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Cable and EMC discussion (Split from "What if the Audio Critic was completely right")

post #1 of 55
Thread Starter 

Quote:

Originally Posted by wakibaki View Post


 

 

I won't bother disagreeing with the rest of what this guy has written, but basically, he starts from a point of disagreeing with PA and just lets his mind flow on. Anybody who thinks that a switchbox invalidates ABX is grasping at straws. At the end he throws in 'EMC' in a vain attempt to garner some scientific credibility with the easily impressed.......snip.....

I've also worked as an electronic design engineer.

 

I know what I'm talking about.

 

w


I hope you don't mind my culling out context which is not important to my response.

 

 

If as you claim, you worked as an electronic design engineer, you should understand what I say..if not, let me know and I will further elaborate.

 

Take a source component and connect it with two coaxial IC's to a two channel amplifier.

 

When a signal in one channel is passed from the source to the amp, it does so by driving a voltage on the center core wire of that channel's coax.

 

What path does the signal take in order to get back to the source?  If you answered "the shield of the IC which contains the signal", then you are incorrect, and have failed one of the simplest tenets of EMC.  Control of current.

 

When a coax cable carries all the signal current via it's internal core wire, but returns to the source only 50% of that current, is the coax performing as a shield?

 

Again, the answer is no.

 

Now, toss an ABX box into the fray.  Have you controlled the path of the return current? 

 

No.

 

If you wish, I can teach the needed EMC concepts.  If you do not wish for me to do this, I can provide links to some of the works of Tom Van Doren, or recommend a few good books.  I do have a couple of jpegs from one of TVD's booklets when he was here.nice guy..

 

Cheers, jn

 

ps..edit.  I've removed reference to what i do for a living, it should not made a difference, post content should be judged on merit alone.

 

 


 

 


Edited by jnjn - 12/28/11 at 10:58am
post #2 of 55


 

Quote:
Originally Posted by jnjn View Post



On forum, not off. 

 

That way,  everybody can read, everybody can participate, everybody can discuss.  No exceptions.

 

ps.  I did not say the purpose of the article was invalid.  I did say that the engineering context used to support the article was invalid.

jn

ps..sigh, I've tried about 5 times to copy and paste the "lie" and the "truth" part of the first one, the cable lie...I'll see if I can save it to disk and copy/paste...

 


The engineering context?  What engineering context?  TAC is not talking about absolute rules and extremely specific claims with his "Top 10 Lies" article - rather, sweeping generalization and above all regarding audibility as the important metric to be concerned with.

 

You can measure differences in everything up to and including two identical wires, for goodness sakes.  But depending on the context such measurements may or may not make a difference, and anyway, that's not what he's talking about.  Same thing for switch-boxes - in fact, what grounds are there against ABX'ing a switch box versus no switch box?  If the difference isn't audible, and the measured difference is negligible, then what difference does it matter whether there is or isn't a switch box?

 

On top of that, you're deliberately - or at least consciously - misconstruing his statements.  For example, the CD treatments one - I think we can safely assume that he's not talking about scratch treatments that attempt to match the index of refraction of the plastic.  That has basis in real science, clearly.  Similarly, when he talks about self-proclaimed golden ears he specifically calls out ear training as both legitimate and essential - yet you ignore that completely.

 

After that, I can't help but thing - did you actually read the article or just the section titles?

 

I'd go into more depth, but I'm at work and lunch has ended so it will have to wait.  In the meantime, yes, we want your full, unabridged explanations if you really want to pick this apart.  You know, some of the rest of us here are scientists and engineers and are genuinely interested in this and what you have to say.

 


Edited by BlackbeardBen - 12/28/11 at 10:34am
post #3 of 55
Thread Starter 
Quote:
Originally Posted by BlackbeardBen View Post


 


The engineering context?  What engineering context?  ...snip....

On top of that, you're deliberately - or at least consciously - misconstruing his statements.  For example, the CD treatments one - I think we can safely assume that he's not talking about scratch treatments that attempt to match the index of refraction of the plastic.  That has basis in real science, clearly....snip....  Similarly, when he talks about self-proclaimed golden ears he specifically calls out ear training as both legitimate and essential - yet you ignore that completely.

 

After that, I can't help but thing - did you actually read the article or just the section titles?

 

I'd go into more depth, but I'm at work and lunch has ended so it will have to wait.  In the meantime, yes, we want your full, unabridged explanations if you really want to pick this apart.  You know, some of the rest of us here are scientists and engineers and are genuinely interested in this and what you have to say.

