Silversmith Audio Interview

gene · Apr 19, 2004

Jeffrey Smith from SilverSmith Audio was nice enough to engage in an informative interview about his cable philosophies and self proclaimed sciences behind them.  While his ideas about cables and signal propagation are unconventional, they do sell a very interesting story.  Read on to learn more….

Silversmith Audio Interview

Dan Banquer · Apr 19, 2004

To apply transmission line theory to audio band cables and power cords is just flat out absurd. If anything needs to apply here it's keeping RF/HF frequency content out the audio band and attenuate it coming into the components via the AC line.
d.b.

Rip Van Woofer · Apr 19, 2004

Holy cow. The "Essex Echo" article by Hawksford is still alive and kicking? The Audio Critic did a refutation of that over five years ago. They had a PhD specialist in EM theory take a look at it. Basically, he said that the calculations were valid, but the conclusions Hawksford drew from them were rubbish.

Also, the Essex Echo paper was not published in a peer-reviewed technical journal, but in the British mag Hi-Fi News and Record Review way back in '85, and then rehashed in Stereophile some years later. TAC speculated that Hawksford knew it would never pass muster in a technical journal.

Strangely, Hawksford is (or was) a respected EE and academic.

One "how 'bout that?" kind of thing I learned in the TAC article is that, according to EM theory, specifically "Maxwell's equations", signals (as opposed to the current) travel in a field outsideof the conductor. Any signal that penetrates the conductor is lost forever as heat. So that is another reason to be skeptical of stuff about the microcrystal composition of wire, or "break-in" by atoms aligning, etc.

Guest · Apr 19, 2004

A minor (but longwinded) correction to the above statement about 'signals' traveling in the field outside of a conductor. This is a bit oversimplified. You are of course alluding to the concept of skin depth that gets bandied about in all of these discussions.

An AC signal traveling down a wire (metal of course) consists of the electrical currents and associated electric and magnetic fields. The current (actual moving electrons) is restricted to the wire of course, but the fields exist both inside and outside of the metal wire. The signal consists of the combined AC current and associated electric and magnetic fields. One cannot exist without the other so the distinction should really not be made.

As 'signal' penetration into wires : for good metals, the current flow in the wire is concentrated  near the surface and falls off exponentially as you look towards the center. The length at which the current density drops by about 2/3 (66%) is called the skin depth. The skin depth is frequency dependent and goes like 1/sqrt(f), i.e. one over the square root of frequency. For copper it is about 0.85cm at 60Hz and hence is about 0.05cm at 20kHz. So the signal at audio frequencies actually penetrates quiet far into most wires except at the the very highest frequencies.

Guest · Apr 20, 2004

Rip Van Woofer : Strangely, Hawksford is (or was) a respected EE and academic.

Is a respected academic.

He is a professor and department chair (I believe)at some school in England, his staff is two grad students and some visiting profs.

W/R to DSP analysis, some of his papers are rather "high end"..translation: it would take me about a year to learn enough to be able to critique some of his current publications (and yes, in peer reviewed pubs.) I honestly could not vouch for his abilities and talents along those lines, as I am not experienced in DSP..

I was unaware of the Audio Critic refutation.

Cheers, John Escallier

Guest · Apr 20, 2004

Guest : A minor (but longwinded) correction to the above statement about 'signals' traveling in the field outside of a conductor.

But a very nice one Richard

A further elaboration on skin depth..

The equation is

delta=5033 sqr {p/uf}

delta is skin depth in cm
p is resistivity of conductor, ohms per centimeter cube
f is frequency hertz
u is magnetic permeability, =1 for air

for copper, it reduces to depth in cm = 6.62/sqr(f)
giving .85cm at 60 hz, as you correctly stated.

This equation, of course, is useful only for wire diameters greater than about 5 times the skin depth, and is in fact, a planar solution. For typical wires used for speakers, it is incorrect..when the exact solution for skin depth of small round conductors is used, this exponential solution is found to be off by a factor of three...giving too much skinning..

If I find myself in a situation where EMP warfare equations are needed, I'll revisit the Hawksford paper.

Cheers, John

Rip Van Woofer · Apr 20, 2004

Thanks for the correction, Richard. When it comes to understanding such things "simplified" is about the best I can do!

Yes, after a quick Google I see that Dr. Hawksford is still alive and in academe, at Essex University in the UK. His bio page on the University site makes passing mention of his writing on cables ("He likes to write articles for the hi-fi press , yes including cables....&quot

, but emphasises his presumably more mainstream and valid work. I know I've seen him cited in other areas of audio. Perhaps in the case of cables and EM theory he is like other respected scientists who, when they leave their area of expertise to write on another specialty, fall on their faces (like, say, Linus Pauling)?

The Audio Critic article appeared in the "Hip Boots" column, Issue #24, Spring 1997.

Guest · Apr 20, 2004

Rip Van Woofer : The Audio Critic article appeared in the "Hip Boots" column, Issue #24, Spring 1997.

Thank you, Bruce..

Cheers, John

Mudcat · Apr 20, 2004

["he is like other respected scientists who, when they leave their area of expertise to write on another specialty, fall on their faces (like, say, Linus Pauling)?"]

I'll bite, in what endeavor did Linus Pauling fall on his face. I'm only fanilar with his anti-nuke stance, and his chemistry/physics/medical accomplishments. Oh yeah, his two solo Nobel Prizes.

Rip Van Woofer · Apr 20, 2004

Mudcat : ["he is like other respected scientists who, when they leave their area of expertise to write on another specialty, fall on their faces (like, say, Linus Pauling)?"]

I'll bite, in what endeavor did Linus Pauling fall on his face. I'm only fanilar with his anti-nuke stance, and his chemistry/physics/medical accomplishments. Oh yeah, his two solo Nobel Prizes.

I was thinking of his Vitamin C theory. As far as I know it's been discredited, and was always seen as a bit wacky by mainsteam scientists.

Not to deny his undeniable brilliance and accomplishments otherwise, of course.

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