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speaker cable, why is it never twisted
john11
post Nov 7 2012, 08:31
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Hi. And thanks for reading this post.

I have owned quite a few different speaker cables in my time and have always noticed the copper strands of wire within the cable run straight and parallel to each other I.e. they are not twisted. In fact the same is true of mains cable.

Can anyone tell me why this is I was told the electricity has trouble flowing through twisted strands, if each strand was enameled you might get an inductance effect but obviously it is not so the electricity should take the straightest path, so if the strands are twisted or not should have no overall effect.

Can anyone tell me why the copper strands are never twisted.

Thank you in advance. John.
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Garf
post Nov 7 2012, 12:34
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My understanding is that twisting cables only makes sense if the pair is a differential pair where you're relying on the receiver to do common-mode rejection. Typical speaker cables aren't differential pairs, likely because that's only really needed for HF signals. If the cables aren't differential, twisting can't produce an advantage as it's really spreading the noise over both cables (which eliminates it in a differential pair, but doesn't help in regular cabling).

Balanced pairs are used for audio when the cable needs to be long, and I do believe those are twisted.
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Phlogiston
post Nov 7 2012, 13:15
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How about twisted cables use more copper and pvc?
Cheaper to make straight / parallel cables
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pdq
post Nov 7 2012, 14:59
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Twisting the pairs reduces the emission or reception of RF, i.e. frequencies in the many kHz and upward range. The signals to the speakers have no such frequencies, and are not affected by their reception, therefore twisting is not needed and adds an unnecessary expense.

Also, the signal to the speakers is very low impedance and high power, so it would take a very strong interfering signal to have any effect, but being low impedance also means that it has inherently low emission as well.

Besides, there is nothing to prevent one from twisting the speaker cable before connecting it should one desire an extra measure of immunity.
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Speedskater
post Nov 7 2012, 15:46
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Really all cables be they power, signal interconnects or speaker should be twisted! (save for co-ax)

Jim Brown writes:

Twisting Cable pairs are twisted together for two very important reasons. First, bringing them
more tightly together reduces the coupling of external magnetic fields (while increasing the
coupling between the conductors) by reducing the loop area between them. Second, twisting
them together in a very symmetrical fashion causes any noise coupled onto one conductor to
be more perfectly cancelled (in the receiver) by noise coupled onto the other conductor.
Twisting reduces both magnetic (inductive) and electric (capacitive) coupling.
To understand how twisting does this, consider a magnetic field from a source that is closer to
one side of the cable than the other. At any point along the cable, one conductor will be
closer to the source than the other, so the induced voltage will be greater in that conductor
than in the other. But one half twist along the cable in each direction, the other conductor
will be closer to the source, and so will have the greater induced voltage, but the polarity will
be opposite. The more symmetrical the twisting, and the "tighter" the twisting, the more perfectly
the two induced voltages will match each other over the length of the cable, and thus
be better cancelled by the receiver. The number of twists per unit length is called the "lay" of
the cable.
Twisting also reduces capacitive coupling onto the cable, and for the same reasons. The ability
of twisting to reduce coupling extends to very high frequencies. Ethernet networks run on
high quality, unshielded, twisted pairs at frequencies in the hundreds of MHz, and require
good crosstalk rejection to function well.


Cables, Transmission Lines, and Shielding for Audio and Video Systems
by Jim Brown - Audio Systems Group, Inc.
http://audiosystemsgroup.com

http://audiosystemsgroup.com/TransLines.pdf


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Speedskater
post Nov 7 2012, 15:51
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Also Henry W. Ott writes about twisted pairs in chapter 2.12 "Coaxial Cable Versus Twisted Pair" in his big new book.

http://www.hottconsultants.com/EMCE_book_f.../emce_book.html


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pdq
post Nov 7 2012, 16:07
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I somehow doubt that either of these writers had speaker cables in mind.

I don't know if you will remember this, but in the old days TV antenna lead-ins were typically 300 ohm twinlead, i.e. not coaxial and not twisted pair. It actually was recommended that a few twists be made in the cable where it connected to the outdoor antenna, not for reasons of noise pickup, but because the cable had less tendency to flap in the wind, which could eventually lead to it breaking.
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Apesbrain
post Nov 7 2012, 16:41
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It's not accurate to say that the "copper strands are never twisted" in speaker cable. For example, here is a photo of the original Monster Cable:
http://s.shld.net/is/image/Sears/057991910...usm=0.9,0.5,0,0

Kimber Kable is twisted and twisted again:
http://www.kimber.com/blog/wp-content/uplo...LFOwMmDQ_12.jpg
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mzil
post Nov 7 2012, 16:46
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QUOTE (john11 @ Nov 7 2012, 03:31) *
Can anyone tell me why the copper strands are never twisted.

