This is not possible. They do not offer replacements, only rebuilds as they do not stock parts for these speakers. I guess they only do that for models that cost more than $4.9K.
The rebuild I got back from them last time did not sound like the tweeter in my other speaker. It was not nearly as FUBAR as it is now(the cap popped off of it last night).
Reading avsforum, 2 other people had the same issue in the Thiel thread there, of getting back a tweeter that they said crackled with loud female voices. I don't envy the people burdened with the task of having to rebuild small drivers.
I am thinking of getting two of these.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-555 The original model number looks like a vifa one, and I believe the crossover crosses over at 1.6 KHz, which makes the 1.5 KHz response here seem like it'll work with their 1st order crossovers. Incase it is more or less sensitive, I still have a working one that I can use to match them with, I'll modify the crossover until I get something as close out of the new one as I did out of the old one. It's the same impedance and size, the best thing I can do is put them in both speakers and see how they do. It beats getting a second crackling tweeter.
