Uni Directional Subwoofer Cables - AVS Forum
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post #1 of 189 Old 03-31-2010, 06:20 AM - Thread Starter
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Hello AVS Members,

This is my first post here but I can say that I have visited here on a number of occasions and always found this forum quite informative, which is why I would like to raise a question here.

How do uni directional subwoofer cables actually work?

I have done some research and the only viable explanation is the ground loop theory. This means that the ground shield of the coaxial cable is not connected at the subwoofer end to reduce the chances of hum as a result of "hearing" the amp at the other end.

So I dug out a spare coaxial RCA cable that I had with a screw off plug so I could take a look inside. I could see that the inner core was connected to the inner part of the connector and the woven copper shield was connected to the outer part of the plug (as expected)... So I decided to test out this theory and I cut the part connected to the outer woven copper shield to the outer part of the plug and tested it out on my subwoofer (again a cheaper spare sub as I don't want to risk blowing up some good stuff!)... However, the result was an extremely loud hum! Which is exactly the opposite to what this theory prescribes.

Have I misunderstood something? Which part exactly is meant to be left disconnected to create a uni directional subwoofer cable?
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post #2 of 189 Old 03-31-2010, 08:11 AM
 
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Have I misunderstood something?

Yes, and so did the marketing department.
An unbalanced circuit requires at least two conductors to complete the circuit. Lifting the ground at one end breaks the circuit, the result is no signal and a very loud hum.
There is no such thing as a directional cable, other then in marketing speak. A conductor that only allows current to flow in one direction is called a diode.
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post #3 of 189 Old 03-31-2010, 08:18 AM
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Originally Posted by duvetyne View Post

There is no such thing as a directional cable, other then in marketing speak.

Monster puts little arrows on all their cables so it must be true.
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post #4 of 189 Old 03-31-2010, 08:42 AM
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Since your audio signals are ac (sort of ) the electrons are moving in both directions. If the cable actually lets them move in only one direction, your ac has become dc and your speakers have become mute boxes with wisps of smole coming out.

Bet the marketing wizards didn't tell you that

There are no stupid questions. Stupid answers on the other hand....that's a whole other story...........
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post #5 of 189 Old 03-31-2010, 09:39 AM
 
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Monster puts little arrows on all their cables so it must be true.

Beleive what you want

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Since your audio signals are ac (sort of )

they are AC, there is no "sort of".

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your ac has become dc and your speakers have become mute boxes with wisps of smole coming out.

I don't know what smole is, but pulsating DC isn't going to instantly kill your speakers.
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post #6 of 189 Old 03-31-2010, 09:47 AM
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Originally Posted by duvetyne View Post

Beleive what you want

Guess I wasn't clear. I have edited my post.
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post #7 of 189 Old 03-31-2010, 10:31 AM
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Originally Posted by duvetyne View Post

they are AC, there is no "sort of".

+1. The term "uni-directional" cable is total nonsense. There is no such thing.

Frank

Frank Oesterheld
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post #8 of 189 Old 03-31-2010, 11:05 AM
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I think I may need to go to BB or some other source of AV gear and engage the sales staff in a tecchie chit chat. Purely for amusement, much like going to the comedy store.
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post #9 of 189 Old 03-31-2010, 11:24 AM
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Originally Posted by Gizmologist View Post

I think I may need to go to BB or some other source of AV gear and engage the sales staff in a tecchie chit chat. Purely for amusement, much like going to the comedy store.

Tell them you need reverse direction flow Monster Cable.
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post #10 of 189 Old 03-31-2010, 11:59 AM
 
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Originally Posted by 100db View Post

Hello AVS Members,

This is my first post here but I can say that I have visited here on a number of occasions and always found this forum quite informative, which is why I would like to raise a question here.

How do uni directional subwoofer cables actually work?

I have done some research and the only viable explanation is the ground loop theory. This means that the ground shield of the coaxial cable is not connected at the subwoofer end to reduce the chances of hum as a result of "hearing" the amp at the other end.

