One obvious thing has been missed. If the placebo effect really exists why spoil it. If someone swares by the use of a certain power cable that makes drastic improvments to how his system sounds, then why spoil it for him.
Does my Gilmore amp sound better because I spent months building it? Possibly and subjectivly it would. Why ruin it with a double blind test.
The real point in audio is how people enjoy it. I don't care much about mathematics as long as it sounds good to me. Let me keep my placebo. Just don't tell me that in a double blind test it's identical.
/NOTE: Author of above posts does not believe power cables make a difference
