Reciprocity in electrical networks

[EB1000]

Here you go. A proof of the effect of directionality of a bad cable using simulation.

Input is a 1kHz square wave. Component values remain the same, only the direction was swapped. I'm also showing spectral analysis/

Non symmetrical passive network is directional, yet still reciprocal.
So the claim made by cable manufacturers does make some sense. But it doesn't make the cable any better, as a cable should be transparent and symmetrical.

Remember that you are not injecting current into an audio cable, you're applying voltage.

 

[MarkS]

I started this mess, because I tried to clarify, with an oft quoted expert, who stated that because audio signals are AC, directionality of the cable does not matter.

Well, you dissed the dude pretty egregiously ("lost all respect"). To me the big semantic issue is whether the word "cable" implicitly implies "uniform cable", that is, one without any variation along its length that impacts its electrical properties. Uniform cables are not directional. To me, assuming "cable" implies "uniform cable" is reasonable, especially for someone working in a regime (audio frequencies) where any such variation is of negligible import.

 

[EB1000]

As I said. it is possible for a cable to be directional is it's not symmetrical. I only mistakenly used the term reciprocal instead of symmetrical network. Here is a simulation based demonstration of a "directional cable" . As you can see, directionality of the signal (square wave) affect both time and frequency. Yes, a passive network is always reciprocal (v2/i1 = v1/i2), but it doesn't mean it's also symmetrical.

 

[waynel]

Here you go. A proof of the effect of directionality of a bad cable using simulation.

Input is a 1kHz square wave. Component values remain the same, only the direction was swapped. I'm also showing spectral analysis/

Non symmetrical passive network is directional, yet still reciprocal.
So the claim made by cable manufacturers does make some sense. But it doesn't make the cable any better, as a cable should be transparent and symmetrical.

Remember that you are not injecting current into an audio cable, you're applying voltage.

View attachment 126305

this is not proof of anything , RC filters are directional. However, as I mentioned in the other thread, please refer back to the textbook that you are using and you will see that a cable is represented by a series of tiny LRC filters and in the limit where the filters are tiny enough, the ideal cable is symmetrical. Real cables are also symmetrical at audio frequencies as are RF cables used at RF frequencies.

 

[Raindog123]

Well, here is my latest. As the topic OP, and as I did put myself on the spot. In the name of scientific truth (and fairness to folks)...

While "simple RC networks" (including RLC filters and cables) absolutely are reciprocal... I did wrongly misapply the reciprocity principle to our particular case proposed for discussion by @audio2design (and by association by @EB1000) - of uneven cable resistance distribution (R1 ≠ R2 in the equivalent schematic).

To illustrate it, the principle states that if we move the source (V1) to [any] new point (eg to I1), then the current measured at the source's original position will be exactly the same - I1's in (1) and (2). However, as @audio2design pointed out, if we change the cable direction, the circuits (1) and (3) are no longer equivalent due to R1 ≠ R2.

To clarify what I am saying. I was incorrect stating that the cable 'omnidirectionality' follows from the 'fundamental reciprocity principle alone'. Unfortunately, I am wrong there. And for such asymmetric case, to assess the significance of the effect one would needs to look at the actual impedance numbers (that, as all here agree, will be negligible). And directionality will be absent in case of 'symmetrically distributed' cable resistance (R1 = R2), capacitance, and inductance. [But again, this would be beyond 'just due to the reciprocity principle', so have to revert the guys' grade... ]

 

[maverickronin]

Why does it matter? Because with this alternate truth reality we seem to live in, and the lack of respect given to science within this hobby/pursuit, the people who identify as technical / experts need to hold themselves to a higher standard. If we don't, then why should we expect lay people to trust us?


Grossly exaggerated examples work just fine. Where this all came out was whether cables are not directional because signals are AC. An argument was made and has been made repeatedly that because signals are AC, direction does not matter. The opposite is true. It may not matter because of the magnitude of parameter variation at the frequencies of interest, but not just because they are AC.


This was never about audibility, it was about accuracy of communicated information.

Do you also get angry at people when they give you directions to a place without taking into account general relativity and time dilation?

 

[MakeMineVinyl]

Why does it matter? Because with this alternate truth reality we seem to live in, and the lack of respect given to science within this hobby/pursuit, the people who identify as technical / experts need to hold themselves to a higher standard. If we don't, then why should we expect lay people to trust us?

Let me ask you something - do you actually design anything, or just enjoy debating edge-case theory?

I do design practical stuff which gets sold to actual customers, and if I navel-gazed to the extent you seem to believe is vital, nothing would ever get designed and out the door. I happen to care a damn lot about my designs and as a matter of principle exhaust all due diligence before signing my name to the final result - however there is that, and there is wasting time worrying about how many electrons can fit on the head of a pin.

I think you are in the latter category. Correct me if I am wrong.

 

[MarkS]

There are several things in this paragraph that stand out. They may signify the source of your problems.

Doubling down on insults is not a great plan.

 

[audio2design]

Well, you dissed the dude pretty egregiously ("lost all respect"). To me the big semantic issue is whether the word "cable" implicitly implies "uniform cable", that is, one without any variation along its length that impacts its electrical properties. Uniform cables are not directional. To me, assuming "cable" implies "uniform cable" is reasonable, especially for someone working in a regime (audio frequencies) where any such variation is of negligible import.

