How do microphones work? | Types of microphone compared (2024)

• Home
• A-Z index
• Random article
• Timeline
• Teaching guide
• About us

You are here:Home page >Communications >Microphones

by Chris Woodford. Last updated: May 30, 2023.

Sound—energy we can hear—travels only so far before it soaks away into the world around us. Until electrical microphones wereinvented in the late 19th century, there was no satisfactory way tosend sounds to other places. You could shout, but that carried yourwords only a little further. You couldn't shout in New York City andmake yourself heard in London. And you couldn't speak in 1715 andhave someone listen to what you said a hundred years later! Remarkably, such thingsare possible today: by converting sound energy into electricity andinformation we can store, microphones make it possible to send thesounds of our voices, our music, and the noises in our world to otherplaces and other times. How do microphones work? Let's take a closer look!

Photo: Above: This Samson Meteorite is a typical studio-grade professional microphone that hooks up to your computer for podcasting or other high-quality audio recording. Technically, it's a condenser microphone and picks up sound in a cardioid (heart-shaped) polar pattern. The protective metal grille is meant to reduce wind and pop sounds. Microphones like this turn incoming sound into outgoing electricity.Below: Loudspeakers, like this, work the opposite way to microphones, converting incoming electrical energy into outgoing sound.

Microphones are loudspeakers in reverse

Microphones look very different from loudspeakers so most people never realize how similarthey are. If you've read our article on loudspeakers,you'll already know how microphones work—because they're literally loudspeakers workingin reverse!

In a loudspeaker, electricity flowsinto a coil of metal wire wrappedaround (or in front of) a permanent magnet. The changingpattern of electricity in the coil creates a magnetic field all around it thatpushes against the field the permanent magnet creates. This makes thecoil move. The coil is attached to a big flat disc called a diaphragmor cone so, as the coil moves, the diaphragm moves too. The movingdiaphragm pushes air back and forth into the room and creates soundwaves we can hear.

In a microphone, there are almost identical parts but they work in exactlythe reverse way.

Types of microphones

Photo: A typical BBC-Marconi ribbon microphone used for radio broadcasts from about the mid-1930s. (I photographed this in the Think Tank science museum in Birmingham, England.)

All microphones turn sound energy into electrical energy, butthere are various different kinds that work in slightly differentways.

Dynamic microphones are just ordinary microphones thatuse diaphragms, magnets, and coils—"loudspeakers in reverse," aswe've already seen. Condenser microphoneswork a slightly different way, capturing sound with the moving metal plates of a capacitor (an electric-charge storing device). Ribbon microphones pick up sound with a strip of metal ribbon that vibratesbetween the poles of a magnet.

Most microphones are omnidirectional,which means they pick up sound equally well from any direction. Ifyou're recording something like a TV news reporter in a noisyenvironment, or a rare bird tweeting in a distant hedgerow, you'rebetter off using a unidirectional microphone that picks upsound from one specific direction. Microphones described as cardioid andhypercardioid pick up sounds in a kind of "heart-shaped" (that'swhat cardioid means) pattern, gathering more sound from one directionthan another. As their name suggests, you can target shotgunmicrophones so they pick up sounds from a very specific locationbecause they are highly directional. Wireless microphonesuse radio transmitters to send their signals to and from an amplifier orother audio equipment (that's why they're often called "radio mics").

Photo: The Blue Yeti is a popular podcasting microphone. It works using the condenser (capacitor) principle and can be set to pick up sound in four different ways: cardioid, omnidirectional, bidirectional, and stereo. Photo by Taylor Phifer courtesy of US Air Force and DVIDS.

How microphones work

How does a microphone turn sound energy into electrical energy? Like this:

Dynamic microphones

1. When you speak, sound waves created by your voice carry energy toward the microphone. Remember that sound we can hear is energy carried by vibrations in the air.
2. Inside the microphone, the diaphragm (much smaller than you'd find in a loudspeakerand usually made of very thin plastic) moves back and forth when the sound waves hit it.
3. The coil, attached to the diaphragm, moves back and forth as well.
4. The permanent magnet produces a magnetic field that cuts through the coil. As the coil moves back and forth through the magnetic field, an electric current flows through it.
5. The electric current flows out from the microphone to an amplifier or sound recording device.Hey presto, you've converted your original sound into electricity! By using this current to drive sound recording equipment, you can effectively store the sound forever more. Or you could amplify (boost the size of) the current and then feed it into a loudspeaker, turning the electricity back into much louder sound. That's how PA (personal address) systems, electric guitar amplifiers, and rock concert amplifiers work.

Condenser microphones

If you remember that "condenser" is an old-fashioned word for a capacitor, you can probably guess how a condenser microphone works: much like a capacitor!

