Sound Localization (like stereopsis) requires two normal transducers (ears) .
The brain is still actually receiving two sounds, and processes the time difference between each to produce the illusion of a sound localized in space!
As the sound source moves toward our center (front or rear) the time differential between the ears decreases and the sound appears to move towards the center. We are, at any point in time, only aware of the location of the sound in a single horizontal plane to the right or left.
If it is a brief sound, we can't really ascertain whether its source is to our front or back, or above or below us.
But if the sound persists, we will without realizing it make small adjustments of our head (ears) to sample several different planes and quickly zero in on the sound source.
For the most part it takes two ears to perceive location of the source of a sound.