has anyone used this point source BMS 15CN890

Hello,
Could you immagine what's happen with that kind of design ?
Coax.png
 
What P10 said plus you’re trying to wrestle down one of the most tricky pro drivers on the market with the most basic consumer DSP on the market.
Really good/valid two channel raw data 0-90 degrees and careful modeling in Vcad or a proper pro DSP with a user interface that displays the measurements and plenty of power is absolutely essential.
I learned my lesson hard with these monsters 👹.
 
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The reason you'd want to measure polar responses is to account for the ways which this is not a point source. (A point source doesn't have directivity per se, or lobing, diffractions or reflections off the back of the waveguide.)
 
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- The reason for time alignement is that the acoustic centers of the drivers will differ in the Z-axis on a triax/coax drive, they will also differ with frequency.
You can try this application note for minidsp-rew-umik: https://www.minidsp.com/applications/dsp-basics/time-alignment
but measure at 1m to measure the triax. Plse note that you align the microphone with the center of the triax driver in this case.

- The 10 PEQ per channel capacity of Mini DSP just might be enough to flatten the wild alpine landscape of this driver but you will be driving blindfolded when editing filters without the help of a proper simulation program like VCad or graphic interface displaying the manipulation of the raw driver measurements. I also don’t know if the Mini DSP ‘PEAK’ mode settings follow any Bell standards for setting Q so simulations could give you false results.

- Setting the crossover frequencies for a bucking bronco with this kind of raw response is NOT a matter of placing a named filter symmetrically across two drivers, far from it. Even with perfect anechoic measurements and a great simulator you’re in for hours and hours of optimization. Rewards could be huge though😉