Because the relatively strong signal travels a short distance across your living room, so the likelihood of picking up RFI or EMI is rather low. Microphone level, on the other hand, is much weaker and often travels a greater distance, say across a studio or stage, so it benefits from twisting to reduce these potential noise problems, plus it uses a balanced connection for common mode noise rejection.

[For yucks I have twisted my own speaker cable in my youth by placing one end in an electric drill chuck, pulling it almost taut, and then spinning the drill. It was a waste of my time, however, but I was naive.]

When the internal strands of a multi-strand cable twist around each other in a spiral helix, however they touch all the other adjacent strands, it is done simply for for strength, ease of coiling, and flexibility, but the EMI/RFI rejection aspect of a "twisted pair "[with insulation separating them, that is] is gone.

This post has been edited by mzil: Nov 7 2012, 17:46
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Speedskater
post Nov 7 2012, 21:27
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QUOTE (pdq @ Nov 7 2012, 10:07) *
I somehow doubt that either of these writers had speaker cables in mind.
[******]


Really they do include speaker cables!


Twisted Pair Cable I can't say it enough zip cord is terrible for RFI, and twisted pair solves many
problems. If you have RFI and the cable is anything but coax or a good twisted pair, try to replace
the cable. This is true for virtually all systems anything from the sensor for a smoke detector to
telephone wiring to big loudspeaker cables. Shielded cable rarely solves RFI problems, partly because
to do anything useful cable shielding must continuous with equipment shielding, and lots of
equipment to which you would like to connect it is unshielded!

A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing

Entire Contents Copyright 2007-10 The Audio Systems Group, Inc., except Appendices 2, 3, and 4, which are property
of the cited authors, and product data, which is copyright by Fair-Rite Products. All Rights Reserved
by Jim Brown K9YC - Audio Systems Group, Inc.
http://audiosystemsgroup.com

http://www.audiosystemsgroup.com/RFI-Ham.pdf


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saratoga
post Nov 7 2012, 22:40
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QUOTE (john11 @ Nov 7 2012, 03:31) *
Hi. And thanks for reading this post.

I have owned quite a few different speaker cables in my time and have always noticed the copper strands of wire within the cable run straight and parallel to each other I.e. they are not twisted. In fact the same is true of mains cable.

Can anyone tell me why this is I was told the electricity has trouble flowing through twisted strands, if each strand was enameled you might get an inductance effect but obviously it is not so the electricity should take the straightest path, so if the strands are twisted or not should have no overall effect.

Can anyone tell me why the copper strands are never twisted.


You can twist it if you want, but at audio frequencies its not really all that useful, so usually people don't bother paying for it.
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greynol
post Nov 8 2012, 01:56
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I find that RFI is best reduced if I stand on my head while wiring my speakers.

Seriously, the impedance involved makes this a non-issue. Provide evidence in accordance with TOS8 if you wish to argue otherwise.


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DonP
post Nov 8 2012, 02:22
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QUOTE (john11 @ Nov 7 2012, 03:31) *
Can anyone tell me why this is I was told the electricity has trouble flowing through twisted strands, if each strand was enameled you might get an inductance effect but obviously it is not so the electricity should take the straightest path, so if the strands are twisted or not should have no overall effect.

Can anyone tell me why the copper strands are never twisted.


All these folks posting about twisted pairs didn't notice he was talking about the strands of each wire being twisted, not the + and - wires being twisted around each other. Note he mentions current passing between the twists (or not if the strands are insulated).

As in the link to a monster cable pic, they often are twisted. Sometimes they ARE insulated, look up "litz wire." I'm not claiming skin effect is audible in normal speaker cable applications.

Current passing between strands on a twisted wire could be problematic if there is corrosion and a diode forms across the boundary.

This post has been edited by DonP: Nov 8 2012, 02:27
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Speedskater
post Nov 8 2012, 03:40
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QUOTE (greynol @ Nov 7 2012, 19:56) *
I find that RFI is best reduced if I stand on my head while wiring my speakers.

Seriously, the impedance involved makes this a non-issue. Provide evidence in accordance with TOS8 if you wish to argue otherwise.


Wow, the AES committee chair on EMI/RFI is not enough reference by himself?

link added
http://www.aes.org/technical/emc/

This post has been edited by Speedskater: Nov 8 2012, 03:44


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Speedskater
post Nov 8 2012, 03:51
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From page 2 of the above paper:

Output Wiring is Important Too! It is well known, for example, that RF interference is often coupled
into the output stage of audio equipment for example, the power amplifiers that feed loudspeakers
or headphones. There is always feedback around that output stage, so RF present at the
output will follow the feedback network to the input of a gain stage, where it will be detected and
amplified. This problem is made much worse when parallel wire cable (zip cord) is used to feed
the loudspeakers or headphones, and can usually be solved simply by replacing the zip cord with a
twisted pair of POC (plain ordinary copper). [Pseudo-scientific advertising hype for exotic cables
notwithstanding, it was shown nearly 30 years ago that #12 copper twisted pair (or #10 for very
long runs) is a nearly ideal loudspeaker cable.] [R. A. Greiner, "Amplifier Loudspeaker Interfacing,
JAES Vol 28 Nr 5, May 1980] As we will discuss later, the twisting of a pair greatly reduces the
level of RF that the wiring couples to circuitry.

