I agree totally with Buckeyefan, even if he is probably (based on his name) an OSU fan. (I went to U. of Illinois, which isn't really on OSU's radar screen from a football perspective, but is definitely on it from the basketball perspective. Ohio State of course was the spoiler to Illinois' undefeated regular season this past year.)
Early 70's Large Advent speakers used to be known for blowing tweeters if played real loud with a lot of sustained high-frequency content. In fact, the owner's manual for these used to advise using a slow-blow fuse in series with each speaker, to protect the tweeter from thermal damage. Then, with the New Large Advent speaker (mid-70's), they went to a ferrofluid-cooled ring tweeter which was much more robust. It's basically just a way to get more heat away from the voice coil, when the overall mass of the driver is pretty small. Woofers are large enough so that they usually do a better job of dissipating heat. But, even here, if you are putting hundreds of watts (or even 1000+) into a sub, ferrofluid cooling will help to get the heat away from the voice coil. The reason for it being "ferrofluid", rather than just plain water or some other liquid, is so that the fluid doesn't disrupt the magnetic field around the voice coil and the "moving parts" of the speaker. The iron content of the ferrofluid essentially "passes" the magnetic field, for lack of a more technically-accurate explanation.
