Dave, the graph that Rick posted is actually from the NRC(National Research Council of Canada), made independently as part of a SoundStage review of the M80
here . There's no set standard for the way that a manufacturer rates the impedance of its speakers, but typically an average, rather than minimum, number is used. The M80 curve would appear to justify a rating of maybe 6 ohms, which would have resulted in less discussion, sometimes approaching hysteria, about a supposed difficulty in powering the M80.
It's interesting to note that my M22s, rated at 8 ohms, as measured by the NRC
here , actually drop to 3 ohms in one area.
