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Speaker cables don't influence harmonic distortion!
Speaker cables don't influence harmonic distortion!
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Old 31st March 2018, 04:40 PM   #1
vzaichenko is offline vzaichenko  Russian Federation
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Speaker cables don't influence harmonic distortion!
Arrow Speaker cables don't introduce harmonic distortion,

however, they do influence the overall harmonic distortion of the system (amplifier + cable + speaker) indirectly.

Here are some practical proofs, including the right way to measure:
Correct connection of the audio analyzer
Low-frequency measurements with the real speaker
The way a cable influences the overall performance of the system

Cool thoughts on DF by GoatGuy + futher discussion

~~~~~~~~~~~~~~~~~~~~~~~~~~~~
That's how it all started:

Hi All,

A few weeks ago XRK971 drew my attention to the fact that different quality speaker cables result in harmonic distortion increase - particularly H3 goes up.
As I'm taken by low-feedback designs these days, I decided to run a quick live test with my prototypes. I used two cables I have in hand, both are rather high-quality:
1) stranded copper cable with silver coating (3 meters long);
2) stranded copper cable with no coating (15 meters long).

The results are rather interesting.
  • Distortion increase is significantly more noticeable at 1KHz than it is at 20KHz;
  • Harmonic that grows the most is H3 (H2 even goes down in some cases);
  • The effect is much less noticeable with low-feedback amplifier than it is with "normal" - high-feedback - amplifier. Distortion at 20KHz even goes down with longer cable as soon as the feedback loop gain is low (18db in my case).
Pictures outline:
1) Summary of measurements (R/L/C values are shown for each cable);
2) THD 1 KHz with no cable;
3) THD 1 KHz with 15 meters cable;
2) THD 20 KHz with no cable;
3) THD 20 KHz with 15 meters cable.

Those spectrums are shown for the high-NFB amplifier (Tribute 3000).

I'm going to continue experiments in this area, especially exploring the low-feedback configurations.

Cheers,
Valery
Attached Images
File Type: png Cable_analysis_table-01.PNG (21.2 KB, 1386 views)
File Type: png 01 01K.PNG (49.8 KB, 1378 views)
File Type: png 04 01K.PNG (46.1 KB, 1367 views)
File Type: png 01 20K.PNG (44.2 KB, 1358 views)
File Type: png 04 20K.PNG (44.4 KB, 1350 views)
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Last edited by vzaichenko; 15th April 2018 at 12:30 AM.
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Old 31st March 2018, 05:01 PM   #2
5th element is offline 5th element  United Kingdom
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That's a large increase in third harmonic right there with the cables attached.

Interestingly, when I was building, and troubleshooting class A/AB amplifiers etc I did do measurements with some speakers attached and didn't actually find a tremendous difference in harmonic spectra. I am going to contradict myself as much as saying there was an obvious difference, the distortion rose, but not by a tremendous amount.

I wasn't testing at particularly high power levels though and distortion was down at 0.0005% for the 1kHz, short cables, dummy load, test. Your amplifier is quite different. I don't remember the distortion rising by anywhere near as much as your results are showing but I could be remembering incorrectly.
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Old 31st March 2018, 05:09 PM   #3
jwilhelm is offline jwilhelm  Canada
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Were these measurements taken with a speaker attached or a dummy load? I wonder if the speaker crossover may be affecting this too?
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Old 31st March 2018, 05:11 PM   #4
Nelson Pass is offline Nelson Pass  United States
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Speaker cables don't influence harmonic distortion!
Quote:
Originally Posted by vzaichenko View Post
I'm going to continue experiments in this area, especially exploring the low-feedback configurations.
I would recommend testing with a zobel attached at the far end of
the cable, something like .047uf in series with 5 or 10 ohms.
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Old 31st March 2018, 06:13 PM   #5
BesPav is offline BesPav  Russian Federation
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Hi, Valery, itís better to add something low-freq, say 30-100 Hz.

The main issue with the cables is its intrinsic resistance.

Feedback to the ampís core is taken from the ampís output terminals, so the wire resistanse with load forms simple divider.
Additionally long or thin wire formally acts as ampís output resistanse, which in case drops damping factor.

Taking feedback from the load could be a good way, but you will need to dissolve and compensate/exclude common mode error and noise.

The best way is to use Calvin 4-wire load connection and fully-differential amplifier. In this case you can simply put common mode chokes at both output and feedback terminals.
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Old 31st March 2018, 06:15 PM   #6
vzaichenko is offline vzaichenko  Russian Federation
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Speaker cables don't influence harmonic distortion!
I forgot to mention - all measurements are done at 10V RMS, 8R dummy load, measuring at the load end of the cables.
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Old 31st March 2018, 06:24 PM   #7
vzaichenko is offline vzaichenko  Russian Federation
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Speaker cables don't influence harmonic distortion!
Quote:
Originally Posted by Nelson Pass View Post
I would recommend testing with a zobel attached at the far end of
the cable, something like .047uf in series with 5 or 10 ohms.
Thank you Nelson, I will try adding zobel at the load end of the cable.

Cheers,
Valery
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Old 31st March 2018, 06:28 PM   #8
vzaichenko is offline vzaichenko  Russian Federation
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Speaker cables don't influence harmonic distortion!
Quote:
Originally Posted by BesPav View Post
Hi, Valery, itís better to add something low-freq, say 30-100 Hz.

The main issue with the cables is its intrinsic resistance.

Feedback to the ampís core is taken from the ampís output terminals, so the wire resistanse with load forms simple divider.
Additionally long or thin wire formally acts as ampís output resistanse, which in case drops damping factor.

Taking feedback from the load could be a good way, but you will need to dissolve and compensate/exclude common mode error and noise.

The best way is to use Calvin 4-wire load connection and fully-differential amplifier. In this case you can simply put common mode chokes at both output and feedback terminals.
Hi Pavel, yes, in the end of the exercise I thought I will measure some low frequency spectrums as well. It would be also interesting to see what the square wave is going to look like - to see what happens to fast transients.
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Old 1st April 2018, 09:11 AM   #9
Elvee is offline Elvee  Belgium
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Very strange: I think all serious people agree that the intrinsic distortion of the cable itself is vanishingly low, well under the ppm.

This leaves the amplifiers or unknown artifacts as possible explanations.

Such a gross increase in THD caused by a relatively minor change in the load impedance would seem to indicate a pathological behavior from the amplifier(s).

Tests I have done myself show that the THD is indeed dependent on the nature of the load, inductive, capacitive or resistive, but the change is at most like 1 to 2 or 1 to 0.5, and that's for a purely reactive load whose magnitude at the test frequency equals Znom.

I would look at possible artifacts: for example the grounding: the test generator has its ground connected to the amplifier side, whilst the THD meter is connected to the far end of the cable.
If both equipments are earthed, this will cause a ground loop, with unpredictable results.
That is only one example, many other possible pitfalls exist
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Old 1st April 2018, 10:00 AM   #10
vzaichenko is offline vzaichenko  Russian Federation
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Speaker cables don't influence harmonic distortion!
Hi Elvee,

Load impedance change is very small. Look at it from a different perspective (from the load side of the cable) - output impedance of the amplifier is changed dramatically (I measure at the load, so the cable complex impedance adds up to the output impedance of the amplifier).

This is confirmed by my measurements with the low-feedback amplifier, having much higher output impedance, than the other one - distortion increase is much lower at 1KHz and it comes to decrease at 20KHz.

Try to measure at the load side of the cable - you'll see the difference.

Cheers,
Valery
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