piece but not really relevant to my point here.
My thoughts were about eliminating the magnet, to remove the obstacle to the backwave, so instead of being 'dealt with' (reflected back through the cone) by a steel basket with holes in and a giant slab of steel, it was free to be absorbed/used in the cabinet, properly.
So my question is this: Why use a DC electromagnet - why not simply remove the magnet and put a slightly bigger speaker coil in it's place, driven by the amplifier in the opposite direction to the one glued to the cone tube?
So there is no DC, just two coils in opposition, one glued to a thin (wooden?) frame, the other glued to the cone tube, and maybe even put a small spider right at the end too (Surround -> cone -> tube -> coil(s) -> spider)
I'm guessing it's going to be an efficiency thing, but in this case - does it actually matter?
Has anyone tried it? Thanks
Loudspeaker motor especially in fullrange applications are very sensitive to the magnet gap strength. For example 12g 8inch cone construction, with more winding will create higher Bl as the magnetic gap strength increases. As a result when the magnetic strength increases, the frequency starts to form an incline shaped responses with the mid/high range starts to becomes louder than the lower half.
A field coil allows the fine adjustment to set the sweet spot for the gauss level.
Fix magnet motor don't have the luxury to do so, and it is a lot of effort trying to design using alnico or neodymium to get that prefect range which prevent the driver from behaving like a maniac. And every builder has a different design for enclosure, different baffle size and so designing a motor with one size fits all will be a challenge. So an electromagnetic comes in handy.
A field coil allows the fine adjustment to set the sweet spot for the gauss level.
Fix magnet motor don't have the luxury to do so, and it is a lot of effort trying to design using alnico or neodymium to get that prefect range which prevent the driver from behaving like a maniac. And every builder has a different design for enclosure, different baffle size and so designing a motor with one size fits all will be a challenge. So an electromagnetic comes in handy.
Yes I understand the benefits of the DC field coil, and the tuning..
.. but do not understand the drawbacks of two air coils next to each other (one inside the other), wired to repel each other, so the two coils push against each other.
The outer coil could be longer to minimise Xmax distortion, and I realise that without an (optional) laminated pole piece the magnetic field would be a bit weak - but I wonder what it would sound like
Air cores, no big magnet or basket assembly in to reflect the backwave - even if efficiency is low.. perhaps the sound will be special.
Maybe one day I'll have to try building one, maybe just from balsa, paper, superglue and some spare enamelled wire.. pop it on a baffle and see what the midrange is like ..! Even if it is too inefficient, it is a cheap and cheerful idea to try.
.. but do not understand the drawbacks of two air coils next to each other (one inside the other), wired to repel each other, so the two coils push against each other.
The outer coil could be longer to minimise Xmax distortion, and I realise that without an (optional) laminated pole piece the magnetic field would be a bit weak - but I wonder what it would sound like
Air cores, no big magnet or basket assembly in to reflect the backwave - even if efficiency is low.. perhaps the sound will be special.
Maybe one day I'll have to try building one, maybe just from balsa, paper, superglue and some spare enamelled wire.. pop it on a baffle and see what the midrange is like ..! Even if it is too inefficient, it is a cheap and cheerful idea to try.
Hi Globu,
Yes, it´s important to have the rear side of your driver free from obstacles, especially in an OB arrangement. But to replace the magnet with a coil wouldn´t work, because there´s no magnet anymore...
Efforts to avoid reflections behind the cone have thus to be more conventional.
All the best
Mattes
Yes, it´s important to have the rear side of your driver free from obstacles, especially in an OB arrangement. But to replace the magnet with a coil wouldn´t work, because there´s no magnet anymore...
Efforts to avoid reflections behind the cone have thus to be more conventional.
All the best
Mattes
Attachments
So to put it simply,( which is my level!) ….
The voice coil attached to the cone in a speaker is really “wimpy”. It’s just a few turns of fine wire.
The only reason it can move the cone so effectively is that the coil is in an immense magnetic field created by a very powerful
magnet or a very powerful electromagnet (field coil). The wimpy coil becomes powerful because it is reacting to this powerful magnetic force.
I think a wimpy voice coil reacting against another wimpy coil on the same pole piece would technically move, but hardly, because: 2 wimpy coils.
You could make both voice coils much bigger and powerful, but then the coil attached to the cone would be massively heavy and the cone would only be able to reproduce frequencies so low they would probably be below human hearing.
The voice coil attached to the cone in a speaker is really “wimpy”. It’s just a few turns of fine wire.
