By Tobias Carroll If you look at enough photos of Led Zeppelin during their heyday, you might begin to realize something: Robert Plant is likely the platonic ideal of a rock and roll singer. (That he is also, literally, the singer of “Rock and Roll” is further evidence of this.) Some of that comes from Plant’s physical presence and some comes from his substantial vocal chops, of course. But there’s also the way he handled the microphone in those days — an oddly tantalizing, visceral approach to one of the tools of his trade. Turns out much of that iconic stance happened accidentally. In a rece…