So I dug out a spare coaxial RCA cable that I had with a screw off plug so I could take a look inside. I could see that the inner core was connected to the inner part of the connector and the woven copper shield was connected to the outer part of the plug (as expected)... So I decided to test out this theory and I cut the part connected to the outer woven copper shield to the outer part of the plug and tested it out on my subwoofer (again a cheaper spare sub as I don't want to risk blowing up some good stuff!)... However, the result was an extremely loud hum! Which is exactly the opposite to what this theory prescribes.

Have I misunderstood something? Which part exactly is meant to be left disconnected to create a uni directional subwoofer cable?

This thread has already derailed, but to answer your question, YES there are actually audio cables that one might consider "directional." It has nothing at all to do with the cable being better in one direction than another, I am not at all referring to snake-oil BS that has arrows printed on it because somebody thinks the electrons "flow better" in one direction.

What you likely are asking about are cables with the shielding lifted at one end, which is not an uncommon practice for professional installations. You can't do this with coaxial cable, as you discovered, because the shield is your neutral return. If you lift the shield at one end, then you break the circuit and get no sound (and also get a whole lot of noise as a result.).

Instead, this is usually done with twisted-pair audio cabling which has a separate shield. One of the conductors is your positive signal, the other conductor is the neutral return(ground). Then around that you have usually a foil shield(and often a drain wire too). In any case, in many cases an installer will only terminate the shield at the source end, so any noise induced on the shield will go back to the source and not on to the next piece of equipment in the chain. If you were to turn that cable around, then all the noise moves forward in the system, not backwards, so to speak.

Obviously is you were to terminate the shield on both ends, then there's nothing at all directional about the cable and it doesn't matter.
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post #11 of 189 Old 03-31-2010, 12:13 PM
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Quote:
Originally Posted by ChrisWiggles View Post

Instead, this is usually done with twisted-pair audio cabling which has a separate shield. One of the conductors is your positive signal, the other conductor is the neutral return(ground). Then around that you have usually a foil shield(and often a drain wire too).

What's the shield connected to? Because if it's connected to something, it's no longer a pair, but rather a tri-something, isn't it?

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In any case, in many cases an installer will only terminate the shield at the source end, so any noise induced on the shield will go back to the source and not on to the next piece of equipment in the chain. If you were to turn that cable around, then all the noise moves forward in the system, not backwards, so to speak.

Whether it's disconnected on the one side or the other, noise that would be on transmitted onto that shield can't propagate, just like any wire that's only plugged in on one side cannot transmit anything.

"He who asks feels dumb for a few minutes, but he who does not ask remains dumb forever."

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post #12 of 189 Old 03-31-2010, 12:15 PM
 
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Instead, this is usually done with twisted-pair audio cabling which has a separate shield. One of the conductors is your positive signal, the other conductor is the neutral return(ground).

No, neither of the signal carrying conductors in a balanced interconnection are 'neutral'.
A differential connection is not referenced to ground, therefore a ground (or neutral as you like to call it) is not required, nor is it necessary.
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post #13 of 189 Old 03-31-2010, 01:28 PM
 
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Originally Posted by duvetyne View Post

No, neither of the signal carrying conductors in a balanced interconnection are 'neutral'.
A differential connection is not referenced to ground, therefore a ground (or neutral as you like to call it) is not required, nor is it necessary.

Who said anything about a balanced interconnect?

The original post asked specifically about RCA cabling, and there is nothing balanced about that.

Work on your reading comprehension next time.

Nice try though.
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post #14 of 189 Old 03-31-2010, 01:31 PM - Thread Starter
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Wow, I woke up this morning (Australia) to find an abundance of comedy hour! As I would have expected now that I can see the result.

I really didn't think my experiment would work as a Subwoofer Cable (as some have also pointed out) is an AC circuit. However, I just had to find out for myself. This is also why I posted my question/experiment here as I wanted to confirm this query one way or the other. Looks like it's well and truly clear now!

So it is safe to assume that uni directional subwoofer cables are impossible, right? And PLEASE let's not get into a conversation of electrons flowing better one way! Hehe...
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post #15 of 189 Old 03-31-2010, 01:33 PM
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Quote:
Originally Posted by ChrisWiggles View Post

The original post asked specifically about RCA cabling, and there is nothing balanced about that.

