While the ZV28 includes interlocking feet for horizontal stacking, you can also stack your ZV28s vertically, which creates a lot of output in a small (and tall) footprint.  This vertical configuration works great against a wall, or even better firing into a corner.  Before stacking your ZV28s vertically, there are a few things to keep in mind.

To create the stack, place the first ZV28 vertically and place a Shorty Pole in the 1 3/8" pole socket.  This pole will serve to join the two cabinets so they do not easy separate.  We recommend adding some foam rubber, such as McMaster Gasket Tape (See here: https://www.mcmaster.com/8694K113/ ) to keep the pole from rattling in the socket.  Then place the second ZV28 upside-down so the Shorty Pole inserts into it's "top" pole socket.  

Ideally, the stack of two ZV28s would be secured to a wall using the included fly points.  However if the stack is not permanent, we you can secure the stack to a large, heavy base to keep it from tipping.