If you re-read Igor's posting, the measurement is taken from the pre-outs. By toggling Audyssey off and on, you can see exactly what is happening without the influence of the listening room. For example, here is a pre-out measurement of my left speaker, one without Audyssey and one with XT32 applied.
In this example, you see Audyssey correction down all the way to 20Hz because Audyssey sets my speakers to "Large", i.e. the F3 point is probably below 30Hz. (Actually 30Hz, +/- 3dB on axis, according to the manufacturer)
Jerry, how exactly do you take a pre-out measurement? I'm curious to figure out why Audyssey XT32 is setting the crossovers of my surrounds to 40Hz? I suppose it could be room effects but I guess I would've expected the opposite (i.e. a higher crossover setting)?
Well, I haven't tried this since we started experimenting with USB mics for REW. With the legacy REW setup, you would connect an audio cable from the Pre-out connection on the back of the AVR and connect it to the Input side of the sound card in place of the mic.
For the new REW setup, I don't know how this would work. I'll post a question on HTS.