Eddy Currents
Eddy currents are induced by the speaker’s coil AC magnetic field into any metal present in the vicinity of the coil.
The thus produced eddy currents, consume energy evidenced by the Joule heating (circulation into these metals) and by the effects that they produce (modulation of the DC magnetic flux B of the magnet system through the AC magnetic field that they create).
Where do they draw this energy from?
Regards
George
PS Instead of introducing some higher electrically conductive metals (Faraday rings) close to the coil, so adding some more Joule-heating energy consumers, I would expect loudspeaker manufacturers use silicon-steel laminated strips or iron powder as the material for the pole plates and center pole. This way they would have managed to minimize the eddy currents that they circulate into the bulk iron that they use instead.
Eddy currents are induced by the speaker’s coil AC magnetic field into any metal present in the vicinity of the coil.
The thus produced eddy currents, consume energy evidenced by the Joule heating (circulation into these metals) and by the effects that they produce (modulation of the DC magnetic flux B of the magnet system through the AC magnetic field that they create).
Where do they draw this energy from?
Regards
George
PS Instead of introducing some higher electrically conductive metals (Faraday rings) close to the coil, so adding some more Joule-heating energy consumers, I would expect loudspeaker manufacturers use silicon-steel laminated strips or iron powder as the material for the pole plates and center pole. This way they would have managed to minimize the eddy currents that they circulate into the bulk iron that they use instead.
Perhaps I misunderstand your question, but you stated the answer in your opening line:
Regarding steel laminations: They might help achieve the desired goal, but the architecture for effective orientation can be tricky in a radially symmetric thing like a loudspeaker motor. Iron powder in a binder may be an approach quite similar to ATC's SLMM. The downside might be reduced maximum flux density due to the "distributed air gap" effect of the powder.
The upshot of either would be increased Le that would have to be accounted for in the total design goal.
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If your goal is to stop circumferencial eddy currents in the yoke and top plate, this can be accomplished simply by cutting a narrow radial slot in a standard woofer or midbass top plate from the outer edge to the inner gap face. This effectively changes it from an "O" shape to a "C", interrupting the eddy-current racetrack. Do the same to the yoke, cutting from the outer edge all the way through into the pole vent opening. Now glue the top plate and yoke into a complete motor with a standard ferrite ring magnet (which doesn't need slotting because of its already high resistivity).
I'd love to see a side-by-side test of two otherwise identical drivers--one with slotted motor parts and one without modification--to see the differences. The Le vs. freq. and distortion measurements would be especially interesting, as would a careful charting of thermal performance and power compression.
I suppose the slotted motor would show among other things:
Higher Le
Higher Qt
Higher bass sensitivity
Lower midrange sensitivity
Lower power compression
I'd love to see a side-by-side test of two otherwise identical drivers--one with slotted motor parts and one without modification--to see the differences. The Le vs. freq. and distortion measurements would be especially interesting, as would a careful charting of thermal performance and power compression.
I suppose the slotted motor would show among other things:
Higher Le
Higher Qt
Higher bass sensitivity
Lower midrange sensitivity
Lower power compression
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Hi Bill F.
You haven’t misunderstood me.
The question was 90% rhetoric and 10% a formal question.
The rhetoric part was adopted for the participants who agree with me that the source is the coil, in order to highlight the process of power drainage that the excess eddy currents initiate, in the hope of starting a discussion on the possible means to deal with it and on the consequences (efficiency and acoustically-wise) of this drainage.
The formal part was for the participants who think otherwise.
Your response is very positive.
I am not aware of the ATC's SLMM. I’ll have an (internet)look on them.
As for the tricky architecture needed to be adopted for the laminated construction, I will try to draw some rough sketches and come back to discuss them with you.
Regards
George
You haven’t misunderstood me.
The question was 90% rhetoric and 10% a formal question.
The rhetoric part was adopted for the participants who agree with me that the source is the coil, in order to highlight the process of power drainage that the excess eddy currents initiate, in the hope of starting a discussion on the possible means to deal with it and on the consequences (efficiency and acoustically-wise) of this drainage.
The formal part was for the participants who think otherwise.
Your response is very positive.
I am not aware of the ATC's SLMM. I’ll have an (internet)look on them.
As for the tricky architecture needed to be adopted for the laminated construction, I will try to draw some rough sketches and come back to discuss them with you.
Regards
George
People keep discussing the nonlinearity of the core pole and plates, but my understanding is that the issue was primarily Alnico vs. ferrite. I'm not saying that steel parts aren't nonlinear but a ferrite structure has significantly higher distortion than an Alnico structure. Ferrite structures with flux cancelling rings perform just as well as Alnico.
In all cases the metal parts are similar mild steel. Also note that structures are generally designed to keep well below saturation so as not to waste magnet potential.
David S.
In all cases the metal parts are similar mild steel. Also note that structures are generally designed to keep well below saturation so as not to waste magnet potential.
