Lost all respect for Doug Self

[preload]

Next, audio2design argues that we're all wrong because we ignore quantum physics when discussing audio cables.

I wouldn't be surprised, this guy sounds like a total boson.

 

[waynel]

I found this little ditty in one of his website,

Audio signals are AC. Cables cannot be directional any more than 2 + 2 can equal 5. Anyone prepared to believe this nonsense won't be capable of designing amplifiers, so there seems no point in further comment. (Doug Self)


Obviously in this post, Doug is saying the often repeated, but ridiculously incorrect statement that because audio signals are AC, that cables cannot be directional. Now for those with a half decent understanding of electronics and cables, you understand that a cable is essentially a network of resistors and inductors in series, with capacitors in parallel, with some parasitic additional inductance, resistance and capacitance. Since no cable is perfectly manufactured, those values will vary along the length of the cable, especially capacitance and inductance. Like any other two-port transfer function with capacitors and inductors, at AC frequencies, the input-output function is not the same as the output-input function, especially when source and load impedance is taken into account.

Simple fact, that excluding leakage current, the only time a cable is perfectly non directional is at DC. No this is not a statement of audibility. At audio frequencies, the two port function would be close enough to be the same in both direction, but, that is not what Doug's statement says. It says because the signals are AC, direction does not matter. That is wrong.


Now, I messaged Doug, expecting a "ya, that was not the most accurate statement". Nope, he doubled down on his statement claiming cables are symmetrical, which they absolutely are not as anyone who has done any good RF or even TDR work. I pointed this out, he just responded "you are wrong" and went off in a huff.


I have read much of his stuff, good, not exceptional, and remember thinking some conclusions / statements gave me pause. After this exchange, I have lost all respect for him, and fumbling such a simple concept, or at least being unable to admit a mistake, makes me question a lot more.

RF engineer here. Audio cables are not directional unless the shield is only grounded at one side.

 

[audio2design]

Now do superposition for power

And one of 'interesting' aspects of the reciprocity principle is that an electromagnetic system's behavior remains the same, if we reverse the direction/flow of time...

And one last point. This is the tired (and wrong) argument I often see flaunted that ignores that a linear network does not have to have the same transfer function in each direction (which should be obvious and blows out that "does not need to be symmetric" argument).


The two-port is said to be reciprocal if the voltage v2 appearing at port 2 due to a current applied at port 1 is the same as v1 when the same current is applied instead at port 2. This is normally the case when the two-port consists exclusively of linear passive devices such as ideal resistors, capacitors, and inductors. The fundamental underlying requirement is linearity: That is, outputs must be proportional to inputs, and superposition must apply.


Small problem, the two port network does not exist in a vacuum. There is a source impedance and load impedance external to the network. Again, see my simple 10R, 1uF, 1R circuit. Should be pretty obvious the magnitude of currents will change. It is an exaggeration but it is no less right.

 

[audio2design]

RF engineer here. Audio cables are not directional unless the shield is only grounded at one side.

Oookay. So you have never measured reflections from cable imperfections at 10s of GHz I see.

 

[preload]

Oookay. So you have never measured reflections from cable imperfections at 10s of GHz I see.

Most humans cannot hear beyond 20khz. FYI, genius.

 

[Longshan]

Next, audio2design argues that we're all wrong because we ignore quantum physics when discussing audio cables.

Quantum physics, the perfect excuse we need when we've run out of science!

Quantum physics is bloody awesome, but it gets abused more than Valentino Rossi's kneepads.

 

[audio2design]

Golly gee, nice to know I don't have to worry about putting the C after the R when I do RC low pass filters in the future.... Cause Lorenz Reciprocity! ... What? That won't work?

 

[audio2design]

Most humans cannot hear beyond 20khz. FYI, genius.

Does not change what this thread is about which is not whether we can hear a change but whether AC negates the potential for directionality in a cable.

 

[GDK]

Does not change what this thread is about which is not whether we can hear a change but whether AC negates the potential for directionality in a cable.

...but you posted on Audio Science Review. There’s a clue in the title.

 

[audio2design]

...but you posted on Audio Science Review. There’s a clue in the title.

Whether audio or not, the science does not change genius.

 

[amirm]

Oookay. So you have never measured reflections from cable imperfections at 10s of GHz I see.

10s of Gigahertz? Why did you just say "RF" at the beginning? 10s of Gigahertz is a rarefied field that does not at lend itself to generalization as "RF."
You went hounding an audio designer with claims of issues at 10s of Gigahertz. And even there, you didn't have anything to show him as far as measurements. No wonder he blew you off.

 

[audio2design]

An audio cable as a passive two-port network, if badly designed, may represent itself a non-reciprocal linear network, which may attenuate certain frequencies on one direction more than on the other.

This does not violate the superposition theorem in either direction. Cables marked with directionality arrow, must have some added passive components at one of the terminal ends.

