OP
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Technical Article: Does Audio Cable Skin Effect Matter
- Thread starter DonH56
- Start date
I'd forgotten how pompous some of these articles sound... A lot of them are going on ten years old as well so some references may be out of date.
Yes, skin depth says how much of the conductor will be used, and especially at LF the penetration depth is more reasonable. Pipes, e.g. conductors that are hollow on the inside (e.g. used for high-power transmission systems), are another special case since the EM fields are constrained in the center. Disclaimer: My last EM courses were decades ago so don't ask me to explain that stuff.
Using an ideal inductor as a first-order model with a series R equal to the DCR will get you in the ballpark. Modern simulators allow you to curve fit and/or create a nonlinear inductor that is a better fit. BUT, I have found that to be important at RF/mW/mmW; not so much at audio (where I normally ignore skin effect anyway).
For speaker cables, the often-neglected factor is what impedance the crossover sees. The problem IME with long speaker runs and/or small wires is the impedance rises enough that the crossover no longer sees a near-perfect voltage source and that cause frequency response variations. Very obvious in tube outputs, which tend to be fairly high anyway, but long speaker runs can shift the frequency response as well. Most designers, I am led to believe, use pretty good amplifiers that have very low output impedance. I have also seen the opposite, where the speaker designer used a tube amp for his reference, and a SS amp then provided a different frequency response. And so it goes...
Aside: We undoubtedly share a cross section of friends in and out of ADI. My main career until about ten years ago was designing high-speed data converters and other analog/mixed-signal ICs.
I have hybrid electro stats- user modified Martin Logan Montis with an extra connection added to access the sub woofer amp input- and they're the poster child for variable input impedance. They vary from several K at LF (where the woofer is driven by an internal class D amp and is preceded by a high impedance resistive attenuator, and the electrostatic panels are isolated by the crossover) to less than 1 ohm at c. 30kHz. The tube amps I use- Rogue Audio M180s- cope well enough, but the impedance of the cable can have a significant HF effect. Incidentally, the M180s and the Montis were a common, and well received, combo at audio shows at one time, but I have no knowledge of the cables involved.
GeorgeBynum
Active Member
This is puzzling ... ELECTRICAL, house and building wire, has the "same" resistance for a given gauge whether standard 7 strand, fine 19 strand, extra fine 37 strand or something else stranded or solid. Stranded is larger in diameter because of air space, but that doesn't effect its resistance.
What I don't get is what this stuff is that you measured. 12AWG copper wire (solid or stranded) has a resistance of about 1.6 ohms/1000 feet. 12AWG aluminum wire has a resistance of ABOUT 2.6 ohms/1000 ft. Copper coated aluminum, depending on the copper thickness, will be between the 2. Anything outside that range (ignore the coat hanger) is suspect.
12AWG weighs about 30 kg/km ... single conductor, no insulation ... your weight measures, excepting the Southwire (yeah, you said similar to that spool) are probably for the cable, 2 (4 for the Canare) insulated conductors in an overall sheath.
Can I politely say I doubt your measurements? This was a year ago so perhaps you don't have any notes?
What I don't get is what this stuff is that you measured. 12AWG copper wire (solid or stranded) has a resistance of about 1.6 ohms/1000 feet. 12AWG aluminum wire has a resistance of ABOUT 2.6 ohms/1000 ft. Copper coated aluminum, depending on the copper thickness, will be between the 2. Anything outside that range (ignore the coat hanger) is suspect.
12AWG weighs about 30 kg/km ... single conductor, no insulation ... your weight measures, excepting the Southwire (yeah, you said similar to that spool) are probably for the cable, 2 (4 for the Canare) insulated conductors in an overall sheath.
Can I politely say I doubt your measurements? This was a year ago so perhaps you don't have any notes?
(DC Resistance is per 1000 feet or alternatively in milliohm):
I looked at several of these cables also, and reached an essentially identical conclusion- and no, I don't have my notes, but I do have some pretty decent test gear for this kind of situation, so I'm confident in the result.
The reality is that the manufacturers do not necessarily conform to the expected standards. It's as simple as that.
If they can get away, for example, with using a near 14AWG stranded wire with thick insulation and call it 12 AWG then they, apparently, will in many cases.
Using many small wires that are individually insulated makes up for the increased impedance that would otherwise be there and deals with skin depth at the same time, that is to say litz wire is not necessarily an unacceptable option for speaker wires.
