ferrofluid cooled tweeters....

how long is the average life span on these? how can you tell if they are bad or dried up? thanks...

There are hundreds of types of magnetic fluid, each of which has a different life span under different conditions. Also, not all driver designers know, or have the freedom to apply, best practices. Properly selected and used, a fluid-filled tweeter can last 40 years with very little degradation. On the other hand, many people find their tweeters shot after less than 10 years. (When mag fluids were first introduced, some over-enthusiastic manufacturers erroneously used water-based formulations and/or paper formers, which lasted weeks or less.)

The easiest way to check the condition of the fluid is to run an impedance curve and look at how much bump there is around resonance. Ideally, this should be compared to both a working reference and a non-filled unit. Still, simply looking at the curve can usually tell you a fair amount.

-k
 
The fluid was also used for damping, so when it dries up the driver will obviously change.
There is some school of thought that the fluid inhibits the sound in a negative way.
Personally I always thought the ferro fluid as a compromise, the driver/ compliminting drivers and crossover should be designed with a power rating in mind that shouldn't require cooling fliud.
Probably why I prefer the Great Heil, stick a fuse on it, drive with a nice amp that doesn't clip right away and your good to go. Plus they easily outpreform any domes or cones I have heard in the last 40 years or so.
 
I think most forum users assume ferrofluid is used to prevent voice coils from over heating. It also dampens resonance. I think this became a secondary and complimentary affect to protect the tweeter at lower crossover frequencies.

Does having lubricated voice coils on the tweeter slow transient response.

It has been stated it does.

Having the lowest tweeter inductance should increase transient response compared to tweeters with higher inductance values.

What effect does having tweeters with ferrofluid have in auto sound during freezing temperatures. Do you have to let the tweeters warm up. And what would be the correct method in doing this?

I have learned never to assume anything.
 
I bought some T/E 360's and when I went to refoam the mids the ferrofluid had dried and turned so stiff the cones wouldn't move, they felt like frozen Polk drivers. I had to wash out the residue with acetone.
 
again ferrofluid isnt only used in tweeters. my epicure 3.0 not only have ferrofluid in the tweeters but the midrange have ferrofluid in them as well. the woofer did not have any as i could see.
 
I want to ask the question someone else did, who was the first to use ferrofluid in their tweeters? I was thinking maybe Genesis, but am curious as to who did it.
 
I needed to replace the voice coils in my Paradigm 9SE speakers, and when I ordered the replacements from Madisound he said make sure you check the ferrofluid. Sure enough it was bone dry after 25 years. Ordered 2 packets of ferrofluid from Parts Express for the 1 inch tweeters and filled up the tweeters when I installed the new voice coils. Tweeters sound great. The voice coils lasted about 12 years so I'll know next time they go to check the ferrofluid levels too.
 
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