Jef,
I suppose on a theoretical basis that would be true. But you have to remember that the aluminum former is very thin and from what I know the ring is supposed to be up to 20% of the gap thickness to really function correctly. The other thing is that an aluminum former isn't the nicest sounding former that you can use, it isn't the preferred method used in most speakers. I use a Kapton former with a Tufquin layer to damp the Kapton. It does add weight to the assembly but Kapton like aluminum can get noisy.
I suppose on a theoretical basis that would be true. But you have to remember that the aluminum former is very thin and from what I know the ring is supposed to be up to 20% of the gap thickness to really function correctly. The other thing is that an aluminum former isn't the nicest sounding former that you can use, it isn't the preferred method used in most speakers. I use a Kapton former with a Tufquin layer to damp the Kapton. It does add weight to the assembly but Kapton like aluminum can get noisy.
The only thing I know regarding aluminum formers is that they reduce Qm to some degree. I don't believe they reduce distortion the way a flux ring will. Note that they are always split to reduce the Qm loss, otherwise they would be a shorted turn.
If you ever run across a voice coil with shorted turns you will remember the effect. They slow down cone motion as if it was dragging through Maple syrup (the good Canadian stuff). This has been used by SEAS as motion snubbers at the end of coil travel.
David S.
Would it be possible:
Since I use the alu former as a conductor for the suspensioncoil witch is driven by a current source. So the current within the former wil be unchanged in the whole frequencyrange that this wouldn't affect the cone movement? I tested a time ago to shorten the voicecoil to feel the damping of the coil and indeed this is a not underestimated effect. Therefore I had to eleminate this effect in the suspensioncoil (overdamping was the result)
Why are amplifiers voltage driven and not current driven?? No problems with changing impedance.
Cheers,
Jef
Since I use the alu former as a conductor for the suspensioncoil witch is driven by a current source. So the current within the former wil be unchanged in the whole frequencyrange that this wouldn't affect the cone movement? I tested a time ago to shorten the voicecoil to feel the damping of the coil and indeed this is a not underestimated effect. Therefore I had to eleminate this effect in the suspensioncoil (overdamping was the result)
Why are amplifiers voltage driven and not current driven?? No problems with changing impedance.
Cheers,
Jef
Oke It is always interesting to see new ideas but I understand. You never know...
DXF is possible in autocad thx for the tip I didn't know.
I don't understand why people insist on using a moving shorting ring.... it just doesnt work. There is a reason why manufacturers make a gap in the aluminum voicecoil former. If it added something good it would be a gap there.
If a the shorting coil moves in phase with the voicecoil it will contribute to the flux modulation not fight against it.
If a the shorting coil moves in phase with the voicecoil it will contribute to the flux modulation not fight against it.
Hentai.
Great point there, I wasn't even thinking about it moving. To work as a shorting ring it needs to have no gap. If you made an aluminum former without a gap it would have to be from a tubular piece of aluminum and then you would have to look at the expansion rate and how that would affect the gap clearance. I'll stay with my Kapton thank you.
Great point there, I wasn't even thinking about it moving. To work as a shorting ring it needs to have no gap. If you made an aluminum former without a gap it would have to be from a tubular piece of aluminum and then you would have to look at the expansion rate and how that would affect the gap clearance. I'll stay with my Kapton thank you.
@ Hentai, Moving or not moving it make no difference I think. You have to see it as a transfo where the second winding is shorted so in the primary the resistance drops. It is difficult to make the former out of one piece but do-able. Kapton is better for the sound as most if not all premium brands use. I hope to reduce some typical alu vibrations with the ferrofluid. Maybe I'm wrong but have no choice...
What do you mean? you have a sheet of very thin aluminum which will have a high dc resistance (refered to ideal shortcircuit resistance) moving in a constant magnetic field. What do you think happens in that shorted turn?
Its very hard to discuss about this with so little details from you. I'm not even sure what your goal is low inductance, minimum global flux modulation, minimum gap flux modulation, etc. With a constant B value in an underhung motor and with flux modulation properly addressed then you can count on a linear BL(x) even so you might need to look at Le(i) and BL (i). You need to determine which one dominates the non-linear behavior of your motor and choose a solution for that.
