Help me with adding a variable phase control to a subwoofer

[palesha]

variable phase control

I want to add variable phas control 0~180 degrees to my subwoofer project. Need guidance in the matter. TIA
MP

 

[VSWR]

variable phase schematic

Searching for 'audio variable phase shifter schematic' in Google gives the following result:

http://www.geofex.com/Article_Folders/phasers/phase.html
**broken link removed**
**broken link removed**