Physics of Balanced Audio: XLR vs. MIC Lines

[Rockazella]

I don't know if anyone here is familiar with audio/video recording equipment, or if anyone has ever heard of the 'XLR' standard...But While I was lookin over some specs on on it, I noticed that XLR systems/cables are referred to as balanced while your common MIC lines(used for headphones n such) are not. They say XLR being balanced tends to cut back on picking up noise when you have long runs of cable.

So anyway...reading all this sparked my interest in the basic physics of things, and now I want to know what makes these XLR hook ups 'balanced' while MIC lines are 'unblanced' and also how does being balanced help with maintaining signal integrity?

 

[Jimmy]

A balanced XLR line has three conductors: one ground and two signal wires. The two signal wires, referred to as hot and cold, carry the same signal from the source but the cold is inverted. The receiving end of the balanced line inverts the cold signal and adds it to the hot. This is done to eliminate common mode signals A common mode signal is a signal which appears equally on both conductors of a two wire line. Usually this appears as noise. Since the cold signal is inverted at the source, the common mode signal on the cold, when inverted at the receiving end, gets canceled when signals on the hot and cold wires are added together.

Common Mode Signals

Common mode signal rejection is not possible with a two conductor line. Typically, 1/4 microphone cables are unbalanced. As far as Microphones go, the Sure Beta 58 is an excellent, nicely priced balanced microphone which uses the XLR standard. Many good PA amplifiers, mixing boards, cross-overs and other components use balanced, XLR style connectors. Some also use a 1/4 inch, 3 conductor balanced cable. They look just like a 1/4 stereo cable or headphone cable.

I use balanced equipment and cables whenever possible. They are much better than the 1/4, 2 conductor cables. They cut down on a lot of noise. Especially if you have a complex system with lots of components and long cables.

 

[ravenprp]

Balanced audio refers to a type of electrical signal that is used in professional audio equipment, such as microphones, mixers, and amplifiers. It is designed to reduce noise and interference, resulting in a cleaner and more accurate sound.

The main difference between XLR and MIC lines is the way the signal is transmitted. XLR uses a balanced signal, while MIC lines use an unbalanced signal. This means that XLR cables have three conductors, while MIC lines have only two.

In a balanced signal, the audio signal is split into two equal parts, with one part being inverted. These two signals are then sent through the two conductors of the XLR cable. At the receiving end, the inverted signal is flipped back to its original phase and combined with the other signal. This process cancels out any noise or interference that may have been picked up along the way, resulting in a cleaner signal.

On the other hand, unbalanced signals only have one conductor, which carries both the audio signal and the ground. This makes them more susceptible to picking up noise and interference, especially over longer cable runs.

In terms of physics, the balanced signal is able to cancel out noise due to the principle of electromagnetic induction. When two signals of opposite polarity are combined, they create an equal and opposite electromagnetic field, canceling each other out. This is why balanced audio is often used in environments with high electromagnetic interference, such as live performances or recording studios.

In summary, the main difference between XLR and MIC lines is the type of signal they use. XLR utilizes a balanced signal, which helps to reduce noise and interference, while MIC lines use an unbalanced signal, making them more prone to picking up noise. Understanding the physics behind this can help in choosing the right type of cable for different audio applications.