Sarang,
It's a tricky concept to understand, but by using one or two subwoofers for the very low non-directional deep bass energy and relatively smaller speakers (center, surrounds and even mains), you really can achieve highly realistic bass imaging.
As others have pointed out, we do NOT hear very low frequencies in a directional sense. It is the upper bass and midrange sounds that provide the directional cues that tell your ears and brain where the bass sounds are coming from.
For example, if a mallet hits a big bass drum (about 30 Hz or lower depending on the diameter of the drum), the deep 30 Hz sound issues from the subwoofer, but the "crack" of the mallet hitting the skin of the drum (likely around 800 Hz or higher)is what tells your ears where the drum is located. The deep bass reverberates through the room (or the concert hall) but your ears/brain instantly locate the "thwack" of the mallet which, for example, comes from the front right or left side of a typical orchestra.
Regards,
Alan
