How do microphones work? I just do not get it.
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The sounds we hear are vibrations of air molecules. The pitch of those sounds relates to the frequency of those vibrations. Microphones have a lightweight sheet in them that easily starts to vibrate with the vibrations in the air. The sheet is attached to a magnet, (or a coil of wire) which also starts to vibrate.
Around this magnet, there’s a really long coil of very thin wire. Whenever a magnet moves inside a coil of wire, (or a coil moves around a magnet) an electric current is induced into that wire. In a microphone, that current is very small, so the wire is connected to an amplifier which reads the current and makes it stronger while keeping its frequency untouched.
We can then take this current and feed it to a speaker or a recording device.
Fun fact, speakers are reverse microphones. Sound waves vibrate a magnet in a microphone which generates a current. A current vibrates a magnet in a speaker which generates sound waves.
At their simplest sound waves (literally just air moving) hits a diaphragm that’s connected to a coil. This is next to a magnet. As the air pushes the diaphragm at certain frequencies, the diaphragm moves the coil at those frequencies. The coil moving back and forth in relationships to the magnet changes the electrical signal, which is carried down the wires to whatever input.
edit: i think it’d be more accurate to say generates a current rather than changes the signal.
edit2: and funny enough that’s just how electric guitars work. The pickups are coils with magnetic fields that are affected by the metal strings vibrating. And speakers work in the reverse way, starting with the signal and going to a diaphragm.
The simplest ones work inversely to speakers. Sound waves in the air collide with a paper cone and so cause it to vibrate. This moves a cool of wire relative to a magnet, which generates tiny electrical currents. These are amplified and measured, and voila you have a signal that you can store and play back or whatever.
The trick is precisely balancing the cone, isolating it from eg ground vibrations, and getting enough sound energy into it.
There are two main types of microphone, broadly speaking: Condenser and Dynamic.
In a dynamic microphone, the sound captured ‘wobbles’ a magnet up and down a coil. An electrical signal is created by this movement that copies the ‘shape’ of the sound the same way a camera captures the shape of what’s in front of it.
In a condenser microphone the same effect is achieved with a super thin sheet of metal placed really close to another sheet of metal. As the sound captured ‘wobbles’ the thin sheet of metal, it gets closer and farther from the second sheet of metal. This can be turned into an electrical signal that looks like the ‘shape’ of the sound.
A speaker is a paper cone attached to an electromagnet which can make it move. When moving, it creates sound waves that we can hear.
Conversely, if we make sound waves, it could move the paper cone a little bit. This in turn creates a tiny bit of energy through the electromagnet. We can measure this and convert it to digital sound.
Sound is just waves of pressure in the air. Pick up something flat and wave it at your ear like fanning yourself and you can hear the air thumping against your ear.
A microphone has a strip of flexible material that moves when the air pressure hits it (hold a thin piece of paper in front of your face and breathe in and out – note how it moves with the change in air pressure). The flexible piece of material has a magnet taped to the back, so the magnet moves with the material. If you put a loop of wire near a magnet, the movement of the magnet produces a bit of electrical current. The electrical current is higher the farther the magnet moves (greater air pressure change / louder sound), and it has the same frequency as the movement. The microphone simply converts the mechanical force of sound waves into waves of electrical current.
I’ll go and actually say how I’d explain it to a 5yo.
Sound is just air vibrating at some speed. A microphone uses a membrane with a magnet that moves when vibration of the sound hits it, and a wrapped coil of wire, because magnets moving through coils cause eletricity to appear in the coil. There’s also a different type of microphone that uses two thin sheets of metal foil + electricity flowing from one to the other when vibrations hit them, instead of magnets. Bottom line is – microphones are devices that vibrate because the air vibrates, and that vibration is then translated to electricity also „vibrating” in that same way.
sound travels through the air in waves. picture two people holding two ends of a slinky toy. one person pushes and pulls their end back and forth really quickly. you’ll see waves travel to the other side. this is a very close to what the air would look like as sound waves travel through it. (but air is invisible so we can’t see this)
waves are just anything that oscillates. that’s just a fancy word that means something that goes back and forth in some way over and over. when you speak, your vocal chords vibrate back and forth. it’s equivalent to pushing and pulling the slinky. instead of a spring like the slinky, in the case of speaking, the air is what the waves travel through. air is compressible, meaning you can squish it or stretch it. inside a car tire, it’s squished, and up where airplanes fly, it’s stretched really thin, to the point where it’s not enough oxygen to breathe. the sound waves are just the air being squished and stretched over and over, sending ripples through the air.
