Balanced microphone cables are constructed with three wires, often enclosed within a tube of wire mesh that provides a degree of shielding from outside interference. One of the three wires is the ground connection between the microphone and the amplifier or mixing board, the while the other two carry the audio signal, split into two parts. Any interference encountered along the way will create a similar degree of line noise on each wire. When the cable reaches its destination, the two feeds are recombined, at which point the audio signal is made whole again, but each line's noise cancels the other out.
Unbalanced microphone cables, by contrast, have only two connections. One wire carries the signal, while the ground wire makes up the braided tube of shielding that surrounds it. These cables lack the noise cancelling of balanced cables, making them best suited for short runs of cable in areas of relatively little interference. Because the grounding cable is always attached at both ends with an unbalanced cable, it can also introduce a problem known as a "ground loop," meaning it produces a loud hum when two pieces of equipment are joined together.
Balanced and unbalanced cables are easily recognized by their connectors. The two connectors for balance cables are the heavy-duty XLR connector, consisting of a round metal shell containing three pins or three holes in a triangle shape, and a 1/4-inch round connector, referred to as a tip-sleeve-ring connector or TSR. Unbalanced connectors also use the 1/4-inch round connector, but those only have one black ring on the connector, while the TSR has two black rings. Some unbalanced cables also use RCA connectors, the same kind used on the back of a home stereo.
Unbalanced cables are typically much lower in cost than balanced cables, making them useful in schools and other budget-sensitive settings. They are best used for cables of 30 feet or less, and for simple installations where there will not be many other cables to create interference. They're also often used with lower-priced karaoke machines. Balanced cables are used for live bands and other professional audio situations, where longer cabling and better shielding are important.