The XLR cable is widely used in the recording industry, due to it being able to be used as a balanced cable. However, in some cases, you may see it being used as a stereo cable. So how do we know if XLR cables are mono or stereo?

Here’s a short answer for you:

A 3-pin XLR cable (XLR3) can be used as balanced mono or unbalanced stereo. For most microphones, it is used as balanced mono. However, there are different variations of XLR cables with a different number of pins. For some headphones, the XLR cable is used to transmit a stereo signal.

Here’s a table for the most common use cases, and whether the XLR used is mono or stereo:

Now let’s look at different situations where XLR cables are used to send mono or stereo audio signals!

Are XLR cables mono or stereo?

Microphones

Most microphones record mono audio signals, and therefore only need a single mono channel. By using an XLR cable, a microphone can transfer its audio signal using balanced mono. Due to the nature of balanced cables, electronic interference is eliminated, resulting in a cleaner audio signal at the end of the transmission.

By far the most common XLR connector type used for microphones is the 3-pin XLR (XLR3). Having only 3 pins, it is only able to transmit a balanced mono signal or an unbalanced stereo signal. Since most microphones are mono and by using a balanced cable not only can we eliminate electronic interference but also supply phantom power (+48V) to the microphone, we commonly use the XLR cable as a balanced mono cable.

Studio Monitors

Many studio monitors use either 1/4″ TRS cables or XLR cables to connect to the audio interface or mixer. Usually, for a stereo setup, there are 2 studio monitors used: one left and one right. Therefore, for each speaker, we are actually sending a single mono signal. In that case, each XLR cable for each of the studio monitors is used as a balanced mono cable.

Similar to microphones, studio monitors that use XLR typically use the 3-pin XLR (XLR3) connector.

DI Box

If you’re using a DI box for recording instruments including guitars and keyboards, you will most likely see an XLR cable being used for its output. Most DI boxes take an unbalanced 1/4″ TS mono input from your instrument and transfer the signal to the audio interface or mixer using a balanced mono 3-pin XLR (XLR3) output.

Note that some DI boxes allow you to connect 2 individual unbalanced mono inputs, and it will convert those signals to a single balanced mono XLR output. Either way, the 3-pin XLR (XLR3) is being used as a balanced mono cable.

Headphones

Although the majority of headphones do not use XLR cables, some actually do, and the type of XLR connector they use differ.

Headphones that use XLR connection are usually intercom headsets. Depending on the requirements, they may use 4-pin, 5-pin, or even 6-pin XLR. With more pins, more signals can be transmitted.

For example, a 4-pin headset can only receive mono sound and send back an unbalanced mono mic return. But a 5-pin headset is able to receive a stereo playback while sending back an unbalanced mono mic return. Finally, with 6-pin the headset can both receive stereo playback and send back balanced mono mic return.

Other gears

Other than the music recording industry, there are many places where XLR cables are being used. For example digital lighting control, intercom headsets, stereo microphones, power supplies, etc. The use cases are endless. Note that not all use cases transmit audio signals through the XLR cables.

If the gear or device you’re using isn’t found in this article, you should look up the device manual to check if it’s using XLR for mono or stereo use.

The design of XLR cables

So how did XLR become so popular? And why are there so many different variations of the same connector type?

Balanced signal

The biggest advantage of using an XLR connector is to be able to send balanced audio signals. Yes, you can use XLR cables to send unbalanced mono signals, but that isn’t its biggest strength.

The most common XLR is the 3-pin XLR (XLR3). The 3 different pins are:

1. Ground/shield
2. Positive/hot
3. Negative/cold

As you can see, both pins 2 and 3 can carry audio signals. Therefore by having those pins carrying the exact same audio signals but with one of the signal’s polarity reversed, we can cancel out the noise introduced by electronic interference at the end of the transmission. This technique is called Common-Mode Rejection.

In other words, if a cable only has one ground/shield wire and another wire carrying the signal, the cable is not able to carry a balanced audio signal.

So what if we want to carry a balanced stereo signal within a single XLR cable? Or what if we want to send audio signals in both directions? That’s where more pins come into play. By having more pins, we’re able to send stereo signals and in both directions in some cases.

Phantom power

The XLR cable has got another crucial advantage over the other cables when it comes to connecting professional microphones, and that is the ability to supply phantom power. Due to it being a balanced cable, voltages can be supplied to pins 2 and 3, and you won’t need another cable for powering the microphone.

Of course, some microphones still need an external power supply, but most condenser microphones simply use the 3-pin XLR (XLR3) to power themselves and transfer the audio signal recorded.

Safety

Last but not least, the XLR cable became extremely popular due to its safe and robust design.

Let’s look at the 3-pin XLR for now. You may have noticed pin 1 is slightly longer than the other 2 pins, and pins 2 and 3 are of the exact same length. That is no accident. In fact, this design prevents your gear from being damaged by electricity when plugging in or out.

Because the ground/shield wire is always connected first, any burst of static electricity will not hurt your gear. And due to the fact that pins 2 and 3 make the connections at the same time, even if phantom power is supplied to microphones that don’t need it, there is never a huge difference in phantom voltages.

Unlike a TRS cable, the pins on an XLR connector are clearly separated from each other. In other words, they will never touch even when connections are being made. This makes the XLR cable extremely safe, as it will never short circuit even if phantom power is supplied.

Another safety mechanism added to the XLR connector is the latch. By having the latching mechanism, even if the cable is moved or pulled while connected, it won’t come off easily. This is great for both studio use and live performances.