A traditional balanced cable uses three cores of wire to carry the audio signals: one shielded core for the hot/positive leg, one shielded core for the cold/negative leg (which is wired in reverse polarity to the positive leg), and a plain outer wrap that functions as the ground. A balanced audio system effectively rejects most induced noise encountered along the cable's length by removing signals that are common to both the hot and cold legs.
StarQuad construction takes that concept even further, by using four cores instead of two: two cores each for the hot/positive and cold/negative legs and a single ground. This helps to further shield the audio from RFI (radio frequency interference) even more than a traditional 3-conductor cable.
What is "Double-Ruessen Shielding"?
Most cable construction techniques use an outer wrap of wire to act as the ground. Some manufacturers braid this wire, while others simply wrap the wires in a highly uniform way to shield the interior wires from electromagnetic interference. Double-Ruessen shielding goes much further than more traditional techniques in two ways: First, the cable is wrapped with not one but TWO separate shields, and second, the outer shield is wrapped in a contrary direction to the inner shield. This creates a stronger and more complete shield from EMI for the internal cores, and result in an astounding reduction of interference. Double-Reussen shielding is a tad more expensive to manufacture, but for those who will accept nothing but the best it represents the pinnacle of balanced cable technology currently.