Download a sound level meter app like db on your smartphone, and stream some whitenoise (available on Spotify, elsewhere).
Then turn the sub level up and play with the crossover control. adjust level up and down until flattest in the bass region. That will give you a reasonable estimate of where your exact level and crossover settings should be. Adjust phase if available for best impact from percussion, etc. then fine tune level and xover settings from there as needed.
You might be surprised what you find this way compared to doing it by ear alone. Probably more good sound out of your sub than expected.
I had original ls50s crossed over at ~ 60-80 hz. WIth new metas, I ended up with crossover on same sub set at lowest point ~ 40 hz and higher levels than prior. Everything sounds fuller and more alive now, and just the right amount of bass on all recordings. Room is 12X12’ square which many will say is horrible for bass, but fact is it sounds really good. BEst bass I have had ever. Sub is Klipsch sw-308, a little 8" dynamo.