A balanced audio cable with XLR connectors

What are Balanced Audio Cables?

Balanced audio cables have three conductors and carry balanced (positive and negative) signals. They can minimize interference due to the way that the balanced signals are processed at the receiving end of the cable. They, therefore, offer better audio quality than unbalanced cables.

In this article we’ll look at:

Balanced vs unbalanced cables

Both balanced and unbalanced cables are used for connecting instruments and microphones to audio interfaces and other audio equipment.

A balanced audio cable has three conductors. Two conductors carry balanced signals—one positive and one negative—while the third conductor goes to ground.

You may also encounter balanced cables that have five conductors—two pairs of conductors for balanced signals plus one conductor that goes to ground. These cables are called star quad cables. The two pairs of conductors allow a star-like configuration that is very effective at minimizing electromagnetic interference.

Unbalanced cables only have two conductors—one for carrying the (unbalanced) signal and one for ground.

Cable construction

Balanced cables consist of two inner conductors (carrying the positive and negative signals) and an outer conducting sheath (or “shield”, the third conductor) made from wire braid, metal foil, or conductive plastic.

XLR cables are an example of balanced cables and are commonly used in the audio industry. They have a three-pin construction, as follows:

  • Pin 1 is ground (connected to the cable’s sheath)
  • Pin 2 is positive (or hot)
  • Pin 3 is negative (or cold)
XLR cable construction

Unbalanced cables have a single conducting core and an outer sheath that acts as the second conductor. The sheath acts as both ground and a signal return path.

Interference

Interference can affect the quality of sound and may impact the signals flowing through either balanced or unbalanced cables.

In balanced cables, if any interference affects the signals flowing through the positive and negative conductors to different extents (ie. in an unbalanced manner), then this may affect the quality of sound.

In unbalanced cables, interference can cause unwanted currents to flow in the (conducting) outer sheath. Since this sheath acts as a signal return path, the unwanted currents flowing through it will impact the (wanted) signal flowing in the core of the cable, affecting the quality of sound.

Phantom power

For certain audio devices, such as condenser microphones, an external power supply is required to operate them. This power supply may be delivered through phantom power provided directly from a device such as an audio interface.

Audio devices that work through phantom power are balanced audio devices. Hence, when using phantom power, balanced audio cables are required.

Balanced vs unbalanced audio quality

Although interference can arise in either balanced or unbalanced cables, balanced cables are better at minimizing interference compared with unbalanced cables. Hence, balanced cables offer a better audio quality than unbalanced cables.

Balanced cables minimize interference through the following approach:

  • The positive and negative signals flowing through a balanced cable are actually two copies of the same signal, but with their phases inverted
  • At the receiving end of the balanced cable connection (eg. in an audio interface), the negative signal has its phase re-inverted and added back to the positive signal, hence restoring the original signal
  • If interference were to develop along the cable, it’s likely to have the same effect on both signals as the positive and negative conductors are in close physical proximity (and are constructed similarly, ie. they have the same impedance), so when the negative signal is re-inverted and added to the positive signal, any common interference will cancel out
Balanced cable interference minimization

It’s worth noting that having two copies of the original signal isn’t entirely necessary for the above approach to work. If the negative signal wasn’t there, for instance, during phase re-inversion at the receiving end of the cable, any common interference on the negative conductor would still cancel out.

How successfully interference minimization works, however, depends on how well balanced the positive and negative conductors are in terms of their impedance, ie. whether they have the same impedance to ground. Any interference that develops on the two conductors will cancel out only to the extent that it is identical on each conductor.

Balanced XLR and TRS cables

XLR cables are balanced cables that are popular in the audio industry.

They have 3-pin connectors—one pin each for the positive and negative signals, and one pin for ground—and are used for connecting balanced microphones and line level signals to audio interfaces and other equipment.

Other pin configurations are also available for XLR cables (eg. 4, 5, or 6-pin configurations), but these are mostly used in intercom, video, and lighting applications.

The name “XLR” comes from the cable’s connector which was originally developed by Cannon Electric (now a part of ITT Corporation)—XLR refers to X Series, Latch, and Rubber, Cannon’s part designation for the connector.

TRS cables are also balanced cables and are used in many audio applications.

The name “TRS” refers to Tip, Ring, and Sleeve—the three main components making up the connector’s construction.

Being balanced, TRS cables have three conductors (positive, negative, and ground signals).

TRS connectors have a jack (instead of pins) which includes the three conductors separated by (two) insulation bands.

TRS connectors come in different jack sizes—most commonly in a 1/4-inch size (sometimes called phone jacks as they were used in early telephone switchboards), and also in 1/8-inch and 3/32-inch sizes.

XLR and TRS cables

Why use unbalanced cables?

Given the benefits of balanced audio cables—primarily their better audio quality due to lower interference—why would you want to use an unbalanced cable?

There are many reasons why you may choose (or need) to use unbalanced cables—here are a few:

  • Connection type—The available connections on your equipment, such as on your audio interface or mixer, may only allow unbalanced cables
  • Length—If the length of the cable you’re using isn’t very long, say no more than a few feet, then you may not have to worry about distortion developing in the cable (as distortion tends to become a problem only at longer lengths)—unbalanced cables may be fine to use in these situations
  • Price—Unbalanced cables are generally cheaper than balanced cables, sometimes only 1/3 to 1/2 the cost of similar balanced cables, so you may prefer to use unbalanced cables if you’re on a tight budget
  • Application—Depending on what you’re using your cables for—connecting to loud guitars or keyboards, for instance—then the possible distortion that could develop in an unbalanced cable may be small enough compared to the main signal and may not matter

While balanced cables offer definite advantages over unbalanced cables in terms of audio quality (or when using phantom power), unbalanced cables may sometimes be the best solution for your particular audio application.

Conclusion

Both balanced and unbalanced cables are popular in audio applications.

Balanced cables have a three-conductor construction while unbalanced cables have only two conductors.

The three-conductor construction in balanced cables means that two of the conductors can carry two copies of a signal (one with an inverted phase). This allows for canceling out of any interference that develops in the cable at the receiving end. Balanced cables, therefore, offer better audio quality (lower interference) than unbalanced cables.

Balanced audio cables are also required in situations where phantom power is being used to connect to balanced audio devices, such as condenser microphones.

Unbalanced cables, nevertheless, may be preferred over balanced cables in some cases. They’re cheaper, for instance, and may be the only cable type that fits an available connection on an audio device for a given application.

Popular balanced cable types include XLR and TRS cables—both are used widely in audio applications.

Balanced cables offer a higher fidelity alternative to unbalanced cables in situations where audio quality is important. They are an indispensable accessory in the audio industry and are widely used in recording studios and in other audio environments.

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