Eli5: why do wired headphones that plug into your phone never need to be charged but wireless ones do?


I thought maybe they got power from the phone but then I remembered old headphones plugged into a phone jack separate from the charging port so how come one type never needs to be charged and one does?

In: 0

Wired ones are drawing power from the phone to work, wireless ones draw power from the battery inside the wireless buds themselves, when the wired earbuds are plugged in, that’s the only time you could use it, because that’s the only time it can draw power, it doesn’t matter if it’s not from a charger port, the charger port is where the phone gets its own power from

Wired headphones to a cellphone, (like wired speakers to a stereo player) get the electric signal from the cable in an analog way, it contains both the energy and the signal.

That is enough to move the magnet&membranes in the speaker and reproduce the sound.

But for wireless speakers, the wireless signal does not transfert [enough] energy. And the headphone needs a source of electric power to : run the Bluetooth receiver/sender, and move the membrane to produce the sound.

[Edited to add remark]

Headphones are basically tiny speakers. A speaker works by having electric current vibrate a magnet attached to a diaphragm, and these vibrations are the sound you hear. In wired headphones the electric current goes straight from the device to the magnet over the wire. With wireless, the headphones are basically little computers with a tiny Bluetooth chip. The device sends a digital signal which the Bluetooth chip receives. Then the chip translates this into the current that drives the magnet. So the chip needs battery power to operate the tiny computer and generate the current. But with wired, since the current is coming over the wire and there’s no tiny computer to power, no charging is needed.

Oh boy. This is a fun rabbit hole.

Tl;dr: the sound waves from the music are converted to electrical waves and sent to the headphones down the cord to the speakers in the ear buds.

The longer version –

Do you understand how a speaker works? There are magnets in speakers. The magnets are connected to the speaker cone.

When an electrical signal is sent to the speaker, the electrical signal goes to a coil in near the magnet.

Now remember, magnets have north and south poles – Positive and Negative. When the electrical signal goes through a wire it creates an invisible electrical field. This electrical field, depending on the orientation, will attract or repel the magnet.

The magnet is attached to the speaker cone. Instead of the coil of wire moving, the magnet and the speaker cone moves. This causes vibrations in the air that we hear with our ears.

So when you put a sound wave as an electrical signal into the wire it will cause the speaker to move.

Here’s an example video illustrating how it works. https://youtu.be/CN6lmC6bgxE

When you have air pods or wireless ear buds, in order to generate the electrical signal to move the magnet you need some sort of power.

FUN FACT: Did you know that a speaker could also be used as a microphone? It may take a lot of yelling to move the speaker cone, but it can be done. The air waves would move the speaker which moves the magnet in the coil. That magnet moving in the coil of wire induces electrical current inside the coil and creates an electrical signal.

Same for computer speakers. Used to have some that just needed the 3.5mm audio jack. Others need usb. And the powerful ones need to be plugged into the wall.