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Re: Where is Jneutron when we need him :)

The test at Bluejeans Cable does not have sufficient information to be able to draw firm conclusions.

First, there is no hard data on the level fo the "hum" that was auditioned. Instead of dB numbers of induced hum, they merely cite an order of leat to most audible hum. This is an entirely subjective ranking, and I am surprised that you even give it any credance at all, considering your normal orientiation toward totally objective metrics.

Second, the test conditons are not fully specified, they could have been wholly unrealistic, and probably were. Some examples of what we know was unrealistic:
A. A heater load draws a constant high level of current, this causes the 60Hz component to predominate, while actual audio equpment, or most any real equipment, draws current in pulses, which causes the frequencies involved to be much higher. Instead of a nearly pure 60 Hz sine wave, we have a harmonic series that can extend through the entire audio abnd before it dies out. This will definitely change how effective the shielding would seem to be, as it would change the frequency band that the interconnects were exposed to.

B. The RMS current level was probably higher tha for ANY audio component, except maybe one of the highest power rating power amps, EVERYTHING else would have current levels way below this, on the order of -20 dB or les compared tothe heater current draw.

C. Exposing a 20 foot IC to 20 feet of power cord straped to it's side would exceed ANY possible scenario for a normal hifi playback system, in point of fact, most audiophiles and music lovers go to great lengths to not only separate the power cords from the signal cables, but to cros them at right angles where they do meet, etc.
This means that the exposure level is again reduced by a huge factorm, perhaps another 20 dB or more. At some point, sheer force ofthe AC power line field was being blasted int these IC's, and while they might work fine for normal conditions, these over-the-top conditions may have exceeded ther capacity to shield. They give the distinct impression that ALL the IC's had SOME level of hum, thus, one could say they were ALL deficient in terms of the test conditions used.

D. The shields were not the same, they did not have the same amount of copper. They did not have the same type of braiding.

While the comparisons of the coaxial cables MIGHT be construed to be one of the points of information that was derived from this 'experiment', as they did vary in their shiled constructions, to attempt to try and draw any conclusions with regard to the single twisted pair that was tested would be an unscientific thing to do.

Based on the amount of shield resistance they stated (I am assuming they got this iinformation from the Belden catalog), it is clear that the AMOUNT of copper present in the 1800F was not even half as much as the coaxial cables that were tested. For 60 Hz magnetic shielding issues, the amount of copper present is everything. So if they used a twisted pair that had less than 1/2 the copper the other shields had, it would be expected to do worse, basic physics would dictate that such would be the case.

Now if they had tested a twisted pair that had the same amount of copper as one of the coaxial cables, then PERHAPS, if everything else had been done correctly, and with relevance to the real world, we could have seen what would occur that MIGHT have some meaning.

E. The shield braid pattern was not the same, it was a French braid shield on the 1800F, instead of the classic braided shield on the coaxial cables.

[ Assuming they hard wired the shield to ground for this test, if one end was terminated to ground via a cap, the result [for low frequency rejection] would have been probably worse ;) ]

Tony, you are still not reading your references, they clearly state that they connected only ONE end of the 1800F shield. In point of fact, terminating the other end with the cap would NOT have made things worse, but rather, if there had been present other sources of interference, such as RFI, it would make things better.

Or are you going to ignore RFI, in favor of ONLY 60 Hz shielding effectiveness under over-the-top conditions, which is not present in the real world?

Finally, the double copper braid shields, and the combo braid and foil shields, while achieving a very low resistance, and large amount of copper in the case fo the double copper braids, do not necessarily SOUND as good as a single bare copper shield on a coaxial cable, as the ground return leg of the signal path is achieved via the shield. In other words, the shield is just as much a part of the over all electrical circuit, and the signal pases through this (compound) conductor just as much as it does the center (hot) wire.

Think about this for just one moment: would you deliberately use an aluminized mylar foil as a center wire conductor? It would not work very well as a signal conductor, would it.
However, when you have a combo shield with braided copper and a foil layer, a portion of the signal will be travfeling through the foil layer. In fact, based on my own measurements, which were reported in the Cable Asylum, a combo shield wil have different levels of current traveling through the copper vs, the foil when the frequency varies. More of the HF's tend to travel through the foil and more ofthe LF's through the copper braid. This was measurable within the audio band.

As for the double braids, we now have a two layer braided construction, and if any oxidation of the copper surfaces occur, then there will be intermittent contact between the these two layers of shield braids, and thus, the signal will not be able to travel as uniformly along the oprefferred layer as easily, it may be contrained for a distance to a shield layer it would not have normally travelled. (This would hold true to a certain extent for the foil as well)

Vibrations from the music being played over the speakers in the same room could easily casue this electrical contact to make and break intermittently with time, and vary according to the bass content of the music. This would be due to the bass having the most energy to move the cables. Thus, these types of shield constructions may in fact, cause signal distortions that a single layer shield would not be as prone to.

Any more citations to prove my point for me? I think a couple more will put the nail in the coffin for your argument.


Jon Risch

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