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Why Expensive power Cables when Romex behind Wall?

Could somebody please help me to shed light on this?
Is there any reason I should invest in expensive power cables when there's low grade cable between my outlet and the wall? I've upgraded most other components in my systems, but I'm just not sure that spending several hundred dollars for power cables makes sense, when the cable running from my outlet to the wall costs less than $.10 per foot. Can anyone shed light on this?

Thanks!
boros
audioengr
3,282 posts
 
Albertporter wrote: "I have Soundlab Ultimate One speakers, and the brands of AC cables connected to them and to my (home theatre use only ) sub woofers make a huge difference in sound. Crazier still, disconnect the sub woofers from the wall and the performance of the Soundlab is improved. The amplifier and resulting magnetic field of the sub woofer ARE interacting with my Soundlab."

This is certainly possible. Sounds like you have a combination of magnetic field coupling and mechanical coupling from the sub. Subs put out a lot of energy that can certainly resonate the shutters and probably some component chassis. Power cords make a difference for reasons other than mechanical resonance or magnetic coupling. However, if the subs are on the same circuit as your other components, they may be causing droops in the AC line that the other components are reacting to. Sounds like a complicated problem at best. There is no way it can be diagnosed over the internet.

The thing I want to point out is that it is easy to get sidetracked from root-causing the real problem, particularly if the physics is not well understood. I have seen posters change interconnect cables over and over to solve a ground-loop problem, when the real problem is the AC power grounding.
audioengr
3,282 posts
 
Frap - I believe that resistance played a part in the added 2 feet, and inductance as well. The 16 gauge cable 2 feet long can have the resistance of 20 feet or more of 14 AWG ROMEX. It has the inductance of about 12 feet of ROMEX. So this was like adding 20 more feet of ROMEX to the circuit.

I agree with you on the air dielectric being the best, however the goal with a power cord is low inductance and resistance. This means large conductors or lots of smaller conductors that are tightly magnetically coupled. Some cords do not do this coupling well and the result is excessive stray magnetic fields. Power cords do not "pick-up" stray fields, but they do create them. If you have unshielded interconnects running side-by-side with a power cord to an amp, you might pick-up some magnetic crosstalk in the interconnect. Incidently, shielding a power cord is a bad idea, IMO, because it adds unnecessary capacitance. Typical shielding also will not stop the stray magnetic fields for the most part. You need MU metal shielding to do this.
audioengr
3,282 posts
 
Nikkidanjo wrote:
I'm not talking about mechanical resonance, I'm talking about EMI from equipment feeding back into the system through the power cord. This sort of phenomena would happen if you placed unshielded interconnects right next to your speaker wire. The output signal would then be fed back into the amp in some form.

I got what you are talking about. This is a common misconception. It can happen from power cords or speaker cables to unshielded IC's. However, power cords are part of a very low impedance circuit, which as a result of being low-impedance,is not susceptable to pick-up of RFI or stray magnetic fields. This is also the case with speaker cables. Even if they did pick-up some high-frequency noise, this would be immediately filtered by the AC transformer in the component. Power cords radiate fields, but do not pick-up much because they are low-impedance. The ferrites that are on computers, for instance are there to prevent RFI that is generated inside the box from using the ground of the power cord as an antenna. This way they pass FCC regulations. The ferrite is not there to prevent noise from entering the computer chassis. Some AC filters for PC's are useful for "surge" protection and lightning strike protection, which can damage a PC power supply. I know about this because I have been a EE for 26 years and have worked in PC design, including for Intel for 16 years.

On the other hand, if there are ground-loops created by several power cords being plugged into one or more circuits, this is an entirely different story. This ground loop makes a very nice antenna for RF or AC pick-up. Shielding these cords will have no effect whatsoever on the ground-loop unless it lowers the ground-wire resistance a bit. The only real fix is to break the ground-loop or go to balanced interconnects.
albertporter's avatar
albertporter
4,949 posts
 
Audioengr said:

This is certainly possible. Sounds like you have a combination of magnetic field coupling and mechanical coupling from the sub. Subs put out a lot of energy that can certainly resonate the shutters and probably some component chassis. Power cords make a difference for reasons other than mechanical resonance or magnetic coupling. However, if the subs are on the same circuit as your other components, they may be causing droops in the AC line that the other components are reacting to. Sounds like a complicated problem at best. There is no way it can be diagnosed over the internet.

My comments were not a cry for help, my system is pretty much full out. Please see the thread:

http://forum.audiogon.com/cgi-bin/fr.pl?vaslt&1022712214&view

I have a dedicated line for every component, including all six boxes that make up my preamp. My comments were meant to bring to light the fact that mechanical, electrical and magnetic interference all produce changes in a high end system.

The sub woofer affects the Soundlabs when there is NO signal going to it and it is sitting idle, two feet from each Soundlab. The fact that the internal amp is on creates enough problems to hear during two channel playback.

Hope that explains my point more clearly. For what it is worth, each position in my system has been tested with a dozen or more better known products.

I liked several of these, but ultimately the Purist Dominus was first choice for two channel and Proteus and Venustus for the HT system.
audioengr
3,282 posts
 
Albertporter wrote:
My comments were meant to bring to light the fact that mechanical, electrical and magnetic interference all produce changes in a high end system.

I certainly agree with this. Particular systems can have effects from all of these. What I do not agree with is that mechanical resonances are one of the most important factors in a typical system.

What might be happening with your powered subwoofer is that it might be using a class-D amplifier or a switching power supply. These can create large switching noise on the power line and create fields that can get picked-up as well. If this is the case, I would recommend using a ferrite on the power cord to each subwoofer. Have you tried this? Unless the other cables are draped on top of the subs, It is hard to believe that they are picking-up noise this way.
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