Another thing to check is that the "straps" that electrically pair the binding posts in the back are connected and snug. Sometimes they come loose in shipping.

Of course, this makes me wonder if the M80s still have two separate sets of binding posts? It seems familiar that I read that the newer speakers ship with one set of posts now....

::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::