Dead Tweet That Uses Ferrofluid

Just ordered the ferrofluid. Pricey. Wish I had a gallon of that stuff to sell on AK!

Ha ha... I do, actually. It is nothing more than extremely low viscosity silicone-based lubricant/hydraulic fluid--used as ferro-fluid, lubricant, TT dampers and lifts, and "shock oil" in RC toys. You're getting the fluid for cheap, but packaging and shipping an ounce or two is what kills you.
 
Ha ha... I do, actually. It is nothing more than extremely low viscosity silicone-based lubricant/hydraulic fluid--used as ferro-fluid, lubricant, TT dampers and lifts, and "shock oil" in RC toys. You're getting the fluid for cheap, but packaging and shipping an ounce or two is what kills you.

Damn I wish I would have known, well if you could have beat $27 that is. Ordered 2 pieces, each for a 1.5 inch tweeter and that was how much I paid.
 
Removing and replacing the fluid is very easy. Disassemble, soak up the old fluid with paper, replace fluid.

Now you have a functioning tweeter and have created a pair of speakers that will easily compete with a pair of "white van" speakers in imaging.

Doing it correctly is a completely different process and it includes running the reassembled tweeters to match their response. Good speaker shops have the equipment, experience, and knowledge and do this. I know of at least one shop locally who claims to be "certified JBL service" and doesn't, so don't count on everyone who has a screwdriver and soldering iron to really understand the importance of matched tweeters or how to accomplish it.

The other side of this is that if you have bad or contaminated fluid your tweeters have probably not been matched or sounded correct for years, so you're not going to make it worse and will probably come fairly close in comparison.
 
Ha ha... I do, actually. It is nothing more than extremely low viscosity silicone-based lubricant/hydraulic fluid--used as ferro-fluid, lubricant, TT dampers and lifts, and "shock oil" in RC toys. You're getting the fluid for cheap, but packaging and shipping an ounce or two is what kills you.

Does extremely low viscosity silicone-based lubricant/hydraulic fluid get drawn into magnets?
 
Does extremely low viscosity silicone-based lubricant/hydraulic fluid get drawn into magnets?

Not sure what you mean. I use a needle and syringe to fill the magnet gap with fluid. But silicone-based fluid is not magnetic, if that is what you are referring to.
 
Not sure what you mean. I use a needle and syringe to fill the magnet gap with fluid. But silicone-based fluid is not magnetic, if that is what you are referring to.

Ferro-fluid is magnetic (that's the "ferro" part), I think this is what he is asking about, ... regular damping fluid is not and will drool out.
 
Sorry, I was being facetious. I meant therein lies the rub of the high cost of true magnetic fluid. I've experimented with magnetic fluids for many decades and one of it's fascinating properties is to defy gravity and literally be drawn into a magnetic gap (or indeed a simple magnet)

I still don't fully understand how it can be used in woofer applications where there is so much excursion, yet Ohm amongst others have used ferro fluids in their woofers for years. In those situations it seems to overdampen the cone's movement to the point of resisting the woofers motor. I would have thought such physical resistance would lower the woofer s sensitivity too much to be practical.
 
I will tell ya this, this little ferrofluid tweeter on my Kef 10's sounds better than the JBL-like tweet that was on my set of Pioneer sx4g's that I just sold. Any sound difference between ferrofluid tweets compared to others? Probably. BUT I guess it all depends on the users ears too and their own listening tastes of course. Anyway, I think it's worth replacing the fluid on a tweet that needs it if you really like the speakers. I will update this thread with pics as per @Bucky Badger request. I should have the fluid in a few days.
 
Ha ha... I do, actually. It is nothing more than extremely low viscosity silicone-based lubricant/hydraulic fluid--used as ferro-fluid, lubricant, TT dampers and lifts, and "shock oil" in RC toys. You're getting the fluid for cheap, but packaging and shipping an ounce or two is what kills you.

Yes, not much magic there, but the formulation is slightly more complicated than this and I wouldn't necessarily use random fluid. I looked into cooking up a batch of ferrofluid for speakers which I still have not rebuilt. I, too, was put off by the expense for an ounce of the stuff and also by the fact that not knowing what is in it, I'm not sure I trust the formulation to last.

The basic idea behind ferrofluid is creating a colloidal suspension of tiny magnetic particles (mostly hematite and magnetite) in a constant-viscosity oil plus some surfactant as a dispersant.
Surfactant: The surfactant is very important, as it functions as a dispersion agent by chemically binding to the magnetic particles, surrounding each one and repelling similarly surrounded particles. This prevents clumping. So the surfactant must be chosen to support binding to the iron and being compatible with the silicone.