 

I also apologize for snipping...also, for typing the text, I can't seem to cut and paste from the article..

 

You ask What engineering context?

 

Quote""The simple truth is that resistance, inductance, and capacitance (R, L, and C) are the only cable parameters that affect performance in the range below radio frequencies.""  End of quote.

 

Do you really believe this is an accurate statement from the point of view of ElectroMagnetic Compatibility  for unbalanced audio systems?  It can be accurate for a balanced drive system where the pin 1 currents are safely diverted away from all star ground wire runs, but for unbalanced systems, this is not possible.  It can also be correct for unbalanced battery driven systems as well. 

 

For CD treatments, we can "safely assume" anything we want, the fact is he stated:

 

Quote"Just say no to CD treatments, from green markers to spray ons and rub ons.""End of quote.

 

He did NOT say "with the exception of sprays which have a dielectric constant equal to polycarbonate and can buffer out scratches which cause laser reflections".

 

As for your general flavor...what part of my statement where I said the brevity of my responses was due to the OP's inital request did you miss?  It was not my intent to hijack the thread to correct all the errors in the article, but some here insist.

 

I would have preferred anybody interested start their own thread and leave the OP's wishes intact.

 

Cheers, jn

 

ps.  Before more attempt to pigpile inaccurately, please.. I already stated that I agree with the general "desire" of the article, a lot of the audio stuff out there is ridiculous and rightly requires an accurate portrayal.

 

But NOT at the expense of engineering accuracy.  In my opinion, Peter has written the article in such a bad fashion with inaccuracies in many aspects, that he actually turns away the intended audience..those of the same mind will simply say "rah rah", and those who do not agree will ignore it.  He really should have vetted the article.

 


Edited by jnjn - 12/28/11 at 11:43am
post #4 of 55

Let's follow your argument through the standard structure of audiophile "theories."

 

1) You've made a statement.

2) You have introduced something scientific sounding which makes that statement true.

 

Now all you have to do is relate electromagnetic compatibility to measurable differences in cables of a magnitude which are likely to be audible. 

 

Good luck with that.

post #5 of 55

First, do an ABX test to see if the switchbox is audible or not......

post #6 of 55
Thread Starter 
Quote:
Originally Posted by Willakan View Post

Let's follow your argument through the standard structure of audiophile "theories."

 

1) You've made a statement.

2) You have introduced something scientific sounding which makes that statement true.

 

Now all you have to do is relate electromagnetic compatibility to measurable differences in cables of a magnitude which are likely to be audible. 

 

Good luck with that.

First things first.  Lets follow the argument from the beginning.

 

Peter claims that ""The simple truth is that resistance, inductance, and capacitance (R, L, and C) are the only cable parameters that affect performance in the range below radio frequencies""

 

I have stated that to be incorrect.  And I presented a clear engineering construct which follows the tenets of electromagnetic compatibility engineering.

 

You don't have problem with my statements.  What you have is a problem with the understanding of a recently started field of engineering.

 

With respect to EMC application, your sentence "Now all you have to do is relate electromagnetic compatibility to measurable differences in cables of a magnitude which are likely to be audible."" has absolutely no meaning...

 

EMC is not about the cables, it's about the control of currents.  Any time you have an unbalanced audio system, things you do not consider are going to bite you in the derrier.

 

I can test any coax or any line cord out the wazoo, and NEVER get any distortion of any kind whatsoever.  But If I put them into a system where the lack of EMC design standards couples the audio stream to power cord currents, or output section currents where it can reduce the phase margin at zero gain (unity gain frequency), I'm just asking for trouble.  Been there, done that, designed it out..However, there are VERY few designers who have designed absolute current path control into their system.

 

As I said, I could teach EMC if you so desire, or I can give ya a link to some stuff..(you are better off with links to Tom Van Doren's stuff).  You will find that you are no longer in Kansas anymore.

 

Cheers, jn

 

 

 

 


Edited by jnjn - 12/28/11 at 1:43pm
post #7 of 55
Thread Starter 
Quote:
Originally Posted by Prog Rock Man View Post

First, do an ABX test to see if the switchbox is audible or not......

 

Good one...biggrin.gif

 

It gets better than that...

 

Take two #12 awg 10 foot speaker cables, one with a characteristic impedance of 4 ohms, and one with a characteristic impedance of 120 ohms.

