Ferrofluid article: http://www.dansdata.com/magnets.htm
Scroll down...some of the images are just plain spooky
Scroll down...some of the images are just plain spooky
Looks like I can't use the Black Kraft formers with ferrofluid. The aluminium foil will have to come out (Bull: 
). Sheesh. It's amazing how many things are coming out of the kitchen...
I need to take a step back now. My magnet assembley was done in haste, but now I need to find out the flux density or at least estimate it. All I know is i'm using 10 NIB magnets 10mm x 5mm with a pull strength of 2.5Kg in contact and 0.9Kg through a 1 mm air gap. Is it possible to derive some useful info from this?
I'll probably order some ferrofluid tommorow. Can't contain my excitement. Those images are just too cool Octopus.
There are a few types - which one? The J Series actually specifies usage for voice coil centering.
). Sheesh. It's amazing how many things are coming out of the kitchen...I need to take a step back now. My magnet assembley was done in haste, but now I need to find out the flux density or at least estimate it. All I know is i'm using 10 NIB magnets 10mm x 5mm with a pull strength of 2.5Kg in contact and 0.9Kg through a 1 mm air gap. Is it possible to derive some useful info from this?
I'll probably order some ferrofluid tommorow. Can't contain my excitement. Those images are just too cool Octopus.
There are a few types - which one? The J Series actually specifies usage for voice coil centering.
Shouldn't be too hard. Just remember the voice coil force formula: Fvc (in newton) = B (in Tesla) * L (in meters) * I (in amperes)
So you'd need a sensitive scale, a DC power supply, a multimeter, and a test former with a few windings around it of known total length (closely spaced so they're commpletely immersed in the gap).
Check out this page--it's right up your alley. (Also includes info on making your own former.)
Err, I've read and re-read that web page about five times now, but I just can't see how it was actually set up i.e. how the weighing scale is used. Have you tried this method before? If not, hopefully I'll get a reply to the email I sent him...
I did some ferrofluid today. Took some metal dust from a sanding machine of my workplace.. Unfortunately the dust seems (partially) to be too coarse for this purpose. The mineral oil and dust go separate when the stuff is put into the air gap. Or at last then when the voice coil is put in. I could strain the dust a bit more, but the whole thing is quite messy to do and I can imagine my new paper diaphragm sucking oil in..
Damned, if I can't find any fine dust I think I'll just have to concentrate to string spider design!
Or buy the magic stuff from somewhere..?
Damned, if I can't find any fine dust I think I'll just have to concentrate to string spider design!
Or buy the magic stuff from somewhere..?
It seems to me that, in a high-excursion environment like a woofer, ferrofluid wouldn't last very long, and when you consider the weight of the motor and voice coil, it seems increasingly unlikely that you will be able to keep ferrofluid in the gap once the driver starts going. I also suspect that it will take a considerable amount of DC voltage in one of your voice coils to keep the thing in the gap.
All told, I think you will need a surround of some kind, if not spider and surround, to make this work.
I'm not aware of any commercial midrange / woofer drivers that use ferrofluid.
All told, I think you will need a surround of some kind, if not spider and surround, to make this work.
I'm not aware of any commercial midrange / woofer drivers that use ferrofluid.
You may be right. I'm expecting my new wires tomorrow so I'll make some crude formers and report back on EM suspension feasibilty - at least for my midrange design.
As for ferrofluid in the context of suspension: I've read that it's really only an aid and not a solution in itself, perhaps more so for larger drivers. Well we can only try. Hopefully by the end of this thread (God forbid it ever dies) we will have all the answers.
I still don't know which ferrofluid to get. Any ideas? Is it applied on both sides of the fomer, or only on the voice coil side?
Agreed, unless you've got a high-flux motor. A dense B field = less DC to obtain the same restoring force from the EMS coils, which reduces mass, which raises the HF rolloff corner and efficiency. Also, the denser the flux, the more radial centering force behavior from the ferrofluid. Bottom line: this EMS/ferrofluid idea is screaming for as much motor as you can afford.
Were I doing it (and I yet may!), I'd spec soft iron top plate/pole and saturate the gap with lots of NdFeB magnet, which should net ~2T.
Also, I wouldn't conceive the driver to be a subwoofer--more of a medium-low excursion wideband.
I've never played with the stuff myself. I would suggest you email Alan Babb, maker of Babb full-range speakers. A while ago, he helped a guy on the fullrange driver forum with some ferrofluid experiments. Nice fella.