when the waves hit your ears, they’re basically just like the air vibrating, and your ear drums convert this to the sound we hear in our heads. speakers do the same thing as your vocal chords.
you can make a magnet by wrapping wire around metal (that contains iron), then running electrical current through the wire. the stronger the voltage, the stronger the magnet that this creates. if you reverse the current (like you switch the + and – on the battery and the coil of wire), the magnetic field reverses. a speaker cone is like your vocal chords. it’s what moves to create the waves. it’s attached to a coil of wire that sits very close to a strong magnet. the magnet is attached to the body of the speaker, and the coil of wire is attached to the speaker cone, which is able to move. remember I said waves are just things that go back and forth. an electrical analog audio signal is just a wave of voltages that go high and low. by high, I mean higher voltage. by low, I mean below zero, into negative voltages. so when the signal goes high, the voltage gets high, and the coil creates a strong magnetic field, and it tries to push away from the magnet inside the speaker, and this moves the speaker cone outwards. when the signal goes low, it goes to a negative voltage, and like I mentioned earlier, if you reverse the voltage, you reverse the electrical field. this causes the coil’s magnetic field to reverse, so now it’s attracted to the magnet and pulls the speaker cone back down. this happens hundreds to even thousands of times per second.
microphones have many types, but the simplest type is the same as a speaker, but used in reverse. when you change the magnetic field around a coil of wire, it creates electrical current. so if you move a magnet back and forth right next to a coil of wire, you would see a voltage coming out of the coil of wire, positive when you move in one direction, and negative when you move in the other direction. in a microphone, instead of a speaker cone, you have a diaphragm. it’s just the same thing as the speaker cone, more or less, just a specific word for microphones. it is much lighter than a speaker cone and is very easily moved back and forth when sound waves hit the diaphragm. just picture standing in the ocean. when the waves come inland, you can feel it pushing you back to land, and when the waves run back out to the ocean, you can feel it pulling you out towards the ocean, and it does this over and over. that’s what the sound waves are doing to the diagram of the microphone. so now you have a magnet (for this specific type, there are other types that work slightly differently) and a coil of wire and the movement of the diaphragm moves the magnet and coil’s location relative to each other to create an electrical signal. the farther the diaphragm moves in or out, the higher the voltage you get from the coil of wire. (both positive and negative). but really this signal is super tiny, so microphones require an amplifier. it just takes the small signal and makes it bigger.
(magnets and coils of wire are how electric motors work, the part that spins will have coils of wires and the outside body of the motor will have alternating magnets north, south, north, south, etc, and you turn coils on, magnetic field pulls towards next magnet, then when you reverse the current, the magnetic field reverses, so now it pushes away from that magnet and pulls towards the next one. that’s how electric motors work. generators are the opposite. you spin the shaft, it spins some magnets that move past coils of wire, and that generates electrical current.
just keep in mind that these are very simplified explanations of these things, and I chose the simplest version of each thing to describe. we have much more complicated version of this stuff. like microphones that use piezoelectric effect. condenser microphones. electric motors exist that have no permanent magnets. etc
Microphones work like a speaker, but in reverse.
With a speaker, when you send a varying current through a coil that’s surrounded by a magnet, the coil will move back and forth. Attach a paper cone to the coil, and the cone will push and pull air as the coil moves. Send an audio signal through the coil which makes the coil go back and forth furiously fast, and the clobbering of air will produce sound.
With a microphone, it’s the outside sound that pushes and pulls on the cone (or usually a dome in the case of microphones), causing the coil to move back and forth against the magnet. That movement produces a tiny electrical current through the coil’s wire, and that current gets picked up by an electrical device where the signal’s either amplified to a speaker or transferred to a recording or transmission device.
Have you ever used a string and cup to talk far away? It’s the same as that but more complex. Vibrations are interpreted electronically and sent through an amplifier.
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