How do microphones work? I just do not get it.
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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
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