I bought a used Yamaha A-700 and M-2 amplifier that have a bandwidth of 10 Hz to 100 kHz. I guess parasitic oscillation is only a problem with litz wire if the bandwidth is above 500 kHz, but would like to learn more about this. For example, it is possible to handle impedance in small wires by buying 0.15 mm² insulated copper wires and twisting 10 of them together carefully with an electric screwdriver totaling 1.5 mm²/16 AWG.
"Litz wire is very effective below 500 kHz; it is rarely used above 2 MHz as it is much less effective there.[1] At frequencies above about 1 MHz, the benefits become gradually offset by the effect of parasitic capacitance between the strands.[7]"
Litz wire - Wikipedia
See for example Instabilities in RF-power amplifiers caused by a self-oscillation in the transistor bias network by Jens Vidkjær.
https://backend.orbit.dtu.dk/ws/files/4651852/Vidkjaer.pdf
You can even find an anecdote about the audible improvement from litz wire on speakers and one should not dismiss Paul McGowan out of hand, because a lot of things he says are true.
Edit: All I meant was that I have been able to extract some useful information from the videos Paul has made, even though there is also way too much BS there.
Is bi-wiring speakers legit?
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One should, unless one is desirous of enstupidation.
I love the cite to a totally irrelevant article about RF amps.
Nope, I have watched a lot of his YouTube videos and found invaluable information. This wanton neglect for the perspective of some audiophiles is probably the reason why some don't like to participate in this forum. By the way, I looked your word enstupidation up and it's not a real word?
The quote was about the wiki article speaking on when parasitic capacitance kicks in. I was hoping someone can elaborate on whether parasitic oscillation is really only a problem at more than 500 kHz. Granted that I don't have the faintest idea about how to understand the RF amp article and merely thought it is interesting.
So who is really the reliable source here if you write some word that can't even be verified and you write something that is irrelevant?
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Enstupidation is a perfectly cromulent word.
Here's the valuable advice:
If you want to actually know how speaker wire works, this was thoroughly analyzed 40 years ago in papers by Richard Greiner and Fred Davis. Executive summary: DCR is really the only thing that matters for audio. The rest of it is FUD from con-men and ignoramuses.
Now I also have to look up cromulent!
Keith
Keith
I'm happy to embiggen your vocabulary.
I seem to remember an Ivorbiggen.
Keith
Keith
Rip City Dave
Active Member
The best part of fried chicken is the skin.
OP
- Thread Starter
- #37
Posting articles here is clearly a waste of time.
Ambiguous comment at its best. Could mean you prefer the skin effect. Could also mean you like litz-type wire that actually has more "skin". I wrote that litz wire is a way to deal with skin effect if one wants, but the difference in impedance is not that great.
You didn't mention anything about litz wire, but talked about the problem with impedance on small wires. So I commented on that. I for one think that your article here is not a waste of time.
Turns out buying 18 gauge insulated copper wires and twisting 2 together to make one 16 gauge speaker wire is even the cheapest deal I have found and deals with the little loss in energy from skin effect, which is nice.
OP
- Thread Starter
- #39
I did not really consider Litz wire relevant for audio frequencies, and it has been known to cause problems with some amp/speaker combinations, so no I did not mention it. I normally use "impedance" as that is what I am normally discussing in my day job, but for audio it is usually resistance that matters. My day job is GHz analog circuits but I don't consider it relevant to audio except as a basis for general understanding of the principles involved. Bringing RF into audio discussions, except perhaps for EMI/RFI, is usually a waste of time.
Two 18 AWG wires in parallel actually yields about 15 AWG if you want to get picky, a hair better than 16 AWG. You gain about 3 AWG for each doubling.
Skin effect is not the major factor in speaker cables, it is the resistance, unless you find some extreme case or wire and/or load. Here is an article about skin effect: https://www.audiosciencereview.com/...cle-does-audio-cable-skin-effect-matter.7157/
Litz wires have been popular off and on but you are trading capacitance for inductance. Whether that matters at audio frequencies is debatable. If you use enough wires in the bundle to provide sufficiently low resistance that is usually all that is needed. The impact on an amplifier depends upon its feedback loop and stability and of course the load (cable plus speaker). Some amps with well under 100 kHz bandwidth have oscillated when connected to certain speakers, and I imagine there are those with over 500 kHz bandwidth attached to other speakers that are fine. For amplifier stability it is important to consider the entire load and not just the speaker cable.
I did not notice that, because I just did a cursory conversion from 0.75 mm² and 1.5 mm² that are the measurements used in Denmark. Turns out those numbers are in between the AWG values.
I overlooked that you did mention litz wire, but not in detail.
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