Hi,
Yes, Permendur is the the best material with the highest permeability. Checking further you´ll notice that it´s extremely expensive, and on top you´ll need to find someone willing to work with it, or try yourself. With FEMM, it´s very easy to simulate different materials - in the case of my motor for an 8" FR driver (no FC, but custom N52 magnet) with an airgap of 40mm diameter, 10mm length and 1,2mm width (1,4mm without the copper cap) Permendur would only be a small percentage better than Pure Iron, an available material with a permeability of 2,14T. But the Pure Iron is quite a bit better than 1010 steel, so I choose it for a compromise. Even so it´s an expensive compromise, the motor alone is nearly 300€ in parts, per piece, in small series. But it has, with a 5mm voicecoil, 1,55T in the airgap, symmetrical across +-2,5mm of travel, with an airgap wide enough to be practicable even with a copper cap inside.
Interestingly, FEMM simulation results were always surprisingly close to measurements in real life (and my cheap gaussmeter was, even if maybe not correct on absolute value, sensible enough to measure differences between different designs).
Interestingly also may be that with an airgap of practicable dimensions, the force in the airgap is of course lower than the max. permeability of whatever material, and I see manufacturers advertise they have 2,4T in the airgap... physically impossible! FEMM will show this as well easily and cannot be praised enough.
All the best
Mattes
That's a work of art, Mattes! Chrome plating?
One big problem I just discovered about 1010,1018,1117, etc., is they require a pretty sophisticated anneal in hydrogen to achieve the optimal magnetic properties. I was just about to pull the trigger on some 1117 bar stock before I realized this problem. I have some 3% Si NGOES that shows a slight performance penalty in FEMM, but I won't have to worry about annealing. On the other hand, perhaps the unannealed low carbon steels will be 'good enough'. I assume pure Iron like you employ is fairly tricky to acquire. I know getting ahold of Si electrical steel was a major pain in the ***. So when I see the performance of 1018 (readily available) in FEMM, it's a very attractive option.
One big problem I just discovered about 1010,1018,1117, etc., is they require a pretty sophisticated anneal in hydrogen to achieve the optimal magnetic properties. I was just about to pull the trigger on some 1117 bar stock before I realized this problem. I have some 3% Si NGOES that shows a slight performance penalty in FEMM, but I won't have to worry about annealing. On the other hand, perhaps the unannealed low carbon steels will be 'good enough'. I assume pure Iron like you employ is fairly tricky to acquire. I know getting ahold of Si electrical steel was a major pain in the ***. So when I see the performance of 1018 (readily available) in FEMM, it's a very attractive option.
Hi Haze,
Thanks! Nickel plating, partly for function, but of course looks don´t suffer... Lots of work and money went into the motor development, and it has been optimized to a point where every single aspect (or most often dimension) is in balance with all other aspects. Or the other way round: couldn´t find any detail no more which makes things "better"; any change above this design will have negative effects in performance. It looks a bit strange, though...
Buying Pure Iron is not that difficult : https://puronmetals.de/en/reineisen/ and https://alliedmet.com/alliedpureiron/ in the US of A. My metal guy complained about the machining properties, but all in all it seems not to be so hard to work with this stuff. Generally I´d describe it as "second best" after Permendur, with the advantage of not costing 4-figure-sums for just one motor...
All the best
Mattes
Thanks! Nickel plating, partly for function, but of course looks don´t suffer... Lots of work and money went into the motor development, and it has been optimized to a point where every single aspect (or most often dimension) is in balance with all other aspects. Or the other way round: couldn´t find any detail no more which makes things "better"; any change above this design will have negative effects in performance. It looks a bit strange, though...
Buying Pure Iron is not that difficult : https://puronmetals.de/en/reineisen/ and https://alliedmet.com/alliedpureiron/ in the US of A. My metal guy complained about the machining properties, but all in all it seems not to be so hard to work with this stuff. Generally I´d describe it as "second best" after Permendur, with the advantage of not costing 4-figure-sums for just one motor...
All the best
Mattes
If by strange you mean awesome! Machine work, plating, all top notch.
