You don’t see "ferrofluid cooled tweeter" advertised much anymore, except in cheaper speakers. Being a big Tannoy fan - this topic is intresting to explore in the 2000s era Tannoy lineup, where they used ferrofluid tweeters in the "tulip" DC drivers (lower lines and pro lines) and no-fluid compression chamber / horn tweeters ("pepperpot" DC - dry coils) in the upper half of their top Prestige line.
I have a few of both kinds, and though ferrofluid tweeters are defnitely out of fashion now, those Tannoy ferrofluid tweeters still do GREAT. Haven’t had a problem with one yet, and their treble response actually tends to be a bit smoother and more extended than the pepperpot one. However, the latter DC lends its magic in the midrange, and with its massive efficiency.
At some point I'll have to check on them and clean / replace the fluid, but frankly that seems pretty easy. The magnetic gap will hold it in place.
