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  • Ferrofluid longevity

    I am still a newcomer here and still might be bringing up a topic that has already been discussed, but here goes.

    These days we find that nearly all tweeters and most midranges (certainly the domed variety) make use of ferrofluid in the coil gap, both to keep things from overheating and to possibly control resonances. The stuff seems to work, and just about everybody is in love with it.

    However, there may be an issue involving deterioration with age. Just how long does the stuff last? And when it does get old does it merely evaporate, leaving a thin metal residue behind, sticking to the magnetic surfaces, with no negative artifacts other than reduced driver power handling and maybe a bit more spikyness to the output? Or, does it turn into a gloppy mess that really causes problems? Nobody I have querried about the issue in the past seems to know the actual answers to these questions. Certainly, as best I can tell, outfits like Ferrotec are not saying anything. One chat group I belong to did discuss it, and one correspondent has dismantled older drivers and discovered that the fluid was gone.

    This situation is actually pretty important to some of those who now own vintage speaker systems, especially if they cannot measure and compare the way the systems sounded when new to how they measure and sound now.

    Incidentally, not every outfit uses ferrofluid for driver cooling. My friend Roy Allison used it in his midrange drivers and in the tweeters of his smaller, two-way systems that had fairly low woofer/tweeter crossover points. However, in his three-way systems, which crossed from the mid to the tweeter at high enough frequencies for "spatter" issues to not be significant, he used silicone grease, which should hold up for a long, long time. Roy claimed that silicone grease was a better damper and heat sink-implementor than ferrofluid, provided you could keep it in the coil gap.

    Anyway, if anybody here has some idea of just how durable ferrofluid happens to be I would be interested, and I assume that some others on hand would be interested, too.

    Howard Ferstler

  • #2
    Re: Ferrofluid longevity

    I'd be curious to hear others experiences too. I cut open a 10 year old Polk tweeter recently and found the fluid still all intact.

    TJ
    Hybrid floor stander build - The Tikki Lau - D8's

    CNC baffle cutting services

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    • #3
      Re: Ferrofluid longevity

      Originally posted by takitaj View Post
      I'd be curious to hear others experiences too. I cut open a 10 year old Polk tweeter recently and found the fluid still all intact.

      TJ
      It is hard to say if it was "all intact" as you say, or not. It may have at least partially evaporated, cutting into its effectiveness as a heat sink transmitter or becoming thicker and therefore capable of causing problems. (Supposedly, brand-new ferrofluid comes in different viscosities, depending upon the required use, and so if it gets thicker with age we will have obvious problems meeting spec for that particular driver.) One midrange cut open by an enthusiast on another chat group I inhabit found that the fluid had entirely evaporated. This driver was maybe 20 years old, however, but otherwise in supposed perfect shape. The sonic impact of this loss remains to be seen, since he had no "new" midrange drivers to compare. Indeed, the actual sonic impact of ferrofluid on speaker performance (here, I am referring to meeting specs and not heat management) seems to be somewhat of a mystery. How many manufacturers offer up response curve and distortion information on various drivers with and without ferrofluid? None that I know of.

      I believe this issue tends to be ignored by both some enthusiasts and some manufacturers, not to mention producers of ferrofluid like Ferrotec, because it may actually be an insurmountable problem that is only solvable by completely replacing older drivers, a not always low-cost process. Just how old can original drivers become before it is time to swap them out? And just how does tweeter and midrange sound deteriorate as drivers age? If a 20-year-old driver is fluid free, and a 10-year-old version is beginning to have problems, will a 5-year-old version still be able to meet factory specs? And what about listening levels? Can a system that is played at high, but still not outrageous levels (say, heavy metal) hold up as well as one that only occasionally played loud, and spends most of its time dealing with string-quarted music?

      One almost wishes for speakers like what they had in the old days (AR-3, AR-3a, AR-LST, original Advent, KLH-6, etc.) where driver deterioration due to ferrofluid issues did not exist, because such fluids were not used. Of course, the price paid with those early systems was reduced power-handling ability. Admittedly, the LST was less prone to power overload, because it used four tweeters and four midranges, and the classic AR-3a tweeter used in both that now-classic system and the LST deteriorated because the damping-foam filling behind the dome crumbled to dust. No ferrofluid issue there.

      There certainly are plenty of classic-speaker enthusiasts in this group, and most probably will be wondering about the status of the drivers they use as the years roll on.

      Howard Ferstler

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      • #4
        Re: Ferrofluid longevity

        That is true, I had no way of knowing what was there originally. I'll re-state...There appeared to be quite a bit of fluid still intact and it didn't seem to be overly thick, however there was no way to tell what condition it was truly in. The stuff is nasty though, it gets everywhere!

