The gauge of a conductor depends on the load impedance, the length of cable required and the amount of power loss tat can be tolerated, and there are also relationships between voltage, resistance, current, and power. All defined by the Ohm’s law.
A speaker cable job is to move an electrical current’s substantial amount from a power amplifier’s output to a speaker system. The current needed to drive a speaker is much higher than the instrument and microphone cables. An example, 8-ohm speaker with a 100-watt amp will have 3 ½ ampere of current. Meanwhile a 600-ohm input driven by a line-level output only pulls about 2 milliamps. The output voltage of the amplifier, divided by the load impedance, determines the current amount pulled by the load. Current flow are limited by resistance, decreasing it increases current flow. If the output voltage of the amp remains constant, it will give twice as much current to an 8-ohm load as it will to a 16-ohm load, and 4x as much to a 4-ohm load. Halving the load impedance doubles the load current.
An example, two 8-ohm speaker with parallel connection will draw twice the current of one speaker, the parallel connection reduces the load impedance to 4 ohms. To make it easier to understand we are using the term resistance and impedance interchangeably, actually a speaker with 8 ohms nominal impedance may have a voice coil DC resistance of about 5 ohms and an AC impedance curve that ranges from 5-100 ohms, depends on the frequency, and the environment’s acoustical loading.
