One of the lessons I learned when building the world's first AC regenerator for stereo systems, the Power Plant, was the effect noise and distortion of the AC waveform had on sound. Or, better said, what effect the lack of noise and distortion had on sound. That which was bright and edgy became natural and without glare riding on the music. A quick AB with and without the regenerator was an easy test to make and the differences were immediately obvious.
So noise on the AC line equaled brightness in the music. We realized music's tonal balance was not changed, the added glare came from power line noise and increased harmonics riding on the sound, creating an edge to it. And heavy gauge power cables, with their lower surface area, tended to restrict high frequency noises entering the equipment or regenerator, thus sounding fuller, bigger and with less edge. The balance had shifted from edgy bright 'listen to me!' noise, to clean, right and 'listen to the music!' instead.
This effect is easy to demonstrate with an inline power filter. If you have one available - not the parallel types like those made by Audience, Shunyata or Richard Gray - but a series filter like those of Monster, PS Audio, or Furman (or the ferrite core I first proposed when starting this series), you can experiment easily by plugging into and out of the filter. What you will notice is a reduced sense of brightness when the filter is engaged, like what happens with lowered surface area on conductors. While instructive, this comes with a price in sound quality from the filter's increased impedance, which robs the music of life. Too much of something, executed in the wrong way, isn't beneficial.
And one thing we did not touch on is shielding of power cables. It is a subject deserving of its own series, so many angles and thoughts controlling the outcome.
I think as we end this series on power cords we can reflect on that which we have learned. Power cords make our systems sound different. Built correctly, that difference is a good thing for reducing noise and helping music blossom from the speakers. Depending on the type of power cord and system, those differences can range from barely noticeable to 'oh my gosh'.
