Audio Quad
Where two devices are to be linked by an XLR connection, the basic requirement is for a cable with two signal conductors, one wire is in phase with respect to the source signal, the other wire is reversed in polarity, and at least one separate earth conductor. This principle makes it possible to cancel interference and noise by subtracting the two signals and also permits the use of very long cables. These are typically required for systems which utilise active speakers, or whose output stages are located immediately adjacent to the speaker cabinets. Audio Quad even features additional earth and control conductors.