Sound turned into electricity and back
How Does a Voice Travel Down a Wire?
A telephone does not send your voice anywhere. It sends a copy of the wobble, and builds a new voice at the other end.
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Step 1 of 5
A voice is moving air.
Nothing else leaves your mouth. Copy the pattern and you have copied the voice. Speaking pushes the air in front of your mouth into a fast pattern of squeezes and stretches. That pattern is all a listener ever receives.
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Step 2 of 5
A microphone copies the pattern into electricity.
A thin sheet moves with the air, and its movement changes an electrical current in step. The current now has the same shape as the sound did.
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Step 3 of 5
Electricity carries the shape, not the sound.
Nothing audible travels down the wire. What travels is a wobble in a current, which happens to be the same shape as the wobble in the air.
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Step 4 of 5
A speaker runs the process backwards.
The arriving current drives a coil in a magnet, which pushes a cone, which pushes air. The listener hears a new sound built to the same pattern.
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Step 5 of 5
Modern calls send numbers instead.
The wobble is measured thousands of times a second and sent as numbers. Numbers survive copying perfectly, which is why a digital call does not hiss the way an old one did.
A telephone deliberately throws away the highest and lowest parts of your voice. It only carries the narrow band that speech needs, which is why music sounds so bad down one.
The short version
A telephone copies the shape of a sound into electricity, sends that shape down a wire, and builds a fresh sound at the far end.
Try it yourself
Hold a balloon against a speaker. You can feel the pattern the cone is pushing into the air.