David S.
Ref. “Kitchen Event” (totally off-topic)
I was operating a Pressure cooking - Wikipedia, the free encyclopedia (same one as in the pic.) to cook some food. After the cooker started to get hot, I checked the operation of the pressure regulator (it was OK) and came back to the PC, having in the back of my mind to hear the whistling of the steam escaping from the pressure regulator for to reduce the heating setting.
But some two minutes later, a loud Bang was heard, and the kitchen was filled with steam. I went there and saw the mess.
In the “Accident Investigation Report” I have to report my finding of the safety valve’s operation “as the most probable cause of the accident”. The aged rubber plug deformed due to- normal- pressure, popped out of its seat and part of the cooker’s content was injected out suddenly and spread over all the nearby surfaces (the safety valve is located beneath the horizontal locking bar, thus directing the escaping pressure horizontally and downwards).
New rubber plug installed (I had purchased it some months ago, but I forgot to replace it. Damn
) .
Finally, it was by luck that it happened at a time that nobody was in the kitchen and double luck that I was alone at home.
All traces of evidence cleared up, new food prepared and cooked, all in time before the official evening auditing by the Regulatory Authority (HMTS)
Regards
George
I was operating a Pressure cooking - Wikipedia, the free encyclopedia (same one as in the pic.) to cook some food. After the cooker started to get hot, I checked the operation of the pressure regulator (it was OK) and came back to the PC, having in the back of my mind to hear the whistling of the steam escaping from the pressure regulator for to reduce the heating setting.
But some two minutes later, a loud Bang was heard, and the kitchen was filled with steam. I went there and saw the mess.
In the “Accident Investigation Report” I have to report my finding of the safety valve’s operation “as the most probable cause of the accident”. The aged rubber plug deformed due to- normal- pressure, popped out of its seat and part of the cooker’s content was injected out suddenly and spread over all the nearby surfaces (the safety valve is located beneath the horizontal locking bar, thus directing the escaping pressure horizontally and downwards).
New rubber plug installed (I had purchased it some months ago, but I forgot to replace it. Damn
) .Finally, it was by luck that it happened at a time that nobody was in the kitchen and double luck that I was alone at home.
All traces of evidence cleared up, new food prepared and cooked, all in time before the official evening auditing by the Regulatory Authority (HMTS)
Regards
George
Bill F.
I had a look at ATC site, but they didn’t disclose any technical info, just marketing talk. I did a search for an applicable patent
Patent Searching Database
I found the US2008/0199039 Aug 1, 2008 of Wisdom Audio Inc, which in the “Background Art” section makes note of ATC’s S.L.L.M without reference to any patent number, as well as no specific details.
Wisdom Audio’s application is an Induction motor (in which, magnetic field is intentionally modulated by the stationary excitation coil and eddy currents are intentionally induced into the moving coil), something quite different from the typical electrodynamic speakers we are using and dealing here.
Anyway, Wisdom Audio’s patent does focus on and makes claim for the use of powder iron and of “transformer style lamination” in their magnetic circuit for the reduction of unwanted eddy currents in the magnetic circuit.
This is the important point for our discussion.
Regards
George
[Edit. It would be interesting to study how Wisdom Audio and Sony are dealing with the slip phenomenon inherent in the operation of an induction motor http://en.wikipedia.org/wiki/Induction_motor. I think that slip produces frequency dependent amplitude and phase distortion ]
I had a look at ATC site, but they didn’t disclose any technical info, just marketing talk. I did a search for an applicable patent
Patent Searching Database
I found the US2008/0199039 Aug 1, 2008 of Wisdom Audio Inc, which in the “Background Art” section makes note of ATC’s S.L.L.M without reference to any patent number, as well as no specific details.
Wisdom Audio’s application is an Induction motor (in which, magnetic field is intentionally modulated by the stationary excitation coil and eddy currents are intentionally induced into the moving coil), something quite different from the typical electrodynamic speakers we are using and dealing here.
Anyway, Wisdom Audio’s patent does focus on and makes claim for the use of powder iron and of “transformer style lamination” in their magnetic circuit for the reduction of unwanted eddy currents in the magnetic circuit.
This is the important point for our discussion.
Regards
George
[Edit. It would be interesting to study how Wisdom Audio and Sony are dealing with the slip phenomenon inherent in the operation of an induction motor http://en.wikipedia.org/wiki/Induction_motor. I think that slip produces frequency dependent amplitude and phase distortion ]
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Maybe a littele bit more of history:
Those impedanz flattening measures have been implemented and used even around the 50-60s (!) - at least in Europe
It's only the US patent guys that didn't know (or did not care) – and some big company advertising guys that possibly love(d) to "write history them selfs"...
Michael
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Maybe a littele bit more of history:
Those impedanz flattening measures have been implemented and used even around the 50-60s (!) - at least in Europe
It's only the US patent guys that didn't know (or did not care) – and some big company advertising guys that possibly love(d) to "write history them selfs"...
