Are you measuring the levels from the same position in the room? I.e., at the listening position, for example?
Is this a phase issue? How to fix?
I noticed when I measure individual frequencies in the range of 60-80hz, the measured combined output of both speakers is about 4-5db less than the individual levels. For example, at 70hz the left and right speakers measure 77db but the combined output is 73db. So does this mean I have a slight phase issue in this range? If so, is there a way I can fix it?