Tonight, the Allman Brothers Band begins a 15-night stand at the Beacon Theatre, a New York tradition that recurs with uncanny regularity. Are all jam-band fans afflicted with obsessive-compulsive disorder, or just a vast majority? This year’s cluster of shows marks the 40th anniversary of the band’s inception and, using some fuzzy math, the 20th year of the residency. (While the Allman Brothers Band started playing the Beacon Theatre in 1989, Gregg Allman has claimed the residency commenced in 1994.) I interviewed Allman while he was gearing up for the 2005 shows. He talked from his home outside Savannah, with a poodle on his lap. Upon hearing I had never visited his home state, he promoted a visit with the slick eagerness of a travel agent. “Man, you’d love Georgia!” he said. “People are real nice and friendly and kind, the food is killer, and the women are gorgeous. What more could a man ask for?”