Cross Coax Cables Design vs Zip Cord - Analysis

PSPICE Analysis

Frequency Vs Attenuation Characteristics of 10ft 12AWG Zip Cord and Cross Coax Cables

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 at audio frequencies.

For more information about Skin Effect and its relevance in speaker cables, click here.

Analysis Review

12AWG Zip Cord

Insertion loss within the audio band is about -0.07dB while attenuation at 20kHz is only -0.09dB into a 4ohm load, Not -0.25dB as Jon Risch suggested. Note, if we use Ls = 0.25uH/ft for 12AWG Zip Cord as Jon suggested, it would yield -0.10dB attenuation at 20kHz which is still much less attenuation than Jon Risch claimed. As we approach longer lengths, we see more high frequency roll off primarily due to increased cable inductance.

The insertion loss of a 50ft 12AWG cable is about -0.36dB throughout the entire audio band until rolloff begins about 10kHz resulting in a total loss of -0.70dB @ 20kHz into a 4ohm load, again much less than 1.3dB that Jon Risch claimed. Even if we assumed that Ls = .25uH/ft as Jon Risch suggested, the loss at 20kHz into a 4ohm load would still only be -0.90dB NOT 1.3dB.

Coax Cable

Unfortunately due to the added DC resistance inherent in this cable design, we see uniform insertion loss throughout the audio band of about -0.10dB into a 4ohm load. Note this loss is throughout the entire audio band and represents a greater loss than 12AWG Zip Cord at 20kHz of the same length! This insertion loss will only get worse as cable length increases, or speaker load dips lower due to the more prominent voltage divider relationship between the increased DC cable resistance and the low impedance speaker load. 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.

As cable length approachs 50ft, we see insertion loss ramp up to -0.47dB until we reach about 20kHz where we see a total loss of -.511dB into a 4 ohm load which is certainly higher than the -0.35dB that Jon Risch claimed, and not much lower than ordinary 12AWG zip cord (0.70 - .51 = 0.19dB) difference, or in the extreme case of a poorly designed 12AWG Zip Cord with maximum inductance claimed by Jon Risch (0.90-0.511 = 0.39dB).

It is doubtful that any audible differences between these cables would be perceived based on the attenuation characteristic differences, especially at 20kHz where the human ear is least sensitive and music is only harmonic in nature with little or no energy.

Wrapping It Up

Based on this analysis, it is clear that the Coax Cable design does have wider bandwidth than the 12AWG Zip Cord. However, at audio frequencies this mostly irrelevant since both designs are responsible for less than -0.10dB loss in the 20 kHz audio bandwidth for cable lengths of 10ft in high end systems. 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. It is possible for high capacitive loads of a cable to cause two related effects due to loss of the power amp gain and phase margin. Firstly, in the frequency domain, very significant gain peaking can occur. 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.

In defense of the Cross Coax cable design, 49.9pf/ft is about 5-10 times lower than some of the "exotic" cables we have measured, thus it would probably take quite a long cable run with a not so ideally designer power amp to present a significant problem with amplifier stability. 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?"

A Note About Zobel Networks

Jon Risch's solution to stabilize oscillating amplifiers presented with high capacitive cable loads is to install a Zobel network (Shunt resistor and series capacitor). While this may help stabilize a highly inductive load resulting from the cable/speaker combo by making it look more resistive, it may not always resolve amplifier oscillations resulting from too much capacitive loading, and can sometimes have its own inherent problems, especially if the amplifier itself is already compensated for. Zobel networks should usually be applied (if needed) as close to the source as possible, and not necessarily at the speaker. The speaker, if designed properly, usually has already been compensated for in some capacity. By adding the Zobel network at the speaker like Jon Risch suggested, you can actually increase shunt capacitance (if you choose an improper R & C value) that the amplifier sees and possibly further increase the likelihood of amplifier instability or overshoot. A Zobel network at the speaker end of a cable is (usually) next to useless. While it can provide a termination at very high frequencies, (which the speakers sometimes cannot because of their own inductance), by that time the damage is usually done, and the amplifier is happily oscillating. It is common with many amps to use a series inductor (usually in the vicinity of 0.8uH or so) to isolate the amp from external capacitance, but this rather negates the "requirement" for ultra-low inductance cable. Alternatively a series resistance at the output of the amplifier may dramatically help to reduce risks of amplifier oscillation due to capacitive loading, but at the extreme trade off increasing insertion loss and sometimes of maintaining a decent damping factor (Ratio = R(speaker+cable) / Rout(amp)) if the resistor value becomes large enough.

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. If inductance is truly a concern, then one could certainly choose a closely spaced twisted pair variant of 10AWG or 12AWG Zip Cord, which will maintain low DC Resistance, critical for accurate and high performance realization. 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?

Final Thoughts

Is 10AWG or 12AWG Zip Cord the epitome of high end cable design? Probably NOT. But it certainly should be the minimal guideline cable designers use to judge their "exotic" cables against. The sad reality is, so many of the so called "exotic" cables out there actually achieve less accurate performance than ordinary 12AWG Zip Cord, yet many cable vendors manage to sell it off to consumers at prices between 2 to 10 times more!

We fully encourage audiophiles or hobbyists that wish to experiment with "exotic" cables to first try a design such as this Cross Connect Coax or a Cat 5 variant. Although many of them are higher in capacitance than standard Zip Cord, and sometimes higher in DC resistance, they are an excellent way to "try before you buy", and Jon Risch's recipes are reasonably good and cost effective to produce, even if his claims of their performance are a bit overstated. While there are inherent risks, as previously mentioned in this article, with some DIY Cross Connect Coax and/or other "Exotic" cable variants, they can at times alter the sound of a system to a listeners liking. Our goal at Audioholics.com is to objectively measure and quantify cable performance based on accuracy and transparency, not to determine or dictate what sounds best to the listener. We leave that up to you to make that decision for yourself.

We have just finished acquiring cable samples from various vendors and will be measuring their cable metrics using the WAYNE KERR Precision Magnetics Analyzer and an HP Network Analyzer to determine their accuracy while also verifying their claims. We will report on this shortly. Stay tuned..

See our Results from Speaker Cable Face Off I

Original Publish Date: 4/24/03
Updated 4/29/03 - added comment about mutual inductance of Cross Coax reducing inductance of Cross Coax cable design as per Jon Risch's feedback.
Updated 4/29/03 - corrected Ls for 12AWG Zip Cord calculations by adding self inductance term. Redid 12AWG Ls measurements with longer cable to eliminate errors due to short leads and termination.
Last Updated: 06/01/03