Why does Danny never measure below 200Hz? Is it due to laziness?
In any case. You have good points, which I agree with.
I thought the solution of powering up the bass boxes separately actively was good, but as you say, you can just as well go all the way to make the entire speaker active.
BUT actually as I write this I saw that part two from Danny was posted so after watching; it is, according to Danny, baffle edge diffraction effects that make the tweeter's FR so choppy. He tests it and it seems to be correct. With a lot of felt placed on the inside of the speaker cover, the FR got better:
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Of course some talk from Danny's side about the tube connectors and the new crossover he fixed, but Danny doesn't actually say much about it nor what it would cost.
Starting at 11:00, Danny starts discussing baffle edge diffraction effects: