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Effect of Speaker Cable Length Mismatch

DonH56

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The subject of mismatched speaker wires came up recently and I said it could matter due to varying speaker impedance with the wire as a divider from the amplifier. That was based on tests done long, long ago (but in this galaxy). At that time zip cord from maybe 22 down to 18 AWG was pretty common so I got to thinking my experience was no longer relevant given 14 - 10 AWG is pretty common now.

I had a old schematic with three different speaker models. I am no longer sure exactly the speakers, but one is a fairly benign load similar to my Magnepans. The second is (was) a more common but not terribly demanding load. The last is a speaker with fairly wide excursions and a low-impedance (ribbon) tweeter. I modeled a solid-state amplifier with damping factor of 200 at 8 ohms (0.04 ohm output impedance) rising at high frequency (typical due to reduced feedback). In the simulations SSn shows the result of the amplifier driving speaker n with no wire, and SSn_wire is with the extra 20 feet of speaker wire (modeling the mismatch). I only included wire resistance, no other parasitics (no extra inductance, capacitance, or conductance terms -- usually not terribly relevant at audio frequencies, and/or I was too lazy to include them all, take your pick). The top plot shows impedance in ohms, and the other the voltage at the speaker terminals in dB.

First is a simulation with and without an extra 20 feet of 18 AWG wire. Speaker one shows negligible difference except a slight change in effective gain. Speaker 2 shows more, with a dip in the bass, and the extra resistance actually reduces the HF peak. Speaker 3 shows a bit more deviation. These deviations are not large, making me wonder about my original tests (done ca. 1982 and no I don't have the records) when DBT's showed people could hear a difference. I am not sure what speakers were used then; I think it was a pair of Magnepans (my MG-IIIa), a pair of B&W 801, and an ESL pair (not sure which one, there were several we used).
amp_test4_wire_20ft18awg.png

Now below are the results if instead I use 20 feet of 12 AWG cable instead. The differences are much less as we'd expect, probably inaudible.
amp_test4_wire_20ft12awg.png


So chances are mismatching your speaker cables assuming a reasonable amplifier, speaker, and cable size and length is not going to be audible. Of course this is one example and certainly does not cover all systems but I tried to use somewhat real-world examples.

FWIWFM - Don
 

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McFly

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Ive just finished prewiring my HT and now I can sleep. 2.0mm speaker cable, 15m to one side and 9m to the other.

At worst i figured one speaker might be like, 0.2db quieter. So virtually inaudible.
 

Emlin

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There is obviously, as long you are using thick enough cable, no audible difference whatever length you use or how different those lengths may be, within bounds.

All that matters is how much you paid for it.
 
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pma

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The subject of mismatched speaker wires came up recently and I said it could matter due to varying speaker impedance with the wire as a divider from the amplifier.

I made similar measurements on real-life amplifiers and cables and some of them I have archived. I was not oriented on length mismatch, but on the influence of cable impedance to FR and on comparison of FR at amp terminals and speaker box speaker terminals. Below is an example of measurement with 6m, 2x4mm2 cable, class AB amplifier. The influence on FR was small, much lower than what I measured recently as an effect of class D output LC filter (no PFFB).

There is obviously, as long you are using thick enough cable,
It is the inductance that possibly matters and you will not get rid off it by cable thickness.

6m_cable_effect2_s.png
 

Kijanki

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Thicker wire has lower inductance, but with cable it is a little bit different, since thicker cable wires are usually spaced further apart, increasing cables inductance. I believe that if speaker cable has effect on the sound then 20% more will have some effect as well. On the other hand i don't buy argument, some people make, about coiling excess length. Coiling doesn't increase inductance since it is not a wire, but a cable (currents in opposite directions). Coiling cable is similar to common mode choke, or bifilar non-inductive resistors that have no inductance for differential signals.
 
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xaviescacs

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I have a Marantz Amplifier, a relatively new one, those with two speaker channels, A and B, you know. Recently I tried channel B with a newly made cable of 2.5 mm² copper wire and simple bananas, both from KabelDirekt. To my surprise, not always both speakers sound, sometimes one, sometimes both, sometimes the other. I plug the headphones that doesn't cut the speaker out to check and everything is fine all the time. The speaker cables have different length as the amp was not in the center and I wasn't thinking about electricity when I made them, just about saving cable. Can I discard that the amp has some trouble because of this mismatch due to different resistance or whatever? What do you think?Thanks!!
 

