A technical discussion of the Borresen ironless woofer.

[Snickers-is]

So, over today I will try and figure out some of the dimensions of the Borreson driver. If anyone has any clues, I'm all ears.

I might have a pretty accurate FEMM-model somewhere. I will need to look for it later as I have to head out.

 

[mwmkravchenko]

Step one. As on side a picture as I can find. Educated guess that these are M3 machine screws. My getting old eyes like a large screen so I use a 43 inch 4K TV for my Monitor. As you can see a 730% zoom. This gives me a 12mm cross section on the M3 Machine screws as measured by my ultra precision Hazard Fraut plastic digital caliper. Now Seeing that this is huge! I can now take an educated guess as to the O.D. his will only be reasonably close. Not exact.

Too large for my 1981 CN Tower Memorable Ruler to measure overall O.D. Out comes the tape measure! 405mm on screen for width. Yes there is a bit of parallax. But as we are huge the errors will be a little forgiving. So first guess 405/4 keeping in mind the M3 baseline 101.25mm? Round down to 100mm O.D? Kind of fits the in hand pictures.

Motor height. The ruler gives me 208mm/4 = 52mm overall motor height.

50.6mm magnet height closest to the basket 50.6/4 = 12.65. Lets call that 12mm tall.

Dah Copper ring ( My Precious????) 76.7mm/4 = 19.175. 19mm looks good.

Bottom Magnet Same as the copper ring. Also jives with the picture. So 19mm tall.

So I understand that the numbers are not adding up. This is not an exact science. And as anyone that designs drivers will tell you It matters very little. It's the balance in the gap that gets you somewhere you wish to go. Most of motor design is ratiometric. Not exact dimensions.

Now for figuring out the interior.


All vertical measurements were taken Through the centre of the red dot hoping to have the least lens distortion at this point.

 

[olieb]

The Neodymium will be near $120 for the four magnets. The rest under $20.

Outch! Now I understand why such an ironless design is not exactly common.
Before you reach BOM of 120$ you can do a lot of other stuff instead using a kg of neodymium magnet.
Can you give a ballpark number of how much of your design time / cost of manufacture go to
a. motor
b. surround and diaphragm
c. the rest
for a run of the mill standard (but hifi) driver (mid woofer)?

I started out life as a Cabinetmaker. And figuring out dimensions from photos and drawings are not that uncommon. I'll try and walk you through the thought process.

Awesome! I am very much looking forward to this. Not only a picture of the workshop but actually a guided tour of the process.
Love it!

 

[olieb]

101.25mm? Round down to 100mm O.D? Kind of fits the in hand pictures.

My guess is everything is smaller.
This is a 4.5 inch driver. What would the outer diameter be? 130mm?
@smowry showed a section view from the "patent" in #101. That seems to be pretty much exactly the driver. Much easier to get the dimensions from that picture. This is an overlay over your photo.

It would give a magnet diameter of 70mm for a 130mm basket.

 

[Jimbob54]

Snickers-is,

"Not sure where you are going with this."

I am questioning the credibility of your claimed data.

So here's my position. No one but you have made any personal attacks on the thread participants. This discussion is about transducers and not trying to one up the participants. So it's either you or I. If you stay, I go; if you go, I stay. My mission here from the get go was to share. Unfortunately, I cannot figure out what your mission is and I have come to dislike you.

I think people need to agree to disagree because things are getting a bit tetchy around here .

Let's take personality out of this please everybody or I'll be issuing thread bans .

Thanks

 

[Snickers-is]

View attachment 443435

Step one. As on side a picture as I can find. Educated guess that these are M3 machine screws. My getting old eyes like a large screen so I use a 43 inch 4K TV for my Monitor. As you can see a 730% zoom. This gives me a 12mm cross section on the M3 Machine screws as measured by my ultra precision Hazard Fraut plastic digital caliper. Now Seeing that this is huge! I can now take an educated guess as to the O.D. his will only be reasonably close. Not exact.

Too large for my 1981 CN Tower Memorable Ruler to measure overall O.D. Out comes the tape measure! 405mm on screen for width. Yes there is a bit of parallax. But as we are huge the errors will be a little forgiving. So first guess 405/4 keeping in mind the M3 baseline 101.25mm? Round down to 100mm O.D? Kind of fits the in hand pictures.

