HT room with a large openning

Hey guys...

We have a HT room in a duplex house.
Room size is 20X14X11ft.

The room is not completely closed, because there is a large opening (6ft x 11ft) for the stair case that connects ground floor and first floor.

How necessary is it to close this openning for pressurizing the room with tactile movie bass?? (Basically install a big door)

Is it possible to pressurize the room that has a big openning ??