First of all, the fresh measurement and its graph are much better. With the limits set properly, it is much easier to read. And with the sub isolated, we can now clearly see that the frequency response irregularities are a result of the sub and its interaction with the room.
And the sketch shows that the room shape makes it somewhat difficult to apply the Room Mode calculator to predict a likely spot for the sub. Next step, IMO, would be to try the "sub crawl".
- Temporarily place the sub at your primary listening point, at ear height if possible (perhaps placed on a chair or a couple of boxes)
- Take the REW mic, adjust it so it is at the same height as the cone of the subwoofer (if the sub were on the floor, of course)
- Walk around the room and run a frequency sweep at each potential spot where the sub could be placed.
The hope is that this process will result in the "best" placement, given the room dimensions, and the fact that there is only one sub. Once you have placed the sub in that spot, take another measurement with the sub only, and then three additional measurements, sub+left, sub+right, and sub+left+right (all 15-300Hz). Post these measurements (separate graphs, which will be easier to read), which will represent "as good as it gets", given that you only have one sub. Depending on the measurement results, and your listening tests, you can decide if you want to consider a second sub. BTW, what make and model sub do you have? A second sub should be a matched sub, if possible.
Finally, I have tested out the UMM-6 calibration file that you sent. The file has a sensitivity parameter in the first line:
When I use this file, and open the REW SPL tool to calibrate the mic, I get this message:
REW will indeed not allow the mic to be calibrated if a sensitivity parameter is loaded. I'm not sure I would have coded the program this way, but there is a simple workaround, should you want to calibrate the mic manually. Simply open the calibration file, delete the line with the sensitivity parameter, and save the file with a different name. Then use this edited version the next time you run REW, and you will be able to manually calibrate the mic. So relax, Sean, you are not crazy (what a relief!).
Edit: I think adding this information to the Guide might help others in the future.