[Wayne A. Pflughaupt]

Well, I can see Bosso’s point. I had some trouble with this myself. You EQ with the sub only, run a fresh sweep adding the mains, and see changes that need to be made. Problem is, your new sweep wants to use all-new filters - it won’t allow you to open up and modify your existing filters. You have to tweak Chart B with filters from Chart A, then sweep and check Chart C to see if the filter tweaks got what you wanted. (‘Course, it’s highly possible that REW will allow you do a second sweep using existing filters, and I just don’t know about it...)

Typically response changes when adding the mains will show about an octave above and/or below the crossover point, in my admittedly limited experience. With an 80 Hz crossover, response from the mains should be down more than 30 dB at 30 Hz compared to the sub – too low to register.

Still, I can imagine some scenarios where the mains might make an impact down there. For instance, if your mains were really too big and bass-heavy for your room, effectively flattening much of the crossover roll-out, and you had a room mode at 30 Hz on top of that. The EQ would eliminate the peak in the sub, but it would still be present (albeit to a lesser extent) in the mains, which would show up with a combined sweep. Unusual yes, but certainly not out of the realm of possibility.

Regards,
Wayne A. Pflughaupt