 

The test is: can you tell the difference?

 

So, hook em up to this box so you can switch between them.

 

Problems???

 

Well, considering that the 4 ohm cable has an inductance of about 8 nanohenries per foot vs 150 nanohenries per foot for the other, what exactly are you testing??  The insertion inductance of the box is going to be in the microhenry range, so the low z cable has 80 nH already, so you've swamped the cable inductance by over an order of magnitude..but for the high z cable, it already has 1.5 uH.

 

Is this a controlled test???

 

Certainly not.  It has an added confounder which spoils that which is being tested.  The possibility of accurate testing of a low impedance speaker cable using a switch box is zero.

 

Cheers, jn

post #8 of 55

With a particular switchbox (if the ground of the "unused" source is not floated) you could still readily verify if sloppy EMC design will make a measurable or audible difference in practice, by testing it with and without.  Have you?

 

Certainly there should be no significant high-frequency content (above half the sampling rate) in the signal from the source, unless it has severe issues, which is not impossible.  I'm by no means an expert in EMC, but we're by no means talking about the usual high-frequency systems where such considerations are more important.  Where do you suggest there is significant coupling, between what?


Edited by mikeaj - 12/28/11 at 1:50pm
post #9 of 55
Quote:
Originally Posted by jnjn View Post

I have stated that to be incorrect.


But you haven't yet backed it up with performance differences. As stated in the original quote, those three things are what can impact performance. Performance, in this application, is audio reproduction. The difference caused by something other than those three things has to be audible to impact performance to a meaningful degree.

 

I can write all I want about how the uncertainty of quantum mechanics means that no two cables will be the same even if they measure the same on any given test, but that doesn't mean we can hear the effects of quantum mechanics at work.


Edited by Head Injury - 12/28/11 at 1:56pm
post #10 of 55

Re: Switch boxes

 

A few years ago I did some crude experiments comparing the differences between a single 3' run of RCA analog cable(AR AP031) , two 3' lengths of the same RCA analog cables connected by a $1.00 connector, the two 3' lengths connected via a Niles Audio AXP-1 Switchbox and a 6' length of the same RCA analog cables (AR AP032 - the 6' variation). The measured differences between the different combinations in terms of FR were extremely small.

 

It was admittedly an indirect test using a 16 bit recording device to record the analog output of a CD player using the same wav segment ( a chinese cymbal crash)  - a spectral analysis was done on each sample (carefully trimmed and aligned) and the results exported for a spreadsheet,  the samples were averaged over 10 trials for each combination and the differences calculated and plotted.

 

Thus, I am a bit skeptical that a switch box is death to an ABX...of course only some ABX tests even use a box , others use cable swaps and to date the empirical evidence for audible differences between standard RCA cables (excluding those with exotic boxes inline, or 6m vs 1m of pre-riaa eq cartridge signal cable)  is scant at best.

 

As for the anti-digital thing - this was challenged back in the 80s when Ivor Tiefenbrun(*) was incapable of detecting a (nominal) 16 bit A/D/A segment inserted after the amped output of a turntable, but others have repeated this since including those spanish chaps at matrixhifi - again the presence/absence of an extra digital stage is almost never detected

 

 

[*] - The experimenters detected a subtle relay noise that was different in the two settings but Uncle Ivor did not wink.gif


Edited by nick_charles - 12/28/11 at 3:07pm
post #11 of 55

frown.gif

post #12 of 55
Thread Starter 
Quote:
Originally Posted by mikeaj View Post

With a particular switchbox (if the ground of the "unused" source is not floated) you could still readily verify if sloppy EMC design will make a measurable or audible difference in practice, by testing it with and without.  Have you?

 

Certainly there should be no significant high-frequency content (above half the sampling rate) in the signal from the source, unless it has severe issues, which is not impossible.  I'm by no means an expert in EMC, but we're by no means talking about the usual high-frequency systems where such considerations are more important.  Where do you suggest there is significant coupling, between what?


Don't know how to split quote on this forum...this is to the first Q, the second should extrude from the first answer.

 

Q1...Yes, I have.  The most drastic one I had had this:

 

The input RCA was on the back panel farthest left from front view.  the line cord was on the far right.  The power supply star ground was approximately in the middle of the chassis, on the bottom.  The speaker outputs were next to the line cord entry point.  All the pass transistors for the output were linear across the back of the chassis, taking up the entire length, it was a 3 ru panel.

 

The input pair was on the far left, so the input shielded cable was only about 5 inches long.

