How do wired headphones produce sound if they don’t need to be charged before using them?
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Well, there are actually several “layers” of “Does it get power?”. Here’s how they all work.
A speaker is a coil of wire and a magnet. When electricity runs through the coil, that makes a magnetic field that moves the magnet. That pushes some material that makes pressure waves in the air and that’s the sound you hear. For very simple wired headphones, only the electricity the device sends through the wire is needed to make them work. You can make surprisingly good sound with very low amounts of power.
Fancier wired headphones don’t work very well without an “amplifier”. That just means they have heavier magnets or other characteristics that don’t work well with the tiny amount of electricity that’s normally sent up the wire. The “amplifier” is a small device that usually does some audio processing on the signal *and* adds more output voltage for the headphones. Amplifiers are powered by batteries or some other power source, since they add energy. So this sort of means those headphones use the amplifier like a power supply.
Wireless headphones need their batteries for the circuits that receive audio data. They still use a little bit of that power to “drive” their speakers, but the bulk of the power is spent on those other circuits.
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