<font color='#000000'>Gene recently wrote yet another article on audio cables, this one specifically about one of my original and unique speaker cable designs, the DIY Cross-Connected 89259 speaker cable.
This was apparently done in an attempt to defend Gene's comments about my DIY speaker cable design, when he originally made the following statement:
"Please refrain from posting links to Jon Rischs cable receipts as we feel that his designs can do more harm than good."
I replied, and Gene defended SOME of his comments, in this thread:
http://www.audioholics.com/cgi-bin....4;t=483
This post is my comments on his article regarding my speaker cable design.
The first point of contention, is the actual inductance of a typical 12 ga. zip cord. Gene's reference is the original Monster 12 ga., which is just a clear PVC jacket, bare copper type of zip cord.
Gene says my measured amount of inductance is incorrect.
This depends on the definition of what a typical 12 ga. zip cord is. Some zip cords have a fairly close center to center spacing of the wire conductors, this tends ot lower the overall inductance. Belden 9718 is one example of this.
Then there are the hardware store or electrical supply store zip cords, which is what I am calling typical, that do not have the very close spacing, but a more nominal amount of spacing.
Then there are other cords that have greater than typical spacing, such as some of the Radio Shack flattened zips, and some of the so-called 'premium' zip cords, that use a larger than normal amount of insulation and spacing, so as to make the cable appear larger than it really is. Some have a distinct spacing web down the middle, that tends to separate the two conductors even more than they would be if just the insulation was present side by side. I am not talking about the normal very small web that all zip cords tend to have, but a wider than normal web.
Since I do not have a sample of Original Monster Cable handy any more, I can not re-measure it, but earlier measurements indicated it fell into the middle group, and was not unusual in its LCR parameters.
My own measurements for it, and for most typical 12 ga. zip cords came up with approx. 0.25 uH per foot of inductance. Recent measurements by jneutron/John Escalier posted at AR of several different zip cords indicated that they measured around 0.23 uH per foot.
Fred Davis, in his postings on the newsgroups, and in publication of an article on Loudspeaker cables, "Effects of Cable, Loudspeaker and Amplifier Interactions." JAES, Vol.39 #6, June 1991 (Also later reprinted in mildly edited form in Audio magazine, July 1993, as "Speaker Cables: Testing for Audibility"
states that Belden 9718 12 ga. zip has 0.23 uH of inductance per foot.
This data was provided on the newsgroups, in this post:
http://www.google.com/groups?....xy=1997
So there is a disagreement between Gene's measured data, and my measured data. However, it is well known that the free-field equation for wire inductance is not directly applicable to zip cords, and so, the very fact that Gene's measurements seem to correlate exactly with his theoretical calcluations makes it more likely that his measurements are the ones that are off, and not mine. In any case, I am in the company of other engineer's reported measurements, so I can hardly to be said to be one who is unequivocally incorrect or completely wrong.
BTW, I have been suspicious of Nordosts zip cord inductance figures for some time now, as they do not jibe with the previously established measured data that has been available.
The next portion of his article goes over my measurements for the Cross-Connected 89259, in which he ultimately decides my numbers are reasonable and in the ballpark.
I note for the record, that the twisting of the two coaxes is not necessary for the reduction of the inductance down to levels of 0.067 uH per foot, where the single coax is at 0.092 uH per foot. Since the two cables are cross-connected, the amount of mutual inductance coupling is increased over the single coax, primarily where the two braids run next to each other through the thickness of two very thin teflon jackets. It is this which further reduces the total inductance, and not the twisting.
The twisting is done to render the coax pair more flexible, and to help keep the two conductor systems from being able to move too easily relative to one another, and thus, eliminate the need for the original early design version's adhesive lined heatshrink. When the two coaxes are twisted together moderately, they become much more flexible than when adhesive HSed side-by-side, and yet resist any tendency to be loose relative to one another. I suppose it is also tidier than two coax sections wanting to splay out wildly when run around a bend.
The whole second page of the article compares the two cables.
But there is one thing that is not quite right. Normally,when folks compare speaker cables, one of the primary cirteria is to compare like gauges, so that any difference in resistance does not skew the results. Gene originally, in his first comments about my CC89259, compared it to 10 ga., stating that the CC89259 had almost twice the resistance of 10 ga. zip cord.
In a reply, I stated some values and figures for 12 ga zip cord, because that is the one that is most commonly recommended as being all that is necessary to acheive audio nirvana in terms of speaker cables.
However, if a scientific analysis was to be performed, then why not use an equivalent gauge zip cord?
To take a 13 1/2 ga. equivalent cable to task for having a higher DCR than a 12 gauge cable is a trivial excercise, and does not really compare what the geometry is doing for the Cross-Connect coax vs. the zip cord. Isn't this the place that makes a point of claiming to be "Pursuing the Truth In Audio"?
