The usere defined options in a TF measurement include magnitude threshhold and coherence blanking. I'm guessing that the default settings are too low. look inside the options of TF. The mag threshhold sets a reference signal threshhold that must be met or exceeded before a measurement wil display. The thinking is... In order to compare this (mic) to that ( reference signal) I first must a certain level of that present otherwise the noise floor will become the reference signal. Coherence blanking sets a threshhold of validity before data is displayed. A highly coherent measurement signal is very related to the reference signal. A measurement signal that also contains a vacuum cleaner is not. A high enough coherence setting will blank out the non related info from appearing in the display. If the demo version allows access, try raising the mag threshhold to 50% and the coherence blanking to 30%. See if the high end of the sub measurement goes away. You would not want that info to display. After all, the measurement side ought to be down in frequency response CONSIDERABLY after having travelled through the xover.
I have an old (version 5) Smaart thing I did on this very idea showing how just turning on the program made a beautifulk looking but invalid TF trace when using default settings.
