There are a variety of Audio Spectrum Analyzers available now on the Net and (looks like) as phone apps. Seems they (and whatever mic) should be accurate enough, at your crossover freq, to be of service.
I've never used either, as I've always owned enough hardware, so: I can't swear to anything.
Just pay close attention (set on Slow) to the band levels on either side of your crossover point.
That's if you don't trust your ears. Female voices/vocals (with which you are intimately familiar) should sound way off, given just a slight disparity in levels.