The only reason it can move the cone so effectively is that the coil is in an immense magnetic field created by a very powerful
magnet or a very powerful electromagnet (field coil). The wimpy coil becomes powerful because it is reacting to this powerful magnetic force.
I think a wimpy voice coil reacting against another wimpy coil on the same pole piece would technically move, but hardly, because: 2 wimpy coils.
You could make both voice coils much bigger and powerful, but then the coil attached to the cone would be massively heavy and the cone would only be able to reproduce frequencies so low they would probably be below human hearing.
Last edited:
Ok, I've finally worked out why it's not used
Each coil forms a magnet when current flows - so there are two magnets, created by the current.
The problem is that to push-pull, the magnetic fields need to alternate between attraction and opposition - that is: only one coil, should be reversing its magnetic field.
Alternating both fields, always creates a push or a pull, so some weird 2nd harmonic sound may result.
So the other (usually fixed) coil needs to always stay in the same direction.
Perhaps with a MOSFET diode (bridge!), the field coil could in fact work as I envisage, but that diode may create crossover distortion, but how bad that would be, with a little bias perhaps, I don't know.
I.e the field coil pulsates in strength in a single direction, set by the diode, while the voicecoil takes the alternating current - hence the push-pull requirement is solved.
So it's possible, but the requirement for a perfect diode is a complication. Whether it's a serious limitation - I don't know, and there may be others
I can now see why most choose a fixed DC coil.
Hi Globu,
There´s also the requirement for some power, you want the mobile coil to move with its own and the attached cone´s weight, quick and precisely. So you need to make your fixed coil quite big - and voila, here´s your fieldcoil driver...
In my opinion it is a very good thing to have the back of the cone as open and non-reflective as possible, especially in an OB application. But I fear the traditional ways are to be preferred, so most open basket, smallest possible poleplate, proper ventilation and so on; putting the magnet away will result in more new problems than problems solved...
Some agree with the quest for maximum openness of basket and free area behind the cone (the better ScanSpeak series are nice examples), others disagree and have big amounts of material behind the cones.
Your choice... or in general customer´s choice...
All the best
Mattes
There´s also the requirement for some power, you want the mobile coil to move with its own and the attached cone´s weight, quick and precisely. So you need to make your fixed coil quite big - and voila, here´s your fieldcoil driver...
In my opinion it is a very good thing to have the back of the cone as open and non-reflective as possible, especially in an OB application. But I fear the traditional ways are to be preferred, so most open basket, smallest possible poleplate, proper ventilation and so on; putting the magnet away will result in more new problems than problems solved...
Some agree with the quest for maximum openness of basket and free area behind the cone (the better ScanSpeak series are nice examples), others disagree and have big amounts of material behind the cones.
Your choice... or in general customer´s choice...
All the best
Mattes
I guess even some intelligent back-wave shaping would help, as it is baskets are stamped out, and form reflectors about what - 15mm from the cone, so a 30mm return path, a sound wavelength in air of 11.4kHz, so add in the magnet steel disc etc, then you get all sorts of interesting frequency peaks and troughs..
... which is exactly what we see in the frequency plots of these drivers.
A DIY update would be to use silicone or whatever to change the flat plates into some type of more aerofoil-ly sympathetic shape perhaps.
I'm not sure how inefficient a regular (say 20mm long) voice coil in a 40mm long single wound field coil, with a laminated iron pole piece to focus the field a bit - would be: but the almost total lack of HF reflections would be nice, and in some cases efficiency really doesn't matter much - assuming it's somewhere LOL.
But the need for a precision rectifier with zero crossover might be more of an issue - but perhaps a biased MOSFET might be good enough
When I get a little time and some wire I'll have to try something, just to get an idea of the efficiency, it would have to work without a fan blowing air between the coils LOL
... which is exactly what we see in the frequency plots of these drivers.
A DIY update would be to use silicone or whatever to change the flat plates into some type of more aerofoil-ly sympathetic shape perhaps.
I'm not sure how inefficient a regular (say 20mm long) voice coil in a 40mm long single wound field coil, with a laminated iron pole piece to focus the field a bit - would be: but the almost total lack of HF reflections would be nice, and in some cases efficiency really doesn't matter much - assuming it's somewhere LOL.
But the need for a precision rectifier with zero crossover might be more of an issue - but perhaps a biased MOSFET might be good enough
When I get a little time and some wire I'll have to try something, just to get an idea of the efficiency, it would have to work without a fan blowing air between the coils LOL