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Measurements of speaker cables in frequency and time domain

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pma

pma

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@pma, could you replace the voltage source in #98 with a current source and then plot 1/((V(in)/1A)*(2*pi*frequency))? This is the equivalent capacitance of the impedance the amp will see driving into.

Huh, like this? Thank you Klaus, I will finally learn something here.

Klaus.png


The Y value depends on number of points. The CCS is 1A.

Klaus2.png


C = 1/(2*pi*F*(Vin/I1)), C= 1/(2*pi*F*Z), this was your point ?
 
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KSTR

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Pavel, I've never checked if that kind of analysis is correct for transmission lines but I think it should be as for any normal networks it is applicable.
Before, and really right up to the first peak the load is capacitive (look at the phase of the pure impedance V(in)/1A) with a -90deg phase angle and increasing magnitude (reaching many nF), after the peak it turns inductive (+90deg), and so one, after each peak.
Basically, around the first resonance, the impedance looks like the known curve from a series C+L which has a severe notch at the resonance and the impedance is going down as low as the ESR permits (much lower than |Xc|) and has a phase angle of zero, a full short.
1619945644441.png

blue: impedance of a pure cap.
green: impedance of unterminated transmission line with that DC capacitance.
For my tline example, the "DC capacitance" is 300pF but close to the peak, say at 7.6Mhz, the impedance is almost two orders of magnitude lower and still having 90deg of phase... if that is near the GBW of the amp it will be unhappy....
 
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MrPeabody

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I have hoped this was clear, absolutely clear.
... I have to add that I really do not like the philosophical debates about engineering issues.

What I really do not like is when someone is UNWILLING to make any true effort to explain what they are trying (or pretending) to say and writes something like, "I really do not like the philosophical debates about engineering issues." Pooh.

You have taken some liberties, the latest among them being your use of the word "philosophical" to disparage perfectly technical criticisms of stuff you have written. When people aren't able to follow what you're saying and they ask you to explain, you answer by posting graphs, and you do not explain the graphs or how the graphs are supposed to answer their question. There is a truth here that needs to be said plainly: thus far you have not made any sincere effort to answer peoples' questions, when they have asked questions because they aren't able to make sense of what you are saying.

What I would really like is for you to show the algebra that gives justification to whatever it is exactly you are ostensibly saying. If you truly have a clear understanding of what you are saying, you will be able to explain it using some simple algebra. There are three complex-valued impedances in series. The expression for the voltage drop across any one of the three is much the same for all three of them, the only difference being the numerator in the rational expression. For each of the three impedances, the denominator in the expression is the same: the sum of the three impedances. Each and every one of the voltages you are reading is influenced by all three of the impedances. It is not apparent to me that you realize this. Perhaps you do, but you haven't thus far provided any real evidence that would convince me that you do.

You wrote:
To eliminate amplifier effect, voltage is measured at amplifier output B and speaker input A and the ratio A/B shows the frequency response added by the cable.

What exactly do you mean by "the frequency response added by the cable"? The ratio of those two voltages, A/B, is mathematically equivalent to the ratio of the two impedances. If any of your graphs actually show this ratio (as opposed to the difference A - B, or B - A), then what that graph is actually showing is the ratio of the speaker impedance to the cable impedance at various frequencies. Perhaps it is meaningful in some context to show the ratio of those two impedances, but I can't see as how it would make sense to equate this ratio to "the frequency response added by the cable". If it happens that what is displayed on the screen is actually the difference between those two voltages (as opposed to the ratio), then what it is showing is the difference between the two impedances. Again, it may be useful in some context to show the difference between the cable impedance and the speaker impedance, but I can't see as how it would make sense to equate this difference to "the frequency response added by the cable". In order for this to make sense, you have to first explain exactly what you mean by "the frequency response added by the cable". I honestly do not know what this even means. You obviously think it is a meaningful concept, but I am skeptical as to whether it is.
 
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pma

pma

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Pavel, I've never checked if that kind of analysis is correct for transmission lines but I think it should be as for any normal networks it is applicable.
Before, and really right up to the first peak the load is capacitive (look at the phase of the pure impedance V(in)/1A) with a -90deg phase angle and increasing magnitude (reaching many nF), after the peak it turns inductive (+90deg), and so one, after each peak.

Got it, Klaus.

7mcable_imp.png


Now the effect of 50 ohm terminating resistor:
7mcable50R_imp.png
 
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preload

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This is very equivalent to measuring the voltage drop accross the cable. Assuming symmetrically constructed cable, one side will do. The side grounded at the amp would apply and then this can be trivially be measured with a soundcard, may not even need balanced input.
Cable has resistance, speaker doesn't draw constant current vs. frequency --> voltage loss along the cable isn't constant, speaker's FR will change. Ohms Law, as simple as that.

I’m not quite following what you’re describing there. To be clear I am stating that the voltage vs freq should be measured in one location only, that is, the + and - terminals of the speaker binding posts. We can then change out the speaker wire that connects the amp output to the speaker terminals and take another measurement. The measurements can then be compared.
 

KSTR

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@preload , @MrPeabody, you're overcomplicating things.
Pavel wanted to show that non-negligible impedance (primarily resistance) of a speaker cable, besides a general small level drop, causes a slight frequency response change when the speaker is not a constant load vs. frequency (neglecting current distortion here).
To better quantify the difference it is needed to factor out the (very small) response change seen already at the amp output which is not zero impedance -- but low enough to not disturb the general concept of the sim/measurement. Hence FR(load)/FR(amp) was computed to normalize out the amp's influence.
While it is true that the amp output impedance itself affects the effect it is small enough compared to the other impedance that it can be safely neglected. If it were the same magnitude than the cable the effect would be half as strong and if the amp were a current source there'd be zero effect on frequency response and level.
 
