For this post, I thought I'd discuss a little DIY procedure you might want to think about if you've had your speakers for awhile - like say a decade or more - and know that the tweeter uses "ferrofluid". Not uncommon for tweeters since the 1970's.
Ferrofluid is a substance with ferromagnetic nanoparticles typically suspended inside an organic solvent. These particles are small enough that they're suspended by Brownian motion so over time, the particles do not settle. In tweeters, the ferrofluid surrounds the voice coil which is embedded in the gap between permanent magnets (do electromagnetic speakers use ferrofluid?).
There are benefits to doing this including improving heat transfer away from the wire coil to handle higher power, dampen vibrations (unwanted resonances), and I've heard it said that the ferrofluid can also help suspend the coil within the gap in a way that's better centered (lower distortion).
Now, depending on the type and quality of the ferrofluid, there is the potential that over time this stuff degrades. Some have said that it can dry out, or the consistency becoming more viscous over the years. Here's an interesting video showing degradation of very poor-quality ferrofluid.