I've been experimenting with placing my new Dynaudio 9S sub. Here some measurements + final EQ'd result:
Explanation:
The orange line is where I had the sub to the left of my desk, close to a corner where 2 walls meet. Created a big null around 116hz. Crossover on the sub is set to a 100hz high-pass and 60hz low-pass filter (for the Kali IN8-V2 monitors). That gave the best response in that location.
With the green line I'm showing results of when I moved the sub underneath my desk, close to the right post. I played around with crossover settings on the sub and that led me to a 150hz high-pass filter and 60hz low-pass filter.
Then using REW and a house curve, created EQ filters for use in Equalizer APO to bring down some of the peaks, and applied a +3db low-shelf filter centered at 100hz. Otherwise not boosting other dips independently. Results of this are in the red line.
Overall I'd say a pretty big improvement.
As for the Dynaudio 9S, it seems like a good sub. I just wish that the cross-over and gain knobs had notches. It's challenging to create exact reproducible results as you'll not often get it back in the exact same spot when comparing back and forth.
P.S. the measurements deviating at around 3,000hz are most likely due to me bumping into the UMIK-1 stand, and me probably not positioning it back in the exact same place. Measurements taken from one listening position. I was mostly focused on low-end improvement either way.
Here are distortion measurements, taken with REW and a UMIK-1 at the ideal listening position, and with EQ applied.