how can a line cord affect frequency response ?

bravo tvad,
just when I thought this thread is getting boring again...

Please, I would implore any people seeking to measure the performance of anything "audio", to at least measure it in the context in which it is used, so that we don't have the mess that occured in the past.

I noticed that a very well-meaning poster above sought to use a steady sine-wave test tone and a load resistor in his testing. Is this not what got us into this mess the first time? Doubtless, negative-feedback-equipped power cords will result!

If someone is "hell-bent" on having some numbers to "lean on", then please try to procure them in a way that is meaningful to the way the product is operated when it is in its intended use. The idea(as I see it) is to find out something useful, and not to "make it easier" for the measurer.

Personally, I think that something may come of this, and I would love to see some new measuring protocols introduced that could address this common topic of why we don't seem to be able to measure the observations that we are obviously hearing.

You can't do this "in a vacuum". It needs to be done so that it measures the things you want to find out when the product is operating in the listening environment, playing real music. "In-situ", as it were. Test tones and "dummy loads" are out of the question. It is what happens in the actual reactive environment that we need to know, and test.

"i'm a renaissance man. . ."

Oh wow, and so humble to boot!

TWL: What is a negative feedback power cord?
I also stated that music as well as test tones, perhaps used only to calibrate the measurement technique, be used.

The "dummy load" was not a dummy load across the output of the amp.
It was in series with the Hot line of the outlet, for example. I suggested this. Someone else mentioned using an inductive pickup, and while that may work fine on unshielded cables, the majority of high-dollar aftermarket PCs employ HEAVY shielding. Therefore the inductive "kick" will be attenuated if not totally reduced to noise.

If one were to pull the outlet junction box out of the wall and expose the romex, which is most likely unshielded, then the pickup can be placed appropriately.

Please note, any of this is potentially dangerous and should not be attempted by any individuals not qualified to do so.

Twl...Most of the parameters which are spec'd for audio equipment are good for verifying that the circuit is working properly, but relate only imperfectly to sonic quality. However, there are tests that one can perform which I think would satisfy your objection. One such test is to observe (by oscilloscope or by listening to it) the difference between a signal waveform going into the device and what comes out, adjusted for gain of course. This signal can be any waveform, music if you like, although other waveforms like a square wave may present more of a challenge. Note that I did not say to measure the difference, because quite disparate waveforms may have similar measurements.

For another example, if you drive two identical power amps with the same signal you should (ideally) see nothing when you measure across the two hot output terminals. Note that this can be done with real music and driving real speakers. Now put an aftermarket PC on one of the amps. If the measurement is still zero (or the same tiny number) it is safe to say that the PC did nothing. If there is a difference you could make a recording of it and play it back so you could listen to it, and form some opinion of the sonic effect of the PC.