Speaker wire, CCA vs OFC

[Speedskater]

Jim Brown, an interference guru, often stresses how important it for all unshielded cords & cables (interconnect, speaker & power) to have a twisted construction.
* * * * * * * * *
see the link in my post #85

 

[DonH56]

Yes, twisting a signal-return pair (even a single-ended pair) results in common-mode noise cancellation depending upon the interfering frequency and how tightly are the twists. At least AFAIK...

 

[Julf]

Jim Brown, an interference guru, often stresses how important it for all unshielded cords & cables (interconnect, speaker & power) to have a twisted construction.
* * * * * * * * *
see the link in my post #85

At radio frequencies, yes.

 

[Julf]

Yes, twisting a signal-return pair (even a single-ended pair) results in common-mode noise cancellation depending upon the interfering frequency and how tightly are the twists. At least AFAIK...

Any pointers to a calculation of what the CMMR would be? It really doesn't work very well if the source and drain are unbalanced and have a big impedance difference.

 

[DonH56]

Any pointers to a calculation of what the CMMR would be? It really doesn't work very well if the source and drain are unbalanced and have a big impedance difference.

Hi Julf,

Remember my world is RF, not audio, so I was thinking more of the LF RFI rejection though it should work at audio as well (mainly for power supply noise). As for calculations, not off-hand; I use a little red book by Walker (can't recall the title, have to look it up later) or the old ITT Reference Data for Radio Engineers book. Don't know if either has calcs or curves. One of those things I've "known" for decades from a college EM class plus a lot of work in the field then and since; at one point a couple of us made a bunch of twisted pairs using different tpi and measured their CMRR but I have no idea where that data is now. As others will be quick to point out, I could be completely wrong and making the whole thing up. But, it was also taught in a Besser Associates EMI class a few years ago.

It'd be interesting to repeat the measurements using our VNA but not sure when I'll have the time. My workweek is pretty crazy right now. I am wondering about your assertion on the impedances. Not disputing it, do not know, and am curious. RF tends to use matched circuits, and most of my current world uses differential pairs, but audio tends to have low driving impedance and very high load impedance for interconnects. I am suspecting my experience is (again) not valid for audio though I know folk do it.

IIRC the idea is that the twisting lets the ground act like somewhat a shield even for single-ended singles and that the twists allow signals to impinge "equally" on signal and ground (return) conductors to provide the rejection. Not nearly as effective compared to differential, I agree with you on that! And pretty much a fail at HF where the wavelength (or fractional 1/2 or 1/4 wavelength) approaches the twist distance.

I have no idea the actual CMRR in practice, however. I do it all the time when adding test wires and such, more or less by habit, and very recently a younger engineer hooked up a probe connector without twisting, got lots of noise, then twisted and saw a significant reduction. Didn't measure it, alas; I just saw the noise, looked at the wires, asked him to twist them, and the noise went away (or was at least reduced below the noise floor of the DSO). So I have what we on ASR would call subjective evidence. But not like it's all that hard to get below the noise floor of a DSO...

There are some online references so a search might help. The young engineer I was working with found several but I didn't follow up. I have a vague memory from one of the classes that the twisted pair idea was actually patented by Alexander Graham Bell back in the late 1800's! Would never have guessed that.

Anyway, you can treat all my experience as anecdotal, but I'll keep doing it out of habit if nothing else.

I would like to hear your thoughts on the impedance impact, however. It makes sense but I have not really thought about it.

HTH - Don

 

[Julf]

Sounds like we are actually not far from being on the same page. My go-to white paper for a really good explanation is https://www.hypex.nl/img/upload/doc/an_wp/WP_The_G_word.pdf

 

[Speedskater]

From the Jim Brown paper:

Antenna Action The most fundamental cause of radio interference to other systems is the fact that the wiring for those systems, both inside and outside the box, are antennas. We may call them"patch cables" or "speaker cables" or "video cables" or "Ethernet cables," or printed circuit traces,but Mother Nature knows that they are antennas! And Mother Nature always wins the argument.

