I don't know why people in here keep saying that a standard stereo 1/8" headphone connector only has two metal sections, or that the tip is not used, but they are wrong.
The tip is the left channel (or the mono channel in a mono connector, which is the one with only two metal sections). The ring section is the one next to the tip, and carries the right channel. The sleeve is the third part, and carries ground for both channels (or the mono channel in a mono connection).
There are 4 conductor 1/8" connectors for audio use, which have a seperate ground for each channel, but the new headphones have a 3 conductor connection, so the extra wire must be for something other than audio out.
The fact that when in use as a mic, the left channel of the headphone works is because a mono mic uses a mono connector, which corresponds to the left (tip) and sleeve (ground).
The tip is the left channel (or the mono channel in a mono connector, which is the one with only two metal sections). The ring section is the one next to the tip, and carries the right channel. The sleeve is the third part, and carries ground for both channels (or the mono channel in a mono connection).
There are 4 conductor 1/8" connectors for audio use, which have a seperate ground for each channel, but the new headphones have a 3 conductor connection, so the extra wire must be for something other than audio out.
The fact that when in use as a mic, the left channel of the headphone works is because a mono mic uses a mono connector, which corresponds to the left (tip) and sleeve (ground).