Originally Posted by eljr
someone just suggested to me,
"Power cables that effectively produce an improvement in sonic performance can be doing one or more of the following:
More efficiently transferring the desired power frequency (i.e. 50 or 60 Hz)
Filtering out undesired higher frequency line noise
Providing additional capacitance which provides a larger power reserve"
can this effect measured responses?
OK, I'll answer these specifically:
1) More efficiently transferring the power? OK, purer copper and heavier gauge wire can do this. But what is the percentage of improvement? If I have a generic 12ga power cord and try an audiophile power cord with 0.001% purer copper, how much is the wattage capacity increased? Keep in mind most power cords are only 6 feet long. Moreover when these claims are applied to a CD player that consumes 30 watts of power, it's even more silly. And you still have the 50 to 100 feet of 12 or 14ga wire in the wall back to the breaker panel. The chain is only as strong as it's weakest link.
2) Noise filtration? Yes, some high end power cords do have built in filtering, multiple shielding, made with jackets that reject RFI. But as stated above, most gear already has simple but effective line filtering built in. In fact with switch mode power supplies this is mandatory to keep the power supply noise radiated back into the line suppressed. And if all that's not enough, They, the reputable cable manufactures like Belden, do make shielded power cords that cost up 100% more. So that $2 power cord will now cost you 4-8$ if shielded.
3) Power cord storing energy? As noted above by several folks, that can't happen with AC. And in fact the charging and discharging cable capacitance 60 times a second actually wastes power albeit an infinitesimal amount at 6 feet. And even if you could store AC, well lets assume it's 120v DC, how much capacitance does a power cord have? Even if you made a power with very high capacitance of several thousand pf per foot, how much energy is that going to hold? It would be miniscule!
There is an EE around here, JNeutron, that specializes in EMC theory and practice. He has shown that a power cord may affect the audio performance by altering ground return currents. I agree in principle but these effects are very small and random, most people don't have these issues in a simple system. And he was also careful to point out the differences are merely that. It does not mean the more expensive cord is better, if fact it could easily make a ground loop problem worse. His point is that in some cases a power cord can make a sonic difference. But cost and perceived value if the product are not a factor.