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