So far as I know, it's the graph for the VP180, measured in Axiom's own large anechoic chamber. The latter is a duplicate of the anechoic chamber at the acoustics division of the National Research Council, where Ian did much of the early R & D on Axiom's speakers back in the 1980s.
When I was over at the plant a while ago doing listening tests on the VP180 and other v3 models, there were tweaks made in the crossovers (based on the results of blind listening tests), then the speakers would be measured in the anechoic chamber, and another round of listening tests would be done. So there were lots of curves run by both Andrew, Ian and Debbie.
Axiom Resident Expert