Proac Ribbon Tweeters Damaged

Another possibility, in addition to those that have been mentioned (especially the possibility of an ultrasonic oscillation), is that a fault in the amp is causing a large but very brief transient at turnoff. (I assume, btw, that you are turning the components on and off in the proper sequence -- amp on last and off first).

I once had a high powered solid state amp, in that case a Threshold S-300, which developed a problem that caused it to put out what seemed like nearly a full power transient for a fraction of a second, about 20 or 30 seconds or so after it was turned off. In that case the transient was clearly audible, and produced visible movement of the woofers, but if such a transient is brief enough it might not be audible and might have sufficient high frequency content (corresponding to the rapid change in amplitude) to damage tweeters.

Also, what preamp and what phono stage are you using?

Regards,
-- Al

You may want to check for any DC offset at the amp speaker outputs.
Wondering, are the ribbon tweeters fuse protected? 
My MG 3.5’s have the ribbons fused. Additionally as others have mentioned, the ribbons are  fragile  and can be damaged by excessive air bursts from external sources. Could it be that someone has vacuumed cleaned the speakers? 

Again, thanks to all for your comments thus far.

I am using a Parasound Halo JC2 preamp and Musical Surroundings Phonomena phono amp.However, if I recall correctly, I was not using my turntable when I noticed the problem. Just spinning CD's.

I am unaware of any speaker fuse(s) in the Proacs.

My woofer/midrange drivers appear to be fine.

Unfortunately, I have no other speakers on hand to connect to my amp in question. I did power all down and then re-try, but my tweeters were still not functional. I can't be sure as they are covered by a wire mesh, but the foil ribbons may actually be a bit discolored in spots.

My takeaways thus far:

1. No one appears to believe the speakers themselves could be at fault.
2. "Testing" my amp would be prudent, although I have no idea how to do this (I'm by no means an electronics expert LOL). Who would be able to perform a check on the unit? The dealer I purchased the amp from is no longer in business.
 3.The speaker crossover problem mentioned - could this itself have caused the tweeters to fail or would that problem, if it does exist, have been ultimately related to the amp as well?

Forgot to mention - no vacuuming of the tweeters. I am very careful with my equipment - that's why this is so frustrating.

gnoworyta, no matter how this sounds I am just trying to be helpful. I realize you are trying to find the cause of your problem, not repair of the tweeter. I was just looking online and it seems the most common problem with ribbon tweeters is that the tweeter material, which appears made of an aluminum foil type material, rips. From what I read, if your problem is a ripped ribbon, it appears to be an easy fix for a professional, assuming it is not an exotic material.  Is it possible to visually inspect if it is ripped?  Also, if you can remove it from the speaker maybe you can isolate if it works ruling out a crossover issue.  I hope some of the guru's here can help out on how to test a ribbon speaker detached from the speaker cabinet.

Here is a YT of a RAAL being repaired. https://www.youtube.com/watch?v=bvylZF9eJOA

It may be your dealer knows that something else is burned out within your tweeter making it totally unrepairable. Like maybe a ripped ribbon tweeter still makes some noise, or whatever, and your doesn’t. But if your saying its $800 bucks for a new pair I would definitely investigate further. Millersound is first rate, give them a call. When my woofers needed repair he basically said he can repair most anything on the woofer regardless of problem.