Hence me asking you what the shield would be connected to, because there is no 3rd anything...

"He who asks feels dumb for a few minutes, but he who does not ask remains dumb forever."

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post #16 of 189 Old 03-31-2010, 01:35 PM
 
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Quote:
Originally Posted by Gertjan View Post

What's the shield connected to? Because if it's connected to something, it's no longer a pair, but rather a tri-something, isn't it?

The shield is not part of the signal pair. It would only be grounded at the source end.

Quote:
Whether it's disconnected on the one side or the other, noise that would be on transmitted onto that shield can't propagate, just like any wire that's only plugged in on one side cannot transmit anything.

The noise isn't supposed to propagate, that's the whole point. The noise induced on the shield will just sink to the ground, and if the shield is only grounded at the source which is common practice, the noise doesn't move forward into the next source in your audio chain and that's the whole idea. If you connect it at both ends, then it's almost as if you have completed the circuit for the noise to travel on the next component (that's not really what's happening, just making a metaphor). You want the noise to be absorbed by a ground, that's the strategy.

From Extron:
Whether considering audio or video, the grounding of cable shields is not always clear. There are two scenarios to consider—one for low frequency noise and another for high frequency noise. The hum and buzz in the audio or creeping bar in the video typically falls within the realm of low frequency noise interference. For balanced audio or frequencies below 1 MHz, grounding the cable shield at only one point (the source end) is recommended. Grounding both ends sets up a loop for current to flow along the ground shield. This approach is effective against magnetic pickup, but may not help with low frequency ground loops caused by difference in potential between the grounded shields at each end. If a shield surrounding a twisted pair must be grounded at both ends by virtue of the system connection design, then the scenario in Figure 4 should be followed.

http://www.extron.com/company/article.aspx?id=ts012002

The same remains true for unbalanced audio over twisted pair.
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post #17 of 189 Old 03-31-2010, 01:48 PM
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Originally Posted by 100db View Post

So it is safe to assume that uni directional subwoofer cables are impossible, right? And PLEASE let's not get into a conversation of electrons flowing better one way! Hehe...

Unless its a Monster Cable.
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post #18 of 189 Old 03-31-2010, 02:02 PM
 
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Quote:
Work on your reading comprehension next time.

Nice try though.

Nice try weasiling your way out too!

You mentioned twisted pair with shield....I assumed you meand balanced because a twisted pair with shield used in an unbalanced circuit will gain you nothing and need not be used in an unbalanced circuit.

Quote:
The shield is not part of the signal pair. It would only be grounded at the source end.

You're right, and it's not even necessary to have one....what was your point?

Quote:
If you connect it at both ends, then it's almost as if you have completed the circuit for the noise to travel on the next component

Wow...when laymen try to explain basic electrical circuits the result is comedy gold.

Quote:
So it is safe to assume that uni directional subwoofer cables are impossible, right?

right
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post #19 of 189 Old 03-31-2010, 02:09 PM
 
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duvetyne: your ignorance is staggering. We had this discussion before when you didn't even know that twisted pair could be used for unbalanced audio cabling, despite the fact that it is the most common cabling type used for unbalanced audio.
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post #20 of 189 Old 03-31-2010, 02:11 PM
 
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duvetyne: your ignorance is staggering.

Chris, your ignorance is mind blowing!

Quote:
We had this discussion before when you didn't even know that twisted pair could be used for unbalanced audio cabling,

You ability to lie is staggering...of course a TP can be used for unbalanced....please don't make up lies to further your agenda and cover up the fact that you're clueless, it's pathetic.

Quote:
despite the fact that it is the most common cabling type used for unbalanced audio.

