How loudspeakers and microphones use vibrations
Physics · Key Stage 2 · The School
A microphone catches a vibration
Inside a microphone is a tiny, thin surface called a diaphragm. Sound waves hitting it make it vibrate, exactly like your eardrum does. That vibration is turned into a changing electrical signal, which can be sent down a wire, recorded, or made louder — but it all starts with the diaphragm physically moving.
A loudspeaker does the reverse
A loudspeaker takes an electrical signal and turns it back into sound. Inside it is a cone attached to a coil of wire. The changing electrical signal makes the coil push and pull against a magnet, and the cone vibrates in exactly that pattern. The vibrating cone pushes the air, and that becomes the sound you hear.
Two devices, opposite jobs
A microphone turns real sound into an electrical signal. A loudspeaker turns an electrical signal back into sound. They are almost mirror images of each other, both built around something that can vibrate. That is why a loudspeaker can even work backwards as a very rough microphone if you shout directly into it.
Someone shouts near a microphone at one end of a hall. The diaphragm inside the microphone vibrates with the sound and creates a changing electrical signal. Wires carry that signal to a loudspeaker at the other end of the hall. Inside the loudspeaker, the same changing signal makes a cone vibrate, pushing the air exactly as the original shout did. Nobody at the far end heard the actual sound waves cross the room — they heard a fresh vibration, created by the loudspeaker, carrying the same pattern. That fresh vibration is what a loudspeaker actually does.