 

[Julf]

From the Jim Brown paper:

Antenna Action The most fundamental cause of radio interference to other systems is the fact that the wiring for those systems, both inside and outside the box, are antennas. We may call them"patch cables" or "speaker cables" or "video cables" or "Ethernet cables," or printed circuit traces,but Mother Nature knows that they are antennas! And Mother Nature always wins the argument.

Ah, appeal to extremes. Yes, everything, from a wedding ring to heating radiator is an antenna. So?

 

[NTK]

Jim Brown's recommendations are best looked upon as rules of thumb. If it doesn't add cost, such as twisting two wires together, why not just do it. There is no harm.

Remember that the title of Jim's article is "A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing". The implicit assumption here is that there is probably a 1.5 kW RF amplifier running in the house, and there is a 30 ft antenna radiating in the backyard. Their RFI environment is not necessarily similar to ours .

 

[Dago]

Quick question about wires and signal transmission. If I understand correctly, audio signal is AC and travels on the surface of the wire. I assume that the same principle as antenna would apply here. In that case, why is there such an obsession with the Origen free copper? Isn’t the diameter of the wire that will matter? Are there any scientific measurements that prove that OFC is superior to the copper clad aluminum or steel? Just curious.

Hello,
I just wanten to share a recent experience with cca speaker cable. To make the story short it comes down to this: the use of cca speaker cable (wasn’t aware of it at first) lead me to a very dissapointing quality on my speakers. The whole setup is of a rather good quality (NAD streamer & amp + B&W speakers) and I error-tested the system with some old full copper speakercables. Conclusion: If your system performs with cca then you’re just lucky I guess... but full copper (ofc is used to keep it grom oxidizing) sounds just much better! The only meassuring device I used is my own ears...
Best regards,
Dago

 

[Wombat]

Here we go agaaaiiin, first poster. 'I can hear it' unreferenced, uncontrolled nonsense.

 

[Koeitje]

Hello,
The only meassuring device I used is my own ears...

And that's where you went wrong. CCA or OFC doesn't make any difference if the cable is thick enough (2.5mm2 OFC ~ 4.mm2 CCA). You should do a double blind test.

Or maybe you just tested 0.5mm2 CCA using 10 meter cables?

 

[w1000i]

The critical thing not the cable but the plug/socket thing they use cheap alloy stuff.

very few companies use a material like the cable conductivity, I think the best is anticable and wireworld ( silver-cald type)

 

[Julf]

The only meassuring device I used is my own ears...

Your subjective, unverified perception is noted.

 

[Blumlein 88]

Another tip: I've heard that using THC with cables improves how it sounds to your ears. And this measurable as well.

 

[raistlin65]

In my experience when I used to have a much tighter budget and used CCA, it was not as flexible as the OFC I have used since, in the sense that you can bend it, but then it would lock into the bend. It would not just naturally lie flat. More like coat-hanger wire that's a little easier to bend.

Is that a characteristic of the aluminum? Or is it just the way the cheap wire was made?

 

[Julf]

Is that a characteristic of the aluminum?

Pretty much, yes. Aluminium also work hardens. It should not be used where flexibility is needed.

 

[ClassicGuy]

Is it okay to buy 12awg wires, but strip the ends into 16awg so they would fit those tiny Sony spring clips? If we only care about total resistance from wiring, this sounds feasible, but I am not sure if it can cause issues.

 

[Ordin Aryguy]

Is it okay to buy 12awg wires, but strip the ends into 16awg so they would fit those tiny Sony spring clips? If we only care about total resistance from wiring, this sounds feasible, but I am not sure if it can cause issues.

Absolutely. The total DCR of the wire will barely be effected by the tiny reduction in wire count over that very short distance.

Unless your total cable length is only 2 or 3 inches. Then it might.