Thats an interesting setting. It seems to go against the grain that speakers that go to 40hz should be set at 100hz. I have read that spl meters(the one from radio shack anyway) needed a seperate chart to dial the sub in corectly, if you included it during your measurements. How does it sound with the x over set at 100hz? I would put it where it sounds best to me even if the meter said I was wrong.