I just finished testing this...
As I raise the volume on the SMS, the response line moves up or down; however, the shape of the graph doesn't noticable change. I'm using the SMS with a single sub in a small room with some acoustical treatments. Not sure if any of that makes a difference.
To perform this test, I set my Denon receiver to -15 (my normal listening level) and adjusted the SMS volume to +15. The graph is flat (+/- 3 dbs from 20Hz to 160Hz). I then raised the Denon receiver volume to -10 and the shape of the graph didn't change (it only moved up to a higher dB level). I noticed a smiliar effect when I set the Denon receiver volume to -20 (only the graph moved down to a lower dB level). In both cases, the resulting graph is +/- 3 dB from 20Hz to 160Hz.
I hope this helps. If you want some pics of my results, let me know.
