Audio frequencies are a much more limited band than RF and it can be intuitive to look at a simple hardware consideration. Such as your speaker's voice coil, w

Audio frequencies are a much more limited band than RF and it can be intuitive to look at a simple hardware consideration. Such as your speaker's voice coil, which is a fairly low-resistance length of thin copper wire commonly wrapped around a hollow paper core an inch or two in diameter and enameled in place. The paper form is cemented to the center of the suspended speaker cone, with the coil itself free to move back & forth within the matched gap of the speaker magnet. When the audio signal (which is a series of waves, therefore an AC voltage) comes in on the wires, the coil moves the cone in response to the signal. DC voltage is not allowed to pass to this kind of speaker since DC would just displace the cone in a single direction for the duration of DC voltage application. But when you measure the resistance in Ohms of an individual _8-Ohm_ speaker, it is always less than 8 Ohms, sometimes between 6 & 7 Ohms because regular Ohmmeters are measuring DC resistance using a DC battery inside the Ohmmeter as a reference. The DC resistance of the coil is no different than it would be if the whole coil was unwound, it basically depends on the length of the wire and the diameter of the wire, similar to the way precision wirewound resistors are available for lower Ohm service. Thinner wire and longer wire has higher resistance to current flow. But when audio is passing through the coil alone in free air, IOW no magnetic or ferritic core is present, there will be slight additional resistance to the audio AC (over and above the fundamental DC resistance measurable with the regular Ohmmeter), simply because of the wire being shaped into a coil. This total working resistance to AC is what is referred to as impedance. When a ferritic or magnetic core is in place, there will be that much more of a challenge for the audio signal since it needs to then reverse polarity against the inertia of the magnetic material at whatever frequency it happens to be operating at. This magnetic bump in AC resistance is significant and causes a nominal 6-Ohm-resistance speaker to operate as a characteristic 8-Ohm-impedance audio load. Speakers do work really well with much higher than 8-Ohm voice coils, provided a matching amplifier is available. Practically this is not done since the speaker wires from the power amplifier to the speakers in a high-power system would then be required to carry audio AC voltages as dangerously high as the line voltage coming in to the amplifier. So using the everyday low-impedance speakers we are stuck with, a slightly poor connection having an extra 1-Ohm of unwanted resistance, due to corrosion for instance, will result in that connection dissipating a significant percentage of the power passing through it, as heat, in many cases accelerating a corrosive source of power loss.