Tautologies are all very well and fine, but who is going to argue that a smaller ga. (larger diameter) wire has less resistance?
So most of the second pages comparisons are not really relavent or valid, if you really want to compare the LCR parameters on an equal footing. Another way of saying this, is that for an equivalent ga. zip cord, that the CC89259 will indeed have a much lower inductance, and not that much of a capacitance penalty.
If Gene/AH feels that a much lower resistance is required, then a Star-Quad CC89259 variant using four coax runs per cable will provide the equivalent of a 10 1/2 ga. cable, with even lower inductance than before.
Note that the details of the Star-Quad CC89259 is at:
http://www.AudioAsylum.com/audio/cables/messages/19015.html
and is listed in the Annotated Cable Bibliography at my web site.
Some specifics from the article:
[ While their efforts should be applauded, they should also be cautioned to consider any deleterious effects that may result, ... ]
This implies that the CC89259 may have deleterious effects, and this is in line with what Gene originally said, "Please refrain from posting links to Jon Rischs cable receipts as we feel that his designs can do more harm than good."
However, this is not shown to be the case.
[ In any event, I am not sure where the .25uH/ft estimate that Jon Risch specified came from, but it seems like a bit of a stretch, actually quite a bit, 1.56 times reality! ]
Nope, it was not an estimate, it was a repeated and 2nd source verified measurement consistent with other previously published data, and by another more recently posted engineer. I take exception to Gene calling his measurement "reality", to further denigrate my reported data.
It would be one thing to merely comment on the disparity, but why is it necessary to do it in this manner, if it wasn't meant to be a way of casting even more doubt on my data?
[ As you go to thicker gauge wire (say 10AWG), the radius increases, thus inductance decreases which is exactly opposite of what Jon Risch implied. ]
In the real world, the larger zip cords tend to use a thicker insulation, and so, the 10 ga. zip cords would have the centers of the two conductors spaced further apart due to this AND the increased diameter of the conductors themselves. The net result is higher overall inductance. 12 ga. tends to sit at a "sweet spot" in terms of wire size, center to center spacing, and the thickness of the insulation used, so it does better than the larger diameter conductor wires.
[ Since Jon Rischs cables illustrate twisting, Ls should decrease somewhat depending on amounts of twists and assuming the twists are tightly packed. ]
This comment indicates that Gene is not fully realizing the Cross-Connection paradigm. It is this, and not the twisting of the two coaxes, that causes the inductance to go below that of a single coax.
The close proximity of the two coax braids carrying opposite polarity signals is what does the trick.
Note that because of the two braids carrying opposite polarity signals, the jacket of the coax becomes a portion of the dielectric system, and the fact that 89259 has a teflon jacket is quite helpful here in maintaining a superior dielectric for the entire cable assembly as a whole. Use of another coax with a PVC jacket would then include this as a potion of the overal cable dielectric, and would tend to compromise the properties of the inner coax insulation.
RE the PSpice simulation, all I can say is that I made actual measurements, and that the model used does not necessarily include all the parameters.
[ Note: Skin Effect loses (Rac) were not accounted for either of these cables for simplicity purposes and also because they would generally represent only very minimal losses (< .05dB @20kHz) within the audio band and thus DC Resistance (Rdc) in this analysis is the dominant metric of comparison for resistive losses in speaker cables. ]
I note for the record, that despite the total equivalent ga. of the Cross-Connected 89259, that the skin effect will be much less than for a 12 ga. zip cord., as the dominant factor will be the 22 ga. center wire. The difference in the amount of skin effect between a 22 ga. wire, and a 12 ga. wire, is real, and could be factored in. Of course, adding this in would favor the CC89259, even if just a bit.
[ Unfortunately due to the added DC resistance inherent in this cable design, we see uniform insertion loss throughout the audio band ... ]
But only when comparing apples to oranges. A trivial tautology that is mentioned more than once.
[ Thus the benefit of reduced inductance of this cable design is greatly compromised by the additional uniform insertion loss within the entire audio band do to added DC resistance. ]
But not if compared to an equivalent ga. zip cord, or if a Star-Quad CC89259 is used as the basis for comparison.
And again:
[ Yet the Coax Cable design, because of its increased DC resistance, resulted in a -0.1dB loss within the entire audio bandwidth, which would be even more apparent as cable length increases or speaker load impedance decreases. ]
[ The added capacitance of the Cross Coax cable design can also represent stability problems as cable lengths increase, especially for esoteric tube amp designs with higher output impedance and lower unity gain crossing. ]
And I addressed this in the reply to Gene, that it would take excessive lengths of CC89259 to even begin to pose a problem in the real world. 49 pF per foot, or even around 122 pF per foot for a Star Quad version, is not that high, and not that limiting in terms of allowable speaker cable length.
