Editing Subwoofer (section)

===Phase control===
[[File:Subwoofer downfiring.jpg|thumb|upright|The rear panel of a down-firing, active subwoofer cabinet]]

Changing the relative phase of the subwoofer with respect to the woofers in other speakers may or may not help to minimize unwanted destructive acoustic interference in the frequency region covered by both the subwoofer and the main speakers. It may not help at all frequencies, and may create further problems with frequency response, but even so is generally provided as an adjustment for subwoofer amplifiers.<ref name=Elliot2004 /> Phase control circuits may be a simple polarity reversal switch or a more complex continuously variable circuit.

Continuously variable phase control circuits are common in subwoofer amplifiers, and may be found in crossovers and as [[do-it-yourself]] electronics projects.<ref name=Elliot2004PC /><ref name=Nicholls2002 /><ref name=Slone2001 /><ref name=White2002 /><ref name=Robjohns2007 /> Phase controls allow the listener to change the arrival time of the subwoofer sound waves relative to the same frequencies from the main speakers (i.e. at and around the crossover point to the subwoofer). A similar effect can be achieved with the delay control on many home-cinema receivers. The subwoofer phase control found on many subwoofer amplifiers is actually a polarity inversion switch.<ref name=DellaSala2004 /> It allows users to reverse the polarity of the subwoofer relative to the audio signal it is being given. This type of control allows the subwoofer to either be in phase with the source signal, or 180 degrees out of phase.

The subwoofer phase can still be changed by moving the subwoofer closer to or further from the listening position, however this may not be always practical.