A 'fact' by chris? LOL....give it up, you're completely clueless.
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post #21 of 189 Old 03-31-2010, 02:29 PM
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Play nice guys, before the thread gets locked.
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post #22 of 189 Old 03-31-2010, 02:42 PM
 
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It's alright. Duvetyne is a permanent troll.
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post #23 of 189 Old 03-31-2010, 02:44 PM
 
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Chris is just dumb
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post #24 of 189 Old 03-31-2010, 02:46 PM
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Originally Posted by ChrisWiggles View Post

It's alright. Duvetyne is a permanent troll.

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Chris is just dumb

Hey! Do you want me to get jneutron in here to explain why everyone here is wrong?
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post #25 of 189 Old 03-31-2010, 02:53 PM
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There's only one way to find out folks. Buy the cable and do an autopsy. If you find that there are two conductors inside and an external shield that's only attached at one end, it's unidirectional with the shield being attached only at the source end. If the shield is connected at both ends and becomes part of the electrical return it's marketing mumbo jumbo. Or, you could just ask the vendor for an explanation of how things are laid out and trust the response. Whether a particular geometry confers an advantage or not has never prevented anyone from selling it.

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post #26 of 189 Old 03-31-2010, 06:49 PM
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I would love to see an example of an unbalanced TP IC. shielded cable does NOT count as twisted pair. TP cables have BOTH phase and return wires of identical construction and inside a shield conductor wrap. The shield is NOT part of the signal path.

Balanced circuits, whether differential or transformer coupled, do NOT use single conductor shielded cable, which BTW IS the most common IC cable.

Rule of thumb: If the audio connector has only 2 contacts and one surrounds the other, the cable is NOT balanced and will not be constructed using TP cabling.
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post #27 of 189 Old 03-31-2010, 09:32 PM
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Quote:
Originally Posted by Gizmologist View Post

I think I may need to go to BB or some other source of AV gear and engage the sales staff in a tecchie chit chat. Purely for amusement, much like going to the comedy store.

Be careful They might throw you out as a troublemaker Almost happened to me.
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post #28 of 189 Old 03-31-2010, 09:35 PM
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Quote:
Originally Posted by 100db View Post

.... And PLEASE let's not get into a conversation of electrons flowing better one way! Hehe...

Not here at AVS but there are such web sites where they do just that
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post #29 of 189 Old 04-01-2010, 12:19 AM - Thread Starter
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Ok, at this stage I will assume that uni directional subwoofer cables are marketing hype unless someone else can expain otherwise (clearly with diagrams or something similar).

However, I would like to take this conversation in a slightly different direction. I am looking at getting into my own business which will start with the manufacturing of AV Cables. I have been into Home Theatre/Audio for quite a while so I have a good foundation to build upon.

I do however have integrity pertaining to the fact that I always tell it how it is. I do not like marketing hype and prefer to sell something on it's actual merits. This may come as a surprise to some but it actually has served me very well in a retail environment and I don't see why this wouldn't be the case in my own business.

To the point... What qualities would you guys look for in a quality cable? I am open to ideas on all cables but I would like to hear your thoughts more on analog cables such as subwoofer connects and speaker wire etc. I will be pricing my range extremely competitively (much like the Blue Jeans Cable prices that you guys speak highly of). I will also go to extreme lengths to ensure quality is at the highest and my service will always be second to none. So if you guys could share some of things you look for in a quality cable it would be great... Please no snake oil type features!
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post #30 of 189 Old 04-01-2010, 05:07 AM
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Its Exactly as Chris Wiggles stated ,

With this configuration (unbalanced Telescoping Shield)
You have 3 wires, for argument sake the 2 white (+) /blue (-) wires carry the signal..
White wire (+) soldered to center pins of RCA's, Blue wire (-) soldered to outer pins and the third wire (shield) is tied/soldered to the RCA outer pin(-) Blue wire but only at the "Source component end" but left unconnected at the Amp or Subwoofer end,
the Shield(third wire) runs the full length of the RCA cable but is usualy cut just under where the outer jacket of the cable ends and the RCA plug is terminated
(Sub or Amp end), thus why some cables such as the Monster M1000 has A direction Arrow...

Page 3 of this PDF with wire diagram should inlighten you

http://www.diycable.com/main/pdf/Canare.pdf

Cheers...
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