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Degradation of sound quality by speaker cables with high loop resistances?

oal

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What happens if I use a speaker cable with high resistances? The owner’s manual of my speakers (Revel M105) says “NOTE: High loop resistances that exceed 0.07 ohms (for each wire run) will cause the loudspeaker’s filter network to be misterminated, resulting in considerable degradation of sound quality.” I bought an Amazon Basic’s AWG16 cable which was made of aluminum and its DCR was 52 milli-ohm / meter (yes, I measured). Its loop resistance will be 0.2 ohm for a 2m cable (0.052 ohm x 2m x 2 for a loop). This exceeds 0.07 ohm. What damage do you expect if I use this cable for my Revel M105, and why? For example, because high DCR = high impedance, does the cable act as a low-pass filter like a coil?
 

levimax

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What happens if I use a speaker cable with high resistances? The owner’s manual of my speakers (Revel M105) says “NOTE: High loop resistances that exceed 0.07 ohms (for each wire run) will cause the loudspeaker’s filter network to be misterminated, resulting in considerable degradation of sound quality.” I bought an Amazon Basic’s AWG16 cable which was made of aluminum and its DCR was 52 milli-ohm / meter (yes, I measured). Its loop resistance will be 0.2 ohm for a 2m cable (0.052 ohm x 2m x 2 for a loop). This exceeds 0.07 ohm. What damage do you expect if I use this cable for my Revel M105, and why? For example, because high DCR = high impedance, does the cable act as a low-pass filter like a coil?
No damage, slight change in FR which is probably not audible. Why not just get some 12 gague copper wire and not worry about it?
 
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oal

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No damage, slight change in FR which is probably not audible. Why not just get some 12 gague copper wire and not worry about it?
Levimax, thank you. I was merely curious because the manual said "considerable degradation of sound quality". I actually use 14 gauge copper cable for my speakers.
 

levimax

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Levimax, thank you. I was merely curious because the manual said "considerable degradation of sound quality". I actually use 14 gauge copper cable for my speakers.
Not sure why the manual is so dramatic.. probably trying to make sure people don't do something crazy like running 100 ft of 18 gauge aluminum wire. Added resistance will interact with the speakers impedance curve and change the FR... The more the resistance the bigger the change... But 0.07 ohms is only going change FR a fraction of a dB. In any case enjoy your speakers... They are good ones.
 

JSmith

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What happens if I use a speaker cable with high resistances?
Well the cable has more resistance than is necessary so...
The resistance of the speaker wire that interacts with this variable resistor of the speaker will mess up the frequency response of the incoming signal. Some sounds will be quieter at some frequencies than intended, and the tonal balance will just be plain different from what the speaker designer intended.
http://connectedmag.com.au/what-you-need-know-about-speaker-wiring/

Please just choose the correct AWG and length for your application;

1624683021060.png


https://www.audioholics.com/audio-video-cables/speaker-wire-gauge

52 milli-ohm / meter
I think your measurement is out too... as that would be 170.61 mohm/ft?

image




JSmith
 

alex-z

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How have you measured that wire resistance? Seems extremely high, like the measurement leads aren't making good contact.
 
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oal

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The resistance of the speaker wire that interacts with this variable resistor of the speaker will mess up the frequency response of the incoming signal. Some sounds will be quieter at some frequencies than intended, and the tonal balance will just be plain different from what the speaker designer intended.
JSmith

Thanks, I will try to reproduce the issue when I have time. If the difference between 0.2 ohm and 0.05 ohm is only a dB or so, it will not be audible as Levimax says.

I think your measurement is out too... as that would be 170.61 mohm/ft?
JSmith

No, 15.85 milli-ohm/ft. 1m = 3.28ft.
 
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oal

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How have you measured that wire resistance? Seems extremely high, like the measurement leads aren't making good contact.

I measured it with the digital multimeter. The photo displays resistance of a 2m loop (1m cable). It is because the Amazon's cable is made of aluminum, not copper. I measured a BELDEN's AWG16 copper cable as well, and its resistance was 11.5 milli-ohm/m or 3.5 milli-ohm/ft.
 

