The NRC reported a 9dB swing in the listening window amplitude between ~80 to ~160 Hz. Also the impedance magnitude above 1 KHz looks very different from the one published on the Axiom site.

Ian says the chamber at the NRC will almost never be accurate below 150 Hz as they can’t write a correction curve for each model. He put the tower up so he could measure each model in 4pi and then write a chamber correction curve that was accurate for that model. Even then it is only truly accurate at the amplitude you write the correction for. As for the impedance curve, he says maybe the ferro fluid was not up to temperature. Temperature and ferro fluid is a big deal. When he worked at the NRC, he had to remove all the tweeters from the samples and make sure they were in the front of the car or he would lose a few hours warming the magnets up on heaters.

Very interesting about the ferro fluid. I have noticed and reported on these boards what I believe to be ambient temperature-related changes in my listening sessions. The ferro fluid may be one of the reasons.