Lower Distortion

• Aimed at the floor, harmonic and driver-induced distortions are less audible than when aimed directly at the listener. These distortions are normally higher in frequency than the actual bass signal, with the floor acting as a filter.
  
  

Less Directivity

• Although bass signals tend to be non-directional below 80 hertz, any distortions created by the driver might be. Many manufacturers purposefully aim the driver at the floor, further diffused by an apparatus designed to "spread" the bass more evenly into the room. Additionally, the sound itself carries along the floor's surface, reducing the listener's ability to localize the source of the bass signal.
  
  

Increased Placement Flexibility

• Given that down-firing subwoofers do not fire audio information directly at a single listening position, room placement flexibility is marginally increased. This makes it easier to set the speaker in the room, and allows increased non-directivity of the low frequencies they impart.
  
  

Potential Drawback

• Before diving headlong into selecting a down-firing subwoofer, it is important to understand the major potential negative aspect of the design: gravity. Over time, the driver begins to "sag" towards the floor, reducing the linearity of the driver. This means that the amount of travel heading towards the floor will not equal travel in the reverse direction, given an inverse signal. This reduces overall output.