The dude dissed me too, so I don't feel at all bad. He also dissed everyone who didn't bow down to his statement of AC makes cables non directional. We allow people to put themselves on these pedestals and then raise them up to the point that common sense goes out the window. Within the scientific community it is a big barrier to advancement.

 

[audio2design]

this is not proof of anything , RC filters are directional. However, as I mentioned in the other thread, please refer back to the textbook that you are using and you will see that a cable is represented by a series of tiny LRC filters and in the limit where the filters are tiny enough, the ideal cable is symmetrical. Real cables are also symmetrical at audio frequencies as are RF cables used at RF frequencies.

You are assuming perfect manufacturing. You are using a theoretically perfect cable to prove an argument. No cable is theoretically perfect though for practical purposes they are. An example was given above that is correct. Crimp a coax 1/4 from the end such that the capacitance changes at that location. That cable will not measure with the exact same frequency response in each direction.

 

[amirm]

You all be careful with personal comments.....

 

[audio2design]

Let me ask you something - do you actually design anything, or just enjoy debating edge-case theory?

I do design practical stuff which gets sold to actual customers, and if I navel-gazed to the extent you seem to believe is vital, nothing would ever get designed and out the door. I happen to care a damn lot about my designs and as a matter of principle exhaust all due diligence before signing my name to the final result - however there is that, and there is wasting time worrying about how many electrons can fit on the head of a pin.

I think you are in the latter category. Correct me if I am wrong.

There are millions of my products in the hands of customers. I have also designed uber expensive one offs. However, now I find myself in an industry where I there is a continual parade, practically a whole industry, with the one goal of creating and growing a false narrative about how things work. To compete with that, we need an organized, but factually correct front. ASR at some level exists because of that.


But I ask you, why are you defending the indefensible. This is a technical discussion I started. The statement is correct or not. I saw a lot of bad engineering applied trying to justify that the statement was correct, even though easy and clear examples show it is not. That poorly applied engineering statements were also laden with personal insults. Is this what ASR is? Is this what the technical community is? No wonder there is such a divide.

 

[MarkS]

He also dissed everyone who didn't bow down to his statement of AC makes cables non directional.

Reading what he wrote, I believe he mentioned AC only because DC does have a definite direction, the direction of current flow. And I also believe he was using the word "cable" to mean "uniform cable". And all of this was in the context of refuting various forms of audiophoolery.

Furthermore, this sort of terminology confusion happens all the time in science and tech. Your going nuclear on such a confusion is absurd, and only degrades your own reputation. Of course, you are anonymous here, while the person you attacked by name (in a thread title no less) is not.

 

[audio2design]

Cables, at DC (sans leakage), are effectively not directional. All the parasitic inductive and capacitive elements disappear and you are left with nothing but series resistance, which you can now reciprocal and symmetrical.

 

[audio2design]

To clarify what I am saying. I was incorrect stating that the cable 'omnidirectionality' follows from the 'fundamental reciprocity principle alone'. Unfortunately, I am wrong there. And for such asymmetric case, to assess the significance of the effect one would needs to look at the actual impedance numbers (that, as all here agree, will be negligible). And directionality will be absent in case of 'symmetrically distributed' cable resistance (R1 = R2), capacitance, and inductance. [But again, this would be beyond 'just due to the reciprocity principle', so have to revert the guys' grade... ]

Respect!

 

[scott wurcer]

You are assuming perfect manufacturing. You are using a theoretically perfect cable to prove an argument. No cable is theoretically perfect though for practical purposes they are. An example was given above that is correct. Crimp a coax 1/4 from the end such that the capacitance changes at that location. That cable will not measure with the exact same frequency response in each direction.

So do this to a 1 meter audio IC and show the measurement at 20kHz. I don't think you could get a big enough Smith chart to plot this effect. Breaking things and giving them a pathological behavior does not prove much.

 

[waynel]

You are assuming perfect manufacturing. You are using a theoretically perfect cable to prove an argument. No cable is theoretically perfect though for practical purposes they are. An example was given above that is correct. Crimp a coax 1/4 from the end such that the capacitance changes at that location. That cable will not measure with the exact same frequency response in each direction.

So you are saying a broken cable can be directional . Maybe if it’s broken, might as well add some diodes or a transformer inline too. Anyway I doubt that even a crimped cable will show much difference when measured forward and reverse at audio frequencies. Would you care to demonstrate with measurements ?

 

[MakeMineVinyl]

There are millions of my products in the hands of customers.

Examples, please? No need to get specific as to manufacturer, but I would be curious as to the nature of these 'millions' of products, and especially how you solved the cable conundrum in these products to your standards.

 

[scott wurcer]

Not that it means anything but there are 100's of millions of my products in customers hands (though many probably have found the bin by now). In 50yr. of my experience I have never come across a wire "directionality" issue in any discipline, medical, science, physics at any level that was not simply a gross identifiable defect.

It serves to remember ADSL works over the most horrible infrastructure of (sometimes) 100yr. old #24 twisted pair with hand splices randomly spaced.

I mention again that real names would be a good policy.

 

[phoenixdogfan]

My example of reciprocity:

"They put one of ours in the hospital, we put one of theirs in the morgue!"