 

In practice, the following problems reared their ugly head.

1.  Any ground loop currents flow along the back panel of the chassis, from the rca shield to the line cord ground.  For 60 hz currents, the aluminum basically can be considered as a wide flat conductor, as eddy currents have only started to constrict the current path that a DC current would take.  As the frequency of the loop current increases, the path of the current will become more constricted as the current attempts to take the path of least reactance.

2.  The feedback network which sets both the DC fback gain as well as the hf gain, had a star ground back to the cap bank.  This is a different reference point than the connection of the input jack at the rca.  The two paths form a loop of ground conductor, and this loop was significant enough to trap flux caused by currents along the back panel.

3.  The output devices as wired, did not control the current path of the supply rails nor the current path of the output run.  Done properly, the currents should have all been twisted together to drop the mangetic field caused by the outputs.  They were NOT, and as a consequence, allowed the ground loop formed internal to the chassis to couple to the output currents.

 

As a direct consequence of these design flaws, the amplifier allowed both ground loop currents and internal power draw currents to couple into the analog path, by compromising the star grounding reference points, and more heinous, some of the fields managed to couple directly into the input pair on the pc board.  This is an avenue of ingress which has the FULL GAIN of the amplifier circuitry.

 

As a result, the amplifier was susceptible to line cord selection both because of cord geometry as well as grounding resistance variations.  It was also susceptible to coupling between the IC shield and the total ground loop formed by the source, amp, and the wires.  That susceptibility included a phase margin which changed depending on the cords.  One time, it was sufficiently low that a spike in a record caused both amplifiers in the system to break into oscillation somewhere below the unity gain frequency, and it exploded the crossover caps in both speaker columns.

 

Q2.  The higher the frequency, the less of a problem you have with direct current path issues.  The reason is, for a coax input at very high frequencies, the ground loop inductive reactance far exceeds the impedance the signal would take through the coax..so the signal will return via the shield.  When that occurs, the shield is effective.

 

Cheers, jn

 

ps..Forgot to add.  On the test bench where I checked the amplifier for distortion, there was no ground loop formed by the input (blame good test gear), so the amp read perfectly well into 4 ohms at 300 watts resistive.  And, being resistive, the output draw was only two quadrant..a reactive load swaps the magfield drive loop in rather strange and wonderful ways..

 

 


Edited by jnjn - 12/28/11 at 3:40pm
post #13 of 55
Thread Starter 
Quote:
Originally Posted by Head Injury View Post


But you haven't yet backed it up with performance differences. As stated in the original quote, those three things are what can impact performance. Performance, in this application, is audio reproduction. The difference caused by something other than those three things has to be audible to impact performance to a meaningful degree.

 

I can write all I want about how the uncertainty of quantum mechanics means that no two cables will be the same even if they measure the same on any given test, but that doesn't mean we can hear the effects of quantum mechanics at work.

While quantum mechanics is interesting, I do not see relevance other than a strawman/diversion.

 

The origional qoute states that the three things, R,L, and C are the ONLY things which can impact.

 

Clearly they are not.  If you wish links to understand, please ask.

 

Cheers, jn

 

 

post #14 of 55
Quote:
Originally Posted by jnjn View Post

While quantum mechanics is interesting, I do not see relevance other than a strawman/diversion.

 

The origional qoute states that the three things, R,L, and C are the ONLY things which can impact.

 

Clearly they are not.  If you wish links to understand, please ask.

 

Cheers, jn

 

I used it as an example, not a strawman (that's the wrong use of the term BTW).

 

It stated that those three things are the only things which can impact performance. You haven't shown that anything else impacts performance. I'm defining performance as audible neutrality. This can't be more clear. Please respond with evidence that anything else affects the signal in an audible fashion.

post #15 of 55
Thread Starter 
Quote:
Originally Posted by nick_charles View Post

Re: Switch boxes

 

A few years ago I did some crude experiments.....snip....Thus, I am a bit skeptical that a switch box is death to an ABX


I certainly agree.  Using a box, it's important to consider the confounders.  There are systems out there which are not susceptible to EMC problems, but so far I find that many times it is by accident rather than design.  But it is certainly important to preserve the differences one wishes to test for, so sometimes just swapping or switching doesn't preserve the differences being tested for.  EMC has been one of those "what are y'all talkin bout" things that are only recently being considered.

 

Experiments are great, it's good to see people doing them.

 

Cheers, jn

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