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If you use headphones with a TRS connector, you might also have noticed that if you plug it into your music player and pull it out halfway, the music sounds strange. It seems as if there are some frequencies missing. Why is that?

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I once had a possibly similar experience when I forgot to connect the speakers' ground in an amplifier. You then get just the difference between the two stereo channels. If you extract the connector ground is probably the first to be cut. Depending on the mixing some parts of the signal (some frequencies) may be placed in the center of the stereo image, and those will be filtered out.

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But if ground is deconnected, why does it produce any sound at all? – Max Ried Apr 8 '12 at 9:04
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Because there's still a voltage difference between both channels, though much lower. With the two speakers in series between (their grounds are connected, just not to the system's ground) this difference there will be a current path, hence sound. – stevenvh Apr 8 '12 at 9:16
OK, so same audio on both leads to same voltage level for both channels, zeroing the sound out? – Max Ried Apr 8 '12 at 9:22
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Yes, if the audio is mono you wouldn't hear a thing. – stevenvh Apr 8 '12 at 9:26

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