1. Incoming sound waves carry energy into the front of the microphone.
2. The sound waves hit a flexible diaphragm, which is actually one of the plates (charge-storing metal elements) of a capacitor.
3. As the diaphragm vibrates, it moves closer to or further from a second, fixed backplate.
4. The changing distance between the two plates changes their capacitance (charge-storing ability). The microphone converts this into an electric current that corresponds exactly with the original, changing sound waves.

Ribbon microphones

Ribbon microphones (like the BBC one in the picture up above) use a thin vibrating ribbon of lightweight metal that moves between the poles of a magnet instead of a diaphragm and coil. Old-fashioned broadcasting microphones from the early days of radio worked like this—and some modern microphones still do:

Artwork: How a ribbon microphone works. A pair of crimped ribbons of aluminum foil (blue) are stretched between the pole pieces (green) above a permanent magnet (orange) and move back and forth as sound waves hit them, causing an electric current to flow in the cables (brown) attached to their ends. The yoke (yellow) closes and concentrates the magnetic field. Artwork from US Patent 2,113,219: Microphone by Harry F. Olson and Frank Massa, RCA, April 5, 1938, courtesy of US Patent and Trademark Office (with colors added for clarity).

How do intercoms work?

Intercoms are used as baby monitors and in those desktop gadgets that allow bossesto speak to their secretaries (or vice versa). The simplest kind of intercom has twohandsets in different rooms connected together by a length of coppercable stretching between them. Each handset contains a loudspeaker—and a couple of push buttons. The loudspeaker functions as either a microphone (absorbing sound) or a loudspeaker (giving outsound) depending on which person wants to talk.

Let's suppose Annie (the boss) and Bob (her secretary) are in neighboring rooms. Bobwants to alert Annie that it's time for a meeting so he presses theintercom call button. Annie's intercom beeps so she presses her"talk" button. The loudspeaker on her handset now functions likea microphone. She talks into it and the sound energy produced by hervoice is converted into a fluctuating electric current that travelsdown the wire to Bob's intercom. When the current flows into Bob'sloudspeaker, it gets converted back into sound waves and Bob hearsAnnie's voice. When Annie's done with talking, it's Bob's turn. Hepresses his "talk" button and now the intercoms reverse theirfunctions. Bob's loudspeaker now works like a microphone, capturinghis voice and turning it into an electric current that flows backdown the cable to Annie's office. Annie's handset is now functioningas a loudspeaker and reproduces the sound of Bob's voice.

In the ship's intercom shown below, the same device works as both the loudspeaker and the microphone. There's a PTT ("push to talk") button that you press when you want to speak that turns the device into a microphone. If the button isn't pressed, it works as a loudspeaker. The sound quality isn't too good, though, and that's one of the big drawbacks of simple intercoms: one device can't do a great job as both a microphone and a loudspeaker—there's some compromise involved.

Photo: A simple intercom being used onboard a ship. Photo by Carlos M. Vazquez II courtesy of US Navy andDVIDS.

Photo: Emergency telephones on trains, in elevators, and in public places are usually simple intercoms. There's a single loudspeaker/microphone with a button to press to attract someone's attention. When the button is pressed, the intercom functions as a microphone and transmits your voice. When you release the button, the intercom switches to a loudspeaker so you can hear what the person at the other end has to say in response. An intercom like this is much harder to break or vandalize than an ordinary telephone handset, so it's particularly suitable for use in public places.

Wireless intercoms

From a scientific viewpoint, these simple intercoms are the most interesting: theyteach us that loudspeakers and microphones are opposites. From a user's viewpoint, there are other kinds of intercoms you might prefer to use. Some have both microphones and loudspeakersin each handset so two people can talk simultaneously. Wireless intercoms are more likewalkie-talkies (short-range radio sets) and have no awkward cablesto tangle up or get in the way. Still others plug into householdelectricity outlets and send their voice signals round the householdwiring instead of using a wire cable of their own. (That means theyoperate a little bit like broadband over powerlines or BPL.)

Photo: A wireless baby monitor intercom. There are two separate units that communicate via your home powerlines and normally you'd use them in different rooms, but I've put them alongside just to take the photo. The "baby" unit on the left contains the microphone (and a nightlight). The "parent" unit on the right contains the loudspeaker and also lights up when sounds are heard. Because sounds are transmitted directly from one unit to the other, there's no need for any cumbersome wiring between the two.

Make your own microphone!

Photo: Using an ordinary earbud as a microphone.

Don't have a microphone? What we've just learned about intercoms suggests you can make your own very simply—just by plugging a pair of earbud headphones into your microphone socket and talking into them!

