SOAR graphs, hyperbolas, j-operators

Does anyone know where I could find a tutorial or some other info about the SOAR demands and loadlines of a loudspeaker on the output devices? e.g. where an 8 ohm loudspeaker is expressed as (5.5 ohms + 5.5 ohms j) or similar, and drawn as a sort of arching curve, in contrast to a resistive load which is a straight line. I spent some time looking on the web but not found what I want.