system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does my speaker system make a noise every time I touch the tip of the auxiliary cord with my finger or some other object?
gpt
A speaker generates sound by moving a magnet up and down at a certain frequency to generate a certain pitch. How the magnet moves up and down is determined by the voltage sent to the speaker.

Voltage is the measure of electrical potential. Any potential is measured relative to something else. The potential energy stored in a bowling ball held on top of a skyscraper differs if you set the reference point to the floor below or to the ground.

Thus, the voltage controlling the speaker is set relative to ground which is set to zero volts. When your cord is plugged in, the ground is properly set to a fixed value. The signal connection is changed relative to ground to generate a difference in voltage to drive the speaker.

However, when you unplug cord, the ground and the signal of the speaker is now undefined. Luckily, because the two lines are in close proximity, they act as an antenna and receive the same random signals in the air. Since the speaker only senses the signal **relative** to ground or signal minus ground, these two cancel out.

When you put the end of the tip to your skin or some other object, you are setting the signal to some voltage while the ground voltage is still undefined. this produces a "jump" in the voltage which manifests as a noise in your speaker as the magnet jumps to the indicated position. You will hear a similar "jump" when you remove the tip from the object since the voltage is jumping back to the original state.

This is only destructive to the speakers if you touch the tip to something high voltage which will "blow" the speaker by pushing the magnet in the speakers to a position it cannot recover from.