Thank you for the links--when they say pure they really mean it. Maybe I can hit them up for some scrap chunks to experiment with. You never know with material guys. One time I was at a Professional Plastics distro and the guy hands me 1k$ chunk of Hylar, just to "play around with."
Hi, I have some considerations to make.
if all manufacturers of both field coil and permanent magnet loudspeakers place the voice coil on the edge of the magnetic mass there must be a reason. I suppose that placing the voice coil in other positions generates a series of problems including an uncontrolled excursion of the cone.
if in a field coil loudspeaker I placed the mobile coil along the central trunk of the magnetic mass instead of on the edge I could eliminate the air gap and obtain a greater magnetic flux, then you will tell me why it cannot be done.
apparently the material hiperco 50 in addition to being expensive is difficult to work. perhaps it can be done in another way, using a full hiperco rod to obtain the maximum in magnetic saturation on which the direct current coil is wound and then the external ring in another material but with a very high permeability.
I don't know if in the long term oxidation is created by the contact between two different metals.
other consideration. how many tesla can you reach with a field coil?. it would be nice to adjust the magnetic field strength with a variable power supply to change the frequency response of the speaker but if the magnetic field doesn't exceed that of a fixed magnet speaker then that becomes less interesting.
if all manufacturers of both field coil and permanent magnet loudspeakers place the voice coil on the edge of the magnetic mass there must be a reason. I suppose that placing the voice coil in other positions generates a series of problems including an uncontrolled excursion of the cone.
if in a field coil loudspeaker I placed the mobile coil along the central trunk of the magnetic mass instead of on the edge I could eliminate the air gap and obtain a greater magnetic flux, then you will tell me why it cannot be done.
apparently the material hiperco 50 in addition to being expensive is difficult to work. perhaps it can be done in another way, using a full hiperco rod to obtain the maximum in magnetic saturation on which the direct current coil is wound and then the external ring in another material but with a very high permeability.
I don't know if in the long term oxidation is created by the contact between two different metals.
other consideration. how many tesla can you reach with a field coil?. it would be nice to adjust the magnetic field strength with a variable power supply to change the frequency response of the speaker but if the magnetic field doesn't exceed that of a fixed magnet speaker then that becomes less interesting.
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Roman, I am sorry to have you waiting for so long for an answer. Yes, I use Fusion 360 to model everything in the digital space first, including the cone molds and representations of a single cone segment. For the cone segment shapes, I use a plug-in for Fusion 360 called ExactFlat:
https://apps.autodesk.com/FUSION/en/Detail/Index?id=3499335255055878377&os=Win64&appLang=en
It is insanely expensive, so... I've been careful to get everything done that I need while it's still in trial mode. It does a great job of unwrapping complex surfaces into vector shapes, and showing a heat map of the areas of stress. Once I have the shapes I want, I cut them using a Silhouette Cameo 4. Hope that helps.
Absolutely incredible work, Mattes. Can't wait to see more details, when you're ready to share.
I also 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
Hi Ken,
A very nice review, congrats! But I don´t understand one thing, sorry (English is not my mother language): How did you manage "a highly uniform gap density that is thousands of times higher than a permanent magnet"?
All the best
Mattes
A very nice review, congrats! But I don´t understand one thing, sorry (English is not my mother language): How did you manage "a highly uniform gap density that is thousands of times higher than a permanent magnet"?
All the best
Mattes
Hi Ken
Thanks!
Although all details will be available on my website (footnotes from the old forum are gone, must renew them soon...) in a few weeks, of course I can share details here as well, if there´s interest.
All the best
Mattes
I didn't, @Mattes! 🙂 I really did give it my best trying to correct the technical errors, and while I sent my revisions to Bob some of them did not get applied... that entire paragraph has technical errors in it, which is unfortunate. What he should have said was that the driver has a highly uniform gap density and a permeability hundreds or thousands of times higher than a permanent magnet, depending on the material.
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Hi,
Low carbon steel saturates around 1.9T, depending on the carbon content.
All the best
Mattes
Low carbon steel saturates around 1.9T, depending on the carbon content.
All the best
Mattes