Why Expensive power Cables when Romex behind Wall?

Audioengr, since you singled out the following quote that I gave credit as POSSIBLY being part of the explanation of why cables sound different.

"Shielding the cables as they near this big rack of electronics may make all the difference. Perhaps the worst dirt is the dirt generated by your own system feeding back into itself. This could explain why shielding may help."

YOUR RESPONSE WAS:
Sorry, but this is technically nonsense. Ask an engineer friend whether this makes any sense. You are mixing shielding from EM fields and mechanical resonances. Shielding eliminates susceptibility to crosstalk from nearby EM or magnetic fields. It does not help with mechanical resonance.

MY EXPERIENCE IS:
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 may also be proven by placing a large shield between the sub woofer and the power supply of the Soundlab. I had Purist Audio build such a shield and among a group of six listeners the change of inserting and removing was obvious to every member, every time.

I still contend that there are many things going on in an audio system all at the same time. Any number of changes in equipment and cables can effect RF, magnetic and electrical interference. I've tested TI shield, Purist's shields, Audio Prisms wall filters, dozens of audio grade power cables and ferrite blocks purchased from Ferishield in New York.

Bottom line is they all change the sound. Some can reduce one problem while messing up something else. Ferrite for instance, is not to my liking even though it can reduce or eliminate some radio signals.

As for the wall plate that Bwhite is discussing, I never said that it was effective, only that I am open minded enough to experiment.

I don't know if you are familiar with Marigo dots. They are varying size stick on dots that are manufactured from lead and other materials.

Placing a single dot the size of a pencil eraser on the end of an electrical plug DOES change the sound. The dots work on interconnect cables, equipment faceplates and even on amps beside the speaker posts.

Since these cannot possible have any electrical properties, they are effecting the mechanical properties of the component, regardless if electrical or mechanical in nature.

Seems logical then that electrical plates could contribute to the systems performance.

Anyway, the cost of such a test is miniscule. I have many failed experiments in attempt to improve my music system, but I have also found a number of things that helped.

I think it's important to keep an open mind and experiment with a eye toward learning. Closed minds seldom learn anything new.

In my own experiments, the introduction of 2 feet of stranded 16/3 extention cord onto the end of my preamp, turntable or power amp was enough to influence the sound negatively. Keep in mind, the typical 18 awg cord supplied on equipment, has a up to 7 amp capacity. Resistance played no part in the additional 2 feet. If your speakers have at least the resolving power of an LS3/5A, anyone with an open mind should be able to hear the effects.
A simple tool called an Elfix, can eaisily demonstrate the incredible amount of stray currents surrounding A/C wire.
Shielding almost always results in degredation. The ultimate dielectric is AIR, followed by glass. Since these are all near impossible to achieve in a wire, we are stuck with compromises like teflon.
As usual, everything Albert states is true. I tend to agree with BWhite as well. My guess is the wallplates will most definitely hurt the sound if they are metal.......Frank

The reason is simple: They sound better. Have you listened to a better power cord yet?

Audioengr,
To defend my honor I must clarify my statement about shielding,
"Shielding the cables as they near this big rack of electronics may make all the difference. Perhaps the worst dirt is the dirt generated by your own system feeding back into itself. This could explain why shielding may help."
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.
That being said, I do not make any claim how this could affect the system. I'm simply offering way that I think things could happen. I did say I know just enough to be dangerous :)

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.