Even though the cord is short, it still contributes to the overall inductance. ROMEX has up to 10 times the inductance of good after market power cords. If the the last 6 feet of a 20 foot run to the panel is an after-market cord, it will add very little to the inductance of the first 14 feet. |
It's true that some components are designed to be invariant of the power-line voltage. Some Linn equipment is like this, particularly when switching power supplies are used. However, in most amps, the linear power supply is not even regulated, and the capacitor bank is not infinite and the inductance from the cap bank to the output transistors is not zero, so they are sensitive to the line voltage, particualrly during high-current high-frequency transients. |
Outlet quality and contact resistance is at least as important as the inductance of the power cord itself. Silver-plated brass outlets can work wonders for dynamics and detail.
Back to the question of the last 6 feet. Here are some calculations that I did to demonstrate the effect of a good 6-foot power cord:
A typical 6-foot 14 AWG rubber cord and 25 feet of ROMEX has inductance of 7.2 uH and resistance of 235 mohms, ignoring the plug resistance effect. Therefore, the voltage drop at 20kHz will be I*(wL+R)= I*(.905+.235) = I*(1.14). With a 6-foot Magnum2 and 25 feet of ROMEX, the inductance is 5.9 uH and the total resistance is 147 mohms. This is an 18% reduction in inductance and a 37% reduction in resistance. The voltage drop for this combination will be I(wL+R) = I(.741+.147) = I(.888). So at a fixed dynamic current I, the voltage drop in the entire power feed at 20kHz is 22% smaller with a Magnum2 power cord. I would consider 22% to be significant. The reality is even more compelling. When you add in lower plug and receptacle resistance and the fact that the di/dt on the power cord will have spectra well above 20kHz with some amplifiers, the low-inductance cord makes an even bigger difference. |
"It's in the very last feet that the electric particles/waveform gets shaped prior to entering the audio component. As such, there will be a profound influence on sonics."
This is nonsense and technically incorrect. Just because some saleman says does not make it true. The network created by the conductors from the transformer and then from the panel to the outlet and then from outlet to the component all contributes. You can easily perform a SPICE simulation on this simple model.
There is nothing magical about the last 6-10 feet of wire unless perhaps it has a transmission-line termination in the plug or on the cord. An added network of this sort COULD prevent/reduce high-frequency reflections or resonance on the overall wired network. Whether transmission-line effects occur and if so, whether they would affect the delivery of power is debatable and difficult to prove. |
Psychicanimal - Just because a cord makes a difference does not mean that the last 6 feet is somehow magical. It still has to do with the inductance of the entire run to the panel. The last 6 feet reduces the overall resistance and inductance compared to a typical "rubber" cord. Cryoed cables can perform well because they are lower resistance.
I make cords myself and you can see all of the measurements, analysis and theory on my website:
http://www.empiricalaudio.com |
Bwhite wrote:
"Make sense?"
Not to me. In fact, IMO mechanical resonances account for very little that is audible in most systems. Certainly if you put your components on a thin steel shelving unit, you might get some mechanical resonance effects, but most systems do not experience this. If anything, the electrical resonance of longer cables has a more pronounced effect. You are taking the snake-oil literature out there too seriously. Here are some papers that are not snake-oil:
Technical Papers and Audio FAQ at:
http://www.empiricalaudio.com |
Bwhite wrote:
"Here are quotes from Audioengr's "Technical Papers" - seems he is contradicting himself in claiming that resonance is for the most part not audible"
No contradiction. If you take the time to read the paper, you will see that I am talking about ELECTRICAL resonance, not mechanical resonance. I have extensive measurement and simulation data on this effect proving that it is real.
Mechanical resonance is a second-order effect at best. Electrical resonance is more of a first-order effect.
As for your metal outlet covers, I beleive that you are experiencing the placebo effect. There is no scientific explanation as to why this should make any difference whatsoever. Resonance requires a high-Q system, which this is not. Even if the outlet cover resonated, what electrical effect could this possibly have? |
Nikkidanjo wrote:
"Basically, I don’t by the filter part unless some form of RF filter was deliberately added."
Agree 100%, power cords should not be filters, particularly on power amps.
The best analogy is that the pressure in the outlet of the pipe is the indicator of performance. If the pipe is 2" diameter for 25 feet and the last 6 feet are 6" in diameter, this will yield a much higher pressure at the outlet than if the pipe were 2" diameter the whole length. This is what happens when you add a low-inductance 6 foot cord to a 25 foot high-inductance wire in the wall. It really does work. |
"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."
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 susceptability to crosstalk from nearby EM or magnetic fields. It does not help with mechanical resonance.
"It may be a long wait before technology is developed that "proves" how some power cords work in our systems. Having heard significant improvements with several power cables, I don't intend to wait for a piece of paper telling me what I already know is true."
What is wrong with the analysis I just did above? It proves conclusively that lower inductance power cables reduce impedance to current flow by 22% or more in a typical home scenerio. Do you not understand the analysis? |
"I intend to purchase a couple of plates next time I visit Home Depot. Worse case I return them a few weeks later."
I cannot believe that you guys are inventing your own "snake-oil". Best of luck.
I have tried my best to actually do the science to prove which effects are significant with all types of cables. This is significantly more than 99% of the cable manufacturers do. I even publish the experiments and the results. Evidently the public is hard-pressed to read this and understand the significance. |
Albertporter - something just occurred to me form waht you said. I do not mean to kick a dead-horse, but since you say that the 2-channel system is affected when the subs are plugged-in, but not turned-on, I suspect a ground-loop may be at fault. Usually these cause hum, but not always. One way you can test this hypothesis is to leave the subs on and plugged-in , but disconnect the IC's to both subs. If this has the same improvement effect as unplugging power to them, then it is definitely a ground-loop at fault.
If this is the case, the cleanest solution to this is either to unground both subs with AC cheater plugs or run isolation transformers to one or both subs. |
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. |
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. |
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 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. |