This neat little trick should work with audio equipment, but it won'tnecessarily work on your computer. That's because your earbuds are wired into a stereo jack plug, while your microphone socketwill be wired for mono input (and your computer's internal sound card will most likely be mono too). But give it a go and see. You may need to adjust your sound card properties in your control panel or sound settings. If you're lucky, you'll find one of the earbuds works as your microphone while the other doesn't do anything (because of the mismatch between the stereo plug and the mono socket). I plugged my earbuds straight into my computer's mic socket and got a perfectly reasonable audio input into Skype running on Windows, but I couldn't get sound playing through Windows Sound Recorder. If you want to record stereo sound on your computer with a microphone, your best bet is to use an external sound card (such as a Griffin iMic).

More microphone activities

These great websites go into more detail about making your own mic:

• Telephone Handset Microphone by Randofo. How to make a retro carbon microphone for the digital age.
• The Stealth Mic: Bill Byrne explains how to turn a pair of earbuds into a simple but effective binaural microphone.
• Build Your Own Microphone Pop Screen: This one involves building a simple screen out of pantyhose (tights) to improve the quality of microphone-based sound recordings.
• The Ear and the Microphone by Joseph D. Ciparick, The Science Teacher, Vol. 55, No. 9 (December 1988), pp. 46–47. A simple classroom demonstration of how microphones turn vibrations into electric currents... using little more than a beaker of salt water.

Sponsored links

Don't want to read our articles? Try listening instead

If you'd rather listen to our articles than read them, please subscribe to our new podcaston Apple Podcasts, Spotify, Audible, Amazon, Podchaser,or your favorite podcast app, or listen below:

Find out more

On this website

• Electricity
• Energy
• Headphones
• Loudspeakers
• Magnetism
• Piezoelectricity
• Sound

Other websites

• Lloyd Microphone Classics: A super website charting the history and development of microphones, including a gallery of popular microphones from the USA, UK, Japan, Germany, and other countries. Now offline, sadly, but here is the archived version from the Wayback Machine.

Books

Please note that these are highly technical guides, not well suited to beginners.

• Handbook for Sound Engineers by Glen Ballou (editor). Gulf Professional Publishing, 2015. A huge (1700-page!) reference for professional sound engineers covering the theory of acoustics, electronic components used in audio systems, and practically every aspect of sound recording, both indoors and outdoors. Heavy emphasis on theory.
• The Microphone Book by John Eargle. Focal Press, 2012. A detailed review of how microphones work, the various different types, and applications (mostly focusing on broadcasting and studio use).
• Professional Microphone Techniques by David Miles Huber and Philip Williams. Mix Books, 1999. A practical guide to placing and using microphones for recording a wide range of different musical instruments.

Articles

News

• Insect Ears Inspire Superefficient Microphones by Charles Q. Choi. IEEE Spectrum, May 22, 2023. Small, 3D-printed microphone parts are much more energy efficient.
• What Would You Do With a Waterproof MEMS Microphone? Listen to Whales, of Course by Tekla Perry. IEEE Spectrum, December 23, 2016. The unexpected applications of an underwater piezoelectric microphone.
• How to Set Up Your Own Podcast Recording Studio by J.D. Biersdorfer. The New York Times, September 9, 2016. Basic advice on microphones and software for podcasting.
• Graphene-Based Microphone Could Let You Hear Like a Bat by Dexter Johnson. IEEE Spectrum, July 7, 2015. Sonic scientists at the University of California, Berkeley develop an ultrasound microphone that uses graphene in place of the traditional diaphragm.
• The BBC's ornate 'royal microphone' from the 1930s revealed: BBC News, February 2011: How the British Broadcasting Corporation (BBC) made super-deluxe microphones for the King of England.
• Birth of the Microphone: How Sound Became Signal by Matthew Shechmeister. Wired, January 11, 2011. A fascinating look at the early history of microphones, from Emile Berliner's carbon-button of 1877 to instruments like the RCA 77, popular in the 1940s.
• Fly Lends an Ear to Microphone Design byPeter Weiss, Science News, Vol. 160, No. 23, December 8, 2001, p. 359. How the tiny design of a fly's coupled eardrums inspired a new approach to microphone design.

More technical/scholarly

• Choosing the right microphone by Jim Edwards, The Choral Journal, Vol 21 Number 3, November 1980. A more detailed technical introduction to microphones from a specialist at Electro-Voice.

Please do NOT copy our articles onto blogs and other websites

Articles from this website are registered at the US Copyright Office. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties.

Text copyright © Chris Woodford 2008, 2023. All rights reserved. Full copyright notice and terms of use.

More to explore on our website...

• Communications
• Computers
• Energy
• Engineering
• Environment


• Gadgets
• Home life
• Materials
• Science
• Transportation

• Home
• A-Z index
• Send feedback
• Random article
• Timeline
• Teaching guide
• About us

↑ Back to top