power cables "!"

A sticky wicket it is...

Stimulus:


A customer challenged the claims:

1. "The key to success of our PowerKords is KIMBER's unique cable weave which has proven to dramatically reduce Radio Frequency Interference (RFI) already on the mains supply and to reject further pick up of RFI ...", because he believed the PowerKord cable would have little affect on conducted electromagnetic interference;""

Response:

They sent a number of magazine reviews and customer comments as anecdotal evidence.

Conclusion:
Our expert noted that, although the claim in the catalogue stated that the cable would reduce the RFI already on the mains supply and reject further pick up of RFI, the evidence sent by Russ Andrews concentrated almost exclusively on the ability of the cable to prevent new RFI. He said the research papers did not address the issue of conductive interference and did not include supporting measurements and did not appear to have been peer reviewed or have other forms of independent validation. He said one of the papers discussed the effect of RFI on speaker, rather than the mains cable. Our expert considered that the magazine articles did not provide evidence for the performance of the cables because experimental details for the perceptual measurements were not given and some of the reviews related to speaker cables and not mains cables. We considered that the testimonials represented customers' opinions and therefore did not constitute robust scientific evidence. Our expert disagreed with Russ Andrews assertion that sound quality variations were subjective and not capable of objective substantiation. He said, in the field of audio, the ABX test method was well established and probably one of the most commonly used. We considered that the evidence submitted was not sufficiently robust to show that PowerKords was proven to dramatically reduce RFI which was already on the mains supply and stop further pick up.

Result:

We concluded that the ad was misleading.

Discussion:

The AC feedline to the outlet is comprised of simple parallel run cable. As such, the characteristic impedance of the feed cable will be in the 200 to 500 ohm range.

The characteristic impedance of a braid of hot and neutral will be of the approximate form :

Zcable ~= 100/number of conductor pairs.

If 8 pairs are used in the weave, the transmission line impedance of the cable will be about 12 ohms.

Conducted RFI on a 500 ohm line, when hitting an abrupt termination of 12 ohms, will reflect most of the energy back along the line. If for example, the noise signal is a 50 volt spike, that is 100 mA of spike current....when that hits the 12 ohm impedance, it will cause a 1.2 volt spike in the 12 ohm cable... a reduction of 97.6 percent.

One could also use the reflection parameters, but my description provides a better feel for the problem.

It is therefore VERY easy to prove the customer is incorrect in his assertion.

Why was it the responsibility of Russ Andrews to provide a technical proof of this technically correct assertion?? Shouldn't it have been the responsibility of Kimber?

My analysis is a sophmore level e/m theory level one...this should have been well within the domain of any so called "Expert".

Who was this "expert", what are his credentials, and why is it an "expert" is allowed to provide undocumented proof of the fallibility of a claim without peer review???

While I in general agree with the elimination of falsehoods and inaccurate embellishments in ad copy, this example of censureship under the guise of an "engineering approach by an expert" is a very poor one indeed.

In point of fact, all the expert did was look for paperwork, without any analysis whatsoever.

This type of reaction leaves a bad taste in my mouth. People should know better.

Cheers, John
 
Honestly, anyone who spends that much money on a mains cable is NUTS!

Even if the claims are true and that it does in fact reduce RFI, could it really have a perceivable difference in sound quality? If so, enough to warrant the price tag?

I highly doubt it. It has to be considered that the power supply inside the connected equipment stops most of the conducted RFI if it is well designed from the get-go. That can be as simple as a toroidal transformer with a static shield. The low f2 cutoff of the mains toroid blocks RF from the transformer core, and the static shield greatly reduces any capacitive coupling.

I think the extra money is better spent on higher quality equipment, or to perform modifications to make it better.
 
rafafredd said:
I don't know about you, but I don't see 50v spikes in my line..

I presented an example, complete with theory, equations, and numbers to present an analysis. The number 50 was used to show the magnitude of the reduction of the spikes that would result from the use of an 8 pair braid.

The statement "I don't see 50v spikes in my line" is just a diversion from the analysis. It does not matter if it is 50 volts, 50 kilovolts, or 50 millivolts. The point is, there was a reduction.

As such, the so called "expert" should have been able to realize it. Since the expert did not (but instead relied on the lack of documentation), that tells me the "expert" has absolutely no idea what RFI is.

I've dealt with 175 volt spikes on the line. Killed a copy machine...

If you really need a primer on transient protection, I can recommend some texts or manufacturere.. you may find that what you see is not the same as what is there.

Cheers, John
 
The CAP-Code Rule is:
"Before distributing or submitting a marketing communication for publication, marketers must hold documentary evidence to prove all claims, whether direct or implied, that are capable of objective substantiation.

Relevant evidence should be sent without delay if requested by the ASA or CAP. The adequacy of evidence will be judged on whether it supports both the detailed claims and the overall impression created by the marketing communication. The full name and geographical business address of marketers should be provided without delay if requested by the ASA or CAP."

So, as i hopefully now got it right, the expert should only evaluate if the papers presented by the advertiser are the substantiation required by the CAP-Code or not.
That is of course a totally different message.

Reading this thread in the beginning i understand it exactly the same way as jneutron did and would have totally agree but i did misunderstand what was going on.

Jakob2