If you are going to build an isobaric sub wiring the subs in push electrically is a good idea. When one sub-woofer cone is its maximum travel inwards the other cone will be at its maximum travel in the outward direction. Electrically the amp thinks that the cones have not physically moved
2nd harmonic distortion is reduced when you drive the subs this way. Its a good thing and it is how isobaric subs are commonly built. You at least get some benefit from the buried woofer in addition to being able to halve the size of the enclosure.
Scotty
