Well, that question came to my mind a few days ago actually, and I asked it to a dear friend of mine who has a PhD in theoretical physics (we call him Sheldon
).
He basically told me that when we pull the speaker out the delta between external and internal pressure can be 1 atm at most (assuming the speaker had no physical displacement limits, that means vacuum inside and normal atmospheric pressure outside).
When we push it in instead there's no limit for the internal pressure (until we create a black hole at least) and the delta can be much larger than 1 atm.
This also means that the force needed to push in the speaker by, let's say, 1 inch is more than the force needed to pull it out 1 inch. Pressure basically changes with a different trend so the delta will be larger in the first case.
The question though is if this difference of pressure delta is appreciable for typical speaker displacement range and cab internal volume, we didn't have the chance to do the math and discuss it in detail.
Maybe
@FractalAudio can think about this, even though he probably already did it long time ago