Ironless Motor Assemblies and STEALLUS

[mwmkravchenko]

I strongly agree. At one time Dr. Klippel was of the opinion that the surround should be the displacement limiting component. I disagreed then and I disagree now. In a robust low frequency transducer design the spider(s) should be the limiting component. The surround should not be allowed to pull tight. This is primarily related to reliability. Surround lift is a common failure mode.

Cms(x)/Kms(x) vary with position but they do not vary directly with current, i (A). Motor force varies with both position and current, F(x) = iBl(x) N. So in the limit, as
iBl >> xKms(x) N and x > Xmax, then we are looking at an unstable system. The red curve below is effectively constant! Perhaps I should have said Cms(x) better limit displacement or else! Without additional information, one must consider such a system potentially unstable.

View attachment 442000

Was Anton S attempting to bait me with his cryptic question? So is that a "good" Bl(x) curve?

Using the spider/damper as the "brake" is what I learned to do from the outset. The surround should allow travel unimpeded over the drivers desired travel. You end up with lower distortion this way. I tend to design long throw drivers that are not readily available off the shelf. At times that means some attention to the surround profile to mitigate unwanted midrange reflections.


Working with a quality spider vendor helps in achieving the mechanical limits. And good motor design stops any self destruction.

 

[smowry]

Welcome Mark! Nice to see another transducer guy here.

 

[mwmkravchenko]

Welcome Mark! Nice to see another transducer guy here.

Found out about this from your post on Linkedin.

Some interesting thoughts in this thread. And a lot of facts. A pleasure compared to so many threads full of opinions and armchair quarterbacks.

 

[smowry]

Amir has created something special here.

 

[smowry]

Folks, if you are signed up for LinkedIn, you can go here and help embarrass Elizabeth.

https://www.linkedin.com/feed/update/urn:li:activity:7313594732541050881/?commentUrn=urn:li:commentugcPost:7313594731765104640,7314053568573947905)&dashCommentUrn=urn:li:fsd_comment7314053568573947905,urn:li:ugcPost:7313594731765104640)&dashReplyUrn=urn:li:fsd_comment7314268762814251011,urn:li:ugcPost:7313594731765104640)&replyUrn=urn:li:commentugcPost:7313594731765104640,7314268762814251011)

Elizabeth never replied nor rebutted my claims but LinkedIn took the entire post down, When I was a practicing engineer, I needed LinkedIn. Now that I am retired, I don't them. Anyway I have 7,495 followers on LinkedIn and what ever happen to free speech? Elizabeth is in hiding mode now.

However, I caused his post in which he touted his invalid patents to be taken down. That was his first post on LinkedIn in three months. Anyway I posted his Puffing on this thread.

Note that my first comment got more than 500 impressions in just a few hours before it was taken down.

 

[smowry]

 

[smowry]

30% Bob said, increase the magnet spacing by 30%.

 

[smowry]

Elizabeth Borresen has effectively done nothing to me. I do not claim to own the 4 x Neo ring magnet ironless motor assembly. On the contrary, I published and fully disclosed the concept. In February 2009, that concept moved from my desktop into the public domain. So what's the problem? As modest as that concept is, it was part of almost 10 years of independent research that included STEALLUS, STEALLUSX, and Almost Air Core motor assemblies. Elizabeth is attempting to steal the concept from the public and thus the loudspeaker industry. His business model is to lie, cheat and steal his way to profitability. How can folks standby and let this happen? As a min, we should promote a boycott of Borresen loudspeakers and the related snake oil products. As a norm, we should debunk his claims whenever we can. I claim that he is dangerous and will drag the loudspeaker industry et al. down. The loudspeaker industry is already technically retarded and falling farther behind the other A/V industry segments every year. We need loudspeaker companies to follow the TOPPING business model, no rhetoric, just performance. There is no better group than the ASR community to throw a net over Borresen et al.

 

[smowry]

 

[Danish ear]

Just a minor detail.
The company filing for the patent Upper level Holding ApS was only alive for little over a month before it was shut down.
It has been split into Daperi holding ApS, M. Borresen Holding ApS and Larserus holding ApS.

 

[smowry]

Danish ear,

Thank you for your kind post and information. And thank you for taking the time to read my post.

I have thoroughly searched for people that have published and/or filed patent applications since 2005, 20 years related to the concept of ironless loudspeaker motors. I could only find four (4). Ironless loudspeaker motors is a highly specialized topic.

1. Steve Mowry
2. Guy Lemarquand et al.
3. Mathias Rémy
4. Michael Borresen

How did the examiner miss the prior art? For an analogy, it's not like trying to find a needle in a haystack, rather more like try to find a haystack in a needle. How could he have missed it?

 

[Snickers-is]

I still think the main claim of their patent are the small hooks marked 26 in the drawing to helt center the assembly.

 

[Snickers-is]

Publishing the STEALLUS concept in 2007 seemed to influence B&W's 800D woofer design.
https://pearl-hifi.com/06_Lit_Archi...s/Mowry_Steve/B&W_Dual_Magnet_vs_Steallus.pdf

View attachment 439271
https://www.linkedin.com/pulse/bw-800d-series-motor-toplogy-review-steve-mowry/?trackingId=E2lcBnaiSi2ZaiAYHRyHYQ==

It also seemed to influence the KEF Blade Woofer design somewhat but we could ask Jack.