Dunno, but I would guess that it might provide more radial centering force if you squirted it into both sides.
Vikash said:
Hi,
it´s applied in the whole gap -> both sides of the former.
For woofer use you need a fluid with high saturation ability (>250)
and fairly lo viscosity (<200) for damping resonance peaks.
For tweeter use the viscosity should be higher (>1000) as the
damping force rises with lower viscosity.
Ferrotec offers development kits.
I would start with a fullrange kit.
Uli
Motor conceptual design - the quest for more B. I've been trying to get to grips with FEMM, and managed to squeeze 1.8-1.9T into the air gap. Apart from the pretty colours in the gap, what else should I be looking out for?
I want to stick with multiple disk magnets instead of a single ring magnet. I assume there will be a penalty due to the non uniformity in magnet-to-plate contact, but to what extent?
For those that haven't tried, FEMM is pretty cool for this kind of stuff. It makes me laugh that I just slapped some plates and magnets together.
I want to stick with multiple disk magnets instead of a single ring magnet. I assume there will be a penalty due to the non uniformity in magnet-to-plate contact, but to what extent?
For those that haven't tried, FEMM is pretty cool for this kind of stuff. It makes me laugh that I just slapped some plates and magnets together.
I wound yet another voice coil, this time with just one layer using higher gauge wire so it fits better in the air gap (each coil = 2.8R). I then applied 3V into the two DC coils (wired in series). In fact 1.5V is enough voltage to keep the former (attached to a paper cone) in the air gap.
Overall, I'm very pleased with the result. This certainly seems the way forward.
Bring on the ferrofluid.
Overall, I'm very pleased with the result. This certainly seems the way forward.
Bring on the ferrofluid.
Hi Vikash,
Your motor design looks very good. You want to approach saturation only near the gap, minimize the short-circuiting flux, and create symmetric fringe fields--all of which it looks like you're pretty much doing. Femm's a great tool.
I think your disk magnets will work fine. If you want more flux, just spec large-diameter top plate/yoke so you can use more/larger-diameter magnets.
Looking forward to seeing how your EMS/ferrofluid experiments work out!
Press on!
Bill
Your motor design looks very good. You want to approach saturation only near the gap, minimize the short-circuiting flux, and create symmetric fringe fields--all of which it looks like you're pretty much doing. Femm's a great tool.
I think your disk magnets will work fine. If you want more flux, just spec large-diameter top plate/yoke so you can use more/larger-diameter magnets.
Looking forward to seeing how your EMS/ferrofluid experiments work out!
Press on!
Bill
Tried some ferrofluid. Quite impressive.
I'm a little dispirited with my current motor assembly, so I didn't want to waste too much time and FF doing tests with it. I did enough for it to convince me that it will work, and potentially work very well.
The former was made out of paper, which I knew would soak up some FF, but I was too eager to care. I applied the FF after the former was in the gap, which in hindsight was done the wrong way round.
The FF had 3 obvious effects:
Firstly, it was possible to make the former jump out of its gap only before application of the fluid, which illustrated the magnitude of damping provided.
Secondly, and most importantly at the moment, there was a clear reduction in lateral movement of the former. My crude former, imperfectly sized, was still grazing the pole piece so it's difficult to say if FF is enough as sole method for lateral positioning. From what I've seen I think it is, but it needs thorough testing.
Thirdly, I felt the motor assembly get hot for the fist time. The heat dissipation properties are clear and welcomed.
On a final note, I recieved 6 different FF samples and only tried 1 at random.
So there's everything to play for.
I'm a little dispirited with my current motor assembly, so I didn't want to waste too much time and FF doing tests with it. I did enough for it to convince me that it will work, and potentially work very well.
The former was made out of paper, which I knew would soak up some FF, but I was too eager to care. I applied the FF after the former was in the gap, which in hindsight was done the wrong way round.
The FF had 3 obvious effects:
Firstly, it was possible to make the former jump out of its gap only before application of the fluid, which illustrated the magnitude of damping provided.
Secondly, and most importantly at the moment, there was a clear reduction in lateral movement of the former. My crude former, imperfectly sized, was still grazing the pole piece so it's difficult to say if FF is enough as sole method for lateral positioning. From what I've seen I think it is, but it needs thorough testing.
Thirdly, I felt the motor assembly get hot for the fist time. The heat dissipation properties are clear and welcomed.
On a final note, I recieved 6 different FF samples and only tried 1 at random.
So there's everything to play for.
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.