Suffolkhifinut

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Thicker wire has lower inductance, but with cable it is a little bit different, since thicker cable wires are usually spaced further apart, increasing cables inductance. I believe that if speaker cable has effect on the sound then 20% more will have some effect as well. On the other hand i don't buy argument, some people make, about coiling excess length. Coiling doesn't increase inductance since it is not a wire, but a cable (currents in opposite directions). Coiling cable is similar to common mode choke, or bifilar non-inductive resistors that have no inductance for differential signals.
Thicker wire has lower resistance not lower inductance. Coiling will increase inductance by condensing longer cable length into a small volume, hence all inductors are made from coils of wire. When it comes to non inductive resistors are you referring to wire wound resistors where the coil direction is clockwise and half way along anti-clockwise so the inductive effects cancel each other out?
 

sergeauckland

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Thicker wire has lower resistance not lower inductance. Coiling will increase inductance by condensing longer cable length into a small volume, hence all inductors are made from coils of wire. When it comes to non inductive resistors are you referring to wire wound resistors where the coil direction is clockwise and half way along anti-clockwise so the inductive effects cancel each other out?
Coiling doesn't increase the inductance of loudspeaker wires as the two wires are both coiled together, so the inductance of one cancels the inductance of the other, and what's left is the inductance due to the separation of the two wires. Similarly, non-inductive wirewound resistors are wound bi-filar such that there's no nett increase.

S.
 

Suffolkhifinut

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Coiling doesn't increase the inductance of loudspeaker wires as the two wires are both coiled together, so the inductance of one cancels the inductance of the other, and what's left is the inductance due to the separation of the two wires. Similarly, non-inductive wirewound resistors are wound bi-filar such that there's no nett increase.

S.
Serge my comments were on general electrical principles as that’s the way kijanki‘s post read. Can’t argue with your comments on two core cables overall inductance when carrying the same current in opposite directions. Although it will still cause them to try to push apart, while the effect is minor it’s still there and coiling will make it stronger.
 
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DonH56

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I have a Marantz Amplifier, a relatively new one, those with two speaker channels, A and B, you know. Recently I tried channel B with a newly made cable of 2.5 mm² copper wire and simple bananas, both from KabelDirekt. To my surprise, not always both speakers sound, sometimes one, sometimes both, sometimes the other. I plug the headphones that doesn't cut the speaker out to check and everything is fine all the time. The speaker cables have different length as the amp was not in the center and I wasn't thinking about electricity when I made them, just about saving cable. Can I discard that the amp has some trouble because of this mismatch due to different resistance or whatever? What do you think?Thanks!!
Sounds like a bad cable irrespective of length. In this case the length is not an issue, but a connector (or more) may be bad. First inspect the connections at both ends (amp and speaker) of each cable and ensure there are no loose strands of wire that might short things out.

Then connect normally and check which speaker is not working. Swap the cable connections at the amp and see if the problem stays with the same speaker or moves to the other. If it stays with the same speaker, the problem may be that speaker or the cable.

It it stays with the same speaker, then swap the connection at the speaker end, so now you have swapped the cable at both ends. If the problem stays with the speaker, then that speaker has a problem. If it moves to the other speaker, then the cable is the problem. Inspect and repair or replace the cable.

If the problem stayed with the same amp channel when you preformed the first swap, then the amp itself is probably bad. Repair or replace.

0. Inspect everything!
1. L amp -> L wire -> L spkr; R amp -> R wire -> R spkr -- note which speaker is bad.
2. L amp -> R wire -> R spkr; R amp -> L wire -> L spkr
2a. If problem stays with same amp channel, now connected to different wire and speaker, then the problem is likely the amp. Repair amp.
2b. If the problem stays with the same speaker, now connected to different amp channel, then there is likely a problem with the wire or the speaker.
3. If the case is (2b), switching amp channels did not change which speaker, then swap the wires at the speaker end:
L amp -> L wire -> R spkr; R amp ->R wire -> L spkr
3a. If the problem follows the wire (switches to the other speaker), repair or replace the wire.
3b. If the problem stays with the speaker, repair or replace the speaker.

Hopefully I got all that right, it's early. You may want to diagram the strategy for yourself and confirm the logic to determine if the problem is the amp, the wire, or the speaker.

HTH - Don
 

xaviescacs

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Sounds like a bad cable irrespective of length. In this case the length is not an issue, but a connector (or more) may be bad. First inspect the connections at both ends (amp and speaker) of each cable and ensure there are no loose strands of wire that might short things out.