Michael
Yes, impedance flattening measures go way back. The JBL and Mac designs were for flux modulation distortion reduction due to ferrite issues, a different thing.
I think one of them deserved a patent but not both.
David
Telling from the distortion figures this is kind a hairsplitting distinction as those early impedance flattend speakers had comparable lower THD as well (the trick works on ALICO as well, just less pronounced) - meaning - who is to say, those measures they applied where *not* done for lowering distortion - be it in the first place or not - who cares ? - its been made sold and used loooong before some US patents have been filed on the topic !
Michael
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Not a hairsplitting distinction. The midrange distortion of Alnico woofers was always low. Copper plated or silver plated core poles (or similar core caps) were added in thea early days with the sole intention of reducing inductance rise to extend bandwidth in fullrange drivers.
Only when Alnico had to be replaced by ferrite in the 70s was it realized that distortion was markedly higher. The flux modulation control rings fixed the problem but only impacted midrange distortion...had no effect on inductance or bandwidth (see the earlier JBL curves).
As I keep saying, these are two different issues with two different fixes.
David S.
Only when Alnico had to be replaced by ferrite in the 70s was it realized that distortion was markedly higher. The flux modulation control rings fixed the problem but only impacted midrange distortion...had no effect on inductance or bandwidth (see the earlier JBL curves).
As I keep saying, these are two different issues with two different fixes.
David S.
No - as said - the THD lowering trick works / worked with ALNICO as well, just not as pronounced - easily seen in comparing measurements of speakers of that days - you just have to have an open eye and not to insinuate that those early guys had "no idea" what they were doing
Michael
Michael
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Isn't that the way with all patents? I've seem many patents that really don't stand a chance. They have some advertising value, but it's getting less and less influential.
What is interesting is that, if the same design acomplishes many things, but you only file for patent on one, does it give others the opportunity to file for another effect? I would say, take away the patented application, if the initially patented effect reduces, then the second patent is invalid, or at least cannot be used without lisensing the first patent.
What is interesting is that, if the same design acomplishes many things, but you only file for patent on one, does it give others the opportunity to file for another effect? I would say, take away the patented application, if the initially patented effect reduces, then the second patent is invalid, or at least cannot be used without lisensing the first patent.
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I am not sure if this has been referenced yet but this seems applicable to the discusion at hand
JBL Technical Notes Volume 1 Number 9
Rob
JBL Technical Notes Volume 1 Number 9
Rob
I am not sure if this has been referenced yet but this seems applicable to the discusion at hand
Rob
Hi Rob,
Yes excellent reference. Notice that the flux modulation ring has absolutely no effect on Inductance or HF response. (Fig. B and C)
The 4411 system mentioned was one of my designs.
David S.
Besides my arguments regarding times and places of ingenious developments have little to do with patent practice - IMO patent laws have been instrumentalized as „economy weapons“ to a very extensive degree by some nations.
There's nothing left in the sense of protecting the „poor ingenious inventors“.
At the place where I come form, patents are handled much more restrictive – putting those in other places into clear advantage.
For example – if you hope to get a patent here your idea has to be practical – meaning it *has to* work practically and you have to clearly outline or even bring a prototype (not a necessity in other nations), also it has to be prior art (and I claim this is more extensively proven then elsewhere), and last but not least your idea has to jump the hurdle to be a *real leap forward* with respect to common ground (again not a necessity in other nations).
As a nice story for illustration, I remember Nespresso coffee machines claiming to have put a 500 (!) patents on their Kluni machine.
LOL
I guess around here, patents office would only have laughed and asked if they never ever have gotten any good coffee elsewhere – and sent those „marvelous inventors“ to the next Viennese coffeehouse.
Michael
There's nothing left in the sense of protecting the „poor ingenious inventors“.
At the place where I come form, patents are handled much more restrictive – putting those in other places into clear advantage.
For example – if you hope to get a patent here your idea has to be practical – meaning it *has to* work practically and you have to clearly outline or even bring a prototype (not a necessity in other nations), also it has to be prior art (and I claim this is more extensively proven then elsewhere), and last but not least your idea has to jump the hurdle to be a *real leap forward* with respect to common ground (again not a necessity in other nations).
As a nice story for illustration, I remember Nespresso coffee machines claiming to have put a 500 (!) patents on their Kluni machine.
LOL
I guess around here, patents office would only have laughed and asked if they never ever have gotten any good coffee elsewhere – and sent those „marvelous inventors“ to the next Viennese coffeehouse.
Michael
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Hi DavidThe 4411 system mentioned was one of my designs.
As you mention it, let me say that I *really* like my 4412s (that are quite similar to the 4411s, only a little bit less expensive to build I guess...).
THANK YOU SO MUCH for that great design!!!
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