Dried up Ferrofluid?

So, how does one know if their ferro fluid is no longer viable?

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?