Dried up Ferrofluid?

What causes ferrofluid to dry up?  Heat, usage, age?  Is there a usual shelf life, as in, do most 15-20 year old tweeters that originally used ferrofluid, need new ferrofluid?

How is it checked, where is it bought, is the replacement generally the same from tweeter to tweeter?

Thanks ahead of time for any info regarding this!  I figure that there are quite a few good speakers out there that are getting up there in age so this may be something I’ll want to learn to do!
Not exactly an end of the world skill I was worried about not having! LOL

What makes you think of this right now? Are you going to be buying some used speakers?
Im a prep’er, lol.  You may have cases of water, I’ll have cases of ferro fluid.

Its just that a bunch of speakers I look at buying are getting up there in age.  Some of them are 20 years old...
I went through the exercise about a year ago with some old soft dome Scanspeak tweeters.  I did watch a few you tube videos explaining how to disassemble the tweeter, clean out the old fluid and install new fluid.

It turns out my Scanspeak classic tweeters were much easier to disassemble than the tweeters on you tube.  Once disassembled, you use blotter paper and I think alcohol to soak up and clean any remaining old fluid in the tweeter "well" (my word) and then buy and install new fluid.

I spoke with Madisound and they thought it would be ok to not replace the fluid at all, and I believe (might not remember correctly) they said many new tweeters don't use the fluid at all. I ran them a little without fluid but ultimately installed the fluid and like the sound better.
If you are interested in getting your hands dirty, consider a new kit instead. Built the whole thing from scratch. :)
Erik, I asked you a while ago, but you never answered.  I read your paper on a pair of speakers you built, but asked how many pairs you have actually assembled?  Is it the one pair, really just curious, I am not handy and wouldn't dare try.

I answered you. Go back and look.

But truth is I have never built cabinets. The cabinet for the SNR-1 was custom built by Lee Taylor of Taylor Acoustics.

The other 2 models used kit boxes. In all cases the part selection and schematics were my own.
Sorry erik, I must have missed your answer.  I wouldn't have expected you to build the cabinets, a whole other deal requiring the woodworking tools.  Just buying a kit with all the parts preselected by someone else seems adventurous to me.  As I mentioned, I am not handy in this way.

I have read several articles by people who have built speakers (not the cabinets) and the tuning via crossover part selection seems not for the faint of heart.
Dried up Ferrofluid?

I posted this up 6 months ago, why some were complaining about harsh Thiel tweeters that get non-linear distortions with sticky old Ferro Fluid that’s gone like tar, it has to be cleaned out, just don't add new fluid to a gummed up voice coil gap, you'll be wasting time and effort  

A lot cheaper than buying new diaphragms. $10 for new fluid vs up to $200 each for new diaphragms, and they could be clones/fakes.
Still have to clean out the old fluid doing either.

Tweeter Ferro Fluid and how to change it.



Cheers George


If you can drill a pilot hole straight, and add glue you can build a kit.

Here's one of the simplest kits out there, get your hands dirty and then after you may not think it was all that difficult. :-)


Fun to do with your kids.
Hey there b-limo,
I went thru this with my Kef Reference 104/2's recently, so I thought I'd add my two cents' worth. First, kudos to you brave diy'ers, I hope you all succeed. I took my Kefs to a trusted repair guy and he told me the ferrofluid had dried up - then led me to Midwest Speaker Repair for a pair of new tweeters, which supposedly have specs close to the original, and some say sound better. They were $60 each, I had them installed and the sound is really good. (Had to also rebuild the woofers, common with this mid-80s model).
Contact Bill Legal at Miller Sound in PA if you want someone to do them for you,

Happy Listening.
Bill is excellent and highly recommended. Just rebuilt one of the acoustic couplers from one of my Vandy 2CE Sig’s. Very very reasonable and a great guy.
As the ferrofluid dries up, the speaker’s high end becomes dull and loses some sparkle. It may not be evident unless one compares it to a speaker with fresh ferrofluid. Typically ferrofluid lasts about 15 to 20 years with normal use. KEF recommends replacing ferrofluid after 15 years. If you go too long with dried up ferrofluid, the tweeter may be permanently damaged. I did the T33 tweeters in my KEF 104/2 speakers a few years ago and it made a significant difference. It was a fairly simple and straightforward process and cost about $15.
So, how does one know if their ferro fluid is no longer viable?
The ferro fluid starts getting thicker after 10-15 years, especially in a hot environments or if driven hard, it becomes non linear (distorts) and yes as ljgerens said  looses it's efficiency "sparkle".

