Impedance is a measure of opposition that an electrical circuit presents to the flow of alternating current (AC) . In audio, impedance refers to the resistance when talking about AC, like in the case of audio signals. It is measured in ohms and is the opposing force presented by a circuit to the flow of alternating electrical current once a voltage is applied. Impedance can affect anything that electrical audio signals pass through, including the highly-conductive copper wire inside many audio cables.

Impedance is especially important when it comes to powering headphones or speakers because youll get the most efficient (and safest) transfer of electrical power by matching your playback device to an amplifier that complements its impedance. For instance, passive speakers have a load impedance, which represents the electrical resistance and reactance they present to the amplifier.

All audio electronics have combinations of resistors, capacitors, and inductors connected in circuits, along with active components like transistors or valves which provide amplification or act as switches. To make life slightly easier for ourselves, we often consider the total resistance of a complex circuit involving resistors, capacitors, and inductors as a composite lump, and thats what we call the impedance.

In summary, impedance is a measure of opposition that an electrical circuit presents to the flow of alternating current, and it is important in audio because it can affect the sound coming out of our own audio devices.