I think the following video shows pretty well what happens when you blow in such a way in a Kaval as to obtain (what they call) the Kaba register sound versus normal 2nd register sound.
You can see how the lowest harmonic, from 1st register, ~313 Hz (D#4 311) comes up depending on how I blow.
The permanent note here is the ~627 Hz (D#5 622)in 2nd register.
Interesting to note how the rest of the harmonics change when the D#4 comes up.
Kaba is very hard for me, I can’t really control it well, and I noticed that when I can’t produce it, it’s because the two notes aren’t exactly at double frequency. This must have something to do with the different air jet in the 2 registers and also with the end corrections being a function of frequency.
I am going to explore how could I improve my instrument to make Kaba more easier to play but until then let me have your comments, curious if there are other people interested in this.
What app are you using to do the frequency analysis/display on the phone in this video? That looks good. I’d like to get something like that to study the frequency components of various notes on some of my own flutes.
As for how to make it easier to play the kaba register on the kaval, I can’t offer much help. I also find it really difficult to play in that register, and the only thing that seems to help me is to focus on blowing really softly. More like gently breathing out rather than blowing.