For example, some Audioquest interconnects, have a series inductance at their sending end and a parallel capacitor at their receiving end, forming a LPF network, which Audioquest claim to remove RF noise... This is an example of a snake-oil directional cable...

Whether the circuitry is intentional or due to manufacturing variation along the length of the cable makes no difference at all. It is all still linear circuitry. Lorenz Reciprocity is wrt same current in either port, get the same voltage the other port. But again you have a source and load impedance external to the network. Swap the cable (circuit) around and ask yourself is the applied current going to be the same (no obviously, just like a simple RC low pass if flipped around. It no longer works at the same frequency).

 

[waynel]

Oookay. So you have never measured reflections from cable imperfections at 10s of GHz I see.

Go back to the textbook or Wikipedia entry where you read about characteristic impedance and you will notice that we are talking about differentially small resistances, capacitances, and inductances (as In differential calculus ) . It’s not a simple RLC network but infinite amount infinitesimal elements , so transmission lines are not directional like RLC circuits. Besides transmission line behavior does not apply to audio frequencies on audio cables.

 

[waynel]

10s of Gigahertz? Why did you just say "RF" at the beginning? 10s of Gigahertz is a rarefied field that does not at lend itself to generalization as "RF."
You went hounding an audio designer with claims of issues at 10s of Gigahertz. And even there, you didn't have anything to show him as far as measurements. No wonder he blew you off.

Btw, I’ve designed circuits in the 12GHz range and the OP is still wrong about directionally.

 

[audio2design]

10s of Gigahertz? Why did you just say "RF" at the beginning? 10s of Gigahertz is a rarefied field that does not at lend itself to generalization as "RF."
You went hounding an audio designer with claims of issues at 10s of Gigahertz. And even there, you didn't have anything to show him as far as measurements. No wonder he blew you off.

The frequency matters not. The statement was made that because audio signal are AC that cables are not directional. That is wrong. They are directional because of AC. You may not measure effects till high frequency but they are there, and you could make a bad cable that showed the effect lower in frequency. Make a cable of out flat nichrome with a super thin dielectric for high capacitance for 1/2 the cable, then spread apart for the rest.

 

[preload]

Does not change what this thread is about which is not whether we can hear a change but whether AC negates the potential for directionality in a cable.

I think then you're posting on the wrong website. This is an audio forum. Most of us would evaluate whether or not an audio cable is directional based on whether reversing it results in audible differences (or measurements accepted to result in audible differences). You have already stipulated that there would be no audible differences. So from the standpoint here and as many have tried to point out to you, for our purposes, cables are not directional.

Perhaps you should try your gripe on an RF enthusiast forum.

 

[amirm]

Btw, I’ve designed circuits in the 12GHz range and the OP is still wrong about directionally.

I haven't go up that high but use to repair VHF gear and we never, ever worried about RF cables being directional.

 

[amirm]

The frequency matters not. The statement was made that because audio signal are AC that cables are not directional. That is wrong. They are directional because of AC. You may not measure effects till high frequency but they are there, and you could make a bad cable that showed the effect lower in frequency. Make a cable of out flat nichrome with a super thin dielectric for high capacitance for 1/2 the cable, then spread apart for the rest.

So you keep turning left and right. First it is 10s of gigahertz and now it doesn't matter? And what do you mean about me making a cable? You started this. Either you have measurements or you don't. And clearly the answer is you don't. Do you have a spice simulation you can share?

And are you an RF designer? If so, in what application you had to use directional cables?

 

[waynel]

So you keep turning left and right. First it is 10s of gigahertz and now it doesn't matter? And what do you mean about me making a cable? You started this. Either you have measurements or you don't. And clearly the answer is you don't. Do you have a spice simulation you can share?

And are you an RF designer? If so, in what application you had to use directional cables?

I’ve used tapered traces to do impedance transformations at RF frequencies but that’s an entirely different thing and would not work at audio frequencies as transmission line effect do not apply.

 

[solderdude]

just like a simple RC low pass if flipped around. It no longer works at the same frequency)

So you are claiming that a cable is basically a capacitor in parallel to the source followed by an inductor with a resistance ?
When you reverse that cable it becomes an inductor with a series resistor that goes into the capacitance ?

Easily shown doing time domain reflectometry even with a scope. I am totally being pedantic, but how can we be respected as technical experts when we can't prosletytize wrong statements. Cables are much more complex than simple LCR networks.

No measurements to back it up though yet is easily shown. No references to research of cables in the GHz range that show this ? No directional markings on any BNC cables ?

Nah. For anything audio related and video related and even digital audio related there is no directionality in cables other than the direction in which you can see the print on the cable. Funnily enough that print direction in audio-land is often said to be the direction it should be used in.
Source side on the first letter side, load on the last letter side.

My viewpoint of DS is not changed at all because of this thread.