Subwoofer calibration quandary...

In my experience, your measurements are typical. Changing one parameter changes all others. Where is your sub placed in the room and in relation to your mains? What is your crossover point? What main speakers do you use? I find that placing a sub in a corner will excite several modes, depending on where you are sitting. I moved my Hsu VTF-3 out from the corner. It has plenty of volume for my room, so i didn't need to place it in a corner. I think my overall response is smoother. I am using floorstanding Dynaudios which are rated down to 34 Hz (-3 dB) anechoic response. I only use the sub below 50 Hz, so it is easier because I have fewer frequencies to worry about. I can't change my mains' position much, but I did move my sub (80 lbs.) around quite a few times!

I hope that I understand your question. If so, there will be many opinions out there, but since you asked......
I believe that it is best to scheive the flatest overall response with a minimum of distortion. Different areas of the room will have different peaks and valleys, so you may have to decide to optimize the response for one or two seats. It is worthwhile to try for +/- 5 dB across the spectrum, but it is difficult to acheive, even with equalizers and room treatments. I would not try to push the sub any lower than it can safely go without distortion (-3 dB). A good sound meter can help plot out your room (tedious) or you can pay for the service. Getting a sub to sound right is difficult and maddening. So much trial and error, but hopefully you will know when its right and actually have some fun trying! Good luck!

The info is appreciated. Am I correct in thinking that the -8 dB drop at 125 Hz is your main speakers? If so, that is a null at your reference location and can only be corrected by moving the main speakers or your seat position. Also, the -6 dB at 20 Hz, is that realistic for your sub to achieve? If not, it will not be terribly important for your overall listening since not much goes below that point at significant volume. Low frequency resonances are one thing, dinosaur footsteps are another! If you could adjust the drop at 125 Hz, then I believe you have an acceptable flat response. Any further adjustments may result in other peaks and valleys. I am interested to find out how things go. Good luck and have fun!

Let us know how you do with moving things around. I think that is the simplest solution. It is harder to tame high peaks, but your room configuration allows the escape of some of the high pressures, so I think your situation is quite manageable. If you like your speakers, crossover at the lowest point since the sub will not be localized and your front speakers will have a more coherent sound. Good luck!