Cable Topics:
» Balanced vs. Unbalanced Cables
» Common Cable Connectors Explained
» Cable Shielding Explained
» Glossary of Additional Cable Connectors

Balanced vs. Unbalanced Cables

A balanced electrical signal runs along three wires: a ground, a positive leg, and a negative leg. Both legs carry the same signal, but in opposite polarity to each other. Any noise picked up along the cable run will typically be common to both of the legs. Assuming the destination is balanced, the receiving device will "flip" one signal - putting the two signals back into polarity with each other. This causes the common noise to be out of phase with itself, thus being eliminated. This noise cancellation is called "Common Mode Rejection,” and is the reason balanced lines are generally best for long cable runs. XLR and TRS cables are used to transmit balanced audio from one balanced device to another.

Unbalanced cables are less complicated (and less expensive), but they're also much more susceptible to noise problems. In general, unbalanced lines should be kept as short as possible (certainly under 25-30' maximum) to minimize any potential noise that may be carried with the signal into connected equipment. Many guitarists claim to hear a difference in their tone when cable lengths begin to exceed just 17'.

Common Cable Connectors Explained

In the live sound world there are six common cable connectors: TRS and XRL for balanced connections; and TS, RCA, Speakon, and banana plugs for unbalanced connections.

	TRS TRS is the abbreviation for “Tip, Ring, Sleeve.” It looks like a standard 1/4" or 1/8" plug, but with an extra “ring” on its shaft. TRS cables have two conductors plus a ground (shield). They are commonly used to connect balanced equipment, or for running both "left" and "right" mono signals to stereo headphones. You will also find TRS connectors on the stem of Y cables. These are used for mixer insert jacks where the signal is sent out through one wire, and comes back in through the other.
	XLR Having positive, negative, and ground connections, XLR connectors are usually used for transmitting microphone or balanced line-level signals. (XLR is the original trademarked name from Cannon Electric, and does not correspond to the three connections.) In audio, you will typically see XLR cables connecting microphones to mixers, and connecting various outputs to powered speakers.
	TS TS is the abbreviation for "Tip, Sleeve" and refers to a specific type of 1/4"or 1/8" connector that is set up for two-conductor, unbalanced operation. One insulator ring separates the tip and sleeve. The tip is generally considered the "hot," or the carrier of the signal, while the sleeve is where the ground or shield is connected. TS cables are best known as guitar or line-level instrument cables.
	RCA "RCA" is the common name for phono connectors used to connect most consumer stereo equipment. (They were so associated with the RCA Corporation in the early 1900s that they became known as the RCA connector.) Typically, you will see tape or CD inputs and outputs using RCA connectors. In the digital audio realm, RCA connectors are also used for S/PDIF connections.
	Speakon Speakon connectors are used to connect power amplifiers to PA speakers and stage monitors. These are often preferred over 1/4" TS connections because of their ability to lock into place. (They also help to avoid problematic cabling mixups, since you should NEVER use an instrument cable to connect an amp to a speaker.)
	Banana Plug A banana plug is an electrical connector designed to join audio wires such as speaker wires to the binding posts on the back of many power amplifiers, or to special jacks called "banana jacks." These jacks are commonly found at the ends of binding post receptacles on the back of power amps.

Cable Shielding Explained

Cable Shielding Explained
Our partners at Pro Co have done an excellent job of describing this issue, so we’ll let them take over: (Courtesy Pro Co)

	Braided Shield A braided shield is applied by braiding bunches of copper strands called picks around the insulated, electrostatically shielded center conductor. The braided shield offers a number of advantages. Its coverage can be varied from less than 50% to nearly 97% by changing the angle, the number of picks and the rate at which they are applied. It is very consistent in its coverage, and remains so as the cable is flexed and bent. This can be crucial in shielding the signal from interference caused by radio-frequency sources, which have very short wavelengths that can enter very small “holes” in the shield. This RF-shielding superiority is further enhanced by very low inductance, causing the braid to present very low transfer impedance to high frequencies. This is important when the shield is supposed to be conducting interference harmlessly to ground. Drawbacks of the braided shield include restricted flexibility, high manufacturing costs because of the relatively slow speed at which the shield-braiding machinery works, and the laborious “picking and pigtailing” operations required during termination.
	Serve Shield (spiral-wrapped) A serve shield, also know as a spiral-wrapped shield, is applied by wrapping a flat layer of copper strands around the center in a single direction (either clockwise or counter-clockwise). The serve shield is very flexible, providing very little restriction to the “bendability” of the cable. Although its tensile strength is much less than that of a braid, the serve’s superior flexibility often makes it more reliable in “real-world” instrument applications. Tightly braided shields can be literally shredded by being kinked and pulled, as often happens in performance situations, while a spiral wrapped serve shield will simply stretch without breaking down. Of course, such treatment opens up gaps in the shield, which can allow interference to enter. The inductance of the serve shield is also a liability when RFI is a problem; because it literally is a coil of wire, it has a transfer impedance that rises with frequency and is not as effective in shunting interference to ground as a braid. From a cost viewpoint, the serve shield requires less copper, is much faster and hence cheaper to manufacture, and is quicker and easier to terminate than a braided shield. It also allows a smaller overall cable diameter, as it is only composed of a single layer of very small (typically 36 AWG) strands. These characteristics make the copper serve shield a very common choice for audio cables such as the Pro Co (XLR20) XLR 20.
	Foil Shield A foil shield is composed of a thin layer of Mylar-backed aluminum foil in contact with a copper drain wire used to terminate it. The foil shield/drain wire combination is very cheap, but it severely limits flexibility and indeed breaks down under repeated flexing. Foil’s 100% coverage advantage is largely compromised by its high transfer impedance (aluminum being a poorer conductor of electricity than copper), especially at low frequencies.

Glossary of Additional Cable Connectors