how can a line cord affect frequency response ?

i have personally auditioned over 10 different manufacturer's line cords. i hear differences. i don;'t understand how a line cord can affect treble response or bass response.

can someone provide an explanation ?
I was joking about the "negative feedback power cord", because of the past history of what happened in measurements to product that end in audio amplifiers during the 70's and 80's.

I'm actually pleased that you are interested in doing things to help us understand what we want to know.

I only qualify that with the hope that the tests are done in such a way as to ensure that past mistakes are not repeated.
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I'm glad that you are looking at ways that could advance what we know about testing audio products, and making those tests as relevant as possible to the real-world operating conditions of the products.

I feel that doing those kinds of tests, and even coming up with newer test protocols to accomplish this would get us further toward the truth about what we test and hear.

While I've been accused by others(not you) of being "unscientific", I actually have no beef with science. I only want the tests to be as accurate as possible in determining the outcome, so that we can ensure as far as possible that no incorrect conclusions are drawn from the tests, as has happened in the past.

My aims are to reveal as much truth as possible, and not obscure it.
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. . . and now blazingly-fast pop-psychologist--MRT volunteers unrequested mental health referral services at no-extra-charge to TVAD. Most magnanimous indeed for a Renaissance man of so exalted a stature! Oddly enough, after the awesomely creative diagnosis of choleric distemper, he is not offering unflappable TVAD his own services for a more regular cycle of counselling sessions. Or is he perhaps not confident in his own therapeutic prowers?