Knowing just enough about sub design to be dangerous...
they are designed to work sitting on a floor in "free space" and that is how they're measured as well.
I would think that if you were to construct a cabinet such that the front face were closed around the sub and flush with the front of the sub (ie: the front of the sub and cabinet are like a wall), you would be ok as long as there was not significant resonance in the enclosure. This might require that the front face be reinforced some way. Is baffle diffraction also an issue with subs?
I could see an open cabinet acting as a resonator and colouring the sound though.
I would think the same goes for a column. As long as the column is properly reinforced so that it does not act as a resonator, you should be OK.