Oil: Which brings us to the oil viscosity issue, which really matters. The original ferrofluids used conventional hydrocarbon oils, but these tended to suffer lowered viscosity with temperature and also tended to crosslink into sludge over time. (Some oils had hydrocarbon thinning agents which rapidly evaporated, but as a general rule oil subjected to oxygen in the air and heat will, over time, polymerize into a tacky mess like the cooking oil deposited on kitchen cabinets) That's why the move was made to silicone oils as these were more temperature stable and tended to not as readily crosslink. The whole point is to cool the tweeter, so the temperature is hot enough to matter. But the downside of low-weight silicone oil is that it tends to evaporate.

Particle Formulation and Size: Then there's the particle diameter, and smaller is better. Sometimes instead of pure iron particles ferrite blends with manganese and cobalt are used. These cost a lot more. Pennies for us in the quantities we use. But the quality of the formulation depends upon what particle and what size. Anything larger than 10 nm tends to not stay in solution.​

TL/DR: all ferrofluids are not identical and it behooves one to do some investigation as to quality.

Anyway, I doubt anyone is going to cook up a batch, but it likely matters where one purchases the replacement fluid, as the manufacturer may not have made it for speakers or may not have properly chosen the oil, surfactant, or particle size. One never knows who cooks up this stuff, and not everyone respects the chemistry. So only purchase the finest blue ferrofluid.
 
So could you point me in the direction of a good batch? What you might recommend??
I was thinking of going with the Partsexpress kit but if I can get the real stuff..... Heck.
 
So could you point me in the direction of a good batch? What you might recommend?? I was thinking of going with the Partsexpress kit but if I can get the real stuff..... Heck.

I decided I could replace the tweeters with modern soft-domes which wouldn't ever need replacement fluid, but before I made a decision one way or the other I shelved the project because I have enough speakers and likely would not need these.

Ferrotec has been making ferrorfluids for nearly fifty years and was founded by one of the ferrofluid inventors. It is resold by some of the AK sponsors in smaller quantities. The carrier is either a synthetic hydrocarbon oil or a synthetic ester:
You'll note a variety of products and target applications which pushes the selection one way or the other. I suggest contacting the company's tech support line if you have questions about suitability for a particularly tweeter type.

Lacking direct experience, I can't comment on the suitability of the ferrotec product, but its products did look better on paper than the competition.
 
Thanks. I will check them out.
I will be doing at least 2, maybe 4, BA A400 tweets.
 
Last edited:
So how do you know just how much fluid to use and where did you pick up your new fluid? I have heard folks say to just fill up the gap 1/2-3/4 but it looks like it might be kinda tough to see just how much you have in there.
And what kind of paper did you use to mop up the old fluid? 3x5 cards I hear work.
Sorry if these are stupid questions, I appreciate this thread and any info. I just want to do it right the first time.
 
So how do you know just how much fluid to use and where did you pick up your new fluid? I have heard folks say to just fill up the gap 1/2-3/4 but it looks like it might be kinda tough to see just how much you have in there.
And what kind of paper did you use to mop up the old fluid? 3x5 cards I hear work.
Sorry if these are stupid questions, I appreciate this thread and any info. I just want to do it right the first time.

Picked it up on feebay from simply speakers. My tweets are labeled for sale as 1 inch but they are actually 1.3 inches so I bought the 1.5 inch size packet of fluid. Like it’s shown in the video, first you clean around the tweet with blotter paper (the fluid I bought included a few sheets that worked well) then you add the fluid. The magnet pulls the fluid and it fills around the tweet flush to the top. Glad I bought the 1.5 inch size as it all got used.
 
So how do you know just how much fluid to use and where did you pick up your new fluid? I have heard folks say to just fill up the gap 1/2-3/4 but it looks like it might be kinda tough to see just how much you have in there.
And what kind of paper did you use to mop up the old fluid? 3x5 cards I hear work.
Sorry if these are stupid questions, I appreciate this thread and any info. I just want to do it right the first time.

If anyone is working on an AR tweeter, there's a chance that you can find the original manufacturing print on classic speaker pages. There you'll find the volume and specific type of fluid originally used in the tweeter. I did this and of course couldn't find the original FF formula, or any choice but one for that matter. The specified volume was much less than the gap could contain. I did go get diabetic syringes and tried to extract the exact amount from the fluid vial. Found it was too thick for the needle, so removed the needle and resized the tip, this all turned into a messy process and not worth the effort. An estimate based on the vial size is probably close enough. The print said that the fluid was applied between the coil and the pole. So this must have been done before the coil was glued to the dome/cone. The only way I could think to do this was to energize the coil with a test tone and apply the fluid to the ID of the coil. The electromagnetic force holds the fluid on the coil until it's inserted, then helps centering. The thinner than human hair leads and glued-not-screwed construction made the AR tweeters very difficult to work with compared to most.
 
Back
Top Bottom