Using a shorted aluminum former, you will have 2 windings coupled like in a transformer yes. Because one winding is shorted yes it will lower inductance of the other one in theory. In practice because of the above reasons (high resistance) it won't be very effective and you will probably get only Le(i) more linear. This will not address flux modulation at all.
Jef,
There is a really good paper I have but I am not sure of who posted the link to the paper discussing the various factors in loudspeaker nonlinearities. The title is as follows: Loudspeaker Nonlinearities-Causes, Parameters, Symptoms by Wolfgang Klippel, Klippel GmbH, Dresden, Germany, Klippel@Klippel.de
There are other papers on this subject, some I think are preprints from JBL or AES paper also on the subject. I do not think that your simple aluminum former will work in practice as a flux modulation modulation reduction method. The aluminum former would have to be a single piece, not split and the thickness does not even approach the recommendations for thickness in or out of the gap. Can you explain to us why you think you need an aluminum former in your design? If in fact it does not affect the flux modulation and or eddy currents in the magnetic motor what other parameters are you looking at? I am using Kapton in a very long length former in an underhung device and am having no problems using this material. I see no advantage to an aluminum former and actually I think it could cause you some problems rather than being any advantage. Heat transfer is one of the only advantages I could imagine in this regard, but I must tell you that this should not be a problem with a properly designed voicecoil and motor assembly especially with a ferro fluid in the gap.
There is a really good paper I have but I am not sure of who posted the link to the paper discussing the various factors in loudspeaker nonlinearities. The title is as follows: Loudspeaker Nonlinearities-Causes, Parameters, Symptoms by Wolfgang Klippel, Klippel GmbH, Dresden, Germany, Klippel@Klippel.de
There are other papers on this subject, some I think are preprints from JBL or AES paper also on the subject. I do not think that your simple aluminum former will work in practice as a flux modulation modulation reduction method. The aluminum former would have to be a single piece, not split and the thickness does not even approach the recommendations for thickness in or out of the gap. Can you explain to us why you think you need an aluminum former in your design? If in fact it does not affect the flux modulation and or eddy currents in the magnetic motor what other parameters are you looking at? I am using Kapton in a very long length former in an underhung device and am having no problems using this material. I see no advantage to an aluminum former and actually I think it could cause you some problems rather than being any advantage. Heat transfer is one of the only advantages I could imagine in this regard, but I must tell you that this should not be a problem with a properly designed voicecoil and motor assembly especially with a ferro fluid in the gap.
@ Kindhornman
I need to use alu because i use the aluformer as a conductor for the suspension coil.
I try to explain:
Take a former and wound 1 layer of copper wire around it. then you end on the bottom of the former with your wire. With two layers you end up on top. So i need to get on top of the former therefore I solder the wire on the bottom of the alu former and solder a second wire on top of the former to attach it to the powersupply.
The second solution is to take kapton and IN the gap i go back to top with the wire but I'm afraid the wire will not stay in place (also the gap has to be closen because of the ferrofluid). Maybe with epoxy but not easy.
I need to use alu because i use the aluformer as a conductor for the suspension coil.
I try to explain:
Take a former and wound 1 layer of copper wire around it. then you end on the bottom of the former with your wire. With two layers you end up on top. So i need to get on top of the former therefore I solder the wire on the bottom of the alu former and solder a second wire on top of the former to attach it to the powersupply.
The second solution is to take kapton and IN the gap i go back to top with the wire but I'm afraid the wire will not stay in place (also the gap has to be closen because of the ferrofluid). Maybe with epoxy but not easy.
It is just one coil. On top of this coil there is another 2 layer voicecoil.
I think I can't incorperate the winding between them. (also I have 3 layers in total so i can't go higher)
So the alu former will be shorted or not? Im not sure what level of current you want to put through that but you will need one hell of a current source.
As to the purpose of it i fail to see how it will do anything else than mess up everything.
Basically you will put a dc current through a wire and thus creating a dc magnetic field on the former and you will need a way to counteract the normal offset it will cause. Lets say you did that, any small change in former current will move the voicecoil from it's rest position.
Im interested to see the design working but it seems to me you are just trying to create problems just to apply your sollution.
Maybe but i think the max. value of 0.9A through the former (one winding) is not enough to even move the coil. and even the current is not axial so no moving. You can see the former as a very big wire from the bottom plate to the top plate of the magnetic structure. So there is no force on this only maybe a very little rotating force. But not up and down) are am i wrong.
