ESP said:
High Mechanical Integrity Cordage Construction. A/C power cords handle a signal which oscillates in a regular sinusoidal pattern. This oscillation coupled with the close proximity of the conductors can cause vibrations in the cable. The idea of vibrations in electronic components which handle a/c power should come as no surprise to the learned audiophile. This fact is gaining wider recognition, and is being addressed by an increasing number of High End audio electronic equipment manufacturers. One is likely familiar with a practice employed by a number of manufacturers where the transformer is physically isolated from the "signal carrying" electronic circuitry by putting it in a separate chassis. For the record, transformers vibrate at harmonic frequencies of the a/c current; which is 60hz in North America. Typically, the second harmonic or 120hz is strongest. These vibrations are caused by a fundamental law of physics which states:
Parallel conductors carrying current in the same direction will attract each other; in opposite directions they will repel each other.
The assertion that the conductors in power cables vibrate with alternating current passing through them piqued my interest. I was certainly aware that parallel current carrying conductors will have some force between them but I'd never considered that the conductors in an AC cable might physically vibrate because of it, mainly because I've never observed it, even in cables carrying hundreds of Amps. When I read the above statement, I got my electromagnetics textbook out and ran some numbers. For AWG14 with 1mm insulation in a cable, you're looking at 2mm of separation (at a minimum). At that separation, for 2m of cable, the maximum force exerted between the conductors is about 4.1mN (0.009lbs) @15A of current. Each conductor weighs 10x that, exclusive of the insulation, so it's not really very likely to physically vibrate, especially within the constraints of the cable jacket and the twisting of the conductors. So I put it to the test.
I got a very sensitive accelerometer from the fluids lab, connected a 2m 18AWG IEC cable (which would have
more force between the conductors than 14AWG owing to less separation) to a 6Ohm, 1000W power resistor and the other end to a 30A variac. I checked for vibration at currents from 1A-15A. The results? Nada. No indication of any vibration at all. At 15A, the cable began to heat up noticeably and the power resistor started to crackle so I backed off. I put the accelerometer on the variac and it showed a nice sinusoidal vibration pattern at 120Hz from about 5A and up even though I couldn't feel the variac vibrating until I got to 12A. At 60V/10A the voltage drop was 2.5V across the cable, so about 25W I^2R loss and a cable resistance of 0.25 Ohms.
At any rate, there's no evidence that power cables physically vibrate, not even asking the question: "so what consequences are there if they do?"
This is the kind of thing the high end cable folks do: Find solutions to non-existent problems and pass them off as features, which is a large part of the reason that I distrust them.
And their assertion that the reason transformers vibrate is because of the forces between parallel conductors is not accurate, as I pointed out before, I think. Magnetostriction is a totally different thing.
I'm going to purchase a Musicord Pro this evening.
EDIT: Meant to say that I couldn't feel the variac vibrate until I got up to 12A.
No, I sure wasn't. I haven't read any of his books in years [EDIT: actually, I've never read any of his books ... I momentarily had him mixed up with Edward O. Wilson for some reason], and I can't say I would be able to quote a single phrase from any of them. You want to point me at this supposed quote?