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pma

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Klaus, the physics works. This is the simulated cable terminated by 180 ohm. Almost real impedance without pole/zero peaks and notches, and thus no problem for amp stability.

7mcable180R_imp.png
 

preload

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@preload , @MrPeabody, you're overcomplicating things.
Pavel wanted to show that non-negligible impedance (primarily resistance) of a speaker cable, besides a general small level drop, causes a slight frequency response change when the speaker is not a constant load vs. frequency (neglecting current distortion here).
To better quantify the difference it is needed to factor out the (very small) response change seen already at the amp output which is not zero impedance -- but low enough to not disturb the general concept of the sim/measurement. Hence FR(load)/FR(amp) was computed to normalize out the amp's influence.
While it is true that the amp output impedance itself affects the effect it is small enough compared to the other impedance that it can be safely neglected. If it were the same magnitude than the cable the effect would be half as strong and if the amp were a current source there'd be zero effect on frequency response and level.

Yeah I'm still not following what you're trying to convey. Two tries, I'm out. Ciao!
 

Chrispy

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This whole thread is a bit lost....does it have an actual practical point to express?
 

preload

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This whole thread is a bit lost....does it have an actual practical point to express?

It started off with the poster providing empiric data confirming that speaker cable can cause 0.2dB deviations in frequency response as a result of cable resistance/inductance driving a reactive load). But then it got obfuscated by additional argument about Mhz-frequency differences (sigh), and then all things just kind of went downhill from there.
 

Chrispy

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It started off with the poster providing empiric data confirming that speaker cable can cause 0.2dB deviations in frequency response as a result of cable resistance/inductance driving a reactive load). But then it got obfuscated by additional argument about Mhz-frequency differences (sigh), and then all things just kind of went downhill from there.

It was still obscured in real circumstance usefulness if that's a thing. It boiled down to insignificant the way I read it. I'm starting to think pma is a cable charlatan "designer" myself.
 
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pma

pma

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I made an attempt to measure input impedance of 5m zipcord speaker cable with open end (no termination), with a point-by-point measurement at discrete frequencies and Excel sheet. The result looks quite realistic. There is a dip near 10MHz.

5mzip_open_impedance.png

Measuring range is 100kHz - 24MHz
 
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solderdude

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It was still obscured in real circumstance usefulness if that's a thing. It boiled down to insignificant the way I read it. I'm starting to think pma is a cable charlatan "designer" myself.

Give the man some credit.

His measurements/simulations are based on the fact that some specific amps may get stability issues with long or shorter but high capacitance cables connected to an an amplifier that is active (signal on it) but no speakers are connected or some speaker that has a > 1kohm impedance above 1MHz.
That could potentially make some poorly designed high BW amps unstable.

He is not claiming the cable can lead to sonic differences, just merely attempting to point out that some cables in specific circumstances could potentially oscillate at a high frequency which could in turn affect SQ.

PMA is not wrong but pointing towards very rare circumstances.
 
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KSTR

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WTF, accusing Pavel of being a cable manufacturer's sock puppet is sure the most bizarre thing I've ever read on this forum.

To recap (hopefully some finally get it now):
Amir's fist test used too high source impedance to be useful (and I've explained why), he quickly corrected that and used a real amp with low output impedance. With this he compared the difference of cable effects, using very similar cables with similar lumped RLCD parameters. Therefore only marginal differences showed up. The specific test method with AP he chose is IHMO not the very best for this kind of tests but good enough, assuming he controlled the circumstances (notably avoiding any temperature change of the voice coils of the speaker used as a test load).

Pavel tested, basically, the effect of the length used for a speaker cable. Amir's results would have been exactly the same had he used a cable of zero length comparing to a standard length.

Later, as a side branch, Pavel and I delved into the topic of amplifier becoming unstable from an rather obscure reason (from laymens POV), which is cable length of unterminated cable. The point here is that an amplifier that is close to, or actually breaks out into oscillation (typicall only during parts of the waveform) may, most surely will alter the sound and then the comparision to a different cable will be skewed without knowing it.
 
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pma

pma

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Thank you, Klaus.

All, I will not reply to stupid accusations and also will not go with secondary school textbook explanations. It is not my way. For those who do not like my approach, feel free to put me on the ignore list.
 

Koeitje

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Conclusion
It is impossible to say that "cables make no difference". It is not true. The cables depending on length, construction and speaker used may make an audible difference, even if they are as short as 2m. 5m of 2x1.5mm2 zipcord makes 0.2dB deviation at higher bass, into quite standard speaker load. This starts to be audible. The speaker cable should be as short as possible and monoblocks placed near the speaker are the best option in case of passive speakers.

Edit: the zipcord used was 2x1.5mm2, length 5m.
I think the entire argument always boiled down to get cables that are thick enough. Can you do these tests with cables that are more reasonably close to what you would see as a recommendation. So 4mm2 vs 6mm2 at lets say 5 meters.
 

Matias

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Pavel, I am interested if you could repeat your tests with similar length and gauge cables of different constructions and compare them in the audio band. Would they show any difference say copper or silver, as some cable manufacturers claim? Thanks in advance.
 

solderdude

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There is no need to compare in the audio band. There is no difference between silver and copper when the difference in ohm/meter for the same diamter (7%) is compensated for in either length or diameter (3.6% larger copper conductor diameter is enough compensation).
In the MHZ range (where PMA's article is about) it isn't about the used conductors but spacing between inductors (geometry) which matters at these frequencies.
 
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LTig

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Thank you, Klaus.

All, I will not reply to stupid accusations and also will not go with secondary school textbook explanations. It is not my way. For those who do not like my approach, feel free to put me on the ignore list.
That would be a very stupid thing to do.
 
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