Using only 1 driver of a 2 x 10" push/pull (enclosed) subwoofer, technical explanation?

[ZolaIII]

It's actually rear firing with the longest side upwards. Basically as in the picture.

Thought so, had to ask to be sure.

 

[Geertidow]

I'm considering replacing the drivers with actual subwoofer drivers and leave the sub connected in the original way.
With an internal volume of 65L, any suggestions for ideal drivers?