XS adapter Subwoofer Y Low-resistance interfaces. ViaBlue™ XS adapters Subwoofer Y 2x rca male to 1x rca female are used as splitters for routing signals from two sources to one receiver. This is ideal for using mono subwoofer cables for subwoofers that have stereo inputs. The subwoofer y adapters can be easily attached to stereo rca jacks. The distance between two rca jacks is a standard size.