Twisted pair circuits, such as those that carried plain old telephone service lines, always needed an appropriate multi-phase power source so that they wouldn’t attract the kind of noise associated with mismatched loads. Anybody who remembers the old campaigns about long distance systems that were so clear you could hear somebody drop a pin understands why this is so important. Engineers today might not give as much thought to these kinds of considerations, since POTS devices have largely gone digital, but the actual feeder lines that support these digital systems still need a multi-phase power source to eliminate the possibility of crosstalk.
Audio circuits are still analog as well, especially when it comes to making an electrical waveform that actually feeds into a loudspeaker. Wireless public address systems might seem as though they’re immune to this consideration, but the proverbial last mile still has to be managed via amplitude modulation. Any two electromagnetic waves who have corresponding pieces occurring at the same time are more or less in phase with each other even if they technically exist on separate wavelengths.
Calculating the speed of particular waveforms can help when attempting to install a multi-phase power source. Each wave is determined by both the frequency and wavelength of said structure. Plugging known figures into the equation v=?v is normally enough to figure out what kind of power source is necessary for any given application. Technicians who have to install standard speaker wires will want to make sure that they don’t select any frequencies that could potentially get picked up in the process.
