How Does a Microphone Work?
Table of Contents
What is Microphone and How it Works
A microphone is an essential part of any performance or event. Not only that, but a microphone is also used in broadcasting, filming movies, music production, creating video content on YouTube, and so much more. Microphones are a crucial part of our lives and yet, most of us don’t really think about how microphones work.
In this article, we’ll take a deeper dive into how microphones work, and how the different types of microphones convert sound energy into electrical energy.
The Science of Sound Recording
A transducer is a device that converts one form of energy into a different form of energy. A microphone is a type of transducer, converting mechanical wave energy into electrical energy. In this case, microphones convert sound waves (mechanical wave energy) into audio signals (electrical energy.)
Before we get into the mechanics of how a microphone transducer converts energy, let us first define the two energies: sound waves and audio signals.
Sound Waves and Audio Signals (Mechanical Wave Energy and Electrical Energy)
A sound wave is a type of mechanical wave that’s defined by the pattern of disturbance of particles within an elastic medium. In simpler terms, sound waves (acoustical energy) are a type of energy that’s released when an object vibrates. The acoustic energy travels from its source through a medium, like air or water. When sound waves come into contact with our eardrums, our brains translate them into an audio signal.
An audio signal is the representation of sound, typically using either a changing level of electrical voltage for analog signals. They can also be a series of binary numbers for digital signals. An audio signal can be words or music, signals that we can understand.
Different types of microphones have different ways of converting energy but they all have one thing in common: the diaphragm. In a microphone, the diaphragm is a thin piece of material (such as paper, plastic, or aluminum) that vibrates when sound waves hit it. Typically, the diaphragm is located in the head of the microphone. When the microphone diaphragm vibrates, it causes other components inside to vibrate as well, and then these vibrations are converted into an electrical current, becoming the audio signal.
Do you know another device that is technically the opposite of a microphone? A loudspeaker. As microphones take in sound and put out audio, on the other end of the audio chain we have the loudspeaker, which works in reverse — it converts the incoming electrical energy into sound waves that we can hear. While they look nothing alike – microphones have a protective metal grille meant to reduce wind and pop sounds while loudspeakers have speaker cones that are generally from paper, plastic, or light metals — both a microphone and a loudspeaker almost have the same key components.
Both the loudspeaker and the microphone have a coil of metal wrapped around or, sometimes in front, of a magnet. In loudspeakers, electricity courses through the coil, creating a magnetic field. The magnetic field acts on the magnet, causing the coil to move. The diaphragm moves back and forth along with the coil as well, causing air motion, and delivering sound.
Microphones also have an electrical characteristic called impedance. They are measured in ohms and depend on the design. In more simple terms, it controls the flow of the audio signal. Low impedance microphones have fewer than 600 ohms, medium impedance is considered between 600 ohms and 10k ohms, while high impedance is above 10k ohms.
Most professional microphones are low impedance, with about 200 ohms or lower. They are more preferred than high impedance ones as using a high impedance mic with a long cable will result in loss of high-frequency signal. High impedance cables also tend to pick up more hum and possibly radio-frequency interference.
How Does a Microphone Work Step by Step?
As we mentioned earlier, there are different types of microphones out there but they all follow the basic principles of capturing sound. We’ve written an article that talks in-depth about the different types of microphones but for this article, we’ll only be focusing on dynamic microphones and condenser microphones.
How Do Dynamic Microphones Work?
A dynamic microphone is usually the go-to mic when it comes to loud environments. They convert sounds into an electrical signal via electromagnetic induction. They can be further divided into two categories: moving-coil dynamic microphones and moving-ribbon dynamic microphones.
A moving-coil dynamic microphone is versatile and ideal for general usage. This is the type of microphone that usually comes to mind whenever a person hears the word ‘microphone.’ A moving-coil microphone is robust, typically inexpensive, and resistant to moisture, making them extremely ideal to be used on-stage. They are also suited to handle close-up vocals, certain musical instruments, guitar amps, explosions, and more.
Based on the name, moving-coil dynamic microphones have a wire coil, magnet, and a thin diaphragm to capture the audio signal. The diaphragm is attached to the coil. When the diaphragm moves in response to incoming sound waves, the coil moves back and forth past the magnet. This creates the electrical current in the coil, channeled from the microphone along the wires.
As for moving-ribbon dynamic microphones, they are generally more fragile than their moving-coil counterparts. They see more usage in studios rather than the stage. Ribbon microphones have a mellow sound and a vintage tone to them. Brass instruments, guitar cabinets, and other aggressive sources work well with a ribbon microphone.
Similar to the moving-coil microphone, a ribbon microphone uses induction as well. However, instead of a coil, ribbon mics make use of a pair of thin corrugated aluminum, hence the term ribbon, that is stretched between pole pieces above a permanent magnet. Ribbon microphones work when the ribbon moves back and forth as the sound waves hit, generating an electrical current that flows through the microphone.
In summary, here is how a dynamic microphone works:
- Under the wire mesh of a dynamic microphone is its capsule and membrane.
- The back of the membrane is attached to a coil of wire.
- Both the diaphragm and coil move back and forth according to the incoming sound waves.
- The coil is placed inside a magnetic field. When it moves, an electric signal is induced.
How Do Condenser Microphones Work?
Condenser microphones are also referred to as capacitor mics, drawing from the term ‘capacitor’ which is a device that stores energy in the form of an electrostatic field. Compared to dynamic microphones, condenser microphones tend to be more sensitive and responsive.
This makes a condenser microphone useful for capturing intricate details and subtle nuances. Since condenser mics are highly sensitive, they are not optimal for work that involves high sound pressure as they can cause overload distortion in some mixers and microphone preamplifiers.