Then connect normally and check which speaker is not working. Swap the cable connections at the amp and see if the problem stays with the same speaker or moves to the other. If it stays with the same speaker, the problem may be that speaker or the cable.

It it stays with the same speaker, then swap the connection at the speaker end, so now you have swapped the cable at both ends. If the problem stays with the speaker, then that speaker has a problem. If it moves to the other speaker, then the cable is the problem. Inspect and repair or replace the cable.

If the problem stayed with the same amp channel when you preformed the first swap, then the amp itself is probably bad. Repair or replace.

0. Inspect everything!
1. L amp -> L wire -> L spkr; R amp -> R wire -> R spkr -- note which speaker is bad.
2. L amp -> R wire -> R spkr; R amp -> L wire -> L spkr
2a. If problem stays with same amp channel, now connected to different wire and speaker, then the problem is likely the amp. Repair amp.
2b. If the problem stays with the same speaker, now connected to different amp channel, then there is likely a problem with the wire or the speaker.
3. If the case is (2b), switching amp channels did not change which speaker, then swap the wires at the speaker end:
L amp -> L wire -> R spkr; R amp ->R wire -> L spkr
3a. If the problem follows the wire (switches to the other speaker), repair or replace the wire.
3b. If the problem stays with the speaker, repair or replace the speaker.

Hopefully I got all that right, it's early. You may want to diagram the strategy for yourself and confirm the logic to determine if the problem is the amp, the wire, or the speaker.

HTH - Don
Thanks for your detailed answer. This is too much work on your part for what my problem is. I feel bad for this.

I've tried with another set of speakers and cables and found out that the problem is on the amp, since the behavior is the same on both sets, which are very different. It requires the volume to reach some threshold to start working properly. Before this, I hear some noise and only one of the speakers work, randomly every time I switch on and off, without changing anything else. After this threshold has been reached, I can turn down the volume again and everything works perfectly at any level. o_O
 
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DonH56

DonH56

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Thanks for your detailed answer. This is too much work on your part for what my problem is. I feel bad for this.

I've tried with another set of speakers and cables and found out that the problem is on the amp, since the behavior is the same on both sets, which are very different. It requires the volume to reach some threshold to start working properly. Before this, I hear some noise and only one of the speakers work, randomly every time I switch on and off, without changing anything else. After this threshold has been reached, I can turn down the volume again and everything works perfectly at any level. o_O
You'd feel worse if you didn't ask; ASR is about learning!

That is the classic symptom of a bad coupling capacitor or broken bias circuit inside the amp. I would immediately take it out of service for repair because it can get worse and also send DC or very low-frequency large steps into the speakers.
 

xaviescacs

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You'd feel worse if you didn't ask; ASR is about learning!

That is the classic symptom of a bad coupling capacitor or broken bias circuit inside the amp. I would immediately take it out of service for repair because it can get worse and also send DC or very low-frequency large steps into the speakers.
That's a very valuable information. Thanks!!
 
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DonH56

DonH56

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A reminder that the potential issue with speaker cables is not propagation time, which is in the mud unless the speakers are miles apart, nor simple attenuation from the extra wire impedance (mainly resistance and inductance), but frequency response variation due to how the crossover is terminated. Most speakers are designed AFAIK to be driven by pretty close to an ideal voltage source so the crossover's input expects a very low impedance. Change that, and the frequency response will change a little. Make a drastic change in one speaker's response relative to the other's due to very different wire lengths from amp to speaker, and the frequency response of one speaker will be different than the other.

In the real world, any such effect is likely grossly swamped by other things, like the room, speaker placement and resulting SBIR issues, and normal speaker-to-speaker variance due to manufacturing tolerances in the crossovers and drivers.

The case I had in mind from the primordial past was a speaker with an amp sitting right behind one speaker and connected via a very short cable, and the other speaker was reached by a very long route up the wall, around a door, across the back wall, and finally back down and to the other speaker. There was some reason (forgotten now) the cable could not be just routed straight across the front wall but had to go all around the room to get to the other side. This was before the cable craze, or near the start, and cheap zip cord was used, probably 18 AWG or so. The difference was about half an ohm, but the speakers dipped below one ohm, so the response was measurably and audibly different. And of course my little pea brain goes straight to the worst case imaginable when this is a non-issue for the vast majority of us (myself included).
 
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