Are Microphones Input Or Output Devices?

To fully understand microphones, it's critical to comprehend how audio works in terms of inputs, outputs, and signal flow. When working with computer audio, it's critical to understand the system's input devices and output devices.

Are microphones input or output devices? When a microphone is connected to a computer (via an audio interface or another analog-to-digital converter), it sends/inputs information into the computer. This means microphones are input devices. Digital mics with built-in headphone amps that receive info from computers are input/output devices.

This may be a bit confusing, so we'll go through full definitions of what input and output devices truly are. We'll also talk about the possible inputs and outputs of a microphone without the framework of a computer system.

Be sure to check out My New Microphone's article How Do Microphones Work? (The Ultimate Illustrated Guide)!

Related articles:
• Are Headphones Input Or Output Devices?
• Are Speakers (& Studio Monitors) Input Or Output Devices?

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What Are Input And Output Devices And Why Are Microphones Considered Input Devices?

Before we get into the details regarding microphones as input devices, let's define what input and output devices are.

What is the difference between an input device and an output device? An input device sends/inputs information to a computer system, while an output device receives/reproduces information outputted by a computer system. Think of the computer I/O (input/output) when determining whether a device is an input or output device.

With that definition, we understand microphones to be input devices. A microphone converts sound waves to audio signals, which are then converted to digital audio data and sent/inputted into a computer.

Microphones typically output analog audio signals (AC voltages) that require conversion to digital data to be compatible with a computer. That means that, by our definition of an input device, a mic signal must be converted to digital data before that microphone can truly be considered an input device.

Analog-to-digital conversion of a microphone signal may happen in a variety of ways:

• Audio interface (hub)
• Audio interface (adapter)
• Digital microphone

Audio Interface (Hub)

Audio interface (hub): Hub-style audio interfaces are the most popular type of audio interface and provide the most common method of connecting a microphone to a computer.
One or more microphones can be inputted into the audio interface (depending on the design). An interior analog-to-digital converter (ADC) converts the analog signals into digital data, which are then inputted to a connected computer via USB, FireWire, Thunderbolt, etc.

Hub-style audio interface example: Focusrite Scarlett 2i2:

Audio Interface (Adapter)

Audio interface (adapter): Adapter-style audio interfaces are a much less common method of connecting a mic to a computer.
These interfaces typically have one input (analog mic signal), a simple ADC, and one output (digital audio data). These adapters usually connect to a computer via USB.

Adapter-style audio interface example: Shure X2U

To learn more about audio interfaces and microphones, check out the following My New Microphone articles:
• What Are Audio Interfaces & Why Would A Microphone Need One?
• Best Microphone Audio Interfaces

Digital Microphone

Digital microphone: Digital microphones (commercially sold as USB mics) have internal ADCs and output digital data directly from the microphone body. These mics connect directly to a computer via USB.

Digital USB microphone example: Blue Yeti:

For more information on USB, analog and digital microphones, check out the following My New Microphone articles:
• How Do USB Microphones Work And How To Use Them
• Are Microphones Analog Or Digital Devices? (Mic Output Designs)

All of this is to say that microphones are inherently designed to be input devices. Still, their signals need to first be converted to digital data to truly become input devices to computer systems.

For more information on connecting microphones to computers, check out my article How To Connect A Microphone To A Computer.

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The Input And Output Of A Standalone Microphone

So we've discussed what input and output devices are and what makes a microphone an input device. Now let's talk about the inputs and outputs of a microphone by itself (without thinking about a computer system).

Let's start by defining a microphone. A microphone acts as a transducer, converting mechanical wave energy (sound waves) into electrical energy (audio signals). There are many types of microphones with many methods of converting sound waves to audio signals, but this is the basic purpose of a microphone and is suitable for our discussion.

Electrically speaking, microphones are designed to only output electrical audio signals (in the form of AC voltages, aka audio signals). Microphones are not designed to receive any audio signals (more on this later).

That being said, some microphones require electricity in order to function properly. Note that this does not mean they require audio signals. It simply means they require electricity (in the form of a DC voltage) to power their internal circuitries or to polarize their microphone capsules. Again, this is not part of the signal flow or inputs/outputs but is worth mentioning as an aside.

For more information on microphones, mic signals, and electricity, check out my article Are Microphones AC Or DC Devices?

As for inputs, microphones are not designed to receive any analog (AC voltage) or digital audio signals.

Instead, microphones react to the sound waves (changing sound pressure level) around their diaphragms. This mechanical wave energy is the “inputted information” of a microphone. Again, this mechanical wave energy is neither an analog nor a digital signal.

So in terms of signal flow, microphones (in their intended design) can be summed up in the following two points:

• Microphones only output signal: Microphones transduce sound waves into electrical audio signals which are then outputted from the microphone's output connection. A caveat here is that digital USB microphones have internal ADCs and so they output digital audio data rather than analog audio signals. Mics are the beginning of a signal flow line.
• Microphones are input devices: Microphones send/input data into a computer system for processing. Of course, the microphone audio signals must first be converted to digital audio before being inputted into a computer.

Notice that, thus far, I've been talking about the intended design of a microphone. In the following section, I'll be discussing the potential for microphone signal flow to be reversed.

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Microphones As Speakers

Microphone design is actually very similar to loudspeaker design, particularly the design of moving-coil dynamic microphones.

The capsule of a moving-coil dynamic microphone is designed with a diaphragm that has a cylindrical coil of conductive wire attached to its rear. This coil sits in a cylindrical space without touching magnets to its interior and exterior. As the diaphragm moves in reaction to sound waves, so does the conductive coil. As the coil moves through the magnetic field, an electrical audio signal is created via electromagnetic induction.

The vast majority of loudspeakers are designed similarly, only in reverse and at a larger scale.

A loudspeaker has a large coil of conductive wire, which receives electrical audio signals. This coil is attached to a large diaphragm and sits in a cylindrical space within a larger magnet (designed to occupy space in the interior and exterior of the coil). As AC voltage is sent through the conductive coil, electromagnetic induction causes the coil to oscillate within the magnetic field, pushing and pulling the loudspeaker diaphragm and emitting sound waves.

So then, what's to stop us from using loudspeakers as microphones and vice versa?

• Moving-coil dynamic: In the case of moving-coil microphones and loudspeakers, all we would need to do is reverse the signal flow.
• Condenser: In the case of condenser microphones and electrostatic loudspeakers, we would need to reverse the signal flow while still maintaining a constant polarizing charge on the condenser capsule/diaphragm.
• Ribbon dynamic: In the case of ribbon mics and ribbon loudspeakers, we would only need to reverse the signal flow. Ribbon designs are also dynamic and work on electromagnetic induction. Ribbon microphone diaphragms are very sensitive and so I wouldn't advise attempting to send an audio signal to a ribbon mic.

For a guide to turn your speaker into a microphone, please click through to my article How To Turn A Loudspeaker Into A Microphone In 2 Easy Steps.

The point here is that microphones can be output devices if the signal flow dictates it. Of course, microphones are not designed to be loudspeakers, and the result would be lacklustre. However, it is totally possible to force a microphone into being an output device!

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Related Questions

Are headphones without microphones input or output devices? When talking about computer I/Os, headphones without microphones are output devices. When plugged into a computer, headphones receive information that has been outputted from the computer.

Are headphones with microphones input or output devices? When talking about computer I/Os, headphones with built-in microphones are both input and output devices. The headphones are output devices since the computer sends/outputs information to them. The built-in microphones are input devices since they send/input information into the computer.

Related article: Are Headphones Input Or Output Devices?