Motor height. The ruler gives me 208mm/4 = 52mm overall motor height.

50.6mm magnet height closest to the basket 50.6/4 = 12.65. Lets call that 12mm tall.

Dah Copper ring ( My Precious????) 76.7mm/4 = 19.175. 19mm looks good.

Bottom Magnet Same as the copper ring. Also jives with the picture. So 19mm tall.

So I understand that the numbers are not adding up. This is not an exact science. And as anyone that designs drivers will tell you It matters very little. It's the balance in the gap that gets you somewhere you wish to go. Most of motor design is ratiometric. Not exact dimensions.

Now for figuring out the interior.


All vertical measurements were taken Through the centre of the red dot hoping to have the least lens distortion at this point.

When I had the chance to see the individual parts, I concluded they were quite a bit smaller than what you have here. I did a calculation based on the drawings, with the assumption that it was around 80sqcm. I also did the same assuming 140sqcm. I got these numbers:

140sqcm:
Outer ring OD 83, ID 58, H 15, 307g
Inner ring OD 53, ID 31, H 15, 161g
Total mass 937g

80sqcm:
Outer ring OD 59, ID 41, H 10.5, 110g
Inner ring OD 38, ID 22, H 10.5, 58g
Total mass 334g

(Some numbers are rounded off a bit, so it may seem like there are some minor errors).

Anyway, I got close to the same price, and it all depends on who builds it and what quantities etc. Most of them do not use 3D printed chassis anyway. I also think some assembly is done in Denmark. I think these are really small QTY runs.

 

[Snickers-is]

Yes sure, but Maxwell's equations do not care how it is called.

Hm, I tried to give my input to an argument about heat in the motor (from an induction shorting ring). The argument was, that a good inductor will not produce much heat (as opposed to a part with lower conductivity). And like in an induction heater it is the other way around.
The effect of some copper in the motor on mechanical properties will be very small if not zero (without current the ring does basically nothing).

The main source of heat is Re, which comes before both inductive loss and the actual mechanical work of the driver. When you run 100W into a driver, some 99% or so is just directly converted to heat in the voice coil. While Maxwell's equations do work, we need to use the correct numer for the amount of energy that enters that process.

Again I do not understand as this conflicts with my training in physics (I am not an expert in driver technicalities or magnet structures). Which part of B x L will be lowered, when the voice coil gets warm?

That is a really fair point. The thing is that if you build a 4 ohm driver, and you want to make an identical 8 ohm driver, you will need to increase the force factor by Sqrt(2) because what we are really interested in is not Bl alone, but the ratio between the square of Bl, the resistance and the mass. So when you increase the heat you also increase Re while Bl is unchanged. So I was not precise enough there. However, the effect is the same, we loose force as a function of input signal compared to a driver running cold.

 

[smowry]

Goodbye!

 

[mwmkravchenko]

My guess is everything is smaller.
This is a 4.5 inch driver. What would the outer diameter be? 130mm?
@smowry showed a section view from the "patent" in #101. That seems to be pretty much exactly the driver. Much easier to get the dimensions from that picture. This is an overlay over your photo.
View attachment 443460
It would give a magnet diameter of 70mm for a 130mm basket.

Hard to argue when you are right!

 

[mwmkravchenko]

When I had the chance to see the individual parts, I concluded they were quite a bit smaller than what you have here. I did a calculation based on the drawings, with the assumption that it was around 80sqcm. I also did the same assuming 140sqcm. I got these numbers:

140sqcm:
Outer ring OD 83, ID 58, H 15, 307g
Inner ring OD 53, ID 31, H 15, 161g
Total mass 937g

80sqcm:
Outer ring OD 59, ID 41, H 10.5, 110g
Inner ring OD 38, ID 22, H 10.5, 58g
Total mass 334g

(Some numbers are rounded off a bit, so it may seem like there are some minor errors).

Anyway, I got close to the same price, and it all depends on who builds it and what quantities etc. Most of them do not use 3D printed chassis anyway. I also think some assembly is done in Denmark. I think these are really small QTY runs.

You reminded me of pics I took at the Montreal Audio Show last year. They are smaller than my initial extrapolations. Which means those machine screws are not an M3 for one thing. They are probably an M2 that will resize everything to about the correct guess by olieb.

