A small room, house party, nursing home is no problem when it comes to judging volume. But the bigger halls are a different story. I use a floor monitor, but realize that I am not necessarily hearing the same thing as the audience. I watch them to see if they are flinching from too much volume. I also listen to anyone who comes up to me with a comment, such as, "We can't hear you", "It's too tinny (or bassy)", "you are killing my ears"....etc.

Sometimes corrections are as simple as tweaking the EQ or turning a speaker a little. A couple of years ago, after tiring of complaints from people sitting in the path of the speakers, I started repositioning them at an upward angle of about 30 degrees. What a difference. The complaints almost disapeared. The sound gets a little more difused, but no one gets hurt.