Update:
I've just taken apart 2 Energy Dual Hyperdome tweeters donated to me by a very generous member of CAM.
My observations are just that, I have no scientific facts, just opinions.
One tweeter has an open voice coil and is beyond repair. The other measures about 4 ohms. I will assume it would work but I didn’t put signal to it.
The open one when taking the vc out had wires popping out like a slinky. Obvious signs of severe overheating. The magnet gap is still almost full of ferrofluid.
The 2nd tweeter has some separation of the vc windings. About half the windings are loose but still intact. Another sign of overheating. The magnet gap is almost full of ferrofluid. It’s worth trying to rebuild.
Both have ferrofluid residue on the outside and inside of the outer dome and on the inside of the inner dome. This makes me think that some fluid was forced from the gap either by heat or over excursion of the diaphragm. Obviously finding fluid on the diaphragm some was missing from the gap contributing to the further overheating of the vc once the fluid was displaced. I believe the tweeter's demise came first from being over driven, loosing some of it's ferrofluid, getting too hot and the binding agent that holds the coils of fine wire in place around the plastic vc cylinder breaks down allowing the coils to separate. With further use the fine winding wires get forced down into the gap and due to constant grinding from the vc movement they eventually open.
So are these tweeters more fragile than some? I doubt it but I cant know that unless I know how they were used, or abused. A voice coil gets warm quite fast with use and heavy use over long periods of time can build up a large amount of heat. Of course clipping heats things up much faster and if being hit with high wattage midrange frequencies at the same time causing excessive excursions of the vc, that may be the cause of the now hot and thinner fluid being splashed up onto the domes where it begins to wick, taking more fluid and quickening the heat damage. Either the plastic vc cylinder becomes distorted from the heat and the coils break loose from their binding or the binding itself lets loose.
Once the process of the windings separating begins to happen it snowballs leading to the eventual breakage of one of the fine vc wires. The windings don’t appear to have serious signs of excess heat such as looking black or melted although there is some minor signs of high heat.
I dont believe the fluid "dries" up but rather it is displaced. So what's the answer to keeping these tweeters intact? Probably the same as most speakers. Feed it with good clean power, and don’t run them at high power for hours on end. Give them a cooling break now and then. Anyone who owns 22's and knows them well knows they are very selective of what drives them. If our ears object, the tweeters are objecting and telling us so. If the 22's dont sound amazing with what you're driving them with, feed them what they want and I believe they'll be happy and last as long as any other tweeter. I don’t believe they’re that selective and any high current well behaved amplifier should suffice. Just don’t expect them to be at their best when driven by a lightweight surround receiver for example.
If there's an oily looking film on the outside of the dome(s) you can check if it's ferrofluid by lightly rubbing a Qtip over it and if there's brownish residue, it's ferrofluid and that tweeter will not cool as well as it should and the vc windings may be on their way to separating or worse, already separated.
I'm going to try to reattach the loose coils to the cylinder although I don’t know what to use to do that with. Lacquer, Corona Dope? Any suggestions are always welcome.
It'll be cleaned up to get rid of the fluid all over the domes and windings, the gap will be filled with new fluid (when and if I get it) and put back together. Secured in place and adjusting the vc position while monitoring their output from a mic connected to a scope, fed by a signal generator at about 850 - 1000 hz.
It’s been suggested to coat the inside of the domes but that to me goes against the original design. The domes are not airtight which means they can breath thus dissipate some of the heat. By coating them they cannot breath and may accelerate their demise. I will be leaving the domes uncoated, true to their original state.
Sounds simple.....not. But I do want to try.
And of course any of this is theory on my part.
If anyone knows of where one can get new or intact diaphragms/voice coils for these tweeters I'd be interested in hearing about that.