Unfortunately replacing ferrofluid in tweeters that used them is something you must do ever decade or two.
Thank goodness we have more or less moved away from that. You might also look at DIYaudio for help.
@timlub @jetter @erik_squires Thank u all who posted. And thank u jetter for mentioning Bill from Miller sound. I will definitely be calling him about this. I have a couple questions. By cleaning out the old ferro fluid and putting in new what will I really hear if anything. And what if I do not do this. Would it cause any harm to the tweeters since my speakers were built in the 90s ? Also I will be upgrading all my 8 crossovers (4) in ea speaker very soon also. Like it did mention in post I already think they sound phenomenal. But since they are from the 90s and I do plan on not selling I think it’s a good idea for an upgrade on all I can do for them.
Ok. So I just got off the phone with Bill from Miller sound. Very nice guy BTW. He said that he definitely does that it is very responsible $105 ea tweeter. But he said to be extremely careful shipping them if I can’t make the 2.5 hr drive to PA from NJ where I am. But —— he said IF I still hear good and loud treble with my tweeters they are definitely still good with the ferro fluid and he advised me not to touch them. BTW last night before I even heard about this Ferro fluid thing I was up in my music room for about 5 hrs enjoying my system and I decided to take all 6 speaker covers off and listen for the rest of the time with them off. And as I was listening to the Cars - Dangerous Type , btw I love the drums thundering and exploding on that song with my speakers. So i definitely heard the great loud detailed treble on both tweeters. So I will definitely take Bills advice and until I hear anything different ( negative) with them I’ll leave them be. Bill also mentioned a place closer to me in NYC that he recommended that does great work on speakers too. It’s called Technetron. That way I could bring them in instead of taking a chance and shipping them and having them get damaged in the mail which I very much appreciated him telling me that also.
There is no set rule regarding how long ferrofluid lasts. I have read 10-15 years is typical.
Chances are your ferrofluid is still basically still ok and you will hear little or no difference after having it changed, but who knows. My speakers were also built in the 90's, and I think it is wise to change the ferrofluid to ensure no damage.
About the crossovers, I will leave it to the experts here to recommend whether or not to update them if they still sound great. The question is if crossovers with high quality parts like your (and my) speakers last longer than those with more generic parts? A quality repair guy once told me he thought they do.