Critical Distance   

Critical distance is the distance between the microphone and the sound source at which the level of room reverberation is equal to the level of the direct sound. Placing the microphone farther away than this critical distance may lead to a "muddy" sounding recording because the room sound will be predominant, particularly in rooms with poor or no acoustic design.  Critical distance (sound reinforcement) The distance from the acoustic centre of the source to the point at which the intensity of the direct sound equals that of the reverberant field . 
Typically a recording with clearer definition of detail will be acheived by placing the microphone closer to the sound source in order to minimize the affect of room sound.  Use of directional loudspeaker to increase critical distance over a specific area (audience). This is effective because the sound is more focused on the desired area with the added benefit of reducing reflections from other areas (sides, ceilings, etc.)