# Signal in the wire of headphones

Normally what kind of signal flows through the wire connecting the headphone jacket and the headphone?

I wonder whether there is a standard regulating them. And what wavelength, volts, watts, amps, noise acceptable.

• Audio ones, usually. As for the other things, no standard, wavelength is meaningless at audio frequencies (about 50km!), volts/watts/amps all depend on the headphones power rating, and noise is whatever the person that made them could get away with. – Tom Carpenter Feb 21 '16 at 2:42
• Usually there's a "volume control" that lets the wearer adjust the loudness (sound pressure level), so the output voltage is not regulated by a standard -- it's adjusted by the user. How much voltage amplitude produces how much perceived loudness at the listener's eardrum, depends on the headphones themselves as well as the signal frequency and the condition of the individual listener's cochlea. – MarkU Feb 21 '16 at 5:02

In terms of standards, I'm not aware that there are any (someone correct me if that is wrong). There are nominal voltage levels which range from $500\mathrm{mV_{pk}}$ to as much as $2\mathrm{V_{pk}}$, and they can be AC coupled, but beyond that will depend on the manufacturer.
As for wavelength, well, a $4\mathrm{kHz}$ signal has an electrical wavelength of about $50\mathrm{km}$, so it's not really a concern :)