I connected my speakers to my sound system switching the +ve and -ve one of the speakers I can notice them beating out of phase but how come I don't hear any difference and at what position will it undergo destructive interference and the sound will be of 0 intensity ( I've never experienced it in real life so I'm guessing its not correct but why doesnt my theory happen in real life?).
The pattern of destructive and constructive interference depends on frequency. A single tone will show exact cancellations and amplitude doubling, a narrow band signal will show slight damping and gain, and a wide band signal will show a position dependent filtering.
The positions of gain and dampening also depends on reflections from the surroundings but if you arrange the room to be symmetric about the midplane between the speakers then you should be able to create wide band cancellation in that plane.
You are using a mono signal, right?
In an ideal experiment (say, a large room with sound-absorbing walls) you should be able to readily identify the null points. In practice, however (e.g., in your house) the sound from your speakers will impinge on and reflect from the objects in the room.
The reflected wave may hinder the ability for you to readily detect null points. This will depend on the damping characteristics of the room and objects in the room.