In my time studying audio engineering in college, I remember connecting a microphone to a mic preamp for the first time. Although I had previously performed plenty of times as a guitarist, this was the first time using an XLR cable to connect a microphone to anything.
Why do microphones use XLR cables? Not all mics use XLR. However, many professional microphones connect via 3-pin XLR cables because XLR carries balanced audio and connects the ground-pin first. Balanced audio provides clean audio transfer across long cable lengths and ground-pin-first connection protects mics from electrical damage.
XLR has become such a popular option for professional microphone connections due to its clean sound and protective qualities. Let’s dive deeper into the design of XLR cables and why they are so effective as microphone connections. We’ll also discuss the alternative microphone connections that are commonly on the market today.
Connecting A Microphone Via XLR
The vast majority of professional standalone microphones (whether they be moving-coil dynamic, condenser, or ribbon mics) have an XLR output. These mics, generally speaking, have a 3-pin male XLR connector.
Of course, there are other connection types for microphones, and we’ll get to those later. For right now, let’s keep discussing microphones and XLR.
Similarly, the vast majority of microphone inputs (whether they be in a mixing console, audio interface, audio snake, adaptor, or standalone mic preamps or processors) have an XLR input. These mic inputs are practically all 3-pin female XLR connectors.
If we are to look at a standard 3-pin XLR cable, we’ll see two connection points: one 3-pin male XLR connector at one end and one 3-pin female XLR connector at the other.
- The male 3-pin XLR connector has 3 pins that act as plugs. Male 3-pin XLRs insert into female 3-pin XLRs when connected.
- The female 3-pin XLR connector has its 3 pins act as jacks (sockets) that receive the male 3-pin XLR when connected.
So we have the three devices for a basic microphone connection via XLR:
- The microphone itself (a professional mic with an XLR output connector).
- A 3-pin XLR cable (otherwise known as a “mic cable”).
- A microphone input (let’s say we’re connecting the mic to an audio interface for this example).
Connecting the microphone to the audio interface requires the following:
- Connect the microphone output (male XLR) to the female XLR connector of the cable.
- Connect the male XLR of the cable to the audio interface’s mic input (female XLR).
You could also do this in the reverse order. This is the basic microphone connection via XLR to another device.
Now there are two main reasons why professional microphones use XLR: balanced audio and microphone protection. Let’s discuss each of these in more detail.
What is balanced audio? Balanced audio is a method of connecting audio equipment that allows audio signals to travel through long lengths of cable effectively without loss of clarity. Balanced audio does this by carrying two copies of the audio signal in reverse polarity and cancelling out any induced interference.
Before getting into a more in-depth explanation of balanced audio, let’s revisit our 3-pin XLR. What is each of the 3 pins for in an XLR connector?
- Pin 1: Pin 1 is the ground/shield wire. It provides a reference point for pins 2 and 3 and may also connecting to ground at the microphone and/or mic input. On top of that, pin 1 also acts as cable shield, protecting pins 2 and 3 from electromagnetic interference.
- Pin 2: Pin 2 is the hot/positive wire. It carries a copy of the audio signal in positive polarity. In the case of a microphone connection, it carries the positive mic signal from the microphone to the connected mic input.
- Pin 3: Pin 3 is the cold/negative wire. It carries a copy of the audio signal in negative (reverse) polarity. In the case of a microphone connection, it carries the negative mic signal from the microphone to the connected mic input.
So the microphone outputs its audio signal with equal amplitude on pins 2 and 3 (relative to pin 1) but with opposite polarity. One would think that this would simply cancel the audio signal out. However, this is part of the cleverness of balanced audio. Let’s continue in with our signal path.
These twinned audio signals travel through the balanced XLR cable and are sent to next audio device (let’s continue with our example of our audio interface).
The mic input of any audio interface will likely have a built-in microphone preamplifier. Within a microphone preamplifier, which expects mic level balanced audio signals, there is a differential amplifier.
The differential amplifier sums the differences between the audio signals on pins 2 and 3 of the balanced XLR cable. This effectively doubles the amplitude of the mic signal while ridding of any similarities between pins 2 and 3. This is referred to as common-mode rejection.
Common-mode rejection (CMR) is an effective method of eliminating any electromagnetic interference (EMI) the XLR cable experiences along its length. Though pins 2 and 3 are well isolated, there is still potential for EMI (radio frequencies, 60 Hz hum, etc.) to affect the mic signal. CMR helps eliminate this interference and allows for extremely long cable runs without significant signal quality loss.
For more information on microphone signals and analog audio signals, check out my article What Is A Microphone Audio Signal, Electrically Speaking?
Another big reason professional microphones have widely adopted the XLR connector is that XLRs provide protection from electrical damage. They do so by having pin 1 (ground/shield) always connect first while pins 2 and 3 connect simultaneously.
For this protection, it is critical to ensure your XLR cables are wired properly and not damaged.
So how does this protect microphones from electrical damage? Let’s first look at why and how electricity is sent to microphones.