A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing

Entire Contents Copyright 2007-10 The Audio Systems Group, Inc., except Appendices 2, 3, and 4, which are property
of the cited authors, and product data, which is copyright by Fair-Rite Products. All Rights Reserved
by Jim Brown K9YC - Audio Systems Group, Inc.
http://audiosystemsgroup.com

http://www.audiosystemsgroup.com/RFI-Ham.pdf


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Kevin
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quackalist
post Nov 8 2012, 04:49
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No idea on it's effectiveness or otherwise but its easy enough to DIY if inclined, see:

http://www.youtube.com/watch?v=V6ZecDs0GI4&hd=1

That example is not very long and you'd need a helper for anything longer.
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greynol
post Nov 8 2012, 05:59
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QUOTE (Speedskater @ Nov 7 2012, 18:40) *
Wow, the AES committee chair on EMI/RFI is not enough reference by himself?

Not if we're talking about audible differences in sound quality, no.

I appreciate the insight, however and am glad you've added some actual meat to what was an otherwise egregious appeal to authority. Not that the part I quoted constitutes actual meat (it doesn't). smile.gif

This post has been edited by greynol: Nov 8 2012, 16:31


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julf
post Nov 8 2012, 12:30
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QUOTE (greynol @ Nov 8 2012, 01:56) *
Seriously, the impedance involved makes this a non-issue.


Well, there is a special case - class D amps (or other amps with a significant HF component in the output or a HF feedback path from the output to the input). Bruno Putzeys of Hypex has a number of times pointed out the importance of twisting the output wires from the hypex amp modules.
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pdq
post Nov 8 2012, 13:54
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Despite what has been said, high frequencies generated within the power amplifier are not significantly reduced by twisting the conductors of the speaker leads. This kind of noise is primarily single-ended on one speaker lead, and is not cancelled by complementary noise on the other speaker lead. The only viable approach to minimizing this problem is to place an inductor in series with the speaker lead inside of the amplifier.

The company that I work for designs and manufactures non-audio electronic equipment, and does its own testing to pass FCC regulations. I have been involved in design changes when it has been difficult to get a product to pass these tests, so I have a pretty good idea what works and what doesn't.
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greynol
post Nov 8 2012, 15:43
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QUOTE (julf @ Nov 8 2012, 03:30) *
Bruno Putzeys of Hypex

Again, what is with the continual presentation of logical fallicies of appealing to authority when what is being requested is objective evidence in accordance with this forum's rules?


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julf
post Nov 8 2012, 15:57
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QUOTE (greynol @ Nov 8 2012, 15:43) *
QUOTE (julf @ Nov 8 2012, 03:30) *
Bruno Putzeys of Hypex

Again, what is with the continual presentation of logical fallicies of appealing to authority when what is being requested is objective evidence in accordance with this forum's rules?


Please delete my message. Will repost when I have a chance to post some measurements.
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greynol
post Nov 8 2012, 16:03
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Do be aware that electrical measurements do not fulfill the requirements of this forum by themselves.


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julf
post Nov 8 2012, 16:17
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QUOTE (greynol @ Nov 8 2012, 16:03) *
Do be aware that electrical measurements do not fulfill the requirements of this forum by themselves.


In this case I don't think the OP asked about audibility per se. As far as I understand, the question was about possible reasons for cables to be twisted (or not).
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greynol
post Nov 8 2012, 16:23
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...and that is perfectly OK. smile.gif


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mzil
post Nov 8 2012, 16:38
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Beside perhaps Arnold Krueger, who else here owns an ABX comparator box we might ask to try this? Is Bob Lee (of QSC) a forum member here? [I'm not here often enough to know, unless his forum name isn't obvious to me.] If I'm not mistaken, there is no way to apply a software based comparison in this instance, such as what can be done with fb2k.
---

The noise sources I would be inclined to try would be mostly AC hum based. I would try running the speaker wire parallel and adjacent to some long, active AC extension cord I knew didn't have internal, twisted construction itself (over a full room's length, say 20+ ft or so and ideally running a silent, high wattage appliance like a 300W torch lamp), wrapping the speaker wire around a large IE transformer (not toroidal), and also perhaps looping around or over an AC switching power supply such as a modern cell phone wall wart charger (that's not the older, heavy transformer design).

For the musical selection I'd try dead silence with lots of gain, or if that's "not allowed" I'd try some notably quiet passage.
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