Hi Marc,
It’s great to see other people experiment with this dipole configuration and being able to reproduce a square wave.
By using one driver you will not lose any efficiently, just power handling. The disadvantage with one driver is the depth of the box – it has to be deep enough to accommodate the HF horn and the LF driver.
The advantage using the BMS compression driver with the HF950 horn was being able to crossover low enough to stop the vertical pattern collapsing around 650 Hz.
Here is a SIM of the vertical directivity. Although there are a few compromises with what I have done with the SIM, it does show what happens if you crossover higher (it matches what you have measured in your DIYaudio post) with a 20 dB dip off axis (vertical) around 650 Hz.
FWIW I have been thinking about doing a simpler version of the double12 – it will be cheaper to build, use a B&C DE1090TN compression driver, smaller, lighter, better vertical pattern control … BUT … not as loud.
