They look the same as the Foster ribbons installed in the old Dali 800-series. Troels did some upgrades on those and here is what he said:
'Now, this planar is marketing gimmick and the best you can do is disconnect it. Throw it out! It's a phzzzz-thing supposed to caress you eyes more than your ears.'
Dali 800 renovation
I have a pair of Dali 810's and did some measurements on the ribbons, and they were pretty close to Troels FR measurements. The worst was the distortion measurement, I think it was the worst distortion I've seen in tweeters. However, the tweeters are old and abused, but at least both measured about the same.
'Now, this planar is marketing gimmick and the best you can do is disconnect it. Throw it out! It's a phzzzz-thing supposed to caress you eyes more than your ears.'
Dali 800 renovation
I have a pair of Dali 810's and did some measurements on the ribbons, and they were pretty close to Troels FR measurements. The worst was the distortion measurement, I think it was the worst distortion I've seen in tweeters. However, the tweeters are old and abused, but at least both measured about the same.
that's perfectly fine with me, its his opinion
i do not share it with him
here is my measurements of foster planar
I do like it so much I got more and started new project
i can post distortion measurement, but you already made your mind
so i will not
viral projects, sort of
I have only made up my mind about the old and abused ones I have 
I'm not even sure it's the same tweeter, only looks similar and is made by Foster.
I measured FR of mine without the 'waveguide' in the Dali setup too (metal plate with the two tweeters mounted and a short 'waveguide' for the ribbon), and I think they were something similar to your measurements. Maybe Troels should have measured it without the waveguide and he would have had another opinion, I don't know.
Once the ribbon is out of the Dali waveguide thing, it visually looks the same as the one here.
If you have the distortion measurements, it could help others make up their mind.
I'm not even sure it's the same tweeter, only looks similar and is made by Foster.I measured FR of mine without the 'waveguide' in the Dali setup too (metal plate with the two tweeters mounted and a short 'waveguide' for the ribbon), and I think they were something similar to your measurements. Maybe Troels should have measured it without the waveguide and he would have had another opinion, I don't know.
Once the ribbon is out of the Dali waveguide thing, it visually looks the same as the one here.
If you have the distortion measurements, it could help others make up their mind.
This came up in my email and brought me back to the thread. I was horribly interrupted this winter among everything else with a skin problem which has dogged me hard but got unreasonable this last few months. If anyone likes mysteries. Diagnosed as Grover's Disease. So Back to the Fosters.
I read where Adason built a pair of towers using the fosters. I am curious if he is still using them and have a question on the placement of the foster's.
Great report. My curiosity is.. from the pictures i saw you mounted the tweets (fosters) inside the cabinets and actually beveled the opening to create a flared mouth. Did you make any changes to that and also. I read where these fosters work better when they are set back closer to the coils of the other speakers.
i was just mounting mine on the front of the baffle.
These supertweeter based on construction are meant to be mounted from the back of the baffle.
But if the baffle is thick, that can create deep cavity onfront of the tweeter, and the edges create terrible diffraction.
Thats why i created that shallow horn.
Similar planar tweeters, like beston which i used in another system, have exactly that. Shallow horn, you can call it flare.
That eliminates diffraction and beaming if planar is set too deep.
But if the baffle is thick, that can create deep cavity onfront of the tweeter, and the edges create terrible diffraction.
Thats why i created that shallow horn.
Similar planar tweeters, like beston which i used in another system, have exactly that. Shallow horn, you can call it flare.
That eliminates diffraction and beaming if planar is set too deep.
I saw Adason's Line Array (post 11). Nice!
fyi here's another line array from 2015 Parts Express Forum
Low cost 3" line array
https://techtalk.parts-express.com/forum/speaker-project-gallery/67808-low-cost-3-line-array
GRS 3FR Woofer
https://www.parts-express.com/GRS-3FR-4-Full-Range-3-Speaker-4-Ohm-292-436
crossovers for the tweeters, Dayton ND20FA-6 and Vifa BC25SC06
https://techtalk.parts-express.com/forum/speaker-project-gallery/67808-low-cost-3-line-array/page8
fyi here's another line array from 2015 Parts Express Forum
Low cost 3" line array
https://techtalk.parts-express.com/forum/speaker-project-gallery/67808-low-cost-3-line-array
GRS 3FR Woofer
https://www.parts-express.com/GRS-3FR-4-Full-Range-3-Speaker-4-Ohm-292-436
crossovers for the tweeters, Dayton ND20FA-6 and Vifa BC25SC06
https://techtalk.parts-express.com/forum/speaker-project-gallery/67808-low-cost-3-line-array/page8
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Have you made the less baffling speakers yet? Curious because I was wanting to build something similar. Well, after I finish some honey doo’s.
Room modes are typically in bass and midbass frequencies.
Those are hard to deal with, bass traps are the only way to go, but they are huge.
For better stereo image I find less baffle or no baffle best. This gets more critical for mid and tweeter. Soundstage is someshing I am very keen to have best as possible.
My system right now is 4way open baffle. Works for me. Keeping speakers away from the walls is a must. Still things to experiment with, but I am happy with the sound for now.
Cheers!
Those are hard to deal with, bass traps are the only way to go, but they are huge.
For better stereo image I find less baffle or no baffle best. This gets more critical for mid and tweeter. Soundstage is someshing I am very keen to have best as possible.
My system right now is 4way open baffle. Works for me. Keeping speakers away from the walls is a must. Still things to experiment with, but I am happy with the sound for now.
Cheers!