iFixit

Here we discovered three of the four microphones inside of the Kinect.

There are a total of four downward facing microphones: three on the right side and one on the left side.

Microsoft determined that the best orientation for optimal sound gathering would be downward facing.

In order to properly recognize voice commands, the Kinect must perform an audio calibration for the room that its in. However, if you alter the arrangement of the furniture in your room, you must re-calibrate.