[ Secondly, in the time domain, the step response may have a much higher overshoot, and exhibit excessive ringing (at about the unity gain frequency) due to loss of power amp phase margin from excessive capacitive loading. ]
This would only be the case IF a signal existed that high up to excite any possible resonances. With typical CD or DVD source material, this is almost impossible.
Again, I note that the CC89259 does not have enough capacitance to pose such a problem for any reasonable length of speaker cable, with most any power amp.
[ On a less serious note, some people may prefer the excessive frequency peaking due to overshoot that high capacitance speaker cables may cause, assuming rampant oscillations are not present, as the listener may possibly perceive it as sounding “brighter”. The question should be asked however, “Do you want your cables to act as tone controls, or be as transparent (accurate) as possible?” ]
Of course, none of this actualy applies to the CC89259, but the implication is that it might.
Another instance of stating a "problem" that is not really relevant.
RE Zobel Networks:
[ The speaker, if designed properly, usually has already been compensated for. ]
Not many have an overall Zobel at the speaker crossover input, if a speaker system has a Zobel, it is often only on the tweeter leg, at the tweeter terminals.
[ By adding the Zobel network at the speaker like Jon Risch suggested, you can actually increase shunt capacitance that the amplifier sees and possibly further increase the likelihood of amplifier instability or overshoot. ]
Nope, this is just not the case. The resistor is what makes the difference, and what helps damp the amp.
[ A Zobel network at the speaker end of a cable is (usually) next to useless. ]
Experience over the years with the other super high C speaker cables has shown that placing the Zobel at the speaker does the most good, and is what works. So I have to disagree with this completely and totally. If one peruses the literature, you will find that in reported instances of unstable or marginally stable amps with a high C speaker cable, that the cure was often the placement of a RC damping network (or what we have been calling a Zobel) right AT the speaker terminals.
In fact, Goertz supplies free of charge an RC damping network to owner's of their ribbon cables, and guess where it is to be placed? Yup, right at the speaker terminals, not at the amp.
[ As we can see in the above analysis, there maybe no real apparent benefits to the Cross Coax cable design over ordinary 12AWG Zip Cord for high end audio speaker cable applications. ]
This comment is based on some of the faulty premises I point out above, and so, is not really valid.
[ If inductance is truly a concern, then one could certainly choose a twisted pair variant of 10AWG or 12AWG Zip Cord, which will maintain low DC Resistance, critical for accurate and high performance realization. ]
Not quite spot on either, as the comparison to 12 and 10 ga zip cords is not equivalent in resistance, and the inductance of an equivalent cable (the Star Quad CC89259) would be even lower still, down below 0.4 uH per foot.
[ When you consider the potential negatives of Cross Coax cable designs (IE. Increased DC resistance, excessive capacitive loading), and the hassles (IE. attempting to compensate for stability issues with Zobel networks, series inductance and/or resistance), determine for yourself if it’s really worth pursuing this effort, and if you have the time, patience and know how to proceed? ]
All red herrings, and not relevant to a scientific comparison between equivalent DCR cables.
The CC89259 does not need a Zobel, and it is not going to be hard to make or require undue patience or knowledge. Most folks assemble them, hook them up and just start loving the improved sound.
Of course, none of this simple analysis of the basic LCR parameters takes into account any of the secondary issues such as skin effect and it's related issues, or of dielectric absorption, conductor purity (lack of tin platings, etc.) and so on, and it is in these areas that the CC89259 offer improvements over 12 ga zip cord as well. However, given the policy of making every attemptto dismiss and ignore these types of cable aspects, I focused on mostly just the LCR parameters as did AH. I just wanted to point out that not everyone is as ready to dimsiss and ignore these other aspects, and they should be mentioned at least in passing.
Finally, I posted in reply to a post by Suppers_Ready about an alternative to 12 ga. zip cord, that costs about the same or less, and has superior materials and inductance over zip cords.
I a referring ot the use of Belden 8213. If we compare the cost of this coax and my recommended RS gold plated spade lugs to Dan B.s recent DIY article using 12 ga. zip as the basis for the cable, the 8213 approach comes out cheaper. The cable will have the equivalent round trip resistance of a 12 ga. cable, and have significantly less inductance. Plus, as an added bonus (for those who at least grant the possiblility), the cable uses foamed PE as the insulation, and all bare copper for the conductors.
Capacitance is slightly LESS than most 12 ga. zips, at 17.3 pF per foot. In addition, if the outer braid is connected as the ground lead (a logical thing to do), it would then provide some self-shielding.
I talk about a coup0le of other candidates fotr this type of use at:
http://www.AudioAsylum.com/audio/cables/messages/7637.html
So why would it not be a good idea to use this as a speaker cable, as it would do no worse than zip cord, have potentially superior materials, and lower inductance for those long runs to the rear speakers in a multi-channel DVD-A or SACD system?
Jon Risch</font>