@A4eaudio
I haven't worked with the SB26STAC, mainly because I wanted to avoid 100mm faceplates. But that isn't a concern (or indeed an advantage) for a 3 way, it's arguably better suited that the SB29SDAC.
The 29SDAC can certainly cross lower, and but top octave is definitely in breakup, which is why the response is the way it is:
Here's the 26STAC, taken from SB's datasheet:
29SDAC:
Reference:
www.sbacoustics.com
When I was looking at the datasheet some years ago, I didn't pay much attention to that rise in the top octave for the 29SDAC. If you peek at the pixels, there certainly is a peak just on axis somewhere between 10 and 15Khz. Then at 60 degrees off axis, there's a dip at 15KHz.
After I built this speaker, somewhat as a homeage to the late Jeff Bagby, I measured mine, and that characteristic certainly is there.
These peak/dip combinations suggest diaphragm break up, IME.
Now whether or not it's objectionable, or favorable to the listener, well I couldn't say subjectively. But objectively I'd prefer it not be there.
@hifijim may be able to account for the on-axis response in his crossover, of course, but that won't change the directivity/dispersion characteristic.
Here was the quasi-spinorama of my build of Jeff Bagby's Revolution mini, which uses the MW13P-4, with the SB29SDAC tweeter:
Reference:
https://www.diyaudio.com/community/threads/2020-jeff-bagby-revolution-mini-sd.359083/
Context is important, as always. IIRC, the original design by Jeff was commissioned by SBA, and originally used another 104mm tweeter (SBA brand new at the time SB29
BAC tweeter). I think Jeff wanted a low cost tweeter option builder who may be turned away by the high cost of the beryllium tweeter. And so he found an alternative tweeter the same impedance response and tweeter faceplate size as the original design, for an easy drop in replacement. AND he needed it to crossover at relatively low 1.8KHz acoustic LR4. The B29SDAC fit the bill.
If
@hifijim wanted to experiment with different 100mm tweeters, or offer builders other options eg. SB26
ADC (aluminium), then I can see why the 100mm SB26STAC may be a better option than the 104mm SB29DAC.