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oal

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I have measured FR with a speaker with two speaker cables. One is 4m of the Amazon Basic's - 0.416 ohm (0.052 ohm x 4m x 2). Another one is 4m of audio-technica's - 0.06 ohm (0.0075 ohm x 4m x 2). The speaker's impedance was 4 ohm (so, NOT Revel M105 which has 8 ohm impedance as I wanted to test the cables with a low impedance speaker). Here are the two FR graphs:
FR.png


There are only few differences.
1624974210538.png


Software and equipment I used:
  • ARTA software
  • Steimberg UR24C
  • ECM8000 (not calibrated)
 

pjug

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I measured it with the digital multimeter. The photo displays resistance of a 2m loop (1m cable). It is because the Amazon's cable is made of aluminum, not copper. I measured a BELDEN's AWG16 copper cable as well, and its resistance was 11.5 milli-ohm/m or 3.5 milli-ohm/ft.
16 AWG is ~4 ohms for 1000 ft so your measurement of the Belden looks reasonable. Something is way off with the Amazon cable. Maybe there is a residue or oxidation where you are making contact? Looking at the diff numbers in your FR it would surely be worse than this if the cable were really 0.42 ohms. You can use the Benchmark spreadsheet to get an idea of how much difference you should get with high resistance cable:
https://cdn.shopify.com/s/files/1/0321/7609/files/DampingFactorCalculator.xlsx?v=1591278482
 

DonH56

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The OP is using CCA (copper-clad aluminum), not pure copper. The resistance is higher for CCA so be careful what wire table you use to calculate resistance.

As for degradation. as has been said it results in the crossover network being driven by a higher-than desired (higher than designed for) impedance, which will change the frequency response slightly and may cause other effects during transients and such via higher terminal EMF (electromotive force -- the "back-EMF"). I suspect in the real world it will not be noticed but have no data on it. Worst-case return the CCA and buy some pure copper of the right gauge for your runs (standard copper is about 2x the cost of CCA but we don't usually buy it often).

If you can't, or do not want, to return the CCA, then hook it up and see if it matters (probably not).

IMO - Don
 

preload

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Thanks, I will try to reproduce the issue when I have time. If the difference between 0.2 ohm and 0.05 ohm is only a dB or so, it will not be audible as Levimax says.

It depends on what the impedance vs freq curve of the speaker looks like. At 0.2 ohms wire dcr, there could potentially be the equivalent of several <1db wide-band peaking filters across the audible spectrum. That is potentially audible. People don’t seem to understand that you can get audible-range FR deviations from speaker cables when you stray from 12ga short runs. That being said just changing the position of your speaker by a couple inches in your room will probably have a more noticeable effect on FR.
 
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KSTR

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A little bit of EQ on the frequency response from a highish termination impedance as seen by the speaker is just that, a little bit of overlaid EQ... which, that is if required at all, can be catered for with counter-EQ on the amplifier input signal. When the signal on the speaker terminals is exactly the same it does not matter if there is any series resistance in front of it (assuming non-pathological cases of well below 1Ohm total loop resistance).

I would say considerable degradation of sound quality is a quite exaggerated statement, even without counter-EQ you'd be hard pressed to identify 200mOhm vs the recommended max of 70mOhm in a controlled listening test.
 

pjug

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The OP is using CCA (copper-clad aluminum), not pure copper. The resistance is higher for CCA so be careful what wire table you use to calculate resistance.

As for degradation. as has been said it results in the crossover network being driven by a higher-than desired (higher than designed for) impedance, which will change the frequency response slightly and may cause other effects during transients and such via higher terminal EMF (electromotive force -- the "back-EMF"). I suspect in the real world it will not be noticed but have no data on it. Worst-case return the CCA and buy some pure copper of the right gauge for your runs (standard copper is about 2x the cost of CCA but we don't usually buy it often).

If you can't, or do not want, to return the CCA, then hook it up and see if it matters (probably not).

