So I finally put up the M22's out on my porch (with a drip loop!) - and they're awesome! The openness seems to be a positive, which really surprised me; or maybe it's just different, and that sounds interesting to me. Either way I'm extremely happy.
I was worried about power and stereo separation after reading Andrew Welker's blog post,
https://www.axiomaudio.com/blog/outdoor-sound-system, but that's not even close to a problem (using an older Yamaha HTR-6230). I pointed them at the house (so one wall to bounce off of) because they're more for me to sit and look at the trees and listen to good music than for being in the pool. But sound at the pool is great (pool's another 15-60 feet away. I'd say the sound from the M22s facing backward is better than that of my N2 sitting near the pool.
One last item, which was really the point of the post - I installed the M22 upside down, so the tweeter would be closer to the correct location (since I hung them near the porch roof-line). Does anyone think there's any structural problem with hanging upside down?
