As to the graph posted for the M80s, it does appear the 80s start to fall off at around 80Hz. As Ian has stated a few times, as well as others, the NCR chamber is accurate to only 85Hz. The graph does not take into account in room response.
From Soundstage
"One should recognize that since these measurements are performed in anechoic chamber, they will generally show less bass than what you can expect in a real room."
From the Soundstage review. "I’d estimate bass to a solid 30 or 35Hz in my room"
