Eiron wrote:

You're supposed to be able to tell by placing the speakers face to
face, swapping the connections to one, and playing a mono source.
So one driver pushes while the other pulls, and there is little
output. If one midrange is inverted, there will be lots of output.
I never tried it myself. It might not work for HF where the wavelength
is short.


Yes, that is exactly how I determined that the bass drivers were correctly
phased. But I agree that this might not work well with the midrange and hf
drivers.