SilverSmith Audio Cables Interview - page 2
Audioholics: Correct me if I'm mistaken, but isn't cryogenic freezing a form of stress relief for some metals? I'm a Mechanical Engineer so you're speaking my language on this subject, as I've been through many metallurgy materials classes. I believe cryo freezing is sometimes applied to brass instruments which rely on resonating for their tonal qualities. When they are formed into shape during manufacturing, internal stress build up at the bends, which may change the sonic resonance of the instruments. Note, I said change, not degrade. Some people or manufacturers then stress relieve the instrument after forming either by heat below melting, or via cryogenic freezing. Since heat costs money, and energy along with associated risks, most who do this stress relief use cryo freezing. With this, it only works and is valid on certain metals as a form of stress relief, and it has been known to alter (improve to some) the sonic resonance of brass resonating instruments.
Could it be that some companies actually believe this form of stress relief changes electrical properties of AC signals too? I wonder if this is where the confusion is and somehow, cable companies have latched
on to this valid process in an invalid way.
John Escallier Response
I gave an example of the FCC to BCC lattice change as an example, because I had to use that a while back. You are correct in the stress relief apps, I only gave an example which provided an atomic level lattice change, because I was discussing conductivity at the atomic level. Nobody here (at work) gives a hoot about wire changes through cryo, as they have found nothing, from kiloamp to nanovolt levels..only the fact that kapton is really the only polymer that is flexible at 4.5K.
I think you are right that some have latched onto a valid thing in an invalid way.I will admit, I see a high percentage of engineers who really don't understand e/m theory. At work, though, the percentage is a whole lot lower than outside the lab.
Audioholics: There are even a higher percentage of exotic cable vendors that don't understand basic E/M theory. I suppose its because most of them actually don't have degreed engineers on staff. They simply repackage cable products from China.
Silversmith Audio
4. Connectors will have an audible effect on signal transfer.
Audioholics: I suppose that's true for bad connectors. Since I assume you utilize only good connectors, this should be a problem right?
Silversmith Audio
5. The true cause of skin effect is also has the single greatest audible affect on signal transfer (and it has nothing to do with impedance).
Audioholics: OK you got me there. But you may wish to run that one by a few PHD's in the field of electromagnetics and signal propagation. BTW, here is such a PHD that graciously wrote an article for us. Since you sound like a scientific guy, I am sure you know Dr. Howard Johnson. Check out his article about Skin Effect here . While your at it, you may wish to peruse some of the peer reviewed analytical analysis (based on proven and well documented relationships of skin effect), and measurements (utilizing $40,000 test gear specifically designed to measure it).
Skin Effect Relevance in Speaker Cables
(What you will find in this article are measurements that illustrate Skin Effect causes an increase in AC resistance, while at the same time a reduction in internal inductance) at the frequency extremes. Seems to me that skin effect has everything to do with impedance changes in a cable. Of course it's obvious that at audio frequencies this plays little role in measurement changes, let along audible ones.
Silversmith Audio
I have read the work of Dr Johnson. His description of the skin effect as it relates to impedance is correct. However, he uses the "water in pipe" analogy of electrical flow and does not seem to realize how true nature of the skin effect affects audio cable design. It has nothing to do with impedance. Understanding skin effect in the transmission line world is the key here. And yes, it has the blessing of the PHD types. Again, you accurately discuss the skin effect as it applies to impedance. However, this is a very narrow application. Understanding skin effect in the transmission line world and how it really applies to cable design is the key. It has nothing to do with impedance.
Silversmith Audio
6. Dielectric effects, like "break in" will be audible.
Audioholics: Great, if they are audible, certainly they are measureable, else how would you know when you have reached dielectric nirvana?
Silversmith Audio
7. There is one, and only one, wave guide design that will eliminate, or reduce to the greatest possible levels, ALL signal altering mechanisms.
Audioholics: What Star Trek Episode was this from? I seem to remember this line :-)
Silversmith Audio
A common misunderstanding is that only the super high frequencies travel between the conductors. This is simply not true. ALL frequencies do. It's only the high frequency engineers who have to deal with those affects on their circuit.