A capacitor has two metal plates near each other. Condenser mics have two metal plates as well; however, one of the plates is made of a very thin, light, flexible material that acts as the microphone diaphragm. The diaphragm then vibrates in the presence of acoustical energy (sound wave), changing the distance between the plates, which then, in turn, varies the capacitance. These changes are then picked up by the sound recording device.
Unlike dynamic mics, condenser microphones need an external power supply or phantom power to work. Back in the day, a condenser microphone relied on external power supplies or cables to operate. However, these days, it is more common to see condenser microphones running on phantom power.
Labeled as P48 or +48 V on some audio equipment, phantom power is called that way as the supply voltage is effectively invisible to microphones that don’t require its usage. Phantom power is supplied directly from the microphone input on a mixer, console, or audio interface instead of the standard XLR cable.
To summarize, here’s a step by step of how a condenser microphone works:
- Sound waves that are created carry the energy (vibrations) towards the windscreen of a microphone.
- The diaphragm can either be small or large, acting as a very thin membrane that is electrically charged, and behind it is a fixed backplate. Together, they form a capacitor.
- When the sound hits the membrane, the capacitance changes. Since the two plates are attached to each other, both of them move, creating a magnetic field. The magnetic field converts the change in capacitance into an electric signal. This output signal is basically the proportional representation of the change in the diaphragm’s default position.
- The electrical signal that the microphone just created streams out to the sound recording device. You have now successfully changed an original sound into electricity. You can save the sound you have created or use an amplifier and a loudspeaker to make your sound energy louder.
How Do Other Microphones Work?
We went into detail about how dynamic and condenser mics work. Other microphones essentially work in the same way. Here are a couple of examples of how the technicalities of other mics work:
Carbon Microphone
Let’s start with the carbon microphone. Back in the day, before vacuum tube amplifiers became popular, carbon mics were the only way to obtain high-audio signals. Carbon mics worked by having carbon granules pressed between two metal plates. A voltage across these plates would then cause a current through the granules. These mics were also used as amplifiers as they could boost weak signals, sending them down the line. However, they were mostly abandoned with the development and rise of vacuum tube amps.
Contact Microphone
Next are contact mics. A contact mic uses specific materials that respond to mechanical vibrations as opposed to air vibrations. These mics are only concerned with the sound that travels through objects or structures.
Wireless Microphone
A wireless microphone works to convert sound into audio in the same way a wired microphone does. A wireless transmitter is what makes a mic wireless. It takes the outputted mic signal and embeds it into a single-frequency radio signal. It then sends it wirelessly to a compatible receiver. This technology is applied to wireless microphones such as radio mics and lavalier mics.
Intercom
One interesting thing is an intercom. We’ve established beforehand that microphones and loudspeakers are just the reverses of each other. However, thinking about it, an intercom functions both as a microphone and a loudspeaker. Generally, an intercom is used to both hear and speak to someone in a different room. Intercoms usually have handsets with a number of simple buttons, and their function as a loudspeaker or a microphone depends on which button is being pressed.
On a basic intercom, one person will push a button to talk, and the microphone part of the device will be utilized. When the button is released, the same device will function as a loudspeaker. For example, person A pressed the button on the intercom to speak to person B who is in another room. The incoming sound wave is converted into electricity flowing into the other end.
As soon as the energy reaches the loudspeaker, it is converted back into a sound wave. The moment the other person B releases the button for the loudspeaker function and presses the mic button, the process is then reversed, with the electric current traveling through the copper wire.
On the other hand, wireless intercoms have no cables to utilize. They instead rely on invisible radio frequencies which carry the signal that enables all other wireless devices to operate. While intercoms are handy to have, their major problem is that they mostly have poor sound quality, which is what usually happens when a device tries to provide opposite functions.
Bottomline
Mics are such an important part of our lives, whether we use them on stage, or plugged into our computers, or used to capture different media. While microphones may vary in type and some of them are powered using different technologies, all of them have the same goal. All microphones convert our voices and music into electrical currents for the rest of the world to hear.
Frequently Asked Questions
Which is better, a dynamic microphone or a condenser microphone?
There is no direct answer to this as the better microphone between the two depends on how you will use them. Dynamic mics are great for loud environments, live vocals, guitar cabinets, snare and kick drums, and the like. Condenser mics are ideal to use in situations such as studio recording, detailed sounds, acoustic instruments, ambient noise, and more.
What are microphone polar patterns?
Microphones have a property called directionality. Also referred to as polar pattern or pickup pattern, this describes the mic’s sensitivity to sound from a variety of directions. Omnidirectional mics pick up sound evenly from all directions. On the other hand, a unidirectional microphone picks up sound predominantly from one direction. Bi-directional mics pick up sound equally from two opposite directions. Meanwhile, a microphone with a cardioid polar pattern captures sound mostly from the front, the sides to a lesser extent, and minimally from the rear.
Can I make my own microphone?
If you don’t have an actual mic, you can make your own using a regular earbud. All you have to do is to plug the earbud headphones into a microphone socket. With this, you have essentially reversed the function of earbuds from being a loudspeaker and turning it into a mic.
Do note that it may not work on your computer even though it works with audio equipment. It’s trial and error with computers. You may be able to get it to work by adjusting the sound settings on your device.
What are electret condenser microphones?
An electret condenser microphone is a type of condenser mic that comes with a permanent charge built into it. Due to the permanently charged plastic element (electret) placed in parallel with a conductive metal backplate, electret microphones don’t require an external power supply. This allows the powering method to be distributed more effectively to other resources inside the electret mic, such as the impedance converter, printed circuit board, and other active components.
Without the need for a high-supply voltage, electret microphone technology can be found in cell phones, laptops, mobile recorders, and video cameras as they are devices that work on low battery voltage. Some less expensive studio mics also use electret condenser capsules.
