Interesting, Randy. I'm not familiar with that CD or the "thumps", but I'll throw out a thought. One possibly relevant point is that when two speakers(or a speaker and a sub)are playing the same frequencies, there's a partial cancellation near frequencies where the driver cones are separated by about half a wavelength. If the crossover is at 80Hz, this is a wavelength of about 14', so cones about 7' apart would tend to cancel around the 80Hz area if they were driven in-phase(i.e. using zero). If those thumps fall near that area, reversing to 180 might be reducing the cancellation with the right(not left)speaker, which is probably 6-7' away?