Don't get me wrong i'm not trying to discuss that i am right but i ask because i am not certain.
Cheers
Jef,
Staying out of the magnetic properties of your dc current loop let me touch on another subject here. The former from Kapton can be closed by a simple overlap of the Kapton by either a secondary piece of Kapton, or as I suggested earlier a secondary wrap of Tufquin. I have my voicecoils made by Precision Econowind and they put the Tufquin across the gap when doing the secondary wrap. This closes the former and it is impervious to the ferro fluid. Typically the ferro fluid is on both sides of the former and not only on one side. This is to balance the hydraulic centering forces of the ferro fluid. I think trying to keep the ferro fluid on only one side will be difficult in any instance, it is going to want to migrate to both sides through any path it may take. This was one of the reasons earlier I said that the fluid would be expensive when considering the total volume of fluid needed to fill the gap. I think in my gap I calculated that it would take 5cc's of fluid to fill my gap minus the former and coil. Not an inexpensive proposition in a production application. My gap length is over 25mm so it does take an inordinate amount of fluid.
Staying out of the magnetic properties of your dc current loop let me touch on another subject here. The former from Kapton can be closed by a simple overlap of the Kapton by either a secondary piece of Kapton, or as I suggested earlier a secondary wrap of Tufquin. I have my voicecoils made by Precision Econowind and they put the Tufquin across the gap when doing the secondary wrap. This closes the former and it is impervious to the ferro fluid. Typically the ferro fluid is on both sides of the former and not only on one side. This is to balance the hydraulic centering forces of the ferro fluid. I think trying to keep the ferro fluid on only one side will be difficult in any instance, it is going to want to migrate to both sides through any path it may take. This was one of the reasons earlier I said that the fluid would be expensive when considering the total volume of fluid needed to fill the gap. I think in my gap I calculated that it would take 5cc's of fluid to fill my gap minus the former and coil. Not an inexpensive proposition in a production application. My gap length is over 25mm so it does take an inordinate amount of fluid.
Oke in that case I can use kapton (it will be thicker as the alu i use => a can of redbull very thin 
). I tested the fluid on one side and both sides. I prefer one side because the side of the voicecoil in an underhung system is not smooth flat. the inside is therefore is super smooth less counterforce. It wil work i tested no problem...
). I tested the fluid on one side and both sides. I prefer one side because the side of the voicecoil in an underhung system is not smooth flat. the inside is therefore is super smooth less counterforce. It wil work i tested no problem...
Last edited:
Jef,
If you are using an underhung design then you are using less ferro fluid than the gap length or you could not keep the fluid on one side unless the former is much longer than the windings. As soon as you would fill the gap length I would love to see how you keep the fluid in containment on the outside of the former only? Something isn't adding up here.
If you are using an underhung design then you are using less ferro fluid than the gap length or you could not keep the fluid on one side unless the former is much longer than the windings. As soon as you would fill the gap length I would love to see how you keep the fluid in containment on the outside of the former only? Something isn't adding up here.
That my friend is classified
No now serieus, because I use the suspensioncoil overhung and the voicecoil underhung my former is much longer and the fluid could not travel from one side to the other. I was forgotten that in your case it won't work.
Why would you use ferro, cooling? In my case for centering (there is no other way) but the extra damping isn't always welcome for the detail conservation in sound. With high viscosity fluid I think it is not such a big issue.
Jef,
There are some low viscosity fluids also and these are more of interest to me. My device has an upper frequency cutoff at about 2.5khz and I shouldn't have much problem with upper frequency output at this level. Now in a dome tweeter things would be different. I really don't need to use the ferro fluids for heat dissipation as there is so much material always around the voicecoil to transfer heat but it does take care of any possible problems with rubbing of the coil in such a long excursion device. I haven't had much trouble with that, but in production it is really a safety factor to eliminate warranty problems.
There are some low viscosity fluids also and these are more of interest to me. My device has an upper frequency cutoff at about 2.5khz and I shouldn't have much problem with upper frequency output at this level. Now in a dome tweeter things would be different. I really don't need to use the ferro fluids for heat dissipation as there is so much material always around the voicecoil to transfer heat but it does take care of any possible problems with rubbing of the coil in such a long excursion device. I haven't had much trouble with that, but in production it is really a safety factor to eliminate warranty problems.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.