 

[thewas]

This thread is unfortunately a textbook example that it isn't sufficient to be just competent in your field of work but it takes also some social skills and professionalism on communication to not undermine your own efforts, even if those are noble.

Hope the really interesting technical discussion will continue though.

 

[Salt]

This thread is unfortunately a textbook example that it isn't sufficient to be just competent in your field of work but it takes also some social skills and professionalism on communication to not undermine your own efforts, even if those are noble.

Hope the really interesting technical discussion will continue though.

+ 1

 

[mwmkravchenko]

Hope the really interesting technical discussion will continue though.

It will. Busy today. Last night was dealing with questions from China.

 

[mwmkravchenko]

+ 1

Now that I have a better handle on the size. I should go back and rework my guestimates.

 

[Pearljam5000]

How important is the zirconium?

 

[olieb]

How important is the zirconium?

My guess is that it is as important as cryogenic treatment and using silver "demodulation" rings in an ironless motor.
As the silver rings (they actually have them) are handcrafted, they might keep vampires away - you never know.
But this is a new driver, not the one from the pictures.

 

[mwmkravchenko]

How important is the zirconium?
View attachment 443604View attachment 443605

Anything non-magnetic would be just as good. The shape has some utility. But to sell this at 500 000 Euros you need some craziness. I started to read their sales technobable. I had to stop. I was searing at my defenceless monitor. To bad you can't grow flowers with all that stuff if the best way to sum it up.

Mark

 

[Old_School_Brad]

How important is the zirconium?
View attachment 443604View attachment 443605

I’d say it’s critically important from a strategic business perspective.

 

[mwmkravchenko]

When I had the chance to see the individual parts, I concluded they were quite a bit smaller than what you have here. I did a calculation based on the drawings, with the assumption that it was around 80sqcm. I also did the same assuming 140sqcm. I got these numbers:

140sqcm:
Outer ring OD 83, ID 58, H 15, 307g
Inner ring OD 53, ID 31, H 15, 161g
Total mass 937g

80sqcm:
Outer ring OD 59, ID 41, H 10.5, 110g
Inner ring OD 38, ID 22, H 10.5, 58g
Total mass 334g

(Some numbers are rounded off a bit, so it may seem like there are some minor errors).

Anyway, I got close to the same price, and it all depends on who builds it and what quantities etc. Most of them do not use 3D printed chassis anyway. I also think some assembly is done in Denmark. I think these are really small QTY runs.

I know who could build it. The main trouble is that it must be assembled with the magnets pre-charged. Magnetized. That requires a press, and special jigs. We are talking seriously harmful forces with this much neodymium. Also the exotic crazy Neodymium grades are not exactly a huge gain on flux. I get this question weekly from people that I'm doing design work for. Generally I spec N38. Tack on the high temperature designations that you wish. Higher than this is pretty much a lot of money for very little gain. Even in a very high efficiency dome wideband I did for pro-sound. Once you have a motor that is saturated, there is no where left to go. In this case the B field is between magnets. And that is an interesting concept.

Lastly No iron? Well Neodyium magnets are over 97% iron. There are reluctance paths inside when you apply an exterior magnetic field via the voicecoil.

Oh voicecoil!

I see inner outer dual layer. And I see them connected. So probably parallel as the wire diameter is tiny, and the Re is 6 ohms. Not to hard to work out.

 

[racingpht]

I think Snickers-is is right on faraday rings. Putting a copper ring around voice coil don't introduce any more mech loss(QMS).

The example of moving a magnet around a conductive material is right, but here, the voice coil is moving, not the magnet.

on the contrary, in this system the copper ring and magnet stays stationary since they are glued together. The voice coil, when shorted(by a votage amplifier) is just another conductive material, a conductive material moving around a fixed conductive material don't gererate any more loss. It's the magnet.

I think the huge copper ring has an effect on help avoiding demagnetize. An example is here:

1500AL

He specified a huge copper shorting ring that would buck any changes in the global field that was induced by the voice coil signal. The result was that the major drawback of using Alnico for a loudspeaker magnet had been completely eliminated.

Anyway, I really appreciate the techncial info in this thread posted by Steve.