IMO - Don
Really? Amazon Basics sells this as speaker cable? This is interesting. Is this the cable?
https://www.amazon.com/AmazonBasics-16-Gauge-Speaker-Wire-Feet/dp/B006LW0W5Y

Edit: This one says CCA. I had no idea this was common.
https://www.parts-express.com/Audte...d89XQa3wjQk27Fuur-iBiRj7BJCc-FWhoCZRcQAvD_BwE
 
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pjug

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The CCA issue is good to know about, but the OP measured a 4X difference between Amazon and Belden, which can't be right can it?
 
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DonH56

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Really? Amazon Basics sells this as speaker cable? This is interesting. Is this the cable?
https://www.amazon.com/AmazonBasics-16-Gauge-Speaker-Wire-Feet/dp/B006LW0W5Y

Edit: This one says CCA. I had no idea this was common.
https://www.parts-express.com/Audte...d89XQa3wjQk27Fuur-iBiRj7BJCc-FWhoCZRcQAvD_BwE

The CCA issue is good to know about, but the OP measured a 4X difference between Amazon and Belden, which can't be right can it?

I don't know what to expect for the difference off-hand; I don't like CCA for other reasons than higher resistance. The only number I remember is for some Ethernet cables our lab accidentally bought and the resistance of the CCA was about 50% higher than then copper wires (using a Kelvin measurement). I would expect speaker cables, being larger, to not be quite as bad but really do not know. A quick search led to a couple of articles saying 4 AWG (!) CCA speaker cables had about 33% higher resistance compared to copper. That is not 4x, but I do not know how the OP measured. Without a four-point (Kelvin) scheme or very careful probing it is difficult to measure low resistances using a standard DMM.

Since copper prices have skyrocketed the past few years (decades) CCA has become very common. It can be hard to to determine from the description; often your only clue is it is about half the price of regular "pure" copper wire.

The arguments for CCA are usually lower cost and lighter weight. At RF frequencies skin effect actually matters (as you know) and CCA may be less an issue in some applications. At audio frequencies all, or at least a significant fraction, of the wire is used, so CCA will be a bigger real-world hit in resistance.

Whether that is audible, meh, above my pay grade.
 

mhardy6647

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Edit: This one says CCA. I had no idea this was common.
CCA got common (again) with the "recent" (last few years) run-up of copper prices (again).
Aluminium is a pretty darned good conductor (though not as good as copper) -- but it gets a bad rap, I think, mostly because it's cheap...
that said, when it comes to 20 or even 50 feet of pure copper wire, the incremental cost against that of a whole hifi system is slight enough that going with CCA seems like a bad place to scrimp.

Just an opinion, though -- not immutable fact! :)
 

pjug

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The only number I remember is for some Ethernet cables our lab accidentally bought and the resistance of the CCA was about 50% higher than then copper wires (using a Kelvin measurement). I would expect speaker cables, being larger, to not be quite as bad but really do not know. A quick search led to a couple of articles saying 4 AWG (!) CCA speaker cables had about 33% higher resistance compared to copper.
These sound more like it. So I think the OP's measurement is way off.
 

DonH56

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The bad rep for CCA is due to connection issues when the thin copper layer is worn (or tightened) through and Al exposed. Al oxide (or whatever it is) is hard and an insulator (nonconductive) IIRC. I know switching to Al wire in houses and industrial buildings led to some poor connections that led to fires. These days you use adapters to ensure a good connection that is mechanically stable (one can hope) to alleviate problems. But for me, having been burned a few times with CCA connection issues, I just pay the extra for regular old copper. In the overall scheme of things $25 vs. $50 for a spool to connect several thousand dollars worth of speakers and amps is not worth worrying about.

Disclaimer: Metallurgy is not my day job so I could be misremembering, though not about the fires Al wires caused in a shed many years ago. The fire investigation laid the blame right on the Al wire connections in the breaker box.

Edit: I am not saying your Al speaker cables will cause a fire -- that was AC power wiring. But they may exhibit high resistance moreso due to the connections than the wire itself.
 
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