do a search for the author djk on this and audioasylum.com under speaker or high efficiency.
Push pull (when slot loaded and closely coupled) creates an almost 20db reduction of 2nd order harmonic distortion (cleaner than a bass horn). This results in a sub that is clean and deep but without the distortion (above 80hz) that causes an "in your face" or "slam" effect. Think live real organ, deep but not in your face. It is a different sound (much cleaner) and takes some getting used to.
M&K is close but drivers need to be closely coupled.
