MasterT Posted February 1, 2004 Share Posted February 1, 2004 I did my first diaphragm swap on my RF-5 tweeters. The voice coil separated from the dome. While taking them apart I noticed a brown oily substance which I later found out was Ferrofluid. I can only assume that this fluid is used to dampen the voice coil. Is this correct? What is this fluid made from? Also, from the way I understand it, the fluid is only supposed to be in the magnetic gap. When I took them apart the fluid was all over the place underneath the diaphragm assembly. How much of this fluid loss is acceptable? Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2004 Share Posted February 1, 2004 MasterT, It's my understanding that the ferofluid is intended to keep the voice coil cool under power. I think the damping effect is not desirable. I have't had any experience with the stuff though. Al K. Quote Link to comment Share on other sites More sharing options...
WMcD Posted February 1, 2004 Share Posted February 1, 2004 I have limited knowledge. It is my understanding that it is made of mineral oil with a slurry of iron oxide (hence the "ferro" from Latin for iron). The latter being the type of stuff used on recording tape, floppies, mag stripes, etc. The goal is to have a fluid trapped in the magnetic gap with the voice coil in between. Thus there is a path for heat transfer. It seems the slurry remains there because of the magnetic attaction on the iron. I'd have thought that the particles would eventually be attacted to one side of the magnetic field or the other and thus precipitate out. But evidently not so. Quite ingenious. My guess is that there is some mechanical damping just due to the fact that any liquid is going to have some resistance to motion. Dim recall is that there are various grades of the stuff. Perhaps that is for woofers and mids. Fuzzy logic tells me that the stuff is too viscous to use on a tweeters where it is most needed. I dunno about how much loss is accepable. Gil Quote Link to comment Share on other sites More sharing options...
D-MAN Posted February 2, 2004 Share Posted February 2, 2004 The ferro fluid is an magnetically attracted oil composite that transfers more heat from the source to the surrounding air than an uncoated source would by itself. Technically it does this through convection in that an oil absorbs (or draws) heat and therefore tends to hold it better than most other things. Being that the oil coating is very thin it tend to loose the heat faster in that it has a large surface (repectively) exposed to the air which would hopefully be cooler than the heat source. It also resists evaporation. It is the heat "drawing" action of the oil that makes it useful to "cool" a voice coil where it is "painted". It has very little effect on "damping" if at all as it doesn't actually touch anything or restrict movement in any way...although it could present a very slight surface dynamic (air resistance) that could possibly be measured and regarded as "damping". I would not know if you could actually hear the difference. DM Quote Link to comment Share on other sites More sharing options...
D-MAN Posted February 2, 2004 Share Posted February 2, 2004 p.s. to my knowledge, it does not fill the air gap. ...that would be messy for sure. DM Quote Link to comment Share on other sites More sharing options...
djk Posted February 3, 2004 Share Posted February 3, 2004 "p.s. to my knowledge, it does not fill the air gap." Of course it fills the gap, that's how it works. Improperly designed tweeters blow out ferrofluid when shipped air freight. Improperly designed tweeters have their voice-coil formers fall off the dome when used with ferrofluid. The magnetic particles are Magnetite (Fe3_O4). The oil is a long-chain type allowing the smaller magnetite particles to be homogenized. Cheap tweeters use a high viscosity oil for damping, woofers use a low viscosity oil. There are two different base oils. All the different adhesives used in the speaker assembly must be compatible with the out-gas products of one of these oils or the driver will fall apart. To insure proper function after repair, clean all the old ferrofluid out, re-fill from the pre-measured squeeze package for your driver, replace diaphragm. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted February 3, 2004 Share Posted February 3, 2004 I recently put in a new diaphram in a 2" compression driver, and whereas the voice coil on the diaphram was coated in fluid, the air gap on the magnet structure definately was reasonably clean and dry and had never been opened before as I bought it new. I will research further, but that has been my experience... Are anybody's tweeters leaking oil? (must be British). DM Quote Link to comment Share on other sites More sharing options...
BEC Posted February 3, 2004 Share Posted February 3, 2004 Link http://www.amiaintl.com/speakers/ferro/ Bob Quote Link to comment Share on other sites More sharing options...
MasterT Posted February 4, 2004 Author Share Posted February 4, 2004 Thanks for all the info. I learn a lot here. Don't try to download the attachment. I screwed it up. It's way to large. Sorry. Thanks for the link Bob! Quote Link to comment Share on other sites More sharing options...
Dome Posted February 4, 2004 Share Posted February 4, 2004 Here is a much smaller (~250k) version of those instructions. 1 Quote Link to comment Share on other sites More sharing options...
MasterT Posted February 5, 2004 Author Share Posted February 5, 2004 Thanks Dome! Quote Link to comment Share on other sites More sharing options...
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