        TJ

        Originally posted by Howard Ferstler View Post
        It is hard to say if it was "all intact" as you say, or not. It may have at least partially evaporated, cutting into its effectiveness as a heat sink transmitter or becoming thicker and therefore capable of causing problems.
        Hybrid floor stander build - The Tikki Lau - D8's

        CNC baffle cutting services

        Comment


        • #5
          Re: Ferrofluid longevity

          Originally posted by Howard Ferstler View Post
          Indeed, the actual sonic impact of ferrofluid on speaker performance (here, I am referring to meeting specs and not heat management) seems to be somewhat of a mystery. How many manufacturers offer up response curve and distortion information on various drivers with and without ferrofluid? None that I know of.
          Seems to me that what you really want is not that, but comparative measurements of the same driver taken x years apart.
          --
          "Based on my library and laboratory research, I have concluded, as have others, that the best measures of speaker quality are frequency response and dispersion pattern. I have not found any credible research showing that most of the differences we hear among loudspeakers cannot be explained by examining these two variables." -Alvin Foster, 22 BAS Speaker 2 (May, 1999)

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          • #6
            Re: Ferrofluid longevity

            After some years other variables will be at play as well - suspension, surround, etc.

            Comment


            • #7
              Re: Ferrofluid longevity

              To your first questions about what happens when ferrofluid "disappears"....

              1. There is a definite and real change in the specs of the tweeter, as it is easy to observe the effects that differing amounts of ferrofluid have on a drivers impedance curve.

              2. I think the disappearance is far from a benign process. The results MAY be harmless in some instances, but in others you may end up with a tweeter that is "gunked up" with sticky, clumpy particles in the voice coil gap.


              I would put forth the proposition that the initial quality of the ferrofluid may be more important to the analysis rather than making generalizations about ferrofluid as a whole. I have seen old (15-20 year) tweeters that still have nice looking ferrofluid. I have seen old tweeters with "disappeared" ferrofluid. I have also seen relatively young tweeters that are having issues with ferrofluid clumping and drying out and leaving gunk on the voice coil and in the gap.

              I suspect that some low-cost "ferrofluid" suppliers are using poor quality carrier fluids that are not stable over time and temperature. For example if they cheap out and use a fluid that has some evaporative tendencies or that can't take the heat of the voice coil, then they may end up with a gunky tweeter after just a few years.

              I agree that this is a topic that is often ignored, but I honestly don't think there is much science out there on it. I think you're suppositions have enough merit that if I were personally building a speaker that I wanted to operate for a 10+ years, then I might choose to use drivers without ferrofluid.

              Oldhat

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              • #8
                Re: Ferrofluid longevity

                Energy 22 speakers have a history of the tweeters going bad in time.......primarily due to ferro fluid failure?

                This site offers a link to the sole repair shop in Canada. The proprietor will certainly be able to tell you the cause of the failures.

                http://www.vinylengine.com/turntable...ic.php?t=22169

                Marv

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                • #9
                  Re: Ferrofluid longevity

                  Here is my 12 cents (6x2).

                  In general, in speakers, I think ferrofluid has remarkably good longevity. But I got burned buying some tweeters from a surplus dealer, who bought them from M&K clearance sale (maybe going out-of-business sale?). I don't know if it was a bad batch or reworked with non-standard ferrofluid. But they were all gummed up. BTW "educational ferrofluid" for lab demos has a bad reputation for longevity.

                  The big player in speaker ferrofluid is Ferrotec. For a long time, it seemed unavailable to DIY. But now PE has it:

                  http://www.parts-express.com/wizards...rrotec&x=0&y=0 :applause:

                  Although my favorite tweeters don't use ferrofluid, YMMV.

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                  • #10
                    Re: Ferrofluid longevity

                    strange the energy 22's were mentioned. i had to replace both tweeters in the con. ref. that i have because of the fluid getting very thick. other than that, and for the time they were a good 2 way.
                    craigk

                    " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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                    • #11
                      Re: Ferrofluid longevity

                      Is it possible to dissolve and remove the dried ferrofluid from the voice coils and replace it with fresh?
                      "We are just statistics, born to consume resources."
                      ~Horace~, 65-8 BC

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                      • #12
                        Re: Ferrofluid longevity

                        Originally posted by Tin_Ears View Post
                        Is it possible to dissolve and remove the dried ferrofluid from the voice coils and replace it with fresh?
                        I don't know the best solvent, but you would want to go slow. The ferro in ferrofluid is iron filings; which are attracted to the magnets. You don't want to wash the oil away and leave the iron filings.


                        It's been reported that wiping the gap with a paper towel will remove liquid ferrofluid. So I would add a few drops of solvent or light oil so that the dried fluid becomes sticky and try to wipe it out. As the old ferrofluid is cleared, then add more solvent, and wipe some more.

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