Crossover issue.

Well my suggestion was just a start.  DATS is a great tool for diagnosing all sorts of problems.  By looking at the bad impedance curve you can tell if one or another section looks like it is missing, and the LCR measurements can discover bad drivers or components.

Yeah @erik_squires and a less elegant (kindergarten approach) is just to swap left parts between and right…

If one had a scope they could drive both LHS and RHS XOs and plot them against each other.
But you’ve also reminding me that I need to find my DATS.

A microphone and test signal would only tell you if they performed differently. 

DATS will give you a very good idea why.

@erik_squires I did not mean a microphone, I mean to just test the XOs with just a signal and probably some power resistors where the speakers go.

Your idea of the DATS does the speakers, so it is conceptually the same type of thing, just I am aiming it the other way to look solely at the XOs.

Either way we are both splitting the system down the center to figure whether (in your case) the back half is working (speakers), and in my case, whether the XOs are NOT working.

Our approaches are matched (like a Darlington pair).

DATS does it all, end to end, and lets you measure the individual components as well, including the drivers.  Everything else to me seems like trial and error.