Why does a single speaker have two inputs?
Are they something like negative and positive channels, left and right, or something else? If they are left and right inputs, what is the use in that, as there is a single driver?
Note that I know very little about electronics and acoustic equipment.
An electronic circuit is what the name implies - a circuit. For it to work there has to be a continuous unbroken loop from the power source (in this case the amplifier) through the load (the coils in the speaker) and back to the amplifier. Hence the two wires. Without an unbroken loop no current can flow, and nothing can happen.
Another way to look at it is that the signal that comes from the amplifier is the voltage difference between the two wires. One wire on its own can't carry a signal because there is nothing to compare its voltage to.
If you're interested in audio production I would suggest that you learn some basic circuit theory. It will explain a lot of what goes on.
It's to bridge the speaker, usually it's two 4 ohm coils + - , + - . In series it gives you 4+4 = 8 , or parallel 4-4=2 ohms,
The speaker is composed by a coil that interact with a magnet. The coil itself will drive the speaker cone to produce the sound waves. The interaction is due to the magnetic field generated in the coil and the fixed one produced by the permanent magnet. In order to create a magnetic field in the coil, you have to drive some current into it, and a current needs two pole to flow through, so the reason. There are marked as "positive" ( red ) and "negative" to give a convention to the flow. If you invert the two pole the current will flow in the opposite direction, and the effect is the same to apply a phase offset of 180 degree to the signal that drive the speaker, which of course would sound weird.
it's the same as your wallplug, it's AC voltage with live and neutral wires, and volume of the sound in any microsecond is equals to the voltage of the AC live wire. it needs a neutral to compare itself to.