Active microphones require external power in order to function. When dealing with active mics with XLR outputs, this external phantom power is most often supplied with phantom power.
Phantom power is +48V DC on pins 2 and 3 (relative to pin 1) that is sent from a mic preamp (like the preamp within our audio interface example) to a microphone in order to power its active circuitry.
Microphones that require phantom power are designed to accept and utilize this DC voltage on pins 2 and 3 (relative to pin 1). Similarly, most microphones that do not require phantom power (some vintage dynamic mics have issues) are designed to block the DC voltage on pins 2 and 3 (relative to pin 1).
Electrical shorting issues would arise if pin 2 was connected before pin 3 or vice versa. Similar issues would arise if pin 1 (ground) was not connected before pins 2 and 3. XLR solves this with its design. XLRs connect pin 1 first, followed by pins 2 and 3 simultaneously, protecting our microphones from electrical damage and allowing for safe and effective phantom powering.
For more information on phantom power and ribbon microphones, check out my article Will Phantom Power Damage My Ribbon Microphone?
Note that +48V DC on both pins 2 and 3 does not affect the mic signal at all, which is where the term “phantom” came from. This is again, due to the cleverness of the aforementioned balanced audio.
Note also that other balanced lines do not provide the same amount of protection. Tip-Ring-Sleeve (TRS), for example, is a common balanced audio connection (and is even used with some cheaper consumer mics), but does not provide the same protection. In fact, multiple shorts happen as a TRS plug is inserted into a TRS jack.
Speaking of TRS and other balanced lines, let’s get into the other (non-XLR) microphone connectors.
Other Microphone Connectors
Though 3-pin XLR is the most common connection for professional standalone/non-integrated microphones, there are many other microphones connections. They are:
- Other XLR patterns.
- Phone connectors.
- Multi-pin circular connectors.
- Many others.
Other XLR Microphone Connectors
Though 3-pin XLR is the most common connection for professional microphones, other variations of the XLR connector are also used for microphones. For example:
- 4-pin XLR: A standard for headsets (2 pins for the mono headphone signals + 2 pins for the unbalanced microphone signal). Also used with broadcast mics that have an LED on/off air light.
- 5-pin XLR: These connections are the standard for stereo microphones (1 common ground + 2 balanced audio signals). Stereo mics that output 5-pin will come with 5-pin to dual 3-pin XLR adapters. 5-pin XLRs are also used with stereo headsets (3 pins for the stereo headphone (left, right, and ground) + 2 pins for the unbalanced microphone signal).
- 6-pin XLR: Used with stereo headsets with a balanced microphone (3 pins for stereo headphone + 3 pins for balanced microphone signal).
- 7-pin XLR: A method for connecting some tube condenser mics to their power supplies, carrying signal, polarization voltage, heater and HT.
For more information on 5-pin stereo microphones, check out my article Do Microphones Output Mono Or Stereo Signals?
USB Microphone Connectors
USB microphones have been increasing in popularity. Their digital outputs via USB allow for quick and easy “plug-and-play” with computers and digital audio workstation softwares.
For more information on digital USB microphones, check out my article Are Microphones Analog Or Digital Devices? (Mic Output Designs).
Phone Microphone Connectors
Whereas XLRs are the most common connectors for professional-grade microphones, phone connectors are the more common type with consumer-grade microphones. Phone connectors for microphones come in the following sizes and arrangements:
- 2.5 mm Tip-Sleeve (unbalanced)
- 2.5 mm Tip-Ring-Sleeve (balanced mono or unbalanced stereo)
- 3.5 mm Tip-Sleeve (unbalanced)
- 3.5 mm Tip-Ring-Sleeve (balanced mono or unbalanced stereo)
- 1/4″ Tip-Sleeve (unbalanced)
- 1/4″ Tip-Ring-Sleeve (balanced mono or unbalanced stereo)
Multi-Pin Circular Microphone Connectors
Multi-pin circular connectors are screw-on connectors that have been used with microphones. There are no standardized wiring designs for these multi-pin connectors and models range from 2 to 8 pins. Multi-pin connectors are uncommon, but are usually found with lavalier/wireless transmitter combinations.
Other Microphone Connectors
There are many other microphone connectors that have either neither risen to popular use or have become obsolete.
Also, there are many integrated microphones (like in cell phones, laptops, etc.) that are connected directly within the circuitry of the electronic device they are designed into.
What does XLR stand for? XLR stands for X Latching Resilient. The XLR cable was invented by Cannon Electric Company and the first edition was called the Cannon X connector. After adding a latch (L) and resilient neoprene/rubber (R), the connector was named “XLR.”
What is unbalanced audio? Unbalanced audio is audio carried via one signal wire that carries the audio and one ground wire that acts as a return and ground. It is relatively noisy (susceptible to EMI) and incapable or running long lengths. Unbalanced audio is most often carried via TS, RCA, and TRS-stereo connections.