However, while it does not affect the circuit at relatively low frequencies of human hearing, the consequences are easily audible. A simple way to confirm this is to look at the equation for the speed of electricity flow down a wire.
Audioholics: OK so if cable A is propagating at .7C and Cable B is propagating at .8C, where C is the speed of light, how does this affect audio frequencies? The wavelength of audio frequencies (3*10^8m/s /20*10^3kHz = 49,200 ft or 9 miles!). Surely you would be more concerned with resistive losses with cable lengths that long? I know, don't call you Surely ;)
Silversmith Audio
Actually you are incorrect. I am very concerned about propagation speed. It has a far greater impact on cable sound quality than resistive losses. However, your example of propagation has nothing to do with cable sound quality and is a good example of the mis-application of the concept. Again, properly applied transmission line theory is the key.
Silversmith Audio
It's parameter's are primarily dielectric related, not conductor related. Dr. Malcolm Hawksford, an Acoustical/Electrical Engineer at the University of Essex in England, also has several papers on audio topics that have been presented at AES and other venues that would also be helpful for you.
Audioholics: It's funny how cable soothsayers (aka Black Knights, Forum Cult Hobbyists) cling to the alleged research of Dr. Hawksford. I appreciate the reference. Perhaps you should check your reference in these discussions:
http://db.audioasylum.com/cgi/m.mpl?forum=cables & n=63636 & highlight=malcolm+hawksford
http://db.audioasylum.com/cgi/m.mpl?forum=cables & n=63801 & highlight=hawksford
http://db.audioasylum.com/cgi/m.mpl?forum=prophead & n=1373 & highlight=hawksford
[John Escallier] Regarding Dr. Hawsford
I note that you mentioned Hawksford. The equations he derived are absolutely valid equations, well manipulated to provide some interesting relationships. That is not where the problem with his essex echo paper lies.
The Hawksford analysis, as printed in the Essex Echo, neglects to include the storage of energy within the conductor...the 15 nHenry per foot number with copper. This is a result of the treatment of the wires as conductors whose voltage and current arise as a consequence of external fields. This is not the case for current carrying conductors. In addition, Hawksford neglected to test various guages of copper wire conductors, instead, substituted a steel conductor with a mu of approximately 100. Since the internal inductance is proportional to mu, the actual inductance he did not accout for was 1.5 microhenries per foot per wire, or 3 microhenries for the pair. On the assumption he used a meter of wire, that is about 10 microhenries unaccounted for in his simulation, and hence, the inductive overshoot in his test. Clearly, had he modelled this inductance, with the loop resistance of his wire, he would have found that the wire matches the formula for inductance provided us by Termen in 1947.[John Escallier] Regarding Transmission Line Relevancy and Cryo Treatments
I have worked with transmission lines, transmission line theory, and application..and I am unable to understand how high frequency transmission line theory relates directly to analog audio applications. Although I note you have referred to transmission line theory several times in your responses to Gene, you have not elaborated in the least..Please do. I deal with superconductors. For me, skin effect is a way of life. Please elaborate on how properly applied transmission line theory deals with skin effect, and how it pertains to audio.
Audioholics Response: Jeff, do you have anything else to add to this discussion?
Silversmith Audio
I can't think of any additional comments but if I do in the next few days, I'll drop you a line. Thank you.
Please feel free to use my name in association with this correspondence. For you, and your readers, I am in no way trying to say that snake oil salesmen do not exist in the audio world. Unfortunately they exist in too many areas of our lives, audio or otherwise. In the world of audio, all cables, indeed all components, degrade the sound of an audio system. The key is to use properly applied engineering principals to design cables and other components to cause the least degradation possible.
Properly applied engineering and physics principals describe exactly why these components behave the way they do and even allow us to predict how a component will sound compared to one of a differing design, but same specs. These principals have never been disproved. Regardless of the math, however, there is a personal and subjective side to the music. Do not buy on the basis of a white paper, technical description, impressive sales pitch, or the ears of a reviewer. They can be useful tools, but LISTEN for yourselves. If you find yourself tapping your foot, moving and grooving to the music, there is probably something right about the sound, and it's not the frequency response. If you have the ears to tell the difference between live and recorded music, you have the tools to make the right decision.
