Agreed. The trade-off in using this type of tweeter has never been a good one. We've yet to see one that can check as many boxes as a good dome tweeter.
(Especially when crossing to a larger six inch driver, like in this application.)
People have been objectively testing these fragile tweeters for many years.
John Krutke did a dive on these twenty years ago.
The results are as expected.
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There's nothing wrong with the type of the tweeter. Ribbons are tools like any other drivers. As an example, narrow vertical off axis response can be beneficial in the rooms with hard floors and reflective ceilings while wider horizontal off axis can compensate for vertical and build different presentation. In this application I would use more robust ribbon like larger Raal or Viawave that can in fact cross lower to the woofer and produce much less distortions, handle higher spl, better polar etc. And you can load a ribbon in a wave guide or use one that already has a waveguide.
Decisions by commercial manufacturers are not solely made on the performance tho. It's always budget, form VS function and potential customer base. How many 2-way designs in a shiny black box have you seen over last 30 years? Why so many are produced?
In a way, this situation with the speaker shows how Klippel is also a tool and the results are really dependent on the objective and the user.
In a DIY world, people would caution from using such a combination of drivers because the results would be simply mediocre. Klippel just shines a much better light on it.
It has to be mentioned that a much better speaker could be build by simply adding a small midrange driver and making the cabinet slightly taller. You could let the ribbon work within it's limitations, decrease linear and non-linear distortions, intermods and frankly have something special.
As far as Denny's upgrade goes, IMO it's immoral to piggy bag on other current commercial company design. He is not doing it to be nice, it is all done for moooonnney. So, he is stepping on other man's toes. Why? Money of course.
And that's aside from the fact that everything he did in this upgrade is half-a.sed. Measurements are smoothed out garbage, tweeter is pushed too low. He has tools, he just chose not want to spend enough time on the project.
I would've liked to see Amir dissect the crossover before and after and see the tweeter response in more detail but that would probably infringe on Sierra design rights.