Cheers George
Hi b_limo!
Ferrofluid typically has a very long life span, but some of the older models of speakers are experiencing drying of the ferrofluid because the older formulations do not have the same long term properties of the new generations.  That being said, excess heat, long duty cycles at high voltage and dust and grime from decades of use will cause ferrofluid to gel and solidify.
There is hope!  The fluid can be replaced and it is not really that difficult to do.  Please contact me at vrene@ferrotec.com and I can walk you through the process.
Dumb question, do all tweeters have ferrofluid?
No, you'll have to ask the manufacture if your does, it served two purposes, a way of getting heat away from the voice coil via the ferro fluid to the magnet which acts as a heatsink, also it served to damp"oil can" resonance at hf especially in metal dome tweeters.

Cheers George
Thanks George, I believe Thiel does in fact have ferrofluid per Rob at Coherent Sound .

Thanks George, I believe Thiel does in fact have ferrofluid per Rob at Coherent Sound .

This correlates now with what many older Thiel owners are now finding and starting threads saying their speakers are harsh and/or have no sparkle. Their tweeter have lost a couple of dB’s and hf extension, and are now working very non linearly.

And this happens over time so you don’t even realize the tweeter performance is slowly degrading, and you enjoy your music less and less blaming your own age, your amps, your source ect ect

When all you need to do for $10 and a little labor-love is to clean out and change that ferro fluid in the tweeter.


Cheers George
Thank you!
I have a pair of Kef Reference 3-2 speakers...They have ferrofluid cooled speakers.  I will be replacing in the near future.  Is all ferrofluid the same or is there different types?
Is all ferrofluid the same or is there different types?

I would use this one from Parts Express (audio parts specialist) you'll know it'll be good quality.

Cheers George
Thank you George!  
My tweeters are Kef pn SP1353.
They do contain ferrofluid.
I am going to attempt a R & R.  Seems straight forward.
Great thread!  I never knew you could 'change the oil' in your tweeters!
I also never knew that it could 'go bad'.
Once again the Audiogon helps out a fellow member!
Guess I’m officially a cheapskate. 

I made my own ferrofluid. I have a bag of ferrite cores I bought for making coils. I used a smooth knife sharpening stone and ground the ferrite core into a fine powder. I used 30 wt Mobile 1 synthetic oil. I mixed the powder into 1 ounce of the oil until it was dark like strong coffee. Then I let it sit and settle overnight. The big particles settled to the bottom. Then I poured the clean ferrofluid into a clean glass bottle with a tight cap. I used an inkjet refill kit syringe to inject the fluid into my dome tweets and midranges.

BTW, that was 17 years ago. Mobile 1 is more stable than regular ferrofluid oil; it has heat stabilizers, antioxidants, detergent, in its additive package. Probably time to check my drivers and do a refill. Also, I used contact cleaner to FLUSH OUT the old ferrofluid. Paper tape will not remove all the old gunk.
quincy196 posts03-14-2020 12:44pmThank you George!
My tweeters are Kef pn SP1353.
They do contain ferrofluid.
I am going to attempt a R & R. Seems straight forward.

And if not old enough yet or sounding ok, just like doing preventative maintenance.

I used contact cleaner to FLUSH OUT the old ferrofluid. Paper tape will not remove all the old gunk.
I think even petrol would be fine for the magnet gap, but anything on the voice coil something milder as the coil insulation lacquer needs to be looked after. 

Cheers George

If I have a pair of brand-new-in-the-box unused tweeters as spares for a speaker sold 20 years ago, is it likely that they would still be "as new" or might they also need the ferrofluid replaced due to age?

If they have ferrofluid they won’t sound as good as new for sure. What tweeters?