I am about to buy Pure Note power cable for my Krell equipment and they told me that length DOESN'T matter, so I'm going with the 3-ft length. The answer may be cable dependant.
On some powercords like the filled Shunyata cords it makes a bigger difference than say the Electraglides or Synergistic. We have experimented with many powercords and on every single brand that we tried a super long powercord it was better than a short one - - marginally. But for the costs difference it was just not worth it. Plus, where do you stick all the excess?
Some cords use specific geometries to achieve "filtering action". As such, altering the length can change the amount of total capacitance or inductance of the design which in turn alters the amount of "filtering" taking place. That would explain why a shorter cord ( less filtering ) might sound slightly inferior to a longer cord ( increased filtering ) cord. This assumes that the cords DID have some specific design and type of attenuation built into them. Otherwise it would not matter one iota other than the potential for greater series resistance and voltage drop with a longer cord. Sean
For all audio applications, shorter is better. For IC's, speaker cables, digital cables and power cords. For power cords and speaker cables, inductance is the parameter to be minimized and it increases with length.
If you are using the cable as a tone-control, then none of the above applies. But doing this guarantees that you will never get an accurate reproduction of the original performance.
Audioengr, are you trying to say that a highly capacitive cable design becomes more inductive as you lengthen it ? I am having a REAL hard time following your statements both here and on AA. Either we are having a REAL hard time communicating our ideas or we have some phenomenally different ideas about things. Seeing that i have primarily agreed with most of your findings in the past, i'm wondering what kind of stumbling block we've recently run into with PC's.
When it comes to power cord design, my goal is to remove everything but the original 60 Hz sine wave that was generated by the power supplier and minimize the transfer of noise from conductor to conductor or conductor to ground. I "think" that this is your goal also but i'm not sure given our recent "debates". Sean
What I am saying is that all cable designs become more inductive as you lengthen them. The inductance per foot does not change, just the total inductance. Just as all cables add capacitance as they get longer.
Designs that have very low inductance tend to have higher capacitance per foot, due to coupling between the conductors.
My goal is to minimize the inductance in a power cord. I dont believe in filtering-out high-frequencies because this puts impedance in the way of transient currents, which must flow unimpeded. Particularly bad for power amps. Some filtering may make sense for line-level and digital components.
Okay, now i can better understand where you are coming from. I was thinking along the lines that you would want to start off with a very low inductance design to begin with. If the inductance truly is negligible, the increased length and commensurate amount of capacitance involved with a longer cord would outweight the small increase in inductance. Overall, i think that we are on the same page and just phrased things differently.
My experience is that, in order to reproduce a specific frequency and the majority of its' harmonics in reasonable fashion, you need to have appr 10x that frequencies bandwidth. In other words, in order to pass a 1 KHz signal linearly and preserve the harmonic content to a great extent, you would need a bandwidth that was at least 10 KHz wide. Anything less than this and you get phase shifts occuring in band. This would allow you to hear the primary source ( 1 KHz ) and up to / including the 3rd harmonic untouched. Anything above that frequency ( in terms of harmonics or "noise" ) would be attenuated. A gentle slope above that point should be fine. If one wanted to be "extra careful", you could go to 20x the primary frequency. This would leave you very well covered in terms of not disturbing the harmonics or introducing phase shift and be able to use a sharp slope for greater filtration purposes.
As such, a 60 Hz signal ( which is what we are "modulating" out of the wall ) would require a bandwidth that was linear up to at least 600 Hz into the component. If one were to choke off anything WELL above that range via a PLC or filtered cord, i don't see any way that it could audibly effect what we hear or limit the amount of current available at the much lower 60 Hz primary. That is, so long as the components used in the filter were not current limiting or suffering from saturation at any point in the operating curve.
I think that we run into problems with PLC's because the filter slopes create phase shifts within the audible band-pass or are limited in terms of passing enough power on dynamic demands. I have not pulled apart enough PLC's to actually study the circuitry and hinge freq's, but i do know that most of them make use of inductors that either use too small of a gauge of wire, too small of a ferrite core, a poor choice of materials for the ferrite core or a combination of all of the above.
Any thoughts on those observations / comments ? Sean
As far a power cords are concerned, I dont pay much attention to the fact that the voltage is a 60 Hz sinusoid. I pay more attention to the di/dt of the current, of which the spectrum can contain very high frequencies. This is what any inductance in the cord will impede.
As for speaker cables, we are definitely on the same page. I believe that extremely small phase shifts in the audio range (2-5 degrees at 20kHz) can be audible. This is why cables with 1 MHz bandpass sound so good. However, I am also proponent of band-limiting the speaker cable to 1 MHz or so. This is to attenuate natural resonances that are in the 10's of MHz. In a really low-loss, high-bandwidth cable, these resonances can sustain themselves for long peiods. I believe the result can become audible with most amps. I must be doing something right, since the reviewers really like my speaker cable.