Best Regards,
Jeffrey Smith
Silversmith Audio
Audioholics Epilogue
We would like to thank Jeff Smith of Silversmith Audio as well as John Escallier for participating in this informative discussion.
I find it interesting to note that Silversmith stresses the importance of applying proper transmission line theory to audio cables to understand the nature of their sonic attributes, yet furnishes no concrete proof, analysis, or technical contribution in this regard. While transmission line theory has relevancy at much higher frequencies (starting in the MHz range, depending on cable length), these frequencies are decades past the audio range of human hearing and the audio equipment in question. When designing high performance audio gear, it is critical to limit the analog bandwidth of such gear in order to attain optimal Signal to Noise (SNR) ratio and stability of the system. As example, Redbook CD incorporates a brickwall filter at 20kHz to bandwidth limit the payback system. While DVD-A and SACD have slightly higher analog bandwidths (about 100kHz), these frequencies are still far too low to be concerned with transmission line issues (reflection, return loss, power loss, etc) for any reasonable cable lengths. For more details, Current Trends article. We must also consider the fact that no current loudspeaker system (as example see our article on Skin Effect ) offers any reasonably controlled dispersion characteristic at frequencies much higher than 20kHz (the limit of human hearing). Let us also remember that most musical content is harmonic in nature at frequencies beyond 8kHz and based on the Fletcher & Munson curves, human hearing sensitivity is dramatically impaired at our 20kHz range limit. The argument of transmission line relevancy, or lack thereof at audio frequencies can be easily analyzed without delving into classical S parameter or Smith chart analysis. If we use classic and proven transmission line theory to determine the importance of cable impedance matching at audio frequencies, we derive the following:
wavelength (in meters) = v / (f*sqrt(er))
where f is the frequency of the signal in Hz, v is the velocity of the signal = 3x10^8 meters/second (vacuum) and er = velocity of propagation factor
If we consider the audio bandwidth limitation of 100kHz (based on maximum bandwidth of high resolution audio formats, considering sharp rolloff of power amplifiers to preserve SNR and stability), using a solid dielectric, with approximately the same dielectric constant for our cable as PE, we're running at around 66% velocity of propagation. This cuts the physical wavelengths where impedance matching matters to 1,980 meters or 6,496ft. A quarter wavelength, which is often used as the benchmark for where the characteristic impedance of a transmission line becomes critical, is then 495 meters or 1,624 feet. Many think a quarter wave is a bit too long to use, and prefer to go with 1/10 wavelength or so. If we are considering ultra high performance, and use the 1/10 th wavelength more conservative estimate to determine the point at which the cable's electrical length becomes long (with respect to a wavelength) to consider transmission line effects for audio cables, we derive 198 meters or 649ft. If you consider using common low resistance 10AWG Zip cord (2 ohm/1000ft loop resistance) as speaker cable at this length, then you would effectively be placing 1.3 ohms of resistance in series with your amplifier and speaker. With a nominal 4ohm impedance speaker, the resistive losses at these cable lengths would dominate and result in over 2.4dB of signal loss alone, not to mention destroying the damping factor of the system. Add in the reactance losses (inductance and capacitance) and we see a whopping 11dB of loss (not factoring in any potential amplifier stability issues from the high reactance of the cable).
My point here is the lumped impedance losses alone would have a far more profound affect than transmission line and/or distributed losses could ever dream of having.
The bottom line here is to consider the validity of sciences some exotic cable vendors enjoy promoting about their products and wonder why they often go through such great lengths of conjuring up such complicated reasoning as to why cables sound different, or for that matter allegedly better despite the lack of proof behind their convictions and claims. Much of the concepts of transmission line relevancy and cryogenically freezing cables contained herein can easily be disproven by classical analytical methods all credible engineers utilize on a daily basis to understand and design electrical systems. There is no rocket science to cable design, and to simply abandon proven critical metrics such as impedance (R,L,C) and geometry/shielding in favor of "just listening" or elaborate pseudo-science reasoning is something all consumers should be cognizant of if their goal is to obtain accurate, quality-controlled products in any facet of electronics and/or cabling.
