I have seen many posts about the difficulties calibrating a sub using a sound pressure leevel meter. Usually the posts are about how one DVD calibration disk yields a different level than another one or how the receiver's own test tones yield different results, or how once set the sub now seems too loud or quiet compared to the mains. I got to thinking that the quality of the sub and/or the room response may be the reason for the variation. For example, when I had a cheap 8" sub I could NEVER calibrate it with any test tones as the darned thing simply could not reproduce the frequency of the test very well so the meter never moved. Also, could one test tone excite room nodes more than another test tone? If so, this too would lead to variations. I'm thinking that we should always use our ears to make final adjustments to our subs.