View attachment 439274
https://www.linkedin.com/pulse/kef-blade-wofer-review-steve-mowry/?trackingId=E2lcBnaiSi2ZaiAYHRyHYQ==

Morel UW958 is very similar to this. I believe it was first shown prior to this, and based on some variants of earlier Morel and Dynaudio designs. What is special in the 800D design is the return paths both on top and bottom of the motor.

 

[Bending]

I got interested in ironless motor assemblies after reading several papers of Guy Lemarquand et al. for my bending wave driver project https://www.diyaudio.com/community/threads/improving-bending-wave-drivers.420495/ about a decade ago. I had a short conversation with Michael Borrensen at the High End in Munich some years ago and I mentioned these papers and he seemed to be aware of them. As far as I understand the only difference of his ironless driver design (only used in the most expensive versions: 0 or T series). is the use of a copper or silver core between the opposing ring magnets. One issue I have with that design in general is that it has a relatively short VC travel distance where B is close to constant so better for midrange of tweeter than woofers

 

[Salt]

I got interested in ironless motor assemblies after reading several papers of Guy Lemarquand et al. for my bending wave driver project https://www.diyaudio.com/community/threads/improving-bending-wave-drivers.420495/ about a decade ago. I had a short conversation with Michael Borrensen at the High End in Munich some years ago and I mentioned these papers and he seemed to be aware of them. As far as I understand the only difference of his ironless driver design (only used in the most expensive versions: 0 or T series). is the use of a copper or silver core between the opposing ring magnets. One issue I have with that design in general is that it has a relatively short VC travel distance where B is close to constant so better for midrange of tweeter than woofers

Welcome to ASR .
Interesting project You started. Feel free to continue in the DIY here.

 

[DanWiggins]

There are benefits from ironless motor designs, as noted: low and flat inductance, no eddy currents/BL modulation, etc.

There's another way to get that, but without the complexity of doing an ironless motor (and the resulting loss in efficiency):

US20100019584A1 - Voice coil actuator - Google Patents

Provided herein is a voice-coil motor that includes a magnetic field having at least two displaced regions of higher intensity separated by a region of lesser intensity and a counter-coil disposed within the region of lesser intensity.

patents.google.com

The patent is expired.

We used a counter coil in the gap to reduce the Le as low as we wanted. Just for shits and giggles, I reduced one sample to have a measured NEGATIVE inductance. Pretty wild to see a driver with a 7 Ohm DCR, a peak around Fs, then the impedance slightly DECREASING down to 3 Ohms at 10 kHz!

We used this countercoil approach (not so extreme as the negative inductance) on the Event Opal woofer. IIRC, the woofer had an Le(X) of less than 100 uH. For a speaker capable of 18mm one way linear motor force (Bl(x); Kms(x) was around 14mm). Down in the range of tweeters.

Needless to say, it made integration with the HF unit a breeze, and there was NO issue with positional-dependent frequency response from the woofer (where the variable Le over stroke acts as a variable inductor in the first order low pass filter of the speaker). A very open and neutral midrange was the result.

 

[mwmkravchenko]

There are benefits from ironless motor designs, as noted: low and flat inductance, no eddy currents/BL modulation, etc.

There's another way to get that, but without the complexity of doing an ironless motor (and the resulting loss in efficiency):

US20100019584A1 - Voice coil actuator - Google Patents

Provided herein is a voice-coil motor that includes a magnetic field having at least two displaced regions of higher intensity separated by a region of lesser intensity and a counter-coil disposed within the region of lesser intensity.

patents.google.com

The patent is expired.

We used a counter coil in the gap to reduce the Le as low as we wanted. Just for shits and giggles, I reduced one sample to have a measured NEGATIVE inductance. Pretty wild to see a driver with a 7 Ohm DCR, a peak around Fs, then the impedance slightly DECREASING down to 3 Ohms at 10 kHz!

We used this countercoil approach (not so extreme as the negative inductance) on the Event Opal woofer. IIRC, the woofer had an Le(X) of less than 100 uH. For a speaker capable of 18mm one way linear motor force (Bl(x); Kms(x) was around 14mm). Down in the range of tweeters.

Needless to say, it made integration with the HF unit a breeze, and there was NO issue with positional-dependent frequency response from the woofer (where the variable Le over stroke acts as a variable inductor in the first order low pass filter of the speaker). A very open and neutral midrange was the result.

Trade some efficiency for a flat BL curve. It is effective. I designed many motors like this for a few clients. Produced a few drivers for them too. And they liked them.

It has some of the characteristics of an underhung. Although the dual gap and long coil have their own distortion characteristics to contend with.

The design concept certainly has it's place.

 

[Lars Risbo]

one huge advantage of ironless is the absence of hysteresis distortion from the iron. I am not sure if the counter coil achieves this?

 

[mwmkravchenko]

one huge advantage of ironless is the absence of hysteresis distortion from the iron. I am not sure if the counter coil achieves this?

No it doesn't. Even an ironless motor has hysteresis within the magnets, and to a degree in the non-iron parts. They are different, but they do exist. What happens is the type of distortion is